Lecture 3-4: Action Potentials

Question 1

List and describe the 3 characteristics of action potentials

Answer 1

all or none principle
self-propagating - each depolarization generates the next action potential on both sides
non-decremental - does not decrease in strength

Question 2

name the 2 types of gated ion channels

Answer 2

ligand gated

voltage gated

Question 3

voltage gates have ___ number of gates, name them

Answer 3

2 gates
activation gate
inactivation gate

Question 4

Action potentials can travel is all directions from the point of stimulation, what does orthodromic direction mean?

Answer 4

the direction normally taken = toward the distal end of the axon —> dendrites

Question 5

Action potentials can travel is all directions from the point of stimulation, what does antidromic direction mean?

Answer 5

opposite of the direction normally taken = toward the axon hillock/neuron cell body

Question 6

why do action potentials typically travel in the orthodromic direction even though they are capable of all directions?

Answer 6

because of refractory period

Question 7

define refractory period

Answer 7

period during which a second action potential cannot be generated until the cell returns to resting state

Question 8

how are nodes of Ranvier significant to propagation speed of action potentials?

Answer 8

they are unmyelinated junctions between schwann cells on axons, thus allowing the signal to jump from node to node. resulting in an increase in propagation speed

Question 9

why do small diameter axons conduct action potential slower than large diameter axons?

Answer 9

a large diameter allows for multiple pathways, thus resulting in less resistance, allowing a faster conductance

Question 10

what would be the characteristic of the fastest conducting axon vs the slowest conducting axon in humans?

Answer 10

fast = large diameter & myelinated

slow = small diameter & non-myelinated

Question 11

what are the two subsets of refractory period?

Answer 11

absolute & relative refractory period

Question 12

define relative refractory period and explain why it is different than absolute refractory period?

Answer 12

relative - period of time right after the abs period in which a second action potential is inhibited but not impossible = requires a stronger than normal stimuli

in abs period = impossible to make a second AP no matter how strong a stimuli

Question 13

-90mV

Answer 13

resting membrane potential

Question 14

+35mV

Answer 14

apex of depolarization

Question 15

-65mV

Answer 15

threshold for action potential

Question 16

describe sodium voltage gated channels at rest

Answer 16

sodium voltage gates have 2 gates
activation gate is closed at rest
inactivation gate is open at closed

Question 17

describe sodium voltage gated channels at +35mV

Answer 17

activation gate in open

inactivation gate is closed

Question 18

describe sodium voltage gates during depolarization and what is voltages?

Answer 18

going from -90 to +35
activation gate opens at -70 and stays open
inactivation gate is open from rest and closes at +35

Question 19

describe sodium voltage gates during repolarization and what is voltages?

Answer 19

going from +35 to -90
inactivation gate closes at +35
activation gate is open and does not close until rest at -90

Question 20

once a channel inactivates, it cannot re-open until it transitions back to resting state

Answer 20

refractory period

Question 21

how can an axon increase speed of conduction?

Answer 21

increase axon diameter

increase axolemma resistance

Question 22

how does increasing axon diameter effect conduction rate?

Answer 22

large diameter = large cross-sectional area for internal flow
a lot of different paths to take = less resistance

Question 23

how does increasing axolemma resistance effect conduction rate?

Answer 23

the current will flow at points of least resistance, which will be the unmyelinated junctions between schwann cells, allowing the AP to jump from node to node

Question 24

how can an axolemma resistance be increased?

Answer 24

by having layers of insulation = myelination or myelin sheath
creating a capacitor effect

Question 25

explain the difference between absolute and relative refractory period

Answer 25

abs - no 2nd AP can be conducted no matter how strong the stimulus is

relative - period right after abs, where a stronger that normal stimulus can produce a 2nd AP

Question 26

describe relative refractory period

Answer 26

in this period a second action potential is inhibited but not impossible
method = increased K+ conductance

Question 27

Na, K, Ca, Cl - permeability at resting potentials

Answer 27

Na - low
K - more than Na
Ca - low
Cl - moderate

Question 28

the intracellular environment is always more _____ than the intercellular environment.

Answer 28

more negative

Question 29

the diffusion potential across a membrane that exactly opposes the net diffusion of a particular ion through the membrane

Answer 29

Nernst potential

Question 30

as long as a concentration gradient exists, diffusion will continue

Answer 30

diffusion potential

Question 31

equilibrium will be reached when the electrical force driving ions out, exactly equals the force driving those same ions in

Answer 31

equilibrium potential

Question 32

the sum of cation concentrations must be equal to the anion concentrations within the same compartment

Answer 32

electrical neutrality

Question 33

equilibrium is only satisfied when equilibrium potentials for both ions is equal

Answer 33

Donnan equilibrium

Question 34

resting membrane potential of nerves

Answer 34

-90mV

Question 35

electrical potential across the membrane must exactly balance the concentration gradients for both ions, when there are two different ion concentrations on each side of the membrane

Answer 35

Donnan equilibrium

Question 36

Nernst equation

Answer 36

=61.5 x log ( [outside] // [inside] )