Lecture 6: Action Potentials

Question 1

What does the term “potential” refer to?

Answer 1

the separation of electrical charge across the membrane

Question 2

What is resting potential?

Answer 2

the membrane potential when a neuron is at rest

Question 3

What is graded potential based on?

Answer 3

the stimulus received by the neuron

Question 4

What may an action potential lead to?

Answer 4

synaptic activity on the next neuron

Question 5

What is diffusion?

Answer 5

net movement of ions from regions of high concentration to regions of low concentration

Question 6

What are two important factors which determine how much current will flow?

Answer 6

electrical potential (V) and electrical conductance (g)
I = g x V

Question 7

What does the movement of any ion through a protein channel depend on?

Answer 7

the concentration gradient and the difference in electrical potential across the membrane

Question 8

What is equilibrium in a selectively permeable membrane?

Answer 8

when there is no net movement of

ions across the membrane, leaving a charge difference between the two sides

Question 9

What are the opposing forces which keep K+ at equilibrium in the cell?

Answer 9

concentration gradient drives K+ out of the cell, while negatively charged proteins pull K+ back inside the cell

Question 10

Why is energy required to keep a cell at resting membrane potential?

Answer 10

sodium-potassium pumps require energy to push ions across the membrane against their concentration gradients

Question 11

What is the state of voltage gated Na+ channels at -65mV?

Answer 11

they are closed

Question 12

What is the state of voltage gated Na+ channels at -55mV and what happens?

Answer 12

they are open
if there are enough open channels there will be a significant influx of Na+ into the cell
if threshold is met then the membrane will become depolarised and the voltage will rise (rising phase and depolarisation)

Question 13

How long are Na+ channels open for and what happens when they close? When will the channel become active again?

Answer 13

open for around 1ms
this will stop the influx of Na+ into the cell and the peak of the action potential is reached
the channel will not become active again until the cell has reached back to -65mV

Question 14

How is the cell repolarised following an action potential?

Answer 14

at 30mV K+ channels are open allowing for an efflux of K+ out of the cell
this will repolarise the neuron and bring it back down to RMP

Question 15

How is hyperpolarisation handled by the cell?

Answer 15

equilibrated by the Na+ and K+ leak channels

Question 16

What is the absolute refractory period?

Answer 16

the period during which the Na+ channels are open and the point at which they are closed and cannot be opened again
another action potential cannot be fired

Question 17

What is the relative refractory period?

Answer 17

the period during which the cell is hyperpolarised and a sufficiently excitatory response is required for another action potential to occur

Question 18

What is saltatory conduction?

Answer 18

when action potentials skip from one node to the next as they travel down a myelinated axon

Question 19

Where are action potentials generated?

Answer 19

the axon initial segment (AIS) is the initiation zone

Question 20

Which two proteins are expressed near the axon initial segment and what is their role?

Answer 20

β4-spectrin and ankyrin-g are proteins that are essential to the organisation of the axonal cytoskeleton
β4-spectrin links ankyrin-g which clusters voltage gated sodium channels and potassium channels to the AIS and the nodes of Ranvier

Question 21

What happens when there are mutations in the genes encoding ankyrin?

Answer 21

severe neurodevelopmental disorders including congenital hypotonia, severe intellectual disability, and motor axonal and auditory neuropathy

Question 22

What is the role of Nav1.9?

Answer 22

amplification of subthreshold stimuli, ultraslow kinetics

Question 23

What is the role of Nav1.1, 1.2, 1.3?

Answer 23

contributes to amplification of subthreshold stimuli, low activation threshold, fast kinetics

Question 24

What is the role of Nav1.7?

Answer 24

contributes to rising phase and amplifies subthreshold stimuli, low activation threshold, fast kinetics

Question 25

What is the role of Nav1.6?

Answer 25

contributes to rising phase, rapid activation and moderate activation threshold

Question 26

What is the role of Nav1.8?

Answer 26

main contributor to rising phase, high activation threshold, slow kinetics

Question 27

When does an action potential occur?

Answer 27

if the combination of graded potentials exceeds a threshold

Question 28

What is the role of dendrites and the soma membrane?

Answer 28

dendrites integrate information

the soma membrane generates graded potentials

Question 29

What must happen in order for an action potential to be generated at the axon initial segment?

Answer 29

the summation of graded potentials must exceed the neuronal threshold

Question 30

Where are voltage gated channels highly expressed?

Answer 30

within the AIS and the nodes of Ranvier with high levels of Nav within the nodal and Kv within the paranondal and juxtaparanodal aspects of the nodes of Ranvier