Brain and Spinal Cord

What two structures make up the CNS?

Sensory Neuron-

–about 10 million

–deliver information to CNS

Describe the roles of the three types of neurons in the spinal cord (sensory, motor, and interneuron). SENSORY

Motor Neuron-

–about 1/2 million

–deliver commands to peripheral effectors

Describe the roles of the three types of neurons in the spinal cord (sensory, motor, and interneuron). MOTOR

Interneuron-

(AKA - association neurons)

–about 20 billion

–interpret, plan, and coordinate signals in and out

Describe the roles of the three types of neurons in the spinal cord (sensory, motor, and interneuron). INTERNEURON

Draw AND label (including the functions of the regions that you label) of a spinal cord cross section.

Diagram AND label the five steps that occur in a neural reflex. Make sure to keep the sensory and motor neurons straight!

Innate reflexes:

• basic neural reflexes
• formed before birth

Acquired reflexes:

• rapid, automatic
• learned motor patterns

Compare and contrast innate and acquired reflexes.

Somatic reflexes:

• involuntary control of nervous system

–superficial reflexes of skin, mucous membranes

–stretch reflexes (deep tendon reflexes) e.g., patellar reflex

Visceral reflexes (autonomic reflexes):

• control systems other than muscular system

Compare and contrast somatic and visceral reflexes.

–monosynaptic - sensory neuron synapses directly onto motor neuron

–polysynaptic - at least 1 interneuron between sensory neuron and motor neuron

Compare and contrast monosynaptic and polysynaptic reflexes.

–spinal reflexes:

• occurs in spinal cord

–cranial reflexes:

• occurs in brain

Compare and contrast spinal reflexes and cranial reflexes.

Have least delay between sensory input and motor output:–i.e. patellar reflex)

Brain cannot override the reflex

Completed in 20–40 msec

Diagram AND label a monosynaptic spinal reflex, using the stretch reflex as an example

Bundles of small, specialized intrafusal muscle fibers:

–innervated by sensory and motor neurons

Surrounded by extrafusal muscle fibers:

–which maintain tone and contract muscle

Explain the roles of intrafusal and extrafusal muscle fibers in the stretch reflex as well as the adjustment of muscles tension in postural reflexes

Get acquainted with some of the common clinical tendon reflexes (as you will be testing these in your patients!)

Diagram AND explain the events that occur during the flexor reflex. Make sure to include that little interneuron!

For Stretch R eflex or the F lexor R eflex to work:

–the stretch reflex of antagonistic (extensor) muscle must be inhibited (reciprocal inhibition) by interneurons in spinal cord

Explain the importance of reciprocal inhibition. Give an example!

Diagram AND label the events which occur during the tendon reflex. What would happen to us if we didn’t have this reflex?

If we did not have the tendon reflex then we would not be preventing skeletal muscles from developing too much tension, tearing or breaking tendons

What would happen to us if we didn't have the tendon reflex?

Ipsilateral reflex arcs:

–occur on same side of body as stimulus

–stretch, tendon, and withdrawal reflexes

Crossed extensor reflexes:

–involves a contralateral reflex arc

–occurs on side opposite stimulus

What does ipsilateral mean? How about contralateral?

Now that you know what ipsilateral and contralateral mean, diagram an example of the crossed extensor reflex.

Occur simultaneously, coordinated with flexor reflex

e.g., flexor reflex causes leg to pull up:

crossed extensor reflex straightens other leg

to receive body weight

Polysynaptic Spinal Reflexes - The Crossed Extensor Reflex

Areas of the brain:

Rostral (toward forehead)

Caudal (toward cord)

Review the meanings of rostral and caudal.

–cerebrum is 83% of brain volume; cerebellum contains 50% of the neurons

What region comprises the bulk of the volume of the human brain?

–Gyri = folds; mountain

–Sulci = grooves; valley

Explain the difference between a gyrus and a sulcus.

Divides cerebral hemispheres

What is a fissure in the brain?

Nuclei = deeper masses of gray matter

Tracts = bundles of axons (white matter)

Explain the difference between nuclei and tracts in the brain

Gray matter = neuron cell bodies, dendrites, and synapses

–forms cortex over cerebrum and cerebellum

–forms nuclei deep within brain

White matter = bundles of axons

–forms tracts that connect parts of brain

Compare and contrast grey and white matter in the brain.

Three Meninges:

Dura Mater- outermost layer- contains the Subdural space

Arachnoid Layer-contains the subarachnoid space

Pia mater-***deepest layer

Two Spaces:

Subdural Space

Subarachnoid space

List the three meninges and the two spaces. Which of these three is located deepest (closest to the brain)?

–from choroid plexus

–through ventricles

–to central canal of spinal cord

–into subarachnoid space around the brain, spinal cord, and cauda equina

Under which layer of the brain does CSF circulate?

Meninges of the Brain

Dura mater

Under which of the layers in the brain are the dural sinuses located?

A subdural hematoma would occur in the space between the dural mater and middle layer of the meninges.

Where would a subdural hematoma occur if someone got hit in the head?

• Inflammation of the meninges
• Usually a disease of infancy and childhood - between 3 months and 2 years of age
• Bacterial and virus invasion of the CNS by way of the nose and throat
• Signs include high fever, stiff neck, drowsiness and intense headache and may progress to coma
• Diagnose by examining the CSF

–lumbar puncture (spinal tap)

Describe the pathophysiology of meningitis? Make sure to include where you would insert a needle during a spinal tap.

Label the locations of the following ventricles:

1. Lateral ventricle
2. Third Ventricle
3. Fourth Ventrilce

Interventricular foramen- connects to LV and 3rdV

Cerebral aqueduct- connects to 3rd and 4th Ventricle

What two ventricles of the brain do each of the following connect:

1. Interventricular foramen
2. Cerebral aqueduct

Brain damage from build up of CSF.

– hydrocephalus

• Enlargement of the head in babies and brain damage in adults

Predict the effects if either the interventricular foramen or the cerebral aqueduct were to become occluded.

Formed by the choroid plexus

CIRCULATES through ventricles, to central canal of spinal cord, into subarachnoid space around the brain, spinal cord, and cauda equina

Functions:

–Forms cushion for brain and other CNS organs

–Gives buoyancy to brain (which reduces weight by 97%) to prevent brain from crushing under own weight

Transports nutrients, chemical messengers, and waste

Where is cerebrospinal fluid made, how is it circulated, and what is its purpose in the CNS? Spend some time looking at the choroid plexus!

Arachnoid villi:

–extensions of subarachnoid space

–extend through dura mater to superior sagittal sinus

Arachnoid granulations:

–large clusters of villi

–absorb CSF into venous circulation

Explain the role of arachnoid villi and arachnoid granulations on the circulation of CSF.

When CSF becomes obstructed

What causes hydrocephalus?

BLOOD BRAIN BARRIER-

Structure: Endothelial cells stitched together by tight junctions

Very effectively protects the brain from many common bacterial infections. Thus, infections of the brain are very rare. ***ASTROCYTES

Compare and contrast the structures involved AND the functions of both blood brain barrier and the blood CSF barrier.

BLOOD BRAIN BARRIER

BLOOD CSF BARRIER- barrier at choroid plexus are ependymal cells joined by tight junctions

Function: Acts as barrier and produces CSF

Compare and contrast the structures involved AND the functions of both blood brain barrier and the blood CSF barrier.

BLOOD CSF BARRIER

–Midbrain

–Pons

–Medulla oblongata

Which portions of the brain make up the brain stem?

Coordinates head and eye movement when we visually follow a moving object or see something out of corner of eye, even when we are not conscious of it

Coordinates head reflex movement to unexpected auditory stimulus – startle reflex

The midbrain is responsible for which functions?

Helps to maintain normal rhythm of breathing

What is the major function of the pons?

Medulla Oblaganta

Which portion of the brain stem adjusts the force and rate of heartbeat, vomiting, sneezing, etc?

Cerebellum

Which major region of the brain coordinates skeletal muscle contractions needed for smooth, coordinated movements of our daily lives?

–Thalamus

–Hypothalamus

–Epithalamus

List the three bilaterally symmetric structures of the diencephalon.

The thalamus makes up 80% of the diencephalon

List the three bilaterally symmetric structures of the diencephalon.

Which of these three makes up the major portion of the diencephalon?

Hypothalamus

List the three bilaterally symmetric structures of the diencephalon.

Which of these three regulates hunger and fullness?

Thalamus

List the three bilaterally symmetric structures of the diencephalon.

Which portion serves as a gateway between the cerebral cortex and the rest of the body (where a sorting out and “editing” process occurs)?

Hypothalamus

List the three bilaterally symmetric structures of the diencephalon.

Which portion of the diencephalon is responsible for regulation body temperature (and does so by initiating sweating or shivering)?

Epithalamus

List the three bilaterally symmetric structures of the diencephalon.

Which portion contains the gland responsible for the sleep/wake cycle?

Hippocampus –organizes sensory and cognitive information into a new memory

Amygdala- emotional memory

They are located in the cerebral hemispheres and diencephalon.

What are some of the structures that comprise the "limbic" system, and where in the brain are they located? What are the general functions of the limbic system?

With Parkinson's Disease, an inhibition of dopamine produces a balanced, restrained output of muscle-regulating signals from the basal nuclei. However with PD, neurons leading from the substantia nigra degenerate and thus do not release normal amounts of dopamine. Without the dopamine the excitatory effects of acetylcholine are not restrained, and the basal nuclei produce an excess of signals that affect voluntary muscles in several areas of the body. Overstimulation of these muscles cause rigidity and tremors of the head and limbs; an abnormal, shuffling gait: absence of relaxed arm-swinging while walking; and a forward tilting of the trunk.

Describe the role of the basal ganglia, using Parkinson’s disease to aid in your explanation. Be specific!

Normal Sleep: decreased activity of Ret. Form. = decreased cerebral cortex activity

Paradoxical Sleep (REM: dream sleep): impulses received by some parts of the brain but not by others.

Comatose: Ret. Form. ceases to function – cerebral cortex can’t be aroused

What are some of the functions of the reticular formation. Make sure to describe the different “types” of sleep.

Fibers that connect areas of the cerebral cortex within the SAME hemispheres of the cerebral cortex

Compare the roles of association fibers, commissural fibers, and projection fibers of white matter. Association Fibers

Fibers that connect one cerebral hemisphere to the other

Compare the roles of association fibers, commissural fibers, and projection fibers of white matter. Commissural Fibers

Fibers that connect the cerebrum and other parts of that brain and/or spinal cord

Compare the roles of association fibers, commissural fibers, and projection fibers of white matter. Projection Fibers

The cerebral cortex

The cerebrum is also called the

Corpus Callosum is a major pathway between the hemispheres.

Aids communication between cerebral areas and between cerebral cortex and CNS

Where is the corpus callosum located, and what is its primary function?

The gray matter makes up the outer portion of the cerebrum and the white matter makes up the inner portion of the cerebrum

The gray matter makes up which portion of the cerebrum? The white matter makes up which portion of the cerebrum?

Locate the following of the cerebrum:

1. Longitudinal fissure
2. Central sulcus
3. Precentral gyrus
4. Postcentral gyrus

Longitudinal fissure

Frontal Lobe

–voluntary motor functions

–planning, mood, smell and social judgment

Parietal Lobe

–receives and integrates sensory information

Occipital Lobe

–visual center of brain

Temporal Lobe

–areas for hearing, smell, learning, memory, emotional behavior

List the four major lobes of the cerebrum AND the main functions of each lobe.

Interpret sensory information

Somesthetic association area (parietal lobe)

–position of limbs; location of touch or pain; shape, weight and texture of an object

Visual association area (occipital lobe)

–identify things we see

–faces recognized in temporal lobe

Auditory association area (temporal lobe)

–recall the name of a piece of music or identify a person by his voice

Describe the location AND functions of the sensory association areas of the cerebrum.

Intention to contract a muscle begins in motor association (premotor) area of frontal lobes

Precentral gyrus (primary motor area) relays signals to spinal cord

–pyramidal cells called upper motor neurons

–supply muscles of contralateral side

Describe the location AND functions of the area(s) of the cerebrum involved in motor control.

Right hemisphere controls left side of body

Left hemisphere controls right side

Decussate is a crossing in the medulla

What does contralateral motor control refer to? Make sure to explain what decussate means!

lots of sensations needed so they have larger area in cerebral cortex

Why are the face and hands represented by such a large region of the cerebral cortex?

Wernicke area posterior

–permits recognition of spoken and written language and creates plan of speech (sensory speech)

Broca area anterior

–generates motor signals for larynx, tongue, cheeks and lips

–transmits to primary motor cortex for action (Motor speech)

Compare and contrast the locations AND functions of Wernicke and Broca’s area in the cerebral cortex.

Lesion to Broca = nonfluent aphasia

–slow speech, difficulty in choosing words

List AND describe the three types of aphasias covered in class. Lesion to Broca

Lesion to Wernicke = fluent aphasia

–speech normal and excessive, but makes little sense

List AND describe the three types of aphasias covered in class. Lesion to Wernicke

Anomic aphasia

–speech and understanding are normal but text and pictures make no sense

List AND describe the three types of aphasias covered in class. Anomic aphasia

a surgical operation involving incision into the prefrontal lobe of the brain

What is a lobotomy?

Left hemisphere - categorical hemisphere

–specialized for spoken and written language, sequential and analytical reasoning (math and science), analyze data in linear way

Right hemisphere - representational hemisphere

–perceives information more holistically, perception of spatial relationships, pattern, comparison of special senses, imagination and insight, music and artistic skill

Highly correlated with handedness

–91% of people right-handed are left side dominant

Lateralization develops with age

females have more communication between hemispheres (corpus callosum thicker posteriorly)

Describe, in detail, the concept of lateralization.

Making Separate Cards.

MEMORIZE the names, numbers, functions, and whether or not each cranial nerve is sensory, motor, or both! You will thank me later for this, even though it seems like a pain in the rear right now! J

Come Back *****

Predict what effects damage to each of the cranial nerves might cause. For example, a person will have trouble moving their right eye in which directions if the Oculomotor Nerve (CN III) is damaged.

Area is monitored by a single receptor cell

The larger the receptive field, the more difficult it is to localize a stimulus

So, when you use the two point pair of blunt dividers, the minimum point to where they can feel both points at the same time then that is where you can locate the nerve densities. Therefore, the further apart the dividers are the more difficult it is to localize a stimulus.

Use the idea of two point discrimination to explain what a receptive field is.

Tonic

–Are always active

Phasic

–Are normally inactive

–Become active for a short time whenever a change occurs

–Provide information about the intensity and rate of change of a stimulus

Compare and contrast tonic and phasic receptors. Draw a couple of graphs!

Use a graph to explain the concept of adaptation.

AKA nociceptors

Pain receptors =

Are common in the:

–superficial portions of the skin

–joint capsules

–within the periostea of bones

–around the walls of blood vessels

Free nerve endings with large receptive fields

Where are pain receptors found?

Myelinated Type A Pain Fibers- Carry sensations of fast pain, or prickling pain, such as that caused by an injection or a deep cut

Type C Pain Fibers- Carry sensations of slow pain, or burning and aching pain

What are the two types of pain receptor fibers and what types of information do each of them carry?

Are free nerve endings located in:

–the dermis

–skeletal muscles

–the liver

–the hypothalamus

Where might one find thermoreceptors?

Tactile receptors:

–provide the sensations of touch, pressure, and vibration

Compare and contrast, in detail, the three classes of mechanoreceptors. Tactile receptors

Baroreceptors:

–detect pressure changes in the walls of blood vessels and in portions of the digestive, reproductive, and urinary tracts

Monitor change in pressure

Consist of free nerve endings that branch within elastic tissues in wall of distensible organ (such as a blood vessel)

Compare and contrast, in detail, the three classes of mechanoreceptors. Baroreceptors

Proprioceptors:

–monitor the positions of joints and muscles

–the most structurally and functionally complex of general sensory receptors

Muscle spindles: monitor skeletal muscle length, trigger stretch reflexes

Golgi tendon organs: located at the junction between skeletal muscle and its tendon, stimulated by tension in tendon, monitor external tension developed during muscle contraction

Receptors in joint capsules: free nerve endings detect pressure, tension, and movement at the joint

Compare and contrast, in detail, the three classes of mechanoreceptors. Proprioceptors

Located in the:

–carotid bodies:

–near the origin of the internal carotid arteries on each side of the neck

Aortic bodies:

–between the major branches of the aortic arch

–Receptors monitor Ph, carbon dioxide, and oxygen levels in arterial blood

Where might you find chemoreceptors? Briefly, how do they work

Exterior white mater – conduction tracts

Internal gray matter - mostly cell bodies

Describe the difference in terms of location AND function of white matter and gray matter in the spinal cord.

Dorsal (posterior) horns – SENSORY NEURONS!

Ventral (anterior) horns – MOTOR NEURONS!

Compare and contrast the dorsal and ventral horns of the spinal cord.

The Afferent (sensory) nervous system is all of the nerve pathways carrying signals TO the brain and/or spinal cord.

Carries toward the central nervous system.

Compare and contrast afferent and efferent neurons. Afferent

The Efferent (motor) nervous system consists of all the nerve pathways carrying signals OUT of the brain and/or spinal cord.

Carries away from the central nervous system

Compare and contrast afferent and efferent neurons. Efferent

Draw out, in detail, the following SENSORY pathways from the spinal cord to the brain, making sure to include what type of information is relayed in each pathway:

1. Posterior columns
2. Anterior spinothalamic tract
3. Lateral spinothalamic tract
4. Spinocerebellar tract

Carries sensations pressure, vibration, and proprioception

Sensory pathway- Posterior column

Carries crude touch and pressure sensations

Sensory pathway- Anterior spinothalamic tract

Carries pain and temperature sensations

Sensory pathway- Lateral spinothalamic tract

conveys information to the cerebellum about limb and joint position

Sensory pathway- Spinocerebellar tract

Upper motor neuron:

cell body lies in a CNS processing center (i.e. cerebral cortex)

• Synapses on the lower motor neuron
• Innervates a single motor unit in a skeletal muscle:

activity in upper motor neuron may facilitate or inhibit lower motor neuron

Lower motor neuron:

cell body lies in a nucleus of the brain stem or spinal cord

• Triggers a contraction in innervated muscle:

–only axon of lower motor neuron extends outside CNS

–destruction of or damage to lower motor neuron eliminates voluntary and reflex control over innervated motor unit

Diagram AND explain the differences between upper and lower motor neurons.

Medulla Oblaganta

Where do most motor fibers decussate as they descend?

Draw out the following MOTOR pathways from the brain to the spinal cord, making sure to include what type of information is relayed in each pathway:

***Lateral c orticospinal tracts (to skeletal muscles of trunk and limbs)

Draw out the following MOTOR pathways from the brain to the spinal cord, making sure to include what type of information is relayed in each pathway: Lateral corticospinal tract

Draw out the following MOTOR pathways from the brain to the spinal cord, making sure to include what type of information is relayed in each pathway: Anterior corticospinal tract

Draw out the following MOTOR pathways from the brain to the spinal cord, making sure to include what type of information is relayed in each pathway: Corticobulbar tract

As they descend, corticospinal tracts are visible along the ventral surface of medulla oblongata as pair of thick bands, the pyramids

What are the “pyrmids” in the medulla of the brainstem?

Predict the effects of an upper vs. a lower motor neuron lesion in the lateral corticopsinal tract.

a. Medial Pathway Components - Primarily concerned with control of muscle tone and gross movements of neck, trunk, and proximal limb muscles
b. Lateral Pathway Components - Primarily concerned with control of muscle tone and more precise movements of distal parts of limbs

Briefly describe the components and functions of the medial and lateral pathways.