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44 Cards in this Set

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  • Back
what is the difference between graded potential and action potential?
graded: confined to small area; potential change of variable amplitude and duration; it has no threshold or refractory period
action: brief all or none; has threshold and refractory period
Describe where in the cell are the majority of the ions located: K, Na, and Cl.
K is greater intracellulary

Na and Cl greater extracellularly
What is a process? What is a soma?
processes are long extentions of the neurons such as dendrites and axons.

soma are the cell body that contain the nucleus and the ribosomes
describe the functions of the dendrites and axons. what type of potentials do they mostly undergo?
dendrites receive input from neurotransmitters, then undergo graded potential.

axons undergo action potentials to deliver information; involved in output
what part of the neuron is where most signals are generated? where is it located?
initial segment; located between cell body and axon.
what accounts for the different functions of the various parts of the nerve cell?
regional distribution of various membrane-bound channels and pumps
describe how myelin sheaths are formed in the CNS and PNS and what is its role.
in CNS: myelin-foring cells called oligodendrocytes, each may branch to form myelin on many axons

in PNS: individual cells that form individual myelin sheath at regular intervals called Schwann Cells

the presence of myelin allows nerve impulses to be conducted more rapidly
what are nodes of ranvier?
regularly spaced gaps in the myelin sheath around an axon or nerve fiber.
what part of the neuron, myelinated or unmyelinated is where the action potenial is conduced? why is this so?
unmyelinated: nodes of ranvier because contains clusters of Na and K ion channels
Describe the anatomy of an afferent neuron and its location within CNS/PNS.
contains sensory receptors in PNS; axon and cell body also in PNS

the central process is the only part of afferent neuron in CNS

Describe the anatomy of interneueron and its location with CNS/PNS.
it lies entirely within CNS
Describe the anatomy of an efferent neuron and its location within CNS/PNS.
cell bodys of efferent neurons within CNS

axon/axon terminal with PNS
what physical structures constitute the CNS and PNS
CNS: brain and spinal cord

PNS: afferent and efferent neurson
what is axonal transport? what does it depend on?
process involving intracellular filaments by which materials are moved from one end of axon to another

depends on scaffolding of microtubule rails running the length of the axon and specialized types of motor proteins
what is anterograde axonal transport and what protein is involved?
transport from cell body toward axon terminal;
move nutrients, molecules, enzymes, vesicles with neurotransmitters

kinesin protein
what is reterograde transport and what protein is involved?
from axon terminal to cell body; carry recycled membrane vesicles and growth factors

involves dynein
what are neurotrophic factors?
growth factors for neural tissue.
what the criteria for axon repair?
if axon is outside of CNS and there is no damage to cell body
what are glial cells?
surround soma, axon, and dendrites of neurons and physically and metabolically support neurons.
give examples of glial cells in CNS and function.
1. oligodendrocytes: form myelin covering of CNS axons
2. astrocytes: regulated composition of extracellular fluid; stimulate formation of tight jxns to form blood-brain barrier; sustain neurons metabolically
3.microglial: specialized macrophage like cells that perform immune function in CNS
4.ependymal cells: regulated production and flow of cerebrospinal fluid
are lipids conductors or insulators? why?
contain very few qed groups and cannot carry current, therefore regions of high electrical resistance
what is the resting membrane potential?
voltage difference between inside and outside of cell in absence of excitatory or inhibitory stimulation.
what the two factors that influence the magnitude of the resting membrane potential?
1. difference in specific ion concentration in intra/extrcellular fluids
2. difference in membrane permeabilites to the different ions.
what is the equilibrium potential?
the membrane potential at which the concentration gradient force is equal to the voltage gradient. they are equal but opposite. THERE IS NO NET MOVEMENT.
when a neuron is at rest, which ion is still more likely to diffue? why?
K+ because some of its channels are still open, therefore allowing it to diffuse down the concentration gradient
give three examples of graded potential.
1.synaptic potential: produced in postsynaptic neuron in response to presynaptic signals; may be inhibitory or excitatory.
2.receptor potential:produced at peripheral endings of afferent neurons in response to stimuli
3.pacemaker potential: spontaneous or rhythmical behaviors such as breathing, heartbeats
complete the sentences:
1. graded potentials may be...
2. the size of graded potentials is proportional to ...
3. graded potentials decay as...
1. excitatory/inhibitor
2. size of stimulus
3. they move over distance
what is summation?
addition of depolarization events; a graded potential occurs before previous one has died down
what types of channels do graded potentials and action potentials rely on?
graded potentials: leaky K+ channels and Na/K pump

axn potential: voltage-gated
what type of cells are capable of generating axn potentials and graded potentials?
axn: nerve, muslce

graded: all
axn potential: step 1
1. describe resting potential
2. how does stimulus initate axn potential?
1. close to K eq. potential because there are more open K channels
2. opening of voltage-gated Na channels, which leads to depolarization; ENTRY of Na
axn potential: step 2
what period is reached in this step?
membrane reaches critical threshold period; depolarization because POSITIVE feedback loop
axn potential: step 3
Na ions still entering cell. what is happening? what are the charges inside and outside cell?
Na entry causes depolarization which opens more voltage-gated Na channels which causes more depolarization. this process is representated as upstroke of membrane potential and OVERSHOOTS so membrane is positive inside and negative outside.
axn potential: step 4
1. what is the peak value of axn potential?
2. what breaks the cycle and is one contributor of repolarization?
3. what also causes repolarization
1. Na equilibrium potential
2. inactivation gates of Na channels
3. voltage gated K channels, which are slower to open, finally open, causing K to EXIT, moving membrane potential closer to the negative K equilibrium potential
axn potential: step 5
1. the return of membrane to negative potential causes what to happen?
2. what is the cause of hyperpolarization?
1. voltage-gated Na channels go from inactivated to closed state and K channels return to closing state.
2. slow closing of K voltage gated channels; K permeability remains above resting levels and the membrane is transiently hyperpolarized toward the K equilibrium potential
axn potential: step 6
what happens when voltage-gated K channels finally close?
the resting membrane potential is restored.
what prevents cellular accumulation of Na and loss of K?
continuous axn of Na/K pump
how do local anesthetics work?
block voltage gated Na channels, therefore channels cannot open and no axn potential is generated.
inhibit Na influx
what happens during absolute refractory period? why?
nothing... a second stimulus cannot produce another axn potential during this period.

Na channels are either open or inactivated and another axn potential cannot be generated until the Na channels have closed.
what happens during relative refractory period? when and why?
a second axn potential may be generated ONLY if stimulus is greater than usual.

occurs during period AFTER hyperpolarization.

some but not all Na channels have returned to resting state and some K channels that repolarized membrane are still open
what determines the direction of the axn potential propagation?
refractory periods because membrane area that just underwent axn potential is in refractory state and therefore axn potential can only proceed in one direction
why are axn potentials propagated and not graded potentials?
in the axon there are great numbers of voltage gated Na channes therefore small changes in current flow will open many channels and easily reach threshold potential
describe factors that determine the velocity of propagation.
1.fiber diameter: larger is faster b/c larger fibers offer less resistance and more ions flow
2. myelination: present=faster b/c less leakage and jumping also produces faster progagation
what is the phenotype of multiple sclerosis? what effects does this have?
loss of myelin slows or block propagation of impulses, which results in poor coordination, lack of sensation, and partial paralysis