Physio Ch 10, 12 Flashcards

Stimulus intensity can be coded by frequency of action potentials and stimulus intensity can be coded by the amplitude of the receptor potential.

rationale:

With regard to sensory coding, it is true that stimulus intensity can be coded by frequency of action potentials, andstimulus intensity can be coded by the amplitude of the receptor potential. It is important for the central nervous system to be able to determine the intensity of a signal so that the response mediated (if any) is appropriate. A stimulus may produce a receptor potential in the neuron associated with its receptor. A larger stimulus produces a greater receptor potential than a smaller one. The larger the receptor potential, the greater the number of action potentials sent along the afferent neuron to the CNS per unit time. Increasing the frequency of action potentials increases the amount of neurotransmitter released onto the central nervous system. The greater the number of action potentials, the greater the perceived intensity of the stimulus.

The ability to isolate the location of a signal to one afferent neuron is referred to the somatosensory system’s ability to provide lateral inhibition and related to the concept of receptive fields. When neurons have overlapping receptive fields, the neuron most closely positioned to the area of stimulation sends the most action potentials to the CNS and also inhibits the activity of neighboring neurons that are excited to a lesser extent. This produces a sharper contrast in signaling and allows for precision in the location of the signal.

An increase in the stimulus will result in an increase in the frequency of action potentials produced by the sensory neuron. This is how the sensory system codes for intensity. It is not, however, the only correct answer listed.

A strong stimulus can affect the amplitude of the receptor potential. A stronger stimulus will increase the amplitude while a weaker stimulus will result in a smaller amplitude. This results in differences in the amount of ligand (neurotransmitter) released by the receptor and thus in the frequency of action potentials generated in the associated sensory neuron. This is one of the ways in which the sensory system can code for intensity. It is not, however, the only correct answer listed.

involve receptors that consist of a neuron with naked free nerve endings or ones with nerve endings encased in connective tissue capsules

rationale:

The somatic senses involve receptors that consist of a neuron with naked free nerve endings or ones with nerve endings encased in connective tissue capsules. The tissues associated with the neuron ending do not develop a receptor potential or release neurotransmitter. These receptors have specificity to different stimuli as well as the ability to code for intensity and duration.

The receptors associated with the special senses (i.e., sight, sound, smell) are located in highly specialized complex multicellular structures called sense organs.

The receptors associated with the special senses are always located in specific areas of the body (vision, hearing, etc.) while the receptors associated with somatic senses may be localized to particular places (proprioceptors in muscles, tendons and joints or Meissner’s corpuscles in hairless skin) but many are located throughout much of the skin, although the concentration of receptors varies greatly in different areas. For the receptors that consist of free nerve endings, there are no tissue specific differences. The receptors are the same in every tissue.

All neurons associated with special senses and somatic senses will be able to conduct action potentials. Conduction of action potentials is how the signal about the stimulus is sent to the central nervous system.

timing of the input sound signal

rationale:

The direction of a sound is determined by comparing the timing of the input sound signal on each side of the brain. Neurons in the ears are sensitive to different frequencies of sound, but they have no receptive fields and their activation provides no information about the location of the sound. Instead, the brain uses the timing of receptor activation to compute a location.

Action potential frequency is used by sensory neurons to code for the intensity of a stimulus. If a stimulus is strong the sensory neuron will fire with an increased frequency and vice versa for a weaker stimulus.

The amplitude of the hair cell depolarization codes for intensity, not location.

The frequency of the input sound signal will affect how the brain interprets the pitch of the sound but not the location.

transduction; adequate stimulus; threshold

rationale:

The conversion of stimulus energy into information that can be processed by the nervous system is called transduction. Each sensory receptor has a(n) adequate stimulus, a particular form of energy to which it is most responsive. The minimum stimulus level required to activate a receptor is called the threshold.

A threshold is the minimum stimulus needed to elicit a receptor potential and is not related to the specific stimulus that the receptor receives. Additionally, the receptor potential occurs because of the stimulus that arrives and is the result of the activation.

A threshold is the minimum stimulus needed to activate a receptor and is not related to the specific stimulus that the receptor receives, while the adequate stimulus is the stimulus to which the receptor is most sensitive (i.e., light stimulates photoreceptors).

A receptor potential is a change in membrane potential in a receptor cell created by a stimulus. In some cells, an action potential is generated in afferent fibers that carry information to the CNS. In other receptor cells, a change in the receptor potential causes a release of neurotransmitter from the cell.

Thalamus to postcentral gyrus

rationale:

The thalamus is the relay center for all sensory information with the exception of olfaction. Sensory information travels from the sensory receptor to the sensory association in the brain where the sensation is integrated. There are several order neurons that will function in the transduction of the signal. The third-order neuron will send information from the relay center to the sensory cortex.

The precentral gyrus is the origin for the somatic motor neurons and propagates information from the cortex down the anterior and lateral corticospinal tracts to innervate the lower motor neurons stimulating skeletal muscles.

The first-order neurons will send information from the sensory receptor to the spinal cord.

The second-order neurons will deliver information from the spinal cord or medulla to the thalamus.

There will not be one sensory neuron between the sensory receptor and the thalamus. There will be two neurons (the first-order and second-order neurons)that relay the information before it reaches the thalamus.

stimulation of Αβ fibers

rationale:

Αβ fibers will stimulate the inhibitory neurons that synapse with the second-order neurons in a nociceptors circuit. By stimulating the inhibitory neuron, the transmission of pain can be suppressed so that the intensity of the pain is reduced.

Substance P is released by nociceptors afferents onto second-order neurons leading to their activation. Once the second order neurons are activated, painful stimuli are transduced to the thalamus.

C fibers are the nociceptors afferents that are responsible for transmitting painful stimuli.

Inhibiting the inhibitory neuron results in greater activation of the second-order neurons in the nociceptive pathway, which results in the transmission of pain to the thalamus.

Nociceptors and cold receptors

rationale:

The perception of scalding hot water on the skin may involve nociceptors and cold receptors. Once the water hits the skin, the body will have to react to the water in order to protect the limb from the dangerous stimulus. The scalding hot water might cause damage to the skin by burning it. Burning the skin can lead to nerve damage and dehydration. To prevent these things from happening, the body must be responsive to these stimuli and remove the limb from the stimulus.

Nociceptors transmit the sensation of pain. Scalding hot water will stimulate these receptors so that the body reacts to a noxious stimulus, which will result in the removal of the limb from that noxious stimulus. This is not, however, the only receptor involved in this pathway.

Warm receptors are thermoreceptors that are able to sense temperatures between 35°C and 45°C. When these receptors are stimulated, the brain interprets the sensation as warmth. Scalding hot water, however, will be above 45°C and will therefore be outside of the range of the warm receptors.

Cold receptors are thermoreceptors that are activated at temperatures between 35°C and 20°C. When they are activated, the brain will interpret the sensation as cold. Additionally, however, these receptors can be stimulated at temperatures of 45°C or higher, which would include the scalding hot water. This is not, however, the only receptor involved in this pathway.

Mechanoreceptors are activated by some sort of stretch pressure stimulus. Scalding hot water does not provide this kind of stimulus.

joint position receptors, visual system, and somatosensory system

rationale:

Vestibular nuclei in the brain stem are responsible for helping the body integrate sensory information associated with the control of equilibrium and balance. To maintain balance and equilibrium, the body needs to be aware of limb position, objects that might interfere with walking, and other details.

Joint receptors will transmit sensory information to the CNS about the position of the body’s limbs. Proprioception, awareness of the position of the body’s limbs, is an important factor in the control of balance and equilibrium, which is mediated by the vestibular nuclei in the brain stem. This is not the only option, however, that is correct.

If there is an object in front of a person that needs to be avoided, that person must change their direction as well as pivot differently on their legs. Balance and equilibrium must be adjusted in order to ensure that when the response is mediated, the person does not fall over. This requires that visual stimuli be sent to the vestibular nuclei. This is not the only option, however, that is correct

The cochlea is concerned with the perception of sound and although Cranial Nerve VIII carries fibers from the vestibular apparatus and the cochlea, the fibers from these two receptors travel to different target areas in the CNS. The cochlear nerve does not project to the vestibular nuclei as does the vestibular nerve.

Somatosensory signals include all of the general sensations of the somatic system. This includes many sensory signals from skeletal muscle, to joints, to skin. All of these stimuli can send signals to the vestibular nuclei in order to control balance and equilibrium. This is not the only option, however, that is correct.

labeled lines

rationale:

The specific neural pathways that transmit information pertaining to a specific sensory modality are called labeled lines. Each sensory modality follows its own labeled line. Activation of a specific pathway causes perception of the associated modality, regardless of which stimulus actually activated the pathway.

A sensory unit is a single sensory neuron with all of its receptor endings that will transmit the information of a stimulus.

A percept is the brain’s impression of a stimulus.

Sensory pathways include the spinothalamic tract and the dorsal column–medial lemniscal pathway. These are pathways of first-, second-, and third-order neurons that send information about a sensation from the receptor to the cortex of the brain.

somatosensory cortex

rationale:

The somatosensory cortex is the part of the brain that recognizes where ascending somatosensory tracts originate. Located in the parietal lobe, the somatosensory cortex is the termination point of general sensations like temperature changes on the skin. This somatosensory cortex contains a map called a homunculus that shows distorted figures representing the parts of the body. The figures look misshapen because they are drawn to represent the density of neurons associated with the body part.

Pacinian corpuscles are mechanoreceptors located in the hypodermis or dermis of the skin. These receptors respond to deep pressure and vibration.

The olfactory bulb is the synapse location for the olfactory nerves that come from the olfactory epithelium in the nose. From the olfactory bulb, olfactory sensory information is delivered to the brain via the olfactory tracts.

The tympanic membrane is located in the ear and will vibrate when sound waves hit against it. The vibration of the tympanic membrane results in the vibration of the auditory ossicles, which will then transmit motion to the round window of the cochlea. This vibration is ultimately detected by the organ of Corti, the sensory organ for sound.

Information about pressure and joint/limb location remains ipsilateral until the thalamus and the cell bodies of first-order somatosensory neurons are located in the dorsal horn of the spinal cord.

rationale:

thermoreceptors, mechanoreceptors, nociceptors, thermoreceptors and nociceptors

rationale:

With regard to the somatosensory pathways, it is not true that information about pressure and joint/limb location remains ipsilateral until the thalamus. Fibers carrying proprioception cross over at the level of the medulla. It is also false that the cell bodies of first order somatosensory neurons are located in the dorsal horn of the spinal cord; they are found in the dorsal root ganglia.

Information about pressure and joint/limb location remains ipsilateral until the medulla of the brain stem and becomes contralateral by the time it reaches the thalamus. This is not the only statement, however, that is false.

It is true that the information about temperature and pain becomes contralateral at the level of the spinal cord. Thermoreceptors and nociceptors send information through the spinothalamic tract where it crosses at the spinal cord before relaying at the thalamus.

It is true that somatosensory information from the dorsal column-medial lemniscal pathway is relayed through the thalamus on its way to the cortex. All sensory information, with exception of olfaction, is relayed at the thalamus.

The cell bodies of first-order somatosensory neurons are not located in the dorsal horn of the spinal cord but rather are located in the dorsal root ganglion.

Increase the frequency of the action potentials delivered

rationale:

All answers are correct. The types of receptors found in the somatosensory system include thermoreceptors, mechanoreceptors, and nociceptors.

The somatosensory system is responsible for conveying information about general sensations that occur in the periphery of the body to the central nervous system. Some of the types of sensory information that need to be conveyed include temperature, vibrations in the skin, and painful stimuli. In order to sense any of these things, the somatosensory system has to have all of the receptor types listed.

Thermoreceptors are sensory receptors that are sensitive to changes in temperature. They are located in the skin, which makes them part of the somatosensory system.

Mechanoreceptors are receptors that are sensitive to stretch. The muscle spindle found in skeletal muscle is an example of a mechanoreceptor in the somatosensory system.

Nociceptors are receptors that respond to noxious or painful stimuli. There are many nociceptors found in the skin, which help covey information about noxious stimuli experienced by the skin (i.e., burns). Because these receptors can be found in the skin, they are part of the somatosensory system.

tonic; phasic

rationale:

By increasing the frequency of action potentials delivered, the axon terminal of the sensory neuron will release a greater concentration of neurotransmitter. This high concentration of neurotransmitter will result in an interpretation by the brain of an intense stimulus.

The amplitude of the action potential in a sensory neuron cannot vary due to the all or none principle.

When the duration of action potentials delivered increases or decreases, it helps to convey information about the duration of the stimulus but not the intensity of the stimulus.

population coding

rationale:

Sensory receptors that are slowly adapting that respond for the duration of the stimulus are tonic receptors while those that rapidly adapt to a constant stimulus and then turn off are phasic receptors. These different types of receptors help the sensory system filter stimuli that require responses from those that can be ignored. There are some cases where tonic receptors can adapt to a constant change in a stimulus and develop a new threshold.

This answer option represents the opposite definitions. Tonic receptors respond for the duration of the stimulus while phasic receptors quickly adapt.

Only one of these statements defines tonic receptors while the other defines phasic receptors.

Only one of these statements defines phasic receptors while the other defines tonic receptors.

Chemoreceptors

rationale:

In population coding, a stronger stimulus activates, or recruits, a greater number of receptors. These receptors may be associated with a single afferent neuron, in which case the receptor potentials that are generated at the individual receptors sum and produce a greater frequency of action potentials in

that neuron.

Lateral inhibition occurs when the collaterals of an activated afferent inhibit other surrounding afferents in order to increase the acuity of a signal.

Modality refers to the fact that receptors will transmit information about a specific sensation to the brain regardless of what stimulates that receptor. For example, a temperature receptor that is stimulated by electrical stimulation will send signals to the brain that will be interpreted as a temperature change.

Specificity refers to the fact that a receptor will respond to only a certain ligand or stimulus.

Intensity of a stimulus is coded by increasing the frequency of the action potentials delivered from the sensory neuron.

An increase in the duration of the action potentials delivered

rationale:

Blood pH is a measure of the concentration of H⁺ freely dissolved in the plasma. In order to maintain a homeostatic pH to prevent potentially lethal physiological effects, the body needs to be able to sense and respond to changes in H⁺concentration. Because H⁺ are ions that can act as chemical ligands, the chemoreceptor would be the receptor sensitive to this particular stimulus.

Mechanoreceptors respond to various forms of mechanical energy, including pressure, vibration, gravity, acceleration, and sound waves.

Photoreceptors respond to photons and help to transduce light stimuli into electrical signals associated with sight.

Thermoreceptors respond to temperature.

M cells; P cells

rationale:

If you stimulate a sensory neuron for two seconds with a light touch, and then again for 10 seconds with the same intensity touch you will observe an increase in the duration of the action potentials delivered with the 10 second tap as opposed to the two second tap. This helps the brain interpret how long a stimulus is present for or in other words, the duration of the stimulus. Once the delivery of action potentials stops, the brain no longer interprets the presence of a sensation.

The amplitude of the action potential in a sensory neuron cannot vary due to the all or none principle.

By increasing the frequency of action potentials delivered, the axon terminal of the sensory neuron will convey information about intensity, not duration.

If the touch is applied at the same point and with the same amount of force, it would not be expected that the number of neurons stimulated would change.

It is hypothesized that inhibitory interneurons are activated by the collaterals of an activated neuron associated with a mechanoreceptor from the skin. The gate-control theory of pain modulation may account for this phenomenon.

rationale:

Inhibitory interneurons will typically become inhibited by the collateral of the C fiber, which will allow for the transmission of the painful stimulus. If nearby mechanoreceptors are activated, however, the inhibitory neuron will be activated, which will inhibit the second-order neuron, which will lessen the intensity of the painful signal. This is not, however, the only correct option.

The gate-control theory describes the relationship between the collaterals of an Αβ neuron and its ability to activate the inhibitory neuron that communicates with the second-order neuron. This is not, however, the only correct option.

second-order neurons receive information from both somatic and visceral afferents and the brain interprets new sensory information based on past sensory experience

rationale:

Generally, activation of nociceptors in the viscera produces a type of pain called referred pain (because it has been “referred” to the body surface). The two responses listed are the current theories to help explain why referred pain occurs.

Referred pain occurs because the second-order neurons that receive input from visceral afferents also receive input from somatic afferents.

The brain interprets information based on past experiences. Throughout a person’s life, these second-order neurons are activated primarily by the somatic afferents, and thus the brain has learned that signals from these neurons are somatic in origin.

The receptive fields for visceral sensory neurons are in the viscera, and the receptive fields of somatosensory receptors are in the skin and muscles. Therefore, the two types of receptive fields do not overlap.

Visceral sensory neurons do not terminate in the dorsal root ganglia, although some of them do have cell bodies in these ganglia. They do project to the CNS.

More receptive fields, overlapping receptive fields, and lateral inhibition

rationale:

Acuity can be increased by more receptive fields, overlapping receptive fields, and lateral inhibition. Acuity is the body’s ability to localize a stimulus to a specific place on the body. In order to do this, sensory information should come only from the afferents near the stimulus. Additionally, more than one afferent sending information about the stimulus from the location can increase acuity.

Large receptive fields cover a larger area on the skin and therefore make it harder for the brain to perceive the exact location of the stimulus.

Having more receptive fields is often correlated with those receptive fields being smaller. Smaller receptive fields increase acuity, additionally, these receptive fields will likely overlap, which also increases acuity. This is not, however, the only option that will increase acuity.

When receptive fields overlap, the number of afferent neurons activated by a stimulus increases. When more afferents are activated, acuity increases. This is not, however, the only option that will increase acuity.

In lateral inhibition, afferent neurons closest to the stimulus will send inhibitory signals to other afferents nearby through their collaterals. This ensures that the afferents closest to the stimulus deliver a larger signal than the surrounding afferents, thereby increasing acuity. This is not, however, the only option that will increase acuity.

respond to chemical ligands that bind to a cell membrane receptor

rationale:

Chemoreceptors will bind to a variety of chemicals that function as ligands on the receptor. Some examples of these chemicals can be ions or gases. For example, there are chemoreceptors in the carotid artery that are sensitive to plasma levels of O₂, CO₂, and H⁺. Based on the concentration of these various chemicals, the chemoreceptors will transmit information to the medulla oblongata to adjust respiration.

Mechanoreceptors are very sensitive to various forms of mechanical energy.

The steriocilia in the ear will bend when sound waves travel into the ear. When the steriocilia bend, they will open or close mechanically gated channels, which will create a receptor potential that may be transduced onto a sensory neuron and delivered to the brain for sound interpretation. These cells function like mechanoreceptors.

Thermoreceptors respond to temperature changes.

transduction

rationale:

The conversion of the energy in a stimulus into a change in membrane potential in sensory cells is called transduction. Signal transduction is necessary to ensure that a stimulus can be interpreted by the central nervous system. A stimulus can cause changes in cell permeability, which is what will result in change in membrane potential. The change in membrane potential can then result in the release of a ligand (neurotransmitter) that can communicate with a sensory neuron and eventually the central nervous system.

Translation is a process that occurs in protein synthesis when a ribosome attaches a sequence of amino acids determined by the nucleotide sequence of a strand of mRNA to form a peptide.

Coding is a mechanism used by the sensory system to indicate the type, duration, and intensity of a sensory signal.

Receptor adaptation is a decrease over time in the magnitude of the receptor potential in the presence of a constant stimulus.

mechanoreceptors

rationale:

Stimuli such as sound waves or pressure caused by blood will create mechanical stress onto these receptors, resulting in the opening or closing of ion channels. When these ion channels open or close, there will be changes in membrane potential that may result in signal transduction.

Thermoreceptors respond to temperature.

Chemoreceptors respond to chemical ligands that bind to the receptor.

Photoreceptors respond to photons and help to transduce light stimuli associated with sight.

Pain and itching

rationale:

The sensations transmitted by nociceptors are pain and itching. Nociceptors are very important in the transmission of pain in order to protect the body from a noxious and potentially dangerous stimulus. The nociceptors on the visceral organs often result in the phenomenon known as referred pain.

Thermoreceptors respond to temperature.

Mechanoreceptors respond to various forms of mechanical energy, including pressure (light and coarse), vibration, gravity, acceleration, and sound.

convergence of synaptic input is greater at the periphery of the retina and ganglion cells can detect color and contrast (center versus surround)

rationale:

Convergence occurs between receptors and bipolar cells and between bipolar and ganglion cells. However, the extent of this convergence is considerably greater with rods than with cones. Thus, in macula, where cones predominate, little convergence occurs; only a few photoreceptors converge onto one bipolar cell. In the fovea, there is no convergence. Convergence increases toward the periphery of the retina. Because most rods are located at the periphery, convergence is greatest in that location.

Ganglion cells are never quiet. They are always sending action potentials, even in the dark.

Only a few cone cells converge onto a bipolar neuron.

the louder the sound, the more potassium channels open in the hair cells associated with the pitch of the sound and the pitch of a sound is coded by the location of the hair cells which response to a sound wave of a particular frequency

rationale:

In the inner ear the louder the sound, the more potassium channels open in the hair cells associated with the pitch of the sound, and the pitch of a sound is coded by the location of the hair cells which respond to a sound wave of a particular frequency. The sensory receptors in the inner ear are mechanoreceptors that will generate receptor potentials when the stereocilia bend.

When a sound is loud, tectorial membrane will bend the hair cells at a greater angle which will result in more K+ channels opening and therefore a greater receptor potential.

When there are no sound waves present, the stereocilia extend straight up, the potassium channels are partially open and some calcium channels are thus open. A small amount of neurotransmitter is released, which causes a low frequency of action potentials in the associated neuron. The hair cells will bend more when the sound that is coming in is louder. Higher frequency is coded by bending of stereocilia near the basal end of the basilar membrane near the oval window.

Coding for frequency is done by hair cells that are activated based on their location. Some hair cells are activated when the basilar membrane moves due to a low frequency while hair cells in a different location would be activated by a set of hair cell receptors in a different location.

the right visual field is topographically mapped onto the left visual cortex

rationale:

In the visual pathway the right visual field is topographically mapped onto the left visual cortex. This is due to the fact that the axons from left nasal ganglion cells carrying information from the left visual field cross to the opposite side of the brain and axons from the right nasal ganglion cells carrying information about the right visual field cross to the left side of the brain. Axons from each side’s temporal ganglia, which carry information from the visual field of the opposite visual field, remain ipsilateral. This results in the left visual field being mapped to the right visual cortex and the right visual field to the left cortex.

Images from the right temporal visual field are processed in the left optic radiations.

Images from the left nasal visual field pass through the right lateral geniculate body.

c, b, a, e, d

rationale:

With respect to hearing, the correct pathway for sound transduction is the following: hair cell → afferent neuron→ cochlear nucleus → medial geniculate body → auditory cortex. Signal transduction for sound occurs at the receptor/afferent nerve interface where the physical motion of the sound waves in the perilymph of the cochlea is converted by the release of neurotransmitter from the receptor hair cells into action potentials in the afferent neurons of the cochlear nerve. These afferent neurons terminate in the cochlear nuclei and the signal is then relayed via various brain stem nuclei to the medial geniculate nucleus of the thalamus. From the thalamus the signal travels to the auditory cortex in the temporal lobe where sound is consciously perceived.

The hair cell is located in the inner ear and is associated with the basilar membrane. When the basilar membrane vibrates, the hair cells bend, resulting in a receptor potential.

When a receptor potential is produced, neurotransmitters will be released, causing an action potential in the afferent neuron.

The cochlear nucleus will receive information from the afferent neuron and continue propagating the signal.

The sensory information associated with sound is relayed at the medial geniculate body of the thalamus before it is sent to the primary auditory cortex.

The primary auditory cortex is where the sensation of sound terminates in order to be interpreted .

up and down (as in nodding yes)

rationale:

If the endolymph inside your anterior semicircular canals were moving, you would have the sensation that your head is moving up and down (as in nodding yes).

Forward motion is a linear movement that is sensed by the utricle and saccule and not the semicircular canal.

Linear movements, like moving backward, are not sensed by the semicircular canals but rather the utricle and saccule.

Shaking the head side to side as if shaking you head to say no is sensed by the horizontal canal of the semicircular canals.

Cones are most sensitive to light in the red-green range, not the blue-green range.

Cones cannot detect a single photon of light. Only rods can detect a single photon of light.

Cones are not easily saturated by photons.

With regard to the olfactory sense, it is true that the neural pathway for olfaction shows convergence at the level of the mitral cell, the current understanding of olfaction suggests that each olfactory receptor cell responds to only one odorant, and the odor perceived is based on the pattern of activity produced by many olfactory receptor neurons.

The mitral cell is a second-order neuron that transmits information from many different first order neurons (1000:1). This represents convergence of the signal. This is not the only correct option.

Olfaction is a very acute sensation, such that most people have the ability to distinguish between millions of smells. Although the precise mechanism by which the olfactory system codes for different smells is unknown, at least 1000 genes have been identified that code for olfactory receptors; each olfactory receptor cell is believed to express only one type of receptor. Each receptor cell responds to only

one type of odorant.

There are approximately 8000 glomeruli in each olfactory bulb, and a single glomerulus receives all the olfactory input from a specific odorant. The smell ultimately perceived depends on the pattern of activation of olfactory receptor neurons.

yellow cones

rationale:

The red cones are coded by a gene found on the X chromosome and they are one of the most common cone types.

The green cones are coded by a gene found on the X chromosome and they are one of the most common cone types.

Although blue pigment is not as easily perceived as red or green, the retina will still have cones that are sensitive to blue pigment.

Emitted, reflected, and refracted

rationale:

Emitted, reflected, and refracted light reaching our retinas is perceived. Light penetrates the pupil of the eye and hits the back of the retina, where it is absorbed by the pigments of the photoreceptors, rods and cones. Reflected light from objects and refraction by structures of the eye are important in stimulating receptors in the retina.

Emitted light is going to enter into the eye through the pupil to activate the photoreceptors. This is not the only correct answer.

Reflection is a phenomenon in which light waves strike and bounce off a surface. Reflection is important in vision because much of the light we perceive has reflected off the objects we are observing. This is not the only correct answer.

Refraction refers to the bending of light waves as they pass through materials of different optical densities. Refraction occurs because the speed of light is different in varying media. Light passing into the eye is refracted as it passes through the cornea and lens. This is not the only correct answer.

If light is absorbed by an object, it is not able to stimulate the photoreceptors and therefore that light will not be perceived.

Touch

rationale:

Of the options listed, touch is not a special sense. The special senses are the senses of vision, hearing, balance and equilibrium, taste, and smell. Touch is a general sensation that occurs all around the body. Special senses have not only specific receptors, but they also have specific organs that will contain the receptors.

Smell is transduced by receptors in the olfactory epithelium of the nasal cavity. The receptors will respond to odorants, chemical in the air. This is a special sense.

Photoreceptors found in the retina of the eye are specific to the stimulus of photons. This is a special sense.

Taste is transduced by receptors on the epithelium of the tongue in response to chemical signals called tastants. This is a special sense.

Equilibrium is a special sense. The receptors (semicircular canals, the utricle and the saccule) are housed in the inner ear and are concerned with determining the position of the head and movement of the body and head through space. Equilibrium also requires information from muscle proprioceptors and vision also contributes to equilibrium.

Hearing, perception of sound, is a special sense. Transduction of sound occurs at the cochlea of the inner ear.

Helicotrema

rationale:

The helicotrema is associated with hearing. The cochlea of the inner ear is responsible for the transduction of sound waves so that they can be interpreted by the auditory cortex in the temporal lobe. The helicotrema is the portion of the cochlear duct that connects the scala tympani and scala vestibule, which will transmit sound waves.

An ampulla is located in each of the semicircular canals and transduces rotational acceleration.

The saccule is the duct located within the vestibule and transduces linear acceleration.

The kinocilium is the single long cilium of a hair cell located within the ampulla. Movement of cilia of a hair cell toward or away from the kinocilium produces receptor potentials to transduce information about rotational acceleration.

It is more prominent in males and the most common type of color blindness is red-green.

rationale:

With regard to color blindness, it is true that it is more prominent in males and that the most common type of color blindness is red-green. Color blindness is a genetic disorder and the genetic defect where the genes for red and green photoreceptors are not expressed. Men get color blindness more often than women because they only have one X and therefore do not have another chromosome that could contain the functional gene for the photoreceptors. The most common type is red-green, which results in the inability to distinguish red pigments from green pigments.

The genes that code for red and green photoreceptors are found on the X chromosome. Because males have only one X chromosome, they are more likely to inherit this trait, which is recessive in women. This is not the only correct answer.

Red and green is the most common type of color blindness, resulting in the inability to distinguish red from green pigment. It can be caused by mutations in the gene for the green receptor, the red receptor, or both. This is not the only correct answer.

Although blue color blindness does exist, it is much rarer and the gene for blue photoreceptors is not located on the X chromosome.

frequency

rationale:

A high-pitched sound is also a high-frequency sound. The frequency of sound waves is the number of waves that enter into the ear per a unit time. Frequency differences are perceived by hair cells in different locations of the cochlear duct.

Changes observed in amplitude occur when a stimulus changes in intensity.

Duration is a measure of how long the stimulus is applied as opposed to the speed at which it travels.

The decibel is a measure of loudness, which is then linked to a perception of intensity.

d, e, a, f, c, b

rationale:

As visual information moves from the retina to the brain, it travels through the following pathway: ganglion cells → optic nerve → optic chiasm → lateral geniculate body → optic radiations → visual cortex. In order for a light stimulus created by photoreceptors to be interpreted as a shape, the sensory signal that activated the receptors must be delivered along this pathway to the primary cortex for interpretation.

The ganglion cells are located in the retina and in this pathway will be the first to receive the stimulus.

The axons of the ganglion cells collect to form the optic nerve and the signal is propagated back toward the brain.

The optic chiasm is the place at which both of the optic nerves partially cross and the signal will pass along the nerve through the chiasm and then project along the optic tract back to the thalamus.

In the thalamus, the signal from the optic tract will synapse with the lateral geniculate body and be propagated back to the visual cortex.

The optic radiations are pathways that deliver the signal from the thalamus back to the visual cortex where the signal terminates.

cones and fovea

rationale:

The fovea is the area of the retina that has the highest concentration of cones and therefore is the site of the retina that will provide the highest acuity for vision. When the eye focuses on something directly in front of it, light will pass through the pupil and hit the retina right on the fovea.

Although rods are activated by very low light, many rods converge on a single bipolar cell and thus on a single ganglion cell and so do not provide high visual acuity. Rods are in highest concentration at the periphery of the retina. Additionally, as light passes into the eye when focusing on something right in front of the eye, the light will hit the fovea, which is populated with cones.

When the eye focuses on something that is right in front of it, light will hit an area on the retina that is populated entirely by cones. This is not the only option that is correct.

When focusing on something right in front of the eye, like the words on a paper that you read, the light passes through the eye and hits the fovea providing the sharpest vision. This is not the only correct option.

The optic disk is the blind spot of the eye and does not become activated by light stimulus. It is the point at which the fibers of the optic nerve exit the retina.

High cGMP levels

rationale:

In the dark, the photoreceptors will have high levels of cGMP. This results in depolarization of the receptor and the release of neurotransmitters onto the bipolar cells. Some of the bipolar cells are activated (OFF bipolar cells) and some are inhibited (ON bipolar cells). Action potentials are sent along the axons of ganglion cells even in total darkness. Hyperpolarization occurs when the levels of cGMP within the photoreceptor decrease, which occurs with light stimulus.

Phosphodiesterase will degrade cGMP. As cGMP levels decline, the cell will hyperpolarize. These series of steps occur when the photoreceptor is exposed to light because the light initiates a series of reactions that activate phosphodiesterase.

When the photoreceptor is stimulated by light, the sodium channels will close.

rotational movements and rotational acceleration

rationale:

The semicircular canals detect rotational movements and rotational acceleration. The horizontal canal senses rotation of the head as it turns left or right, such as that which occurs when shaking the head “no” The superior canal senses rotation of the head from front to back, such as that which occurs when nodding “yes.” The posterior canal of the vestibular apparatus senses the tilt of the head toward the right or left shoulder. The vestibular apparatus is sensitive only to changes in the rotational velocity of the head. After 25-30 seconds of movement in the same direction at a constant velocity, the velocity of the endolymph in the canals catches up to the velocity of the canal itself and movement is no longer detected.

Linear movements are detected by the utricle and saccule of the vestibule and not the semicircular ducts of the semicircular canals.

accommodation

rationale:

Activation of the parasympathetic nervous system produces accommodation. Accommodation is under control of the parasympathetic nervous system, which triggers contraction of the ciliary muscle for near vision. In the absence of parasympathetic activity, the ciliary muscle relaxes.

Pupil dilation occurs when the dilator muscle around the pupil contracts and is under the control of the sympathetic nervous system.

Hyperopia is a condition of the lens of the eye that will result in an inability to focus well on objects. In hyperopia, the lens or cornea is too weak for the length of the eyeball. Therefore, the eye can focus on distant objects only with accommodation, which means that the lens cannot increase accommodation enough to adjust for near vision.

The lens is flattened when the parasympathetic nervous system is not activated and the ciliary muscle is relaxed.

Bitter

rationale:

Some bitter tastants block potassium channels leading to depolarization of the cell. Bitter tastes are associated with a wide variety of nitrogen-containing compounds, including some that are toxic. The fact that animals tend to avoid eating things that taste extremely bitter is, therefore, a protective mechanism. There are several different types of bitter substances and more than 30 different types of bitter taste receptors that work via different mechanisms. Some bitter foods contain molecules, such as quinine, that can block potassium channels.

Sweet tastants will result in activation of G-protein coupled receptors. This cellular mechanism will result in the phosphorylation of K⁺ channels. When potassium channels close and potassium leakage out of the cell decreases, the taste receptor cell becomes depolarized. Other sweet tastants work through G proteins that activate the phospholipase C - inositol triphosphate pathway, which causes neurotransmitter release due to a rise in cytosolic calcium.

Sour tastants can be related to H⁺ atoms. Hydrogen ions are capable of crossing the membrane of taste receptor cells through the same amiloride-sensitive sodium channels responsible for salty tastes. Because hydrogen ions carry a positive charge, this movement would depolarize the receptor cell.

When sodium levels outside the cell are increased by the consumption of salty foods, the inward electrochemical driving force on sodium ions increases, causing an increased flow of Na⁺ into the cell, which leads to depolarization.

retinal

rationale:

The light-sensitive portion of the photoreceptor visual pigments is a derivative of the compound retinal. In most of the retina light passes through many layers of cells before it is able to stimulate the photoreceptors. Each photoreceptor contains a photopigment molecule composed of retinal, a Vitamin A derivative, bound to the protein opsin. When light strikes the photopigment, the retinal portion of the pigment changes shape and is released from the opsin.

Opsin is the protein component of the photopigment portion of the photoreceptor cells, rods and cones. Humans have four different opsins, one for each of the three types of cones and one for rods. The opsin protein of the photopigment determines the wavelengths of light to which the photopigment is sensitive but the opsin itself does not absorb light.

Melanin is a dark pigment found in the cells of the pigment epithelium. It is not part of the photoreceptor. The function of the pigment epithelium is to absorb light that is not absorbed by the photoreceptors.

Melanopsin is a photosensitive pigment found in a small subset of retinal ganglion cells that may allow these cells to function as photoreceptors.

The signal transduction mechanism for all four tastes either directly or indirectly involves calcium and salty tastes are produced by Na⁺ ions.

rationale:

The variety of taste receptors on the epithelium of the tongue help the body transmit the information associated with all of the different tastants that we are able to perceive. The taste receptors are chemoreceptors and the tastants are working like chemical ligands onto those receptors. To deliver information about a tastant, neurotransmitters must be released via exocytosis, which is mediated by calcium.

The taste receptors are able to react to a variety of different tastants due to the fact that there are multiple binding sites for different chemicals on one receptor.

All of the taste receptors will release neurotransmitters for signal transduction in order to deliver signals to the brain. The release of neurotransmitter is mediated by calcium in the case of all taste receptors.

Sour tastes are produced by either H⁺ that dissociate from acidic compounds or organic acids or perhaps both.

Na⁺ will be the main chemical responsible for the perception of salty taste.

INCLUDES: malleus, incus, stapes (connects to oval window)

changing shape: rounding up or flattening out

rationale:

The lens focuses light on the photoreceptor cells by changing shape: rounding up or flattening out. This process is known as accommodation and is controlled by the parasympathetic nervous system. When the lens adjusts its shape, it can focus light on the back of the retina leading to the transduction of light energy and the beginning of the visual neural pathway.

The lens is held in place by suspensory ligaments that prevent it from moving around in the eye.

The suspensory ligaments that attach to the lens hold it in place, preventing it from moving in or out.

Opening and closing is a function of the pupil that will adjust the amount of light coming into the eye but not the focus point of that light onto the back of the retina.

where the optic nerve exits the eye

rationale:

The blind spot of the eye is where the optic nerve exits the eye. This region is called the optic disk and signal transduction does not occur from this area. Therefore, anything that falls within the field of the optic disk will not be perceived by the brain.

The location of the retina that has more cones than rods is referred to as the fovea centralis.

The area of the retina where more rods are located than cones is the outer periphery of the retina.

The lens correctly focuses the light on the fovea of the retina.

The sarcomeres shorten during isometric and isotonic contractions.

rationale:

Sarcomeres shorten during both isometric and isotonic contractions. During isometric contractions, the muscle generates increasing amounts of tension on the muscle, but the muscle length remains constant due to the load being greater than the force generated by the muscle. During isotonic contractions, the muscle generates a tension just greater than the force opposing it, which allows the muscle length to change. In order to generate the tension in both types of these contractions, the sarcomeres must shorten.

Only isometric contractions are considered all or none events. The size and shape of an isotonic contraction is dependent on the size of the load placed on the muscle.

Many body movements involve isometric contractions.

Only isometric contractions are considered all or none events. The size and shape of an isotonic contraction is dependent on the size of the load placed on the muscle. In addition, many body movements involve isometric contractions.

b, d, c, a

rationale:

The sequence of events in the crossbridge cycle beginning with myosin binding to actin are: the myosin head releases P_i, the power stroke occurs, which moves the thin filament inward, next the myosin head releases ADP, and the myosin head detaches from the actin filament in order to bind ATP. ATP is hydrolyzed to ADP and P_i, which provides the energy to cock the myosin head and the myosin head binds the actin filament again.

The release of ADP follows the power stroke in crossbridge cycling; it does not precede it.

The myosin head binding ATP follows the release of ADP by the myosin head; it does not precede it.

The release of P_i precedes the power stroke; it does not follow the power stroke.

calcium is bound to the troponin complex and myosin is in its high-energy form

rationale:

Two events must occur prior to myosin binding to actin forming crossbridges. First, the myosin head must be in a high-energy cocked position. By hydrolyzing ATP to ADP and P_i, the energy released is utilized to cock the myosin head. Second, calcium must bind to troponin in order for the tropomyosin to move aside, exposing the myosin binding sites on the actin filament. Following these two events, myosin will bind to actin.

In order for myosin to bind to actin during the crossbridge cycle, calcium must first bind to troponin in order for tropomyosin to move aside, exposing the myosin binding site. However, there is a better answer.

In order for myosin to bind to actin during the crossbridge cycle, myosin must first be in its high energy form. However, there is a better answer.

ATP binding to myosin causes the myosin to detach from the actin filament.

In order to cock the myosin head, ATP must be hydrolyzed to ADP and P_i. Once the myosin head is cocked and calcium is bound to the troponin complex, causing tropomyosin to move aside, myosin can bind to actin.

In order for myosin to bind to actin during the crossbridge cycle, calcium must first bind to troponin in order for tropomyosin to move aside, exposing the myosin binding site. However, myosin binding to ATP causes myosin to detach from the actin filament.

They tend to be recruited first during a contraction and they generate less tension than large motor units.

rationale:

Small motor units tend to be recruited first during a contraction and generate less tension than large motor units. Small motor units are controlled by neurons with smaller-than average cell bodies and small axon diameter. In addition, there is a limited number of muscle fibers innervated in small motor units; hence they generate less tension. Motor unit activation proceeds from the smallest motor units to the largest ones.

Small motor units tend to be the first to be recruited.

Large motor units are innervated by motor neurons with a relatively high threshold for firing an action potential.

Since small motor units innervate a limited number of muscle fibers, they generate less tension than larger motor units.

Large motor units require more excitatory input to fire action potentials than small motor units.

Small motor units generate less tension than large motor units and tend be recruited first during a contraction. However, it is large motor units that are innervated by motor neurons with a relatively high threshold for firing an action potential.

Red, slow oxidative muscle fibers

rationale:

Red, slow, oxidative fibers have high capillary density, high myoglobin content, and high resistance to fatigue. The elevated blood flow and myoglobin promote the oxidative capabilities of these fibers. As a general rule, these muscle fibers are small in diameter and generate minimal amounts of tension.

Red, fast, oxidative fibers have high capillary density and myoglobin content. However, they have an intermediate resistance to fatigue.

White, fast, glycolytic fibers have a low capillary density, low myoglobin content and low resistance to fatigue.

Red, slow, and fast oxidative fibers have high capillary density and high myoglobin content. However, red, fast, oxidative fibers have an intermediate resistance to fatigue while red, slow, oxidative fibers have a high resistance to fatigue.

Red, slow, oxidative fibers have high capillary density, high myoglobin content, and high resistance to fatigue. In contrast, white, fast, glycolytic fibers have a low capillary density, low myoglobin content and low resistance to fatigue.

ATP

rationale:

Muscle relaxation requires ATP for two reasons. First, myosin releases actin in order to bind ATP. Second, ATP is required in order to pump calcium against its concentration gradient into the sarcoplasmic reticulum via the calcium ATPase.

The role of calcium is to bind to the troponin complex, which moves tropomyosin aside, making the myosin binding sites available on the actin filament. The removal of calcium contributes to muscle relaxation because the tropomyosin covers the myosin binding sites on the actin filament.

When the myosin head hydrolyzes ATP to ADP and P_i, the released energy is utilized by the myosin molecule to re-cock the head.

Troponin is a protein that calcium binds to, causing tropomyosin to move aside, making the myosin binding sites available on the actin filament.

ATP is needed for muscle relaxation for two reasons. First, myosin releases actin in order to bind ATP. Second, ATP is required in order to pump calcium against its concentration gradient into the sarcoplasmic reticulum via the calcium ATPase. However, the removal of calcium contributes to muscle relaxation because the tropomyosin moves back to cover the myosin binding sites on the actin filament.

excitation-contraction coupling

rationale:

The latent period is due to the time it takes for excitation-contraction coupling.

The latent period is the time between the action potential in the muscle cell and muscle contraction. It is during this period that the action potential travels down the transverse tubule, changes the shape of the DHP receptor, activates the ryanodine receptor, which allows calcium release from the sarcoplasmic reticulum into the cytosol. The calcium binds to the troponin complex, causing tropomyosin to move aside, exposing the myosin binding sites available on the actin filament, which allows myosin and actin to interact.

Crossbridge cycling occurs during the contraction phase of the muscle twitch.

The production of ATP occurs in the mitochondria; there is no connection between the production of mitochondria and the latent period.

The action potential reaches the motor end plate before the latent period begins.

The latent period is due to excitation-contraction coupling, not crossbridge cycling.

The latent period is due to excitation-contraction coupling, not crossbridge cycling. Moreover, the action potential reaches the motor end plate before the latent period begins.

the two products stay attached to the myosin head, the myosin head is cocked and binds to a different G-actin molecule, ready for the power stroke

rationale:

After the myosin ATPase hydrolyzes ATP into ADP + P_i, the two products stay attached to the myosin head, the myosin head is cocked and binds to a different G-actin molecule, ready for the power stroke. Thus, the presence of ATP in the sarcomere is critical in order for crossbridge cycling to occur.

The two products of ATP hydrolysis remain attached to the myosin head, but there are additional events that follow ATP hydrolysis.

The hydrolysis of ATP results in the cocking of the myosin head, and the head binds to a different G-actin molecule. There are additional events that occur following ATP hydrolysis.

Substances bind to the myosin head following ATP hydrolysis, and there are additional events that occur.

cytosolic calcium levels are high enough to saturate all the troponin molecules, action potential frequency is higher than the fused muscle twitch frequency, and action potential frequency is higher than the fused muscle twitch frequency

rationale:

In order for sustained muscle contraction (tetany) to occur, an elevated frequency of action potentials (greater than the frequency observed during fused muscle twitch) will ensure that appropriate amounts of calcium will be in the cytosol to saturate the troponin complex with calcium in order to prevent the tropomyosin from returning to its original position. The high degree of interaction between actin and myosin will prevent the muscle fibers from relaxing and generate fused twitches resembling a single smooth plateau.

During complete tetanus, cytosolic calcium levels are high enough to saturate all of the troponin molecules.

During complete tetanus, action potential frequency is higher than the fused muscle twitch frequency.

During complete tetanus, no breaks (or periods of relaxation) in muscle tension are observed.

During complete tetanus, muscle twitches fuse into a single smooth plateau.

During complete tetanus, action potential frequency is higher than the fused muscle twitch frequency and muscle twitches fuse into a single smooth plateau.

the rising concentration of cytosolic calcium triggers the closure of calcium channels in the sarcoplasmic reticulum

rationale:

When the arrival of an action potential at the sarcolemmma triggers the release of calcium from the sarcoplasmic reticulum, this process does not go on indefinitely because the rising concentration of cytosolic calcium triggers the closure of calcium channels in the sarcoplasmic reticulum. This phenomena turns off the calcium release from the sarcoplasmic reticulum and promotes the removal of the calcium from the cytosol via the calcium ATPase. A drop in cytosolic calcium concentration results in calcium dissociating from troponin and tropomyosin moves into its original position.

Ryanodine receptors do not become inactive in order to stop the release of calcium from the sarcoplasmic reticulum.

Active transport of calcium into the sarcoplasmic reticulum is ongoing; this process does not stop nor does it start.

The rising calcium concentration does not trigger calcium to release from troponin. The elevated calcium triggers a different phenomenon.

glucose that is metabolized to lactic acid

rationale:

Muscle fibers can obtain energy from glucose that is metabolized to lactic acid when the oxygen supply for catabolism is too slow to meet the ATP demands of heavy exercise.

During heavy exercise, the muscle will perform anaerobic cellular respiration, which includes oxidizing glucose to pyruvate, which is then converted to lactate (lactic acid) in order to regenerate the NAD⁺. This NAD⁺ is needed in order for glycolysis to continue in the cell and generate the needed ATP.

Protein metabolism requires proteolysis (hydrolysis of protein to amino acids) and deamination (removal of the amino group). Proteins do not provide energy to the skeletal muscle during heavy exercise.

Muscle can obtain energy from glucose during heavy exercise, but not by aerobic cellular respiration.

Energy in fatty acids can be harvested in beta (fatty) oxidation, which produces acetyl-CoA that enters the Krebs (citric acid) cycle in order to generate NADH, FADH₂, and ATP. Fatty acids are not utilized by muscle during heavy exercise.

Latent period

rationale:

The latent period is the time between the action potential in the muscle cell and muscle contraction. It is during this period that the action potential travels down the transverse tubule, changes the shape of the DHP receptor, activates the ryanodine receptor, which allows calcium release from the sarcoplasmic reticulum into the sarcoplasm. The calcium binds to the troponin complex, causing tropomyosin to move aside, exposing the myosin binding sites available on the actin filament, which allows myosin and actin to interact.

In order to move a greater load, a muscle must generate greater force. Since it is during the latent period that force is generated, one would expect an increase in the latent period in order to generate the force needed to move a greater muscle load.

The velocity of muscle shortening decreases with increasing muscle load.

The duration of muscle shortening decreases with increasing muscle load.

The definition for the velocity of shortening is the rate of change of the distance shortened. The rate of change of the distance shortened would decrease with increased muscle load.

The velocity of shortening as well as the duration of shortening both decreases with increased muscle load.

The latent period increases with increased muscle load; however, velocity of shortening and the duration of shortening both decreases with increased muscle load.

ATPase activity and actin binding sites

rationale:

Thick filaments are made of myosin molecules grouped together. Each myosin molecule has two heads and two intertwined tails. Each myosin head has two binding sites; one site binds ATP and the other site binds actin. It is important to note that the myosin head cannot bind both ATP and actin at the same time. The myosin head has a greater affinity for ATP than for actin. This is important because a myosin head will detach from an actin filament in order to bind ATP.

Tropomyosin is found in the thin filament, not the thick filament.

Thin filaments, specifically the troponin complex, have a calcium binding site; the thick filaments do not bind calcium.

Thick filaments are made of myosin molecules grouped together. Each myosin molecule has two heads and two intertwined tails. Each myosin head has two binding sites; one site binds ATP. There is a better answer.

Thick filaments are made of myosin molecules grouped together. Each myosin molecule has two heads and two intertwined tails. Each myosin head has two binding sites; one site binds actin. There is a better answer.

Tropomyosin is found in the thin filament, not the thick filament. In addition, thin filaments, specifically the troponin complex, have a calcium binding site; the thick filaments do not bind calcium.

tropomyosin, calcium, and actin

rationale:

The troponin complex in thin filaments can bind tropomyosin, calcium, and actin. The troponin complex consists of three proteins. One protein binds to the actin, another binds to the tropomyosin, and the third reversibly binds calcium. Specifically, when calcium is bound to the troponin complex, it causes tropomyosin to move aside, exposing the myosin binding sites and permitting the myosin crossbridges to interact with the actin filament, initiating crossbridge cycling.

The troponin complex binds to tropomyosin.

The troponin complex binds to calcium.

The troponin complex binds to actin.

The troponin complex does not bind to myosin.

The troponin complex binds to tropomyosin and calcium.

an area of partial overlap between thick and thin filaments

rationale:

The A band contains an area of partial overlap between thick and thin filaments. Another way to describe the A band is this band runs the full length of the thick filament (also known as the myosin filament) which overlaps with portions of the thin filament (also known as the actin filament).

The A band contains the full length of the thick filament, but there are additional filaments found in the A band.

The A band contains the thick filament, but there are additional filaments found in the A band.

The A band contains M line proteins, but there are additional filaments found in the A band.

red

rationale:

Skeletal muscles with the most endurance (resistance to fatigue) are red in color. Red fibers have a high oxidative capacity, meaning these fibers utilize aerobic cellular respiration to generate ATP. In addition, these fibers contain high amounts of mitochondria, capillaries and myoglobin. Myoglobin is a protein in the sarcoplasm of muscle fibers that has a red appearance with the binding of oxygen. These muscle fibers have a slower speed of contraction as well as myosin ATPase activity; these fibers are utilized during aerobic activities.

White skeletal muscle fibers are predominantly utilized during anaerobic exercise, which requires short bursts of high-intensity movement. Elevated glycolytic capacity, speed of contraction and myosin ATPase activity in the muscle make it possible for these fibers to execute short bursts of high-intensity exercise.

Blue skeletal muscle fibers are low in oxygenated blood, which would result in poor endurance.

Yellow skeletal muscle fibers are not healthy.

force generated by individual muscle fibers, number of muscle fibers contracting, and number of active crossbridges formed

rationale:

Tension on a muscle is synonymous with force. The force generated by a muscle depends directly or indirectly on the force generated by individual fibers, the number of muscle fibers contracting, and number of active crossbridges formed.

The force generated by individual fibers would contribute to the amount of force generated by a muscle, but other factors would influence the overall force generated by a muscle.

The number of individual fibers contracting would contribute to the force generated by a muscle, but other factors would influence the overall force generated by a muscle.

The number of active crossbridges formed would contribute to the force generated by a muscle, but other factors would influence the overall force generated by a muscle.

The series elastic component does not actively generate force.

All of the answers contribute to the force generated on a muscle except the series elastic components. The series elastic component does not actively generate force.

Each myosin head completes about five crossbridge cycles per second, but each thick filament has hundreds of myosin heads.

rationale:

During contraction, each myosin head completes about five crossbridge cycles per second, but each thick filament has hundreds of myosin heads. Due to this relationship, thousands of power strokes can occur in a second, resulting in sarcomeres and muscle fibers shortening rapidly. In some instances, a muscle can be fully contracted in less than a tenth of a second. In addition, skeletal muscle fibers are capable of shortening to about 60% of their resting length.

During muscle contraction, there is asynchronous cycling of the myosin filaments, meaning that a group of the myosin filaments are bound to actin while other myosin heads are experiencing the power stroke. Yet still additional myosin heads are experiencing rigor while other myosin heads are releasing actin and being re-cocked.

Each myosin head completes about five crossbridge cycles per minute, not several hundred per minute.

A muscle generates force when the myosin head experiences the power stroke, not when the myosin head is being cocked.

DHP receptors in the T-tubule undergo a conformational change and Ca²⁺ flows down its concentration gradient through the ryanodine receptors

rationale:

When an action potential travels along the sarcolemma of a muscle cell, the DHP receptors in the T-tubule undergo a conformational change and calcium flows down its concentration gradient through the ryanodine receptors. Once the calcium enters the cytosol, it binds to the troponin complex, causing tropomyosin to move aside in order to expose the myosin binding sites on the actin filament. Now, it is possible for crossbridge cycling to occur.

An action potential along the sarcolemma of a muscle cell does not directly stimulate the opening of the ryanodine receptors (voltage-gated calcium channels in the sarcoplasmic reticulum).

An action potential along the sarcolemma of a muscle cell causes a change in the shape of the DHP receptors in the T-tubule. There is a better answer.

Calcium ATPase pumps in the membrane of the sarcoplasmic reticulum are constantly pumping; their activity does not increase and decrease.

An action potential along the sarcolemma of a muscle cell triggers a phenomenon to occur, which results in calcium flowing down its concentration gradient through the ryanodine receptors. There is a better answer.

An action potential traveling along the sarcolemma of a muscle cell does not directly stimulate the opening of the ryanodine receptors (voltage-gated calcium channels in the sarcoplasmic reticulum). However, an action potential traveling along the sarcolemma of a muscle cell causes a change in the shape of the DHP receptors in the T-tubule, triggering the release of calcium down its concentration gradient through the ryanodine receptors.

Myofibril

rationale:

Myofibrils are not found in a sarcomere; sarcomeres packaged end-to-end constitutes a myofibril. Myofibrils are considered the contractile machinery of the cell. Actin, myosin and tropomyosin are proteins found within a sarcomere. Specifically, actin and tropomyosin are found in the thin filaments while myosin constitutes the thick filaments.

Actin is the main protein found in thin filaments located in a sarcomere.

Myosin is the protein that constitutes the thick filaments located in a sarcomere.

Tropomyosin is a protein in thin filaments located in a sarcomere.

acetylcholine

rationale:

Specifically, the motor neuron synapses with skeletal muscle at the neuromuscular junction. An action potential travelling down the axon of the motor neuron stimulates the opening of voltage-gated calcium channels located on axon terminal (terminal bouton). As a result, a calcium influx occurs, causing synaptic vesicles to fuse with the axon terminal membrane releasing acetylcholine into the neuromuscular junction. The acetylcholine binds to nicotinic cholinergic receptors on the motor end plate resulting in a net sodium influx that depolarizes the muscle fiber.

Dopamine is involved in the reticular activating system and the basal ganglia (nuclei) in the brain.

Epinephrine is involved in the reticular activating system in the brain and released from the adrenal medulla.

Dopamine and epinephrine is utilized in the reticular activating system in the brain. In addition, dopamine is released from the basal ganglia (nuclei) and epinephrine is released from the adrenal medulla.

the thin filaments at opposite ends of the sarcomere overlap and the Z lines come into contact with the thick filaments

rationale:

When a muscle is considerably shorter than its optimum length, two factors cause tension to decline as the length decreases. First, the shortening of the sarcomere from its preferred length causes the thin filaments from each sarcomere to overlap, which interferes with the thin filament movement. Second, a sarcomere can shorten to such a degree that the Z lines begin to impact the thick filaments. This results in the force generated being exerted on the sarcomere itself rather than being transmitted to the ends of the muscle fiber.

The number of active crossbridges would decrease if a muscle is stretched too far; shortening a muscle below its optimal length would not impact the number of active crossbridges.

The series elastic components would be stretched as a result of muscle length increasing.

When a muscle is shorter than its optimum length, the thin filaments from each end of the sarcomere overlap, which interferes with the movement of thin filaments.

When a muscle is shorter than its optimum length, the Z lines come into contact with the thick filament, which prevents the force from being transmitted to the ends of the muscle fiber. The force generated is exerted on the sarcomere itself.

When a muscle is shorter than its optimum length, the thin filaments from each end of the sarcomere overlap, which interferes with the movement of thin filaments. However, shortening a muscle below its optimal length would not impact the number of active crossbridges.

pyruvate and lactic acid

rationale:

Molecules that are more likely to be found in higher concentrations in a fast glycolytic fiber include pyruvate and lactic acid.

Fast glycolytic fibers are those that perform anaerobic cellular respiration, which includes glycolysis and the oxidation of pyruvate to lactic acid; these fibers contain a greater concentration of glycolytic enzymes in order to quickly produce ATP via glycolysis. These muscle fibers are utilized to perform high intensity exercise for brief periods. In addition, glycolytic fibers tend to be larger in diameter and surrounded by fewer capillaries.

Fast glycolytic muscle fibers would contain higher concentrations of pyruvate. There is a better answer.

Oxidative fibers contain greater concentrations of myoglobin in the sarcoplasm, which has a red appearance when oxygen is bound to it. These types of fibers perform aerobic cellular respiration.

Fast glycolytic muscle fibers would contain higher concentrations of lactic acid. There is a better answer.

Oxidative fibers contain greater concentrations of oxygen than do fast glycolytic fibers.

Elevated concentrations of oxygen and myoglobin in the sarcoplasm of muscle fibers are characteristics of oxidative muscle fibers.

fatty acids in the bloodstream

rationale:

During a prolonged bout of continuous exercise (longer than 30 minutes), ATP stores are replenished by fatty acids in the bloodstream.

As muscles perform light to moderate exercise, they utilize oxidative phosphorylation in order to generate adequate amounts of ATP. The glycogen in the muscle is utilized first, followed by glucose and fatty acids delivered to the muscle via the blood.

Creatine phosphate in muscle fibers makes ATP production possible for a short period, which provides the time needed for other metabolic reactions to begin to generate ATP.

Creatine phosphate and glycogen stored in the muscle are utilized first to provide the energy needed to generate ATP. However, there is another energy source for use for prolonged bouts of exercise.

During prolonged bouts of exercise another energy source is utilized rather than glucose.

Myosin ATPase activity is found in smooth, cardiac, and skeletal muscle. Myosin ATPase activity is important in crossbridge cycling. ATP is hydrolyzed to ADP and P_i by the myosin ATPase, which provides the energy for the cocking of the myosin head in preparation for the power stroke.

Myosin ATPase activity is found in smooth and cardiac muscle.

Myosin ATPase activity is found in smooth and skeletal muscle.

Myosin ATPase activity is found in cardiac and skeletal muscle.

An increase in the force generated by a muscle is achieved by the recruitment of more motor units.

If a small amount of tension is needed to complete a task, then only a few motor units are stimulated. As a general rule, small motor units are utilized to complete the task. (Small motor units have fewer muscle fibers per one motor neuron.) However, if a greater force is required to accomplish a task, then more motor units are recruited and the motor units are larger. (Larger motor units have many muscle fibers per one motor neuron.)

Fatigue is a decrease in a muscle’s ability to maintain continuous tension during lengthy, repetitive stimulation.

Glycolytic capacity refers to a muscle fiber possessing a high glycolytic enzyme concentration in the cytoplasm, which increases the cell’s ability to produce ATP via glycolysis. Such a capacity would increase the muscle’s ability to perform high-intensity exercise for a short period of time, but is not directly related to the mechanism for generating greater tension on a muscle.

Myosin ATPase activity refers to the enzymatic ability of the myosin head to hydrolyze ATP to ADP and P_i. Different muscle fiber types have various myosin ATPase rates depending on the function of the muscle fiber type.

Calcium binding to calmodulin triggers contraction in smooth muscle. The calcium-calmodulin complex binds to the myosin light chain kinase and activates the enzyme. Once activated, the myosin light chain kinase phosphorylates the myosin crossbridges, which initiates the crossbridge cycle.

Troponin is found in smooth muscle, but calcium does not bind to it in smooth muscle.

Tropomyosin is not found in smooth muscle; hence, calcium cannot bind to it.

Myosin light chain kinase is found in smooth muscle, but calcium does not bind to it.

Dephosphorylation of myosin terminates muscle contraction in smooth muscle, but calcium is not involved in the process.

The thin and thick filaments have an oblique arrangement in smooth muscle, which allows the contraction to occur on various axes. With the assistance of dense bodies (points of attachment between the filaments and the connective tissue within the cell), the contractile force generated is transmitted to the exterior of the cell.

Gap junctions are found in smooth and cardiac muscle. These junctions permit the flow of ions between the cytosol of neighboring cells.

The sarcoplasmic reticulum and the extracellular fluid provide the calcium needed to initiate contraction in smooth muscle. When the cell is depolarized, voltage-gated calcium channels on the sarcolemma open, allowing calcium to enter the cell.

Due to the presence of autorhythmic cells in the heart, cardiac cells do not require input from motor neurons to initiate contraction. The autonomic nervous system innervates the heart with the purpose to regulate heart rate and contractility.

Eccentric contractions perform a lengthening action is a true statement.

There are two types of twitches: isotonic and isometric. These twitches both generate tension but differ from one another as to whether the muscle is permitted to shorten. Isotonic twitches generate just enough force to exceed the load of an object and the muscle length changes, allowing a person to move an object. An example would be picking up a backpack. Eccentric and concentric contractions are types of isometric contractions. Specifically, eccentric contractions result in lengthening of the muscle such as lowering the backpack to the floor. Shortening of the muscle is a concentric contraction; this type of contraction occurs when you pick up a book from a table and bend your elbow. Building tension on a muscle while the length of the muscle remains constant is an isometric contraction. When you attempt to pick up an object that is too heavy to move, isometric contractions occur.

Isotonic twitches generate just enough force to exceed the load of an object and the muscle length changes, allowing a person to move an object.

Building tension on a muscle while the length of the muscle remains constant is an isometric contraction.

Concentric contractions build tension, but the muscle also shortens.

Smooth muscle is subject to the greatest diversity of hormonal control. Smooth muscle is located in various organ systems unlike cardiac and skeletal muscle. Hence, it is reasonable that a variety of hormones are required to regulate smooth muscle activity. For example, epinephrine influences the activity of the smooth muscle in bronchioles and blood vessels while gastrin and cholecystokinin influence the activity of smooth muscle in the gastrointestinal tract.

Cardiac muscle is only regulated by epinephrine.

No hormones regulate skeletal muscle activity.

No hormones regulate skeletal muscle activity, and cardiac muscle is only regulated by epinephrine.

At least one type of muscle is regulated by various hormones.

The amount of force generated on a muscle depends on the number of sarcomeres in parallel, the length of the individual sarcomeres, and the cross-sectional diameter of the muscle fiber.

If a muscle has more sarcomeres in parallel, it means that there are more thin and thick filaments available to generate force.

There is an optimum length for a muscle in order to obtain maximum interaction between the thin and thick filaments to generate the greatest amount of force. When a muscle fiber is too short, a high degree of overlap exists between the thick and thin filaments, which permit a small amount of tension to be generated. If a muscle is stretched too far, there is minimal interaction with thin and thick filaments resulting in a small amount of tension generated. Lastly, more sarcomeres running parallel to each other translates into a larger muscle diameter and a greater ability to generate force.

The number of sarcomeres in series (sarcomeres packaged end to end) does not influence the amount of tension generated.

If a muscle has more sarcomeres in parallel, it means that there are more thin and thick filaments available to generate force.

There is an optimum length for a muscle in order to obtain maximum interaction between the thin and thick filaments to generate the greatest amount of force. When a muscle fiber is too short, a high degree of overlap exists between the thick and thin filaments, which permit a small amount of tension to be generated. If a muscle is stretched too far, there is minimal interaction with thin and thick filaments resulting in a small amount of tension generated.

More sarcomeres running parallel to each other translates into a larger muscle diameter and a greater ability to generate force.

If a muscle has more sarcomeres in parallel, it means that there are more thin and thick filaments available to generate force. More sarcomeres running parallel to each other translates into a larger muscle diameter and a greater ability to generate force.

The fastest way a skeletal muscle cell can generate ATP to power muscle contraction is the transfer of high-energy phosphate on the creatine phosphate (phosphocreatine) to ADP creating more ATP. Direct phosphorylation is one reaction, and it is the fastest means for creating new ATP molecules. Typically, the transfer of the high energy phosphate to ADP produces ATP for a short period of time, but it is an adequate amount of time for other ATP-generating reactions in muscle to begin.

Oxidation of glucose generates considerably more ATP than the amount of ATP produced from utilization of creatine phosphate, but the oxidation of glucose requires more time.

Anaerobic cellular respiration utilizes more enzymatic reactions than producing ATP by transferring the high-energy phosphate from creatine; hence, anaerobic cellular respiration requires more time.

The oxidation of fatty acids involves many reactions, which will require more time to generate ATP than transferring the high-energy phosphate from creatine to ADP producing ATP.

The function of gap junctions is of the greatest importance in maintaining life in cardiac fibers. Pacemaker cells in the heart initiate action potentials which spread to the contractile fibers in the heart via gap junctions, permitting the contraction of the heart and the pumping of the blood. Without gap junctions, each cardiac cell would require innervation, similar to skeletal muscle.

Skeletal muscle does not possess gap junctions.

Smooth muscle, found in the uterus and the gastrointestinal tract, contains gap junctions. However, the heart is much more important in maintaining life.

The amount of force generated on a muscle depends on the number of sarcomeres in parallel, the length of the individual sarcomeres, and the cross-sectional diameter of the muscle fiber.

If a muscle has more sarcomeres in parallel, it means that there are more thin and thick filaments available to generate force.

There is an optimum length for a muscle in order to obtain maximum interaction between the thin and thick filaments to generate the greatest amount of force. When a muscle fiber is too short, a high degree of overlap exists between the thick and thin filaments, which permit a small amount of tension to be generated. If a muscle is stretched too far, there is minimal interaction with thin and thick filaments resulting in a small amount of tension generated. Lastly, more sarcomeres running parallel to each other translates into a larger muscle diameter and a greater ability to generate force.

The number of sarcomeres in series (sarcomeres packaged end to end) does not influence the amount of tension generated.

If a muscle has more sarcomeres in parallel, it means that there are more thin and thick filaments available to generate force.

There is an optimum length for a muscle in order to obtain maximum interaction between the thin and thick filaments to generate the greatest amount of force. When a muscle fiber is too short, a high degree of overlap exists between the thick and thin filaments, which permit a small amount of tension to be generated. If a muscle is stretched too far, there is minimal interaction with thin and thick filaments resulting in a small amount of tension generated.

More sarcomeres running parallel to each other translates into a larger muscle diameter and a greater ability to generate force.

If a muscle has more sarcomeres in parallel, it means that there are more thin and thick filaments available to generate force. More sarcomeres running parallel to each other translates into a larger muscle diameter and a greater ability to generate force.

White, fast glycolytic muscle fibers have a large muscle fiber diameter and a high force-generating capacity. A muscle with a large diameter will contain more actin and myosin filaments. Specifically, muscle fibers with a small diameter generate small forces while large diameter muscle fibers are capable of producing the greatest force.

Red, slow oxidative fibers are small in diameter and generate small forces.

Red, fast oxidative fibers are intermediate in diameter. As a result, these fibers generate medium forces.

Red, slow oxidative fibers are small in diameter and generate small forces. Red, fast oxidative fibers are intermediate in diameter and produce medium forces.

Red, fast oxidative fibers are intermediate in diameter and generate medium forces. However, white, fast glycolytic fibers have the greatest diameter of the three muscle types and are able to produce the greatest amount of tension.

In smooth muscle, the release of calcium from the sarcoplasmic reticulum is regulated by none of the given answers. Depolarization of the smooth muscle causes release of calcium from the sarcoplasmic reticulum and opens voltage-gated calcium channels in the cell membrane, allowing extracellular calcium to enter the cell.

Dihydropyridine receptor is found in skeletal muscle and cardiac muscle. It does not exist in the smooth muscle.

The DAG (diacylglycerol) functions as a second messenger in the phosphatidylinositol system. It does not promote the release of calcium from the sarcoplasmic reticulum in smooth muscle.

A calcium-induced potassium release does not stimulate the sarcoplasmic reticulum in smooth muscle to release calcium.

At least one of the above does not regulate the release of calcium from the sarcoplasmic reticulum in smooth muscle.

The overlap prevents summation of cardiac muscle contractions which allows the heart to relax and fill with blood; it is critical that the heart have time to relax and fill with blood before the next contraction.

It is imperative that cardiac muscle contract in order to pump the blood to its various locations, but it is equally critical that cardiac muscle relax in order for the heart to fill with blood. The high degree of overlap of the action potential and the contractile response ensures that the heart fills with blood before it contracts.

Calcium does not bind to calmodulin in cardiac fibers; calcium binds to troponin in cardiac fibers. Moreover, the binding of calcium to a binding protein is unrelated to the overlap of the action potential and the contractile response.

The binding of calcium to troponin does not prevent calcium from exiting the cell; the rate of calcium entry from the extracellular fluid and the sarcoplasmic reticulum into the cytoplasm of the cell exceeds the rate at which calcium exits the cell.

No relationship exists between the overlap of the action potential and the contractile response of cardiac fibers with the degree of interaction between actin and myosin.

Molecules common to both skeletal and smooth muscle crossbridge cycling include actin. Actin is found in the thin filaments in smooth and skeletal muscle. It is this protein that myosin binds to in order to contract.

Myosin light chain kinase is found in smooth muscle, and activated upon binding with the calcium-calmodulin complex. Once activated, the myosin light chain kinase phosphorylates the myosin crossbridges, which initiates the crossbridge cycle.

Calmodulin is found in smooth muscle, and binds calcium. The calcium-calmodulin complex binds to the myosin light chain kinase and activates the enzyme. Once activated, the myosin light chain kinase phosphorylates the myosin crossbridges, which initiates the crossbridge cycle.

Phosphatases are found in smooth muscle, and they break the covalently bonded phosphate off the myosin in order to terminate contraction.

Actin is involved in both smooth and skeletal muscle crossbridge cycling; however, myosin light chain kinase is unique to smooth muscle.

Actin is involved in both smooth and skeletal muscle crossbridge cycling; however, myosin light chain kinase and calmodulin is unique to smooth muscle.

When a muscle is stimulated at a high frequency such that the twitches build on each other, summation is observed.

An action potential is completed in 2-3 milliseconds, whereas a single muscle twitch may require hundreds of milliseconds to be completed. As a result, a muscle can experience repeated action potentials, causing muscle twitches to build on each other, and greater tension is produced than normally observed with a single muscle twitch. The increased tension produced is a reflection of additional calcium in the cytoplasm of the cell because calcium is being released from the sarcoplasmic reticulum faster than it is being removed.

Fatigue is a decrease in a muscle’s ability to maintain continuous tension during lengthy, repetitive stimulation.

Treppe is observed when single muscle twitches follow each other so closely that the maximum tension of each twitch increases in a step-wise fashion.

An increase in the number of active motor units utilized is called recruitment.

The size principle defines the correlation between size of the motor units and the order in which motor units are recruited. For example, when a small amount of tension is needed, only small motor units are recruited. The greater the tension needed, the larger the motor units recruited.

Actin and myosin generate tension on the muscle through the crossbridge cycle. Unlike skeletal muscle, actin and myosin in smooth muscle are not organized in sarcomeres. The proteins are arranged parallel to one another, but the filaments run in various directions, resulting in contraction occurring along several axes. In fact, dense bodies (points of attachment between the filaments and the connective tissue within the cell) convey the contractile force to the exterior of the cell.

Skeletal muscle receives neural input from the somatic nervous system; smooth muscle is innervated by the autonomic nervous system.

Smooth muscle does not contain more troponin than skeletal muscle. In addition, calcium binds to calmodulin in smooth muscle; it does not bind to troponin.

Skeletal muscle has the fastest myosin ATPase activity compared to smooth and cardiac muscle. In fact, smooth muscle has the slowest myosin ATPase activity.

Both smooth and skeletal muscle possesses actin and myosin. In fact, the crossbridge cycle is identical in both smooth and skeletal muscle. The differences in the two muscle types are the neuronal regulation, the calcium binding proteins they possess and the mode of calcium entry into the cytoplasm of the cells.

The two mechanisms of calcium entry into the cytoplasm of the smooth muscle cells are via the sarcoplasmic reticulum and the extracellular fluid by way of a voltage-gated calcium channel. In skeletal muscle, calcium is released only from the sarcoplasmic reticulum.

Calcium binds to calmodulin in smooth muscle; whereas, calcium binds to troponin in skeletal muscle.

The autonomic nervous system regulates smooth muscle activity; whereas, the somatic nervous system stimulates skeletal muscle.

Both smooth and skeletal muscle contains actin and myosin. However, the two mechanisms of calcium entry into the cytoplasm of the smooth muscle cells are via the sarcoplasmic reticulum and the extracellular fluid by way of a voltage-gated calcium channel. In skeletal muscle, calcium is released only from the sarcoplasmic reticulum.

Smooth and skeletal muscle do not share at least one of the characteristics listed.

Dephosphorylation of myosin by a phosphatase terminates smooth muscle contraction. A phosphatase is required because the phosphate attached to myosin was attached covalently by myosin light chain kinase. Myosin light chain kinase is activated by a calcium-calmodulin complex.

A kinase phosphorylates molecules; it does not remove phosphates.

Calcium does not bind to troponin in smooth muscle; calcium binds to another molecule.

Smooth muscle does not contain tropomyosin; hence, calcium cannot bind to it in smooth muscle.

The false statement is that smooth muscles have more sarcoplasmic reticulum than skeletal muscles. In fact, much of the calcium utilized in smooth muscle contraction comes from the extracellular fluid. When the cell is depolarized, voltage-gated calcium channels on the sarcolemma open, allowing calcium to enter the cell. Calcium binds to the regulatory protein, calmodulin, instead of troponin.

This is a true statement. Calcium binds to calmodulin in smooth muscle; whereas, calcium binds to troponin in skeletal muscle.

This is a true statement. The autonomic nervous system, which is involuntary, regulates smooth muscle, whereas the somatic nervous system stimulates skeletal muscle, which is considered voluntary.

This is a true statement. Myosin ATPase activity is much slower in smooth muscle compared to skeletal muscle. In light of the role of skeletal muscle in innate reflexes, it is important that skeletal muscle myosin ATPase activity be faster.

There are two types of smooth muscle: multi-unit, which lacks gap junctions, but has dense innervation; single-unit, which does have gap junctions, but sparse innervation.

Large arteries and large respiratory passages contain multi-unit smooth muscle. Examples of organs containing single-unit smooth muscle are the gastrointestinal tract and the uterus. In both of these organs, large groups of cells experience synchronized contraction.

Multi-unit smooth muscle lacks gaps junctions while single-unit smooth muscle contains gap junctions.

Multi-unit smooth muscle has dense innervation while single-unit smooth muscle has sparse innervation.

Multi-unit smooth muscle lacks gap junctions, but has dense innervation. Single-unit smooth muscle has gap junctions, but sparse innervation.

Cardiac muscle is similar to smooth muscle in that they contain gap junctions, possess pacemaker cells, and areinnervated by the autonomic nervous system.

The gap junctions permit the flow of ions between the cytosol of neighboring cells. The pacemaker cells in both types of muscle experience increases in membrane potentials due to increases in sodium and calcium permeability. Interestingly, a decrease in potassium permeability also causes an increase in the membrane potentials in smooth muscle. The purpose of innervation of smooth and cardiac muscle is to regulate (not stimulate) the activity of the muscle.

Only cardiac fibers are striated; smooth muscle fibers are not.

Cardiac muscle is similar to smooth muscle in that they contain gap junctions. These junctions permit the flow of ions between the cytosol of neighboring cells. There is a better answer.

Cardiac muscle is similar to smooth muscle in that they possess pacemaker cells. The pacemaker cells in both types of muscle experience increases in membrane potentials due to increases in sodium and calcium permeability. Interestingly, a decrease in potassium permeability also causes an increase in the membrane potentials in smooth muscle. There is a better answer.

Cardiac muscle is similar to smooth muscle in that they are both innervated by the autonomic nervous system. The purpose of innervation of smooth and cardiac muscle is to regulate (not stimulate) the activity of the muscle. There is a better answer.

Cardiac muscle is similar to smooth muscle in that they contain gap junctions and are innervated by the autonomic nervous system. These junctions permit the flow of ions between the cytosol of neighboring cells. The purpose of innervation of smooth and cardiac muscle is to regulate (not stimulate) the activity of the muscle. There is a better answer.

Thick and thin filaments overlap within the A band. The overlap of the thick and thin filaments permits crossbridge cycling to occur.

The H zone is the area where only thick filaments are found.

The I band is the region where only thin filaments are found.

The Z line is the boundary lines for a sarcomere and runs perpendicular to the long axis. It is made of protein, which anchors the thin filaments on one end.

During skeletal muscle contraction, thick and thin filaments bind together forming crossbridges. Calcium must bind to troponin moving tropomysoin aside in order for crossbridges to form. It is during crossbridge cycling that muscle generates tension.

The troponin complex is a combination of three proteins; calcium binds to one of the proteins, causing a conformational change in the complex, which causes tropomyosin to move aside.

The myosin head is the portion of the myosin molecule that binds to actin, forming crossbridges.

Tropomyosin is a regulatory protein attached to actin, but it is not involved in the formation of crossbridges.

The generation of a smooth, steady, maximum tension contraction by a muscle fiber, with no evidence of relaxation, due to a very rapid stimulation of the muscle fiber is known as complete (fused) tetanus.

During tetanus, the calcium levels in the cytoplasm are elevated such that the troponin is saturated and the myosin-binding sites on the actin are continually exposed, allowing maximal interaction between actin and myosin. As a result, maximal tension is generated on the muscle.

The resultant tension generated by an individual muscle cell, a motor unit or a whole muscle to a single action potential is defined as a twitch.

Incomplete (unfused) tetanus is observed when the muscle tension oscillates with small periods of relaxation between the peaks in tension.

The addition of graded potentials generated at a particular site that occurs when it is stimulated at a high frequency is temporal summation. Temporal summation is the mechanism by which tetanus is induced in a muscle.

The burning sensation that is felt in muscles during exercise is due to the buildup of lactic acid. During high-intensity exercise, glycolytic muscle fibers are recruited, and they produce lactic acid because they have low oxidative abilities. Another factor that can promote the production of lactic acid is strong muscle contractions that pinch blood vessels, which decreases the blood supply and oxygen delivery to the muscle.

The depletion of creatine does not cause a burning sensation.

Hydrolyzing ATP to ADP does not cause a burning sensation in muscle.

Pyruvate, a product of glycolysis, does not cause a burning sensation in muscle.

Depletion of glycogen during exercise does not cause a burning sensation in muscle.

Slow wave potentials are found in smooth muscle.

Smooth muscle experiences two types of spontaneous depolarization on a regular basis; they are slow-wave and pacemaker potentials. Action potentials do not necessarily accompany these types of potentials. Slow wave potentials are oscillating depolarizations and repolarizations due to changes in sodium permeability. Pacemaker potentials are slow-wave potential, which are due to change in membrane permeability to sodium, calcium and potassium.

Cardiac muscle experiences action potentials, not slow wave potentials.

Skeletal muscle experiences end-plate potentials and action potentials; slow wave potentials do not occur in skeletal muscle.

Slow wave potentials occur in smooth muscle, but not in cardiac muscle.

The following is in the order from largest to smallest: c. fascicle, b. muscle fiber, a. myofibril, d. thick filament. A fascicle is a bundle of muscle fibers. Muscle fibers are muscle cells and myofibrils are found in the cytoplasm of muscle fibers. Thick filaments are found in sarcomeres, which are contained in myofibrils.

A fascicle and a muscle fiber are larger than a myofibril and a thick filament.

A thick filament is the smallest structure in the list and should be at the end of the list.

A fascicle is larger than a muscle fiber.