Action Potentials

Question 1

what are excitatory events also called/result in?

Answer 1

depolarization

Question 2

what is an action potential?

Answer 2

a wave of membrane potential that sweeps along the axon from cell body to synapse (in the case of a neuron)

Question 3

what forms the wave we see in action potentials?

Answer 3

the wave is formed by the rapid depolarization of the membrane by Na+ influx followed by rapid repolarization by K+ efflux

Question 4

what is threshold?

Answer 4

the potential at which voltage-gated sodium channels open

Question 5

what are EPSPs and IPSPs?

Answer 5

Excitatory postsynaptic potential and inhibatory postsynaptic potential

Question 6

describe how action potentials are all or none

Answer 6

when membrane potential re4aches threshold an AP is irreversibly fired and the amount of depolarization is constant

Question 7

describe the amplitude of action potentials

Answer 7

always the same!

Question 8

what causes more action potentials to be fired? does this change the size of those action potentials?

Answer 8

increasing stimulus intensity can cause MORE action potentials to be fired, but the size of those APs will always be the same

Question 9

what is the absolute refractory period?

Answer 9

a time period where the membrane CANNOT produce another AP because the sodium channels are blocked/inactivated

Question 10

what is the relative refractory period?

Answer 10

this occurs when the voltage-gated potassium channels are open, and potassium is flowing out of the cell, making it harder to depolarize to threshold

Question 11

thanks to cable properties, what happens to resistance to an action potential as the diameter of the axon increases?

Answer 11

resistance decreases as diameter increases

Question 12

what happens to the current produced by an action potential as it moves down an axon?

Answer 12

the current leaks out through ion channels, limiting the distance the depolarization can travel

Question 13

why is the absolute refractory period so important?

Answer 13

an AP sets up a large local circuit that allows depolarization of the membrane next to it as it steps down an axon; but that circuit will also move backwards bc physics so the absolute refractory period keeps the AP from also traveling backwards with that circuit, prevent it from pinging back and forth around membranes

Question 14

describe conduction in an UNmyelinated axon

Answer 14

after the axon hillock (initial segment of axon) reaches threshold and fires an AP, its sodium influx depolarizes regions adjacent to the threshold, generating a new AP in a process that repeats all along the axon; a SLOW process

Question 15

describe conduction in a myelinated axon

Answer 15

ions have minimal flow across a myelinated membrane, so no APs can occur under myelin and no current can leak out, increasing the current speed and allowing the AP to jump from node to node; a FASTER process

Question 16

what characteristics would the fastest conducting axon have? why?

Answer 16

large diameter for least resistance and myelinated for prevent leaks and allow the AP to jump rapidly from node to node

Question 17

how does the membrane get to threshold?

Answer 17

open, leaky sodium channels

Question 18

what happens to the membrane at threshold and how does this impact membrane potential?

Answer 18

the voltage-gated sodium channels fly open, resulting in rapid depolarization

Question 19

why doesn’t the membrane stay depolarized?

Answer 19

the sodium channels snap shut

Question 20

why doesn’t the action potential keep pinging back and forth on the membrane

Answer 20

thanks to the absolute refractory period

Question 21

how would a single cell indicate increase stimulation using only action potentials?

Answer 21

increasing the intensity of the stimulation causes more APs to be fired