Nervous System Resting Membrane Potential and Action Potentials

what is a stimulus in neurophysiology?

something capable of altering the resting membrane potential

what happens if a stimulus is strong enough and reaches threshold?

action potential fires

what is voltage?

potential energy generated by separation of charge across membrane

what is current?

electrical charge between outside and inside of cell

what does current create?

voltage

what is resistance?

hindrance to charge flow

what are the two types of resistance?

insulator, conductor

what is an insulator?

substance with high electrical resistance

what is a conductor?

substance with low electrical resistance

what is ohm’s law?

current (i)=voltage/resistance

what type of relationship does the current and resistance have?

inverse relationship

what type of relationship does current and voltage have?

direct relationship

what is membrane potential?

difference of charge across a membrane

what is resting membrane potential?

-70 mV

describe the resting membrane potential

polarized, negative inside cell, positive outside

how is the resting membrane potential maintained?

leak channels, sodium potassium pump

how do leak channels maintain the resting membrane potential?

sodium and potassium move down their concentration gradients, sodium in, potassium out

how does the sodium potassium pump maintain the resting membrane potential?

3 sodium pumped out of cell, two potassium pumped in 

what are the membrane ion channels?

leak, chemically (ligand) gated, voltage gated

which membrane ion channel is always open?

leak channel

what are gated membrane ion channels?

protein changes shape to open or close channel

what are chemically (ligand) gated channels?

channels that open with binding of a specific neurotransmitter 

what are voltage gated channels?

channels that open and close in response to changes in membrane potential 

what each Na+ channels have?

two voltage-sensitive gates 

what are the two-voltage sensitive gates for sodium channels?

activation and inactivation gates 

which gates are closed at rest and open with depolarization?

activation gates

during activation, what does depolarization allow for?

sodium to enter cell 

what gates are open at rest and block channels once it is open to prevent more sodium from entering cell?

inactivation gates 

what does each potassium channel have?

one voltage sensitive gate

which channel is closed at rest and opens slowly with repolarization?

potassium channels

what is depolarization?

decrease in membrane potential 

what happens to the inside of membrane during depolarization?

more positive than resting membrane potential

what is hyperpolarization?

an increase in membrane potential

what happens to the inside of the cell during hyperpolarization?

becomes more negative than resting membrane potential 

what does hyperpolarization reduce?

probability of producing a nerve impulse

when does membrane potential change?

concentration of ions across membrane change, membrane permeability to ions changes

what causes change in membrane potential?

graded potentials, action potentials 

what are graded potentials?

short lived, localized changes in membrane potential

how are graded potentials triggered?

stimulus that opens gated ion channels 

where do action potential occur?

axon hillock

what is A?

depolarization 

what is B?

RMP

what is C?

threshold is reached, action potential starts 

what is D?

depolarization- graded potentials 

what is E?

hyperpolarization

what is F?

hyperpolarization 

describe the sodium and potassium channels at the resting membrane potential

sodium channels are open but active, potassium channels are closed 

at what membrane potential will action potential free?

action potential will fire

how do graded potentials reach threshold?

summation

what happens to sodium once the threshold is met?

sodium channels open, sodium rushes in

describe the sodium and potassium channels during depolarization

sodium channels are open and active, potassium channels are closed 

describe the sodium and potassium channels at the peak?

sodium channels are closed and inactive, potassium channels are open 

describe the sodium and potassium channels during repolarization?

sodium channels are open and inactive, potassium channels are open

what is the relative refractory period?

action potential can fire but needs a greater stimulus because it is now farther from threshold

describe the sodium and potassium channels during hyperpolarization?

sodium channels are closed and active, potassium channels are open but closing

what is the all or non phenomenon?

an action potential either happens completely or it does not happen at all 

what does the influx of sodium cause?

local currents

what do local currents cause?

depolarization of adjacent membrane areas in direction away from action potentials origin, toward axon’s terminals

what are the types of refractor periods?

absolute refractory period, relative refractory period

what does it mean when a muscle is in the absolute refractory period?

absolutely no action potentials can be fired 

what does it mean when a muscle is in the relative refractory period?

only a very strong stimulus could stimulate an action potential

when does the absolute refractory period begin?

time from opening of sodium channels until resetting of the channels

what does the absolute refractory period ensure?

that each action potential is an all-or-none event

what does the absolute refractory period enforce?

one way transmission of nerve impulses

when does relative refractory period occur?

when most sodium channels have returned to their resting state, some potassium channels are still open

what is happening during the relative refractory period?

hyperpolarization

how does the central nervous system tell the difference between a weak and strong stimulus?

strong stimuli cause action potentials to occur more frequently

how does the central nervous system determine stimulus intensity?

frequency of the impulses 

what does the rate of action potential propagation depend on?

temperature and pressure, axon diameter, degree of myelination

how does temperature affect the rate of action potential propagation?

warmer temperature = faster

how does axon diameter affect the rate of action potential propagation?

larger diameter fibers have less resistance to local current flow so faster impulse conduction

how does the degree of myelination affect the rate of action potential propagation?

continuous conduction in nonmyelinated axons is slower than saltatory conduction in myelinated axons

why does cold temperature and increased pressure decrease blood flow?

decreases supply of oxygen and nutrients, decreases ability to conduct electrical impulses 

which fibers are faster, large, myelinated, have a short absolute refractory period, and sense danger?

A fibers

which fibers are slower, smaller, myelinated, have longer absolute retraction periods?

B fibers

which fibers are slowest, smallest, unmyelinated, and have the longest absolute retraction period?

C fibers

what role do myelin sheaths play in action potentials?

myelin sheaths insulate and prevent leakage of charge

what does myelination allow for?

salatory conduction

why is conduction slow in nonmyelinated axons?

because it takes time for ions and gates to move

why is conduction in myelinated axons fast?

action potentials are generated only in myelin sheath gaps and appear to jump rapidly from gap to gap

what are the advantages of saltatory conduction?

less energy expended by sodium potassium pump to reset resting membrane potential, increases speed of conduction

what is multiple sclerosis?

autoimmune disease affecting primarily young adults

what is destroyed in multiple sclerosis?

myelin sheaths in central nervous system

what are symptoms of multiple sclerosis?

visual disturbances, weakness, loss of muscle control, speech disturbances, urinary incontinence, cognitive decline

what are treatments for multiple sclerosis?

drugs and dietary changes