Action Potential

Question 1

label the structures of the neuron

Answer 1

Question 2

ion permeability in cells

Answer 2

Sodium - leaks a little into cell

Chlorine - doesn’t leak

Potassium has a big amount of leakage out of the cell

Question 3

if the membrane permeability changes allowing more Na⁺ ions to enter the cell will the RMP become more or less negative

Answer 3

less negative

Question 4

if the membrane permeability changes allowing more Cl^- ions to enter the cell, will the RMP become more or less negative

Answer 4

more negative

Question 5

mechanically gated ion channels

Answer 5

deforming the membrane opens the channel

ex) touch

Question 6

chemically gated ion channel

Answer 6

a chemical binding the channel (ligand)

Question 7

voltage gated ion channels

Answer 7

voltage changes in the cell to open the channel

Question 8

label the following diagram and indicate what electrical events are important in each zone

Answer 8

input zone: graded potential

trigger zone: action threshold (depends on if threshold value is reached)

conducting zone: action potential (travels here)

output zone: passes signal to next neuron by releasing neurotransmitters

Question 9

depolarization

Answer 9

cell becomes more positive than RMP

Question 10

repolarization

Answer 10

cell returns to the RMP

Question 11

threshold

Answer 11

the minimum voltage that will initiate an action potential

Question 12

hyperpolarization

Answer 12

a membrane potential that is more negative than the RMP

Question 13

What causes hyperpolarization?

Answer 13

the voltage gated potassium channels are slow to close which allow excess potassium ions to diffuse out the cell to make the cell membrane potential

Question 14

graded potential

Answer 14

• occurs in dendrites and soma
• mechanically gated and chemically gated
• signal strength decreases
• amplitude is directly proportional to stimulus strength
• result is a action potential
• temporary changes in membrane voltage

Question 15

graded potentials do not travel all the way down the axon like action potentials do. Instead, they travel only a short distance and the signal loses strength over time. Why?

Answer 15

the graded potential returns loses strength because the cell’s electric graded potential returns to equilibrium (decay) from ion leak channels

Question 16

action potential

Answer 16

at the axon hillock of the neuron, if the depolarizing stimulus reaches threshold (-55 mV), an action potential will be triggered and will go down the axon (Na⁺ voltage-gated channels open)

• “all or none”
• require sufficient depolarization to reach reach threshold
• are the result of opening voltage gated ion channels
• are the same amplitude and duration in a given neuron
• only travel in one direction down an axon
• will trigger the release of neurotransmitters to pass the signal onto another cell or neuron

Question 17

label and explain each step in the action potential

Answer 17

1-3: Depolarization due to graded potential (Na+ in via mechanically or chemically gated channels opening) to threshold

4: Triggers opening of Na+ voltage-gated channels—Na+ enters (depol.)​
5: Na+ voltage-gated channels quick to close—Na+ stops entering​ (activation gate is open, inactivation gate is closed)

K+ voltage-gated channels slower to open—K+ starts leaving neuron​

6: K+ leaving causes repolarization back to RMP​
7: K+ voltage-gated channels slow to close so K+ continues​ to leave (hyperpolarization)​

8-9: K+ voltage-gated channels close and returns to RMP​

Question 18

voltage-gated sodium channel

Answer 18

has 2 gates, activation and inactivation gate

Question 19

when do voltage gated sodium channels open?

Answer 19

around -55 mV the voltage-gated sodium channels open creating a large influx of sodium into the cell

Question 20

why does the sodium gated channel in action potentials have 2 gates?

Answer 20

the inactivation gate closes and opens much faster than the activation gate, allowing sodium to quickly enter and leave

Question 21

absolute refractory period

Answer 21

during depolarization the sodium voltage gated channels are already opened and so can’t be stimulated to create another action potential

Question 22

relative refractory period

Answer 22

during hyperpolarization when the activation gate is closed and inactivation gate is closed

there can be an action potential, but it would take a greater stimulus than usual to activate it as the cell is more negative than RMP

Question 23

what happens to the gates during depolarization?

Answer 23

cell becomes more positive than RMP

potassium gate is closed

sodium activation and inactivation gate are open

Question 24

what happens to the gates during repolarization?

Answer 24

cell returns to the RMP

potassium gates are open

sodium activation gate is open

inactivation gate is closed

Question 25

what happens to the gates during hyperpolarization?

Answer 25

a membrane potential that is more negative than the RMP

potassium gates are open

sodium activation gate is closed

inactivation gate is open

Question 26

Na+ Voltage-Gated Channel: depolarization (at threshold)

Answer 26

activation gate: open

inactivation gate: open

Question 27

Na+ Voltage-Gated Channel: Structure at -70 mV (RMP)

Answer 27

activation gate: closed

inactivation gate: open

Question 28

Na+ Voltage-Gated Channel: repolarization

Answer 28

at peak of action potential, inactivation gate closes to stop Na⁺ from entering

activation gate: open

inactivation gate: closed

inactivation gate re-opens and activation gate closes at RMP (remaining throughout hyperpolarization)

Question 29

voltage-gated potassium channel

Answer 29

K⁺ voltage-gated channel is much slower to open than the Na⁺ voltage-gated channel

so we dont see the effects until a little later in the action potential

K⁺ leaving causes repolarization and the hyperpolarization of the action potential

has a single gate (activation gate)

Question 30

leak channels

Answer 30

always opened channels

channel-mediated diffusion