Nervous System Physiology Flashcards Preview

dmd 5248 > Nervous System Physiology > Flashcards

Flashcards in Nervous System Physiology Deck (49):

What is resting potential

the transmembrane potential or a resting cell


how is resting potential established

with Na/K pumps, they pump sodium in and potassium out against their concentration gradient


what is equilibrium potential

the transmembrane potential when there is no net movement of a particular ion across the cell membrane


the equilibrium potential of K = -90mv, Na = 66mv. what is the resting potential of a neuron and why

it is -70 mv. its much closer to the potential of K because the membrane is much more permeable to K than Na


What are the characteristics of the sodium potassium pump

it is powered by ATP
it carries 3 Na+ out, and 2 K+ in
it balances passive forces of diffusion
it maintains the resting potential of -70 mv


what causes membrane potential to change

temporary changes in membrane permeability caused by the opening or closing of specific membrane channels


What are the two types of channels that affect transmembrane potential

passive (leak) channels
- always open
- permeability changes with conditions
active (gated) channels.
- open and close due to stimuli
- at resting potential most are closed


What are the three types of gated channels

chemically gated
voltage gated
mechanically gated


what are chemically gated channels

channels found on the cell body and dendrites that open with chemicals (ACh)


what are voltage gated channels

channels found in axons, skeletal muscle, sarcolemma, and cardiac muscle that are characteristic of an excitable membrane. they open and close due to changes of the transmembrane potential


what are mechanically gated channels

channels found in sensory receptors of touch, pressure, and vibration that respond to distortion of the membrane


what is a graded potential

a temporary and local change in resting potential caused by a stimulus. the larger the stimulus, the larger the change in resting potential


what is depolarization

a shift in transmembrane potential toward 0 mv, caused by a stimuli that causes movement of Na+ through a channel. it depolarizes the nearby plasma membrane


what is repolarization

when the depolarizing stimuli is removed, the resting potential of the membrane moves back to -70 mv


what is hyperpolarization

when the resting potential moves away (lower) from -70 mv (example = -80 mv)


What is an action potential

an electrical impulse produced by graded potentials that propogates along surface of axons to the synapse


what initiates an action potential

graded potentials that are large enought (10-15 mv) at the axon hillock to depolarize it to threshold (-60 to -55 mv) (this is the potential at which sodium voltage gated channels open)


what is the all or none principle of action potentials

action potentials don't vary in strength, if threshold is reached the action potential is the same no matter the strength of the graded potential. if threshold isn't reached there is no action potential


what are the four steps of an action potential

1. depolarization to threshold
2. activation of Na+ voltage gated channels
3. inactivation of Na+ voltage gated channels and activation of K+ voltage gated channels
4. return to normal permeability


what happens at -60 mv

voltage gated Na+ channels open, sodium rushes into the cytoplasm, inner membrane changes from - to +, causing rapid depolarization


What happens at +30 mv

voltage gated Na+ channels close (inactivation gate)
voltage gated K+ channels open
repolarization begins


when do voltage gated K+ channels begin, and finish closing

they begin to close at -70 mv, and finish closing at -90 mv. at this point the membrane is hyperpolarized, but it returns to normal and the action potential is over


what is needed for the Na/K pump to work



what is the refractory period

the time period that starts at the beginning of an action potential and ends when it returns to resting potential during which the membrane will not respond normally to additional stimuli


what are the two refractory periods

absolute = sodium channels are open or inactivated and no action potential can occur
relative = membrane potential is close to normal, and a very large stimulus can cause an action potential


what is propagation of an action potential

the movement of an action potential generated in the axon hillock along the entire length of the axon


what are the two types of action potential propagation, and what determines which kind will occur

continuous propagation (unmyelinated)
saltatory propagation (myelinated)


which is faster and why saltatory or continuous propagation

saltatory, because it essentially skips over the myelinated segements and occurs in the nodes of ranvier


what happens to the propagation speed if you have a large diameter axon

the larger the diameter, the faster the propagation due to less resistance


what are the three different groups of axons

Type A, Type B, Type C


what are type A axon fibers

large, myelinated, high speed axons that carry rapid information to/from the CNS (touch, balance, position, motor impulses)


what are type B axon fibers

medium, myelinated, medium speed axons that carry intermediate signals like sensory information and peripheral effectors


what are type C fibers

small, unmyelinated slow speed axons that carry slower information like involuntary muscle and gland controls


What are the three parts of a synapse

presynaptic neuron
synaptic cleft
postsynaptic neuron


what are the two types of synapses

electrical (direct physical contact between cells)
chemical (signal transmitted across a gap by neurotransmitters)


what are the two types of neurotransmitters

excitatory (cause depolarization and promote action potentials)
inhibitory (cause hyperpolarization and inhibit action potentials)


is ACh an excitatory or inhibitory neurotransmitter

it can be both, which one it is is determined by the receptor, not the neurotransmitter (usually excitatory, but inhibitory at cadiac neuromuscular junctions)


what does AChE do

breaks down the ACh in the synaptic cleft, in order to stop the ACh from activating postsynaptic receptors


what is the synaptic delay

the signals stops at a synapse for .3 mseconds, so fewer synapses = quicker response (reflexes sometimes only have 1)


what is synaptic fatigue

when the neurotransmitter can't be recycled fast enough to meet the demands of intense stimuli


what are some important neurotransmitters



what are neuromodulators

chemicals similar to neurotransmitters, but have slow, long lasting effects.


What are the three ways that neurotransmitters and neuromodulators actually affect postsynaptic cells

direct effects on membrane channels
via G proteins (work through second messengers - adenylate cyclase and cAMP, cAMP opens channels)
via intracellular enzymes
(some other enzyme opens channels)


What are EPSPs and IPSPs

they are postsynaptic potentials
EPSP = excitatory (depolarization)
IPSP = inhibitory (hyperpolarization)


what is summation

when multiple EPSPs are added together so that threshold can be reached


what is temporal and spatial summation

temporal summation is when one presynaptic neuron sends multiple, quick EPSPs that are added together until they reach threshold
spatial summation is when multiple presynaptic neurons send EPSPs at the same time, then they are added together and they reach threshold


what is the effect of hormones and neruromodulators on the activity of neurotransmitters

they can affect the sensitivity to neurotransmitters and thus shift the balance of EPSPs and IPSPs


what is presynaptic facilitation

when there is a synapse that sends EPSPs and causes Na gates to open more on another neuron just before that neurons synapse so that it sends more neurotransmittors


what is presynaptic inhibition

when there is a synapse that sends IPSPs and causes Na gates to close on another neuron just before the synapse of that neuron so that less Na comes in, and less neurotransmitters are sent