The Action Potential

Question 1

What is the action potential?

Answer 1

Transientchangein themembrane potentialcapable of nondecremental self propagationalong an axon of the neurone which allows neurones tocommunicatewith other neurones.

Question 2

List the properties of the action potential. (5)

Answer 2

• Robust
• Rapid
• Orthodromic
• All or nothing
• Frequently encoded

Question 3

What is a compound action potential (CAP)?

Answer 3

A population response, sum of action potentials from all the axons simultaneously contributing to the signal.

Question 4

What are graded potentials/postsynaptic potentials?

Answer 4

Small changein membranepotentialbelow threshold that occurs is a small region of the neuronal membrane.

Question 5

What determines the magnitude of graded potentials?

Answer 5

Magnitudeof membrane potentialchangerelatedto thesizeof thestimulus

Question 6

What are the features of a graded potential?

Answer 6

Can be Depolarising (EPSP)orhyperpolarising(IPSP), have a decremental response and are not self propagating.

Question 7

What is summation?

Answer 7

-Process thatdetermines whetheranaction potential will begeneratedfrom the combinationof excitatory and/or inhibitorypostsynaptic potentials

Question 8

What is spatial summation?

Answer 8

Cumulative change inpostsynaptic membrane potentialas a result ofmultiple, differentsimultaneous inputs

Question 9

What is temporal summation?

Answer 9

cumulative change inpostsynaptic membrane potentialas a result ofsequential repeatedinputs

Question 10

Who led key experiments to record the AP extracellularly?

Answer 10

Erlanger and Gasser, 1920’s

Question 11

Who led key experiments to record the AP intracellularly?

Answer 11

Hodgkin and Huxley, 1939.
Electrode is inserted inside the axon and outside of the cell, to measure the differences in membrane potential, whilst also applying a stimulus to see how membrane potential changes.

Question 12

Who invented the Voltage clamp technique?

Answer 12

Hodgkin and Katz, 1949

Question 13

What is the purpose of the voltage clamp experiment?

Answer 13

To identify if Na+ is controlling the peak depolarisation in an action potential.

Question 14

What were the findings of the voltage clamp experiment?

Answer 14

They used various concentrations of Na+ and stimulated an action potential in each, discovering that in lower concentrations the peak and the rate of rise of an action potential was lower.

Question 15

What happens to voltage gated ion channels at rest?

Answer 15

Neither of the voltage gated ion channels are open.

Question 16

When the action potential is rising what happens to the VG ion channels?

Answer 16

Na+ voltage gated ion channels open quickly, causing a sodium influx into the cell, they shut when reaching the peak of the action potential.

Question 17

When the action potential is falling what happens to the VG ion channels?

Answer 17

K+ voltage gated ion channels open causing K+ to efflux out of the cell, they take time to close so they cause hyperpolarisation.

Question 18

How is the refractory period generated?

Answer 18

Voltage Gated Na+ Channels have 2 gates, Inactivation gate and activation gate. After depolarisation the inactivation gate closes to prevent the stimulation of another action potential causing a refractory period.

Question 18

How is the refractory period generated?

Answer 18

Voltage Gated Na+ Channels have 2 gates, Inactivation gate and activation gate. After depolarisation the inactivation gate closes to prevent the stimulation of another action potential causing a refractory period.

Question 19

What occurs as a result of loss of function in voltage gated Na+ Channels?

Answer 19

• Don’t fireaction potentials
• Reduced transfer of information
• E.g.lossofsensations

Question 20

What occurs as a result of gain of function in voltage gated Na+ Channels?

Answer 20

• Over fireaction potentials
• Excess transfer of information
• E.g.increased sensitivitytosensations

Question 21

How is the strength of a stimulus shown through the action potential?

Answer 21

Firing rateof action potentialsencodes thestrength of thestimulus. An Increased stimulus=increased frequencyNOTamplitude

Question 22

How does axon diameter affect conduction velocity?

Answer 22

Inc. diameter → Inc. velocity.

Question 23

How does the presence of myelin affect conduction velocity?

Answer 23

Presence of Myelin increases velocity as well but it is dependant on the size of the axon as axons < 1 micrometre don’t benefit from myelination.