Human Anatomy and Physiology with Interactive Physiology 10-System Suite: Anatomy Test 2 Flashcards

1. Gather sensory information both internal and external
2. Process information, filter and interpret information
3. produce a response: voluntary or involuntary

brain and spinal cord

- nerves not located in the CNS
- hotlines to and from CNS
- spinal and cranial nerves

To CNS
- nerves send impulses to CNS
- Somatic Afferent Fibers
- Visceral Afferent Fibers

From CNS
- nerves carry impulses from CNS
- Somatic (voluntary) nerves
- Autonomic (involuntary) nerves
- sympathetic
- parasympathetic

1. Nerve cells (neurons) - information messengers. Most diverse kind of cells in body
2. Supporting cells (neuroglia) outnumber neurons by up to 9:1
Cells are densely packed so there is little extracellular space

1. Astrocytes
2. Microglia
3. Ependymal Cells
4. Oligodendrocytes

- most abundant glial cells
- outnumber neurons by about 10:1

1. help form a network on which neurons grow
2. anchor neurons to capillaries
3. mop up 'leaked' neurotransmitters

- protective role
- sense microbes and debris
- transform into macrophages and phagocytose debris

- line cavities of brain and spinal cord
- are ciliated - to circulate cerebral spinal fluid

- wrap their branches around large nerve fibers (axons) and create an insulating cover or Myelin Sheath - for up to 60 axons

1. Satellite Cells
2. Schwann Cells

- function unknown
- surround neuron cell bodies in ganglia

- wrap around large nerves to create a Myelin Sheath
- just like Oligodendrocytes but can only surround 1 axon at a time

Cells of nervous systems are neurons
- are ~100 billion neurons in the CNS
- specialized to conduct electrical impulses
- normally 80 times per second
- in epilepsy can fire up to 500 times per second
- last your entire life
- amitotic - do not divide
- very high metabolic rate; need constant supply of glucose and oxygen

- many different shapes
- usually large, complex
- receptive region (dendrites)
- cell body (soma)
- conducting region (axon)
- output region (nerve terminal)

also called the Soma
- contains usual organelles
- nucleus, ribosomes, ER, golgi, mitochondria
- neurofibrils - maintain cell shape and integrity

a cluster of cell bodies in the CNS

a cluster of cell bodies in the PNS

- branching extensions of the cell body
- also contain cytoplasm and organelles
- provide increase in surface area for input signals
- some are 'thorny' - dendritic spines
- transmit incoming information to axon hillock by Graded Response

- one per neuron
- arises from axon hillock
- short or long (nerve fiber)
- can branch (axon collaterals)
- usually has about 10,000 terminal branches
- is the conduction component of a neuron i.e. transmit impulses
- Terminals are the secretory component (Nt's)
- contains organelles, but NO ER or Golgi
- axon relies on cell body for protein synthesis
- axons decay quickly when damaged

plasma membrane of axon

From cell body to terminal
- mitochondria
- replacement molecules for axolemma, NT synthesis
- Transported by the protein kinesin

To cell body from terminal
- molecules and organelles for degradation and recycling
- transported by the protein dynein

- large, long axons are covered in Myelin (fatty protein) that electrically insulates axons
- increases transmission of nerve impulses along axon
- 150x faster than unmyelinated
- Formed by Schwann Cells
- cells wrap themselves around axon many times
- tight coil of wrapped membranes

a gap left between adjacent Schwann cells
axon is exposed at node
axon collateral at node

myelinated fibers

unmyelinated fibers and cell bodies

1. Multipolar
2. Bipolar
3. Unipolar

- 99% of neurons
- numerous dendrites
- 3 or more cell processes

have 2 processes (axon and dendrite)
- rare. found in sensory organs
ex. retina of eye, olfactory mucosa

- 1 process emerges from cell body
- most are sensory neurons in PNS

- neurons communicate with each other by generating nerve impulses
- nerve impulses are electrical currents that travel through neurons.
- in the dendrites and cell body the electrical current is called a GRADED RESPONSE
- in the axon the electrical current is called an ACTION POTENTIAL

a short lived, local change in membrane potential (depolarization). This change causes current to flow that decreases in strength with distance

a large, short depolarization event that does NOT decrease in strength with distance. They occur only in axons, sarcolemma and T-tubules

1. the dendrites and cell body have chemical and/or mechanical gated ion channels
2. The axons, sarcolemma and T-tubules have voltage gated ion channels

First, all plasma membranes must be polarized at rest.
- that means there is a voltage difference across membrane

- Because there are leaky ion channels sprinkled all over the membrane of the neuron
- therefore, more positive ions (K+) leak out of the cell then leak back in (Na+).

allows K+ to leak out of the cell easier than Na+ can leak back into the cell

pumps out 3 positive ions (Na+) for every 2 it pumps in (K+)

more positive charges collect on the outside surface of the cell membrane than the inside surface creating a voltage difference of -70mV, called the Resting Membrane Potential

Inside cell is more negative than outside (-70mv)
- called a polarized state
- occurs ONLY at membrane
- cytoplasm is neutral
- extracellular space is neutral

- a change in Resting Membrane Potential such that the inside now becomes more positive than it was when at rest

- information is carried by nerves in the form of electrical current

1. graded respons
2. action potential

- occur at sensory receptor endings and dendrites
- produced by a stimulus
- are short lived, local changes in RMP
- cause electrical current flow that DECREASES with distance
- magnitude of change in membrane potential is related to magnitude of stimulus

1. A small region of membrane becomes depolarized
2. At point of stimulus inside of cell has the charge
3. positive charge will flow laterally (attracted to negative charge)
- Outside cell positive charges flow to less positive region created by depolarization
- the greater the initial depolarization the greater the currents
- as positive charges move laterally the membrane becomes depolarized
- this effect becomes weaker and weaker the further the current travels from site of initial stimulus

- generated by excitable tissue i.e. nerves and muscle cells
- are brief reversals of membrane potential
- change in amplitude is by about 100mv (never changes)
- takes about 3 milliseconds (never changes)
- is an all-or-none event
- voltage change travels along axon/sarcolema/t-tubules
- in a neuron the traveling voltage change is called a nerve impulse

1. RMP ~ -70mv
2. a depolarization sufficient to reach threshold
Once threshold is reached the depolarization is self-perpetuating
- no further stimulus required
- polarity is reversed. inside now more positive than outside
3. repolarization phase (neuron refractory)
4. after hyper-polarization
- neuron are refractory (will not respond)

1. RMP generated by Na+/K+ pump. Deficit of the positive ions inside cell. RMP ~ -70mv. Na+ and K+ channels closed
2. Voltage gated Na+ channels open causing depolarization fo membrane. At -55mv local depolarization is sufficient to spread along membrane opening more voltage gated Na+ channels
More Na+ enters --> membrane depolarizes further till all Na+ channels open
- before AP peaks - Na+ channels begin to close
- inside of cell begins to repel further entry of Na+
- AP peaks - net influx of Na+ stops
K+ gates open. K+ exits cell i.e. positive ions exit cell. Returns inside cell to negativity (Repolarization)
3. K+ gates are to slow to close causing excessive K+ efflux leading to an after hyperpolarization or undershoot

Repolarization; ionic distributions

from the opening of the Na+ channels to the resetting of the Na+ channels. The neuron cannot respond to another stimulus while in this phase

- action potentials are propagated (transmitted) along the entire length of the axon
- the influx of Na+ establishes a current that depolarizes adjacent membrane areas
- flow of current is unidirectional as no current will flow in a refractory region

- skeletal muscle - faster in nerves
- gut, glands - slower in nerves

1. axon diameter
2. myelination

larger diameter axon means less resistance to flow of ions which means membrane reaches threshold faster and impulses travel faster

in unmyelinated nerves AP's are generated next to each other - one after another - continuous conduction
In myelinated nerves AP's occur ONLY at node of Ranvier
- no Na+ channels under myelin sheath
- current flows under myelin from node to node so nerve conduction of impulses is faster
- called saltatory conduction

1. group A
2. group B
3. group C

mostly sensory and motor fibers serving:
- skin
- skeletal muscles
- joints
Have:
- large diameter, thick myelin sheaths
- speed of conduction is up to 300 mph

Autonomic Nervous system sensory and motor fibers
- small somatic sensory fibers (pain and small touch fibers)
- are medium diameter
- lightly myelinated
- speed of conduction is 40 mph

Same fibers as group B
- small diameter
- unmyelinated
-no saltatory conduction
- speed of conduction is 2mph

1. Multiple Sclerosis
2. Amyotrophic Lateral Sclerosis (ALS)

- an autoimmune disease
Symptoms - poor vision
- poor muscle control:
- clumsiness
- weakness
- paralysis
Immune system makes antibodies to myelin so there is destruction of myelin sheath which leads to slow impulse conduction
- Leakage and short-circuting of electrical current
- eventually impulse conduction stops

- Lou-Gehrig's Disease
- Motor NEuron Disease
- Degeneration of motor nerves - Sporadic 90-95% of cases - familial 5-10% of cases
Familial cases have mutation in gene for SOD1 - no protection from free radicals

- nerve impulses travel along Motor Neurons
- end of axon branches forms a Neuromuscular Junction (NMJ) with a single muscle fiber
- NMJ - motor nerve ending (terminal)
- synaptic cleft
- motor end plate

- contains synaptic vesicles (sacs containing neurotransmitter).
A NEUROTRANSMITTER (NT) is a chemical message.
At the NMJ the NT is Acetylcholine (Ach).

- is a gap between nerve terminal and sarcolemma

A dimple in the sarcolemma
- junctional folds of sarcolemma
- Ach receptors
- transmembrane proteins that bind Ach
- transmit chemical signal into electrical signal

1. Nerve impulse travels down axon
2. Impulse reaches nerve terminal
3. voltage gated Ca2+ channels open
4. Ca2+ flows into nerve terminal
5. Ca2+ fuses with synaptic vesicles
6. Synaptic vesicles fuse with terminal membrane (presynaptic membrane)
7. Exocytosis of Ach into Synaptic Cleft
8. Ach diffuses across synaptic cleft
9. Ach attaches to Ach Receptors on postsynaptic membrane
10. Ach Receptors trigger depolarization of Sarcolemma
11. Depolarization Spreads to T-Tubules
12. Causes Ca2+ binds toponin ... etc

1. decrease nerve impulses
2. Acetycholinesterase in synaptic cleft degrades Ach
- most rapid mechanism
- lifetime of Ach in Synaptic Cleft ~ 200 microseconds
In some cases the neurotransmitter (e.g. Dopamine) is recycled by the nerve terminal

Myasthenia Gravis
- muscle weakness
- difficulty swallowing
- drooping eyelids
Autoimmune disease
- immune system developed antibodies to Ach Receptors
- Ach receptor number is low

Botanical agent from S. America
Binds to Ach R's
Prevents Ach from binding
Causes muscular paralysis
used as a muscle relaxant during surgical anesthesia

drugs that inhibit (block) acetylcholinesterase (AchE)
Ach does not degrade
too much Ach in Synaptic cleft leads to excessive stimulation of Ach R's and leads to muscle paralysis
Phsostigmine
Insecticides - parathion, malathion (organo phosphates)
Nerve gases (organo phosphates) - sarin, tabun, soman and VX (kills within minutes)

to increase tone in smooth muscle of GI tract and bladder
- myasthenia gravis

- one of the most potent poisions known
- found in fugu (Japanese) or puffer fish
- block Na+ channels in skeletal muscle
- cell cannot depolarize
- death is by paralysis of respiratory muscles

BOTOX
- from bacteria Clostidium Botulinum
- block Ach release from nerve terminal
- paralysis of muscles

- procaine, lidocaine, cocaine
- prevent conduction of nerve impules
- block Na+ channels

- synapses release and receive NT's
- NT's act at Receptors to open or close ion channels and cause changes in membrane permeability

1. Nerve terminal - contains synaptic vesicles that fuse with presynaptic membrane to exocytose NT's into synaptic cleft
2. A receptor region - an area of the postsynaptic membrane with specific neurotransmitter receptors

- NT release causes depolarization or postsynaptic membrane
- These Graded depolarizations are called Excitatory Postsynaptic Potentials (EPSP's)
- if enough EPSP's are produced an AP will be triggered at axon hillock

- NT release induces hyperpolarization of postynaptic membrane
- these graded hyperpolarizations are called Inhibitory Postsynaptic Potentials (IPSP's)
- if enough IPSP's are produced generation of AP's at the axon hillock will be prevented

to date there are over 50 NT's
most neurons make 2 or more NT's
neurons can release one or all NT's

NT's are classified based on chemical structure
1. Acetylcholine (Ach)
2. Biogenic Amines
3. Amino Acids

- released at NMJ - excitatory
- degraded by AchE

Dopamine, norepinephrine, epinephrine (adrenalin), serotonin, histamine

Inhibitory - Gamm AMinobutyric Acid (GABA)
Excitatory - Glycine, Aspartate, Gluatmate

found in the walls of hollow organs (except the heart)

- spindle shaped
- one central nucleus
- much smaller than skeletal muscle cells
- endomysium located between muscle fibers
- muscle cells arranged in sheets
- sheets found in all hollow organs except capillaries

- two sheets of smooth muscle found in most organs
1. longitundinal layer
2. circular layer

- one sheet runs parallel to long axis or organ
- contraction --> dilation --> shortening

- fibers run around circumference of organ
- contraction --> constriction --> elongation

alternating contraction/relaxation of muscle sheets

Bladder
Uterus
Rectum
Bronchi --> asthma
Stomach --> cramps

no NMJ
innervated by autonomic nerves
- have varicosities
- wide synaptic cleft
- called diffuse junctions
- less developed SR
- no T-tubules
- Plasma membrane pouches CAveoli - stores Ca+
Caveoli and SR provide Ca2+ for contraction
- no stiations (no sarcomeres)
- do contain thick and thin filaments
- arranged diagonally
- therefore contract like a slinky
Have non-contractile intermediate filaments- to resist tension

Adult Brain Regions - named from embryological development
Brain forms from neural tube (day 26)

Anterior (rostral)
Posterior (caudal)

forebrain
midbrain
hindbrain

Telencephalon
Diencephalon
Mesencephalon
Metencephalon
Myelencephalon

Telencephalon - Cerebrum: cerebral hemispheres (cortex, white matter, basal nuclei)
Diencephalon - Diencephalon (thalamus, hypothalamus, epithalamus), retina
Mesencephalon - Brain stem: midbrain
Metencephalon - Brain stem: pons; Cerebellum
Myelencephalon - Brain stem: medulla oblongata

Telencephalon - lateral ventricles
Diencephalon - third ventricles
mesencephalon - cerebral aqueduct
Metencephalon - 4th ventricle
Myelencephalon - 4th ventricle

1. Outer layer (cortex) - Gray matter (neuronal cell bodies)
- Covers cerebral hemispheres and cerebellum
2. Below cortex is white matter (myelinated axons)
3. Deeper in brain are islands of gray matter - called nuclei
4. Nuclei surround ventricles of brain

Are hollow chambers filled with cerebrospinal fluid (CSF)
- Two lateral ventricles
- One deep in each hemisphere
- connect to the third ventricle by interventricular foramen of Monroe
- One third ventricle
- connects to fourth ventricle by cerebral aqueduct
- one fourth ventricle
- continuous with central canal of spinal cord
- have 3 openings (apertures)
2 lateral apertures
1 medium aperture