Topic 19: Action Potentials

Question 1

What is membrane potential?

Answer 1

the potential to do work

Question 2

What is voltage?

Answer 2

a measurement of membrane potential

Question 3

What are excitable cells?

Answer 3

cells that can rapidly change membrane potential

Question 4

What is the resting potential?

Answer 4

MP of a cell at rest

-70mV

Question 5

Why is the inside more negative than the outside?

Answer 5

because of the Na/K pump

and ion channels

Question 6

What is the sodium-potassium pump? Where is it found? What does it do in relation to action potentials? Active or passive?

Answer 6

transmembrane transport protein
found of PM throughout neuron
3 Na+ out and 2 K+ in
Active transport (charged ions cannot diffuse)

Question 7

What does hyperpolarization do?

Answer 7

becomes more negative inside the cell
MP decreases below RP
it is inhibitory

Question 8

What does depolarization do?

Answer 8

becomes less negative inside cell
MP increases above RP
it is excitatory

Question 9

What is action potentials?

Answer 9

electrical signal within neuron

Question 10

How are voltage gated ion channels opened?

Answer 10

by a stimulus

-> facilitated diffusion of that ion down concentration gradient

Question 11

What forms the concentration gradient?

Answer 11

Na/K pump

Question 12

What happens when the VG sodium channels open?

Answer 12

Na+ rushes into the cell

-> inside becomes more positive (depolarization)

Question 13

What happens when the VG potassium channels open?

Answer 13

K+ rushes out of cell

-> inside becomes less positive (hyperpolarization)

Question 14

What is the membrane potential when the neuron is at rest?

Answer 14

-70 mV

Question 15

What happens when there is a small stimulus?

Answer 15

FEW Na+ gates opne
weak depolarization
MP does not reach -55 mV
No AP

Question 16

What happens when there is a strong stimulus?

Answer 16

MANY VG Na+ channels open
Strong depolarization
if MP reaches -55 mV -> AP

Question 17

During the rising phase, what voltage does the depolarization reach?

Answer 17

+35 mV

Question 18

What happens after the rising phase, when the voltage reaches +35 mV?

Answer 18

Na+ gates close
K+ gates begin to open
by +35 mV, K+ gates now fully open
K+ diffuses out
repolarization

Question 19

What happens during the undershoot phase?

Answer 19

Na+ gates closed
K+ gates start to close slowly
hyperpolarization occurs
when the K+ gates fully close, it then returns to RP

Question 20

Where does continuous conduction occur in?

Answer 20

unmyelinated axons

Question 21

What happens during continuous conduction?

Answer 21

every spot on axon depolarizes, repolarizes

Question 22

Where does saltatory conduction occur in?

Answer 22

myelinated axons with myelin sheath

Question 23

What are internodes?

Answer 23

regions covered in myelin - no depolarization

Question 24

What are nodes of ranvier?

Answer 24

no myelin - lots of Na+, K+, VG channels

depolarization only occurs at nodes

Question 25

What happens in multiple sclerosis? What are symptoms?

Answer 25

immune system attacks myelin sheath and oligodendrocytes in CNS

• > slows AP conduction, exposes nerve fibers to damage
• > weakness, impaired vision, numbness… depends on sites of damage