Action Potentials

Question 1

An action potential

Answer 1

An electrical signal that neurones use to transfer information across the nervous system

Question 2

Action potentials allow

Answer 2

Long range communication
- fast efficient signalling, frequency and pattern of action potentials encode information

Bidirectional communication (forward and backward flow of information)

• Motor commands to muscles
• feedback sensory information (e.g. propiroception, muscle tone, pain)

Question 3

Action potential profile

Answer 3

1. Resting potential
   - A neuron sits at -65mV
   - Sodium channels begin to open
2. Rising Phase
   - If threshold is reached all sodium channels open causing steep depolarisation
3. Falling phase
   - Sodium channels close, K+ channels open repolarising the membrane
4. Undershoot
   - Hyperpolarisation, harder for another action potential to propagate at this time
5. Resting potential
   - When membrane potential returns to resting potential another action potential can then be generated

Question 4

Voltage gated Na+ channels

Answer 4

Channels are closed at rest (-70mV)

Depolarisation to -40mV induces a conformational change in the protein opening a pore

Pore acts as a selectivity filter to allow passage of Na+ ions

Channel opening is very fast and produces rapid depolarisation - then channels become inactive (still open but have physical pore block preventing ion movement

Reopening can only occur when resting membrane potential occurs

Question 5

Voltage gated K+ channels

Answer 5

Require depolarisation to open

Slow to open so doesn’t suppress action of sodium

Channels close when membrane potential returns to rest

Question 6

Refractory period

Answer 6

The time in which an excitable cell is unable to generate a subsequent action potential

Question 7

Absolute refractory period

Answer 7

The period of time where all Na+ channels are open do another action potential could not be generated

Question 8

Relative refractory period

Answer 8

Whether an action potential will be generated is time dependent and also dependent on the strength of the signal due to hyperpolarisation

It’s purpose is to filter the strength of stimulus

Question 9

Threshold

Answer 9

Sufficient voltage gated Na+ channels open to initiate action potentials

Question 10

Influencers of action potential conduction velocity

Answer 10

Na+ channel density
Resistance of cytoplasm/ axon diameter
Resistance of plasma membrane

Question 11

Saltatory conduction

Answer 11

Action potential propagation along myelinated axons

Question 12

Scwhann cells

Answer 12

Produce myelin at different points of the neuron - creating a myelin sheath

Question 13

Myelin sheath

Answer 13

Provides electrical insulation

Question 14

Nodes of rancher

Answer 14

Are where there are gaps in the myelin sheath -> at these points there is a high concentration of sodium channels

Question 15

Axon hillock

Answer 15

Where action potentials are initiated

Question 16

Myelinated axons

Answer 16

Conduct action potentials much faster than unmyelinated axons

Question 17

Action potential propagation along myelinated axons

Answer 17

Domino effect - depolarisation occurs, action potential travels under myelin sheath and passively opens Na+ channels at next node of ranvier

Question 18

Large diameter axons

Answer 18

transport information quicker

Question 19

Thinner diameter axons

Answer 19

Transport information slower

Question 20

Stimulus strength and duration are encoded by

Answer 20

Action potential firing frequency