Chapter 3 B Action Potential

Question 1

What is depolarization?

Answer 1

Depolarization is a decrease in membrane potential. It is when the interior of the cell becomes less negative and closer to zero. Negative ions leave the cell and positive ions come in.

Question 2

What is hyperpolarization?

Answer 2

The interior of the membrane becomes even more negative and farther from zero. Negative ions come into the cell and positive ions leave the cell.

Question 3

What is a graded potential?

Answer 3

A stimulus will cause a small changes in the membrane potential.

Question 4

Stimuli that depolarize enough to reach the threshold will produce a what?

Answer 4

An action potential.

Question 5

Pacinian Corpuscles are sensitive to?

Answer 5

Vibration & pressure.

Question 6

Graded potentials vary depending on the size of the?

Answer 6

Stimulus

Question 7

Action potentials are very quick large electrical pulses in the membrane of the what?

Answer 7

Axon.

Question 8

A change in resting membrane potential has to occur for them to be initiated.

Answer 8

Action potentials. They are voltage dependent.

Question 9

Action potentials are characterized by a rapid reversal of the membran potential from what voltage to what voltage and then back down to what?

Answer 9

-40mV to + 40mV and then back down to -70mv. They are “all or none” they either reverse the membrane potential to +40mv or they do not.

Question 10

Action potentials begin where?

Answer 10

At the axon hillock and always travel down to the terminal button.

Question 11

Amplitude is independent of stimulus size. True or false?

Answer 11

True

Question 12

What are the five phases of an action potential?

Answer 12

1. Depolorization. Threshold. Rising. Falling. Hyperpolarized ( undershoot)* two refractory periods.

Question 13

Define depolarization

Answer 13

Inside of a cell becomes more positive because of an excitatory stimulus. ( Graded potentials or positive current injected via a microelectrode.

Question 14

Threshold phase

Answer 14

This is the level of stimulation required for a neuron to produce an action potential. It represents the opening of voltage-gated ion channels.

Question 16

Where are voltage gated sodium channels located?

Answer 16

At the axon hillock.

Question 17

Voltage-gated sodium channels

Answer 17

Are closed at membrane potential -60 mv. Then open for a milisecond when the membrane is depolarized to about -40mv at the threshold.

Question 18

What is the rising phase?

Answer 18

The membrane potential becomes more positive because sodium rushes into the cell through voltage-gated sodium channels. Voltage-gated potassium channels begin to open.

Question 19

Falling Phases

Answer 19

Potassium rushes out of the cell via voltage-gated potassium channels causing membrane potential to become more negative.

Question 20

Hyperpolarized ( undershoot phase)

Answer 20

Voltage gated potassium channels close slowly , and potassium leaves the cell, until the membrane potential becomes more negative than normal.

Question 21

What do sodium/potassium pumps do?

Answer 21

They restore membrane potential to resing membrane potential. Passive ions are also open and allow chloride to come in.

Question 22

Absolute & relative refractory period

Answer 22

The time the neruon is insensitive to further stimulation and therefore it is impossible to elicit an action potential. It starts at the peak or the action potential and continues through the falling phase. Inactivation gate blocks channel and does not reset until membrane has reached RMP.

Question 23

Relative Refractory Period

Answer 23

Follows the absolute refractory period. A neuron can generate another action potential, but is has to be stronger than a normal stimulus.

Question 24

Intensity of a stimulus is encoded by the?

Answer 24

Firing rate of a neuron and the number of neurons firing an action potential. The more intense stimuli can cause more neurons to fire an action potential.

Question 25

Unmyelinated Axon

Answer 25

Sodium rushing in via voltage-gated sodium channels and depolarizes the membrane, which triggers the opening of adjacent voltage-gated sodium channels.

Question 26

Action potential regenerates where?

Answer 26

At the Node of Ranvier. Electricl current jumps from node to node aka ( Saltatory conduction.)

Question 27

Multiple Sclerosis

Answer 27

Immune system attacks the cells that form myelin on axons of some neurons. Action potentials are not transmitted efficiently.