Module 4

Question 1

What is the difference between excitable and non-excitable cells?

Answer 1

excitable cells (neurons and muscle cells) can use resting membrane potential to generate an action potential; non-excitable cells cannot

Question 2

Describe the events during an action potential of the Na+ voltage-gated channel

Answer 2

depolarization of membrane, activation gate opens immediately, Na+ flow into the cell, inactivation gate closes, channel returns to resting configuration

Question 3

Define the absolute refractory period

Answer 3

the time when the Na+ channels inactivation gate is closed and the channel cannot be opened for another action potential

Question 4

Describe the events during an action potential of the K+ voltage-gated channel

Answer 4

depolarization of membrane, K+ channel opens after brief pause, K+ flows out of cell, gate closes and channel returns to resting configuration

Question 5

Define the relative refractory period

Answer 5

the time when the membrane is hyperpolarized, it is possible to fire another action potential but requires a stronger stimulus

Question 6

Define threshold

Answer 6

the strength of depolarization required to generate an action potential (-55mV)

Question 7

Describe the changes in mV during an action potential in order

Answer 7

-70mV resting, -55mV threshold, +35mv depolarization, -70mV repolarization, -90mV hyperpolarization, -70mV resting again

Question 8

Define overshoot

Answer 8

the highest membrane potential reading of the action potential (+35mV)

Question 9

Define depolarization

Answer 9

when the resting membrane potential rapidly rises due to Na+ flooding the cell

Question 10

Define repolarization

Answer 10

when the membrane potential falls due to K+ channels opening and K+ flooding out of the cell, and Na+ channels inactivating

Question 11

Define hyperpolarization

Answer 11

when the membrane potential falls below resting due to K+ channels being slow to close (reaching K+ equilibrium potential)

Question 12

Describe the conventional direction of current flow

Answer 12

current flows positive to negative

Question 13

Define action propagation or conduction

Answer 13

the movement of an action potential down an axon

Question 14

Define saltatory conduction and its advantages

Answer 14

some neurons are myelinated, and action potential jumps between nodes of Ranvier (unmyelinated areas), allowing the action potential to move faster down the axon

Question 15

Define myelin

Answer 15

a fatty material insulating an axon, produced by Schwann cells in the PNS and oligodendrocytes in the CNS

Question 16

Describe the all-or-nothing principle

Answer 16

if threshold is not reached, the membrane will naturally repolarize and no action potential will generate; if threshold is reached, an action potential will be generated, and will be of the same strength regardless of the stimulus strength