Neuro 4 action potentials

Question 1

In which cells are action potential made

Answer 1

Excitatory cells - muscle, neurone and some endocrine

Question 2

What does AP In nerves allow

Answer 2

the transmission of information reliably and quickly over long distances

Question 3

Give Example os some of the role AP plays

Answer 3

They play a central role in cell-to-cell communication and can be used to activate intracellular processes
Eg – muscle cells, an action potential is the first of a series of events leading to contraction.
Eg – beta cells of the pancreas, they provoke release of insulin

Question 4

What is permeability of ions in membrane dependant on

Answer 4

Conformation of ion channel
Open - depolarisation
Inactivated - sustained depolarisation
Closed - depolarisation/hyperpolarisation

Question 5

If there are changes in membrane potential during an AP, what is it not caused by

Answer 5

Ion pumps, and the resting membrane potential is not caused by Na+/K+ ATPase

Question 6

Where is AP made

Answer 6

axon

Question 7

Phase 1 of AP

Answer 7

Resting membrane permeability
High perm to Na+ small perm to K+
Caused by potassium moving out the cell
Membrane potential nearer equilibrium potential for K+ than that for Na+

Question 8

Phase 2 of AP

Answer 8

Stimulus

depolarises membrane potential, moving to more positive value until reach threshold - -55mV

Question 9

Phase 3 of AP

Answer 9

Upstroke
Starts at threshold potential
Permeability of Na increases because the voltage-gated Na+ channels open quickly
Na+ ions enter the cell down their electrochemical gradient

Perm of K+ decreases as the voltage-gated K+ channels start to open slowly
K+ ions leave the cell down their electrochemical gradient
Less than Na+ entering

Membrane potential moves toward the Na+ equilibrium potential

Question 10

Phase 4 of AP

Answer 10

Repolarisation
Permeability of Na+ decreases as channels are inactivated so Na+ entry stops
Permeability of K+ increases as more channels open and remain open
Membrane potential is closer to equilibrium potential of K+

Question 11

What happens at start of repolarisation

Answer 11

Absolute refractory period
In Na+ the inactivation gate is closes, but activation gate is open, so AP cannot be made, regardless of how bit it is. Also causes more potassium channels to open

Question 12

What happens later in repolarisation

Answer 12

Absolute refractory period

In Na+ the inactivation gate and activation gate is closed

Question 13

Phase 5 of AP

Answer 13

After hyperpolarisation
At rest voltage gated K+ channels remain open, However as membrane equilibrium get closer to K`+ equilibrium potential, some voltage gated Na+ channels close.
Then Membrane potential returns to the resting potential

Question 14

What happens During after-hyperpolarization

Answer 14

Inactivation gate is open

Stronger than normal stimulus required to trigger an action potential

Question 15

Describe the Regenerative relationship between PNa and membrane potential

Answer 15

Once threshold is reached the cycle continues via positive feedback behaviour
Cycle continues until the voltage-gated Na+ channels inactivate
Membrane remains in a refractory state until the voltage-gated Na+ channels recover from inactivation

Question 16

Describe ion movement in an AP

Answer 16

Only a very small number of ions cross the membrane and change the membrane potential so very small concentration changes lead to large changes in potential

Question 17

Ion pumps are NOT directly involved in the ion movements during the Action Potential T/F

Answer 17

T

Question 18

How is the electrochemical equilibrium is restored following the action potential

Answer 18

It is restored by K+ and Na+ ions moving through non voltage gated channels. Some ions are exchanged through pumps but this is a relatively slow process (seconds vs milliseconds)

Question 19

Describe passive propagation

Answer 19

Only resting K+ channels are open.

Axon size and myelination alters propagation distance and velocity

Question 20

Describe hoe an Active propagation moves along axon

Answer 20

Used for action potentials, local currents depolarise adjacent area of the axon; previous section refractory so cannot go backwards

Question 21

How is conduction velocity increased

Answer 21

Increased axon diameter and myelination

Question 22

How is conduction velocity decreased

Answer 22

cold, anoxia, compression and drugs (some anaesthetics)