Action Potentials

Question 1

What is a membrane stimulus for action potentials?

Answer 1

Membrane depolarisation

Question 2

How is an action potential generated?

Answer 2

When the stimulus strength is at a certain level (THE THRESHOLD)

Question 3

What is the all or none law?

Answer 3

Once AP’s are generated they are always the same size, even though the stimuli’s strength might increase.

Question 4

How do action potentials code information?

Answer 4

Action potentials are coded by sequences of AP’s:

1. The frequency of AP’s
2. The duration of AP’s

Question 5

AP’s need an interval between each AP. What is this known as?

Answer 5

The refractory period. Only when the two stimuli are separated by a sufficient time interval will a second AP be generated after the first (~10 milliseconds)

Question 6

What are the two refractory periods?

Answer 6

1. The absolute refractory period
2. The relative refractory period

Question 7

Why is only a small portion of the membrane depolarized at a time?

Answer 7

To ensure precise signaling, allowing for controlled transmission of nerve impulses without simultaneous activation of adjacent regions.

Question 8

Describe the effect of local currents on membrane depolarisation

Answer 8

Local currents facilitate the spread of depolarisation by influencing adjacent membrane areas, aiding in the initiation and propagation of action potentials.

Question 9

Describe the propagation of action potentials in non-myelinated nerves

Answer 9

Action potentials propagate continuously along the entire length of the nerve fiber, without interruption, due to the absence of myelin sheaths.

Question 10

What cells are myelin sheaths produced by?

Answer 10

Myelin sheaths produced by Schwann cells

Question 11

What is the role of myelin sheaths?

Answer 11

Schwann cells in the peripheral nervous system produce myelin sheaths, insulating and speeding up the conduction of nerve impulses.

Question 12

What are myelin sheaths interrupted by?

Answer 12

Nodes of Ranvier

Question 13

What are Nodes of Ranvier?

Answer 13

Nodes of Ranvier are unmyelinated gaps where action potentials are regenerated, ensuring swift and efficient transmission along myelinated nerves.

Question 14

What is Saltatory Conduction?

Answer 14

Saltatory conduction involves the rapid “jumping” of action potentials between Nodes of Ranvier, significantly increasing the speed of signal transmission. It happens in the propagation of action potentials in myelinated nerves.

Question 15

What factors affect the conduction velocity in myelinated and non-myelinated nerves

Answer 15

In myelinated nerves, conduction velocity is influenced by the thickness of the myelin sheath, while in non-myelinated nerves, it depends on the axon diameter.

Question 16

What happens with the release of neurotransmitters at axon terminals

Answer 16

Neurons release neurotransmitters at axon terminals to transmit signals across synapses, facilitating communication with adjacent neurons or target cells.

Question 17

What are the possible effects of neurotransmitters at synapses and neuromuscular junctions

Answer 17

Neurotransmitters can either excite or inhibit postsynaptic cells, influencing the generation of action potentials and, in the case of neuromuscular junctions, muscle contraction.

Question 18

What characterises the absolute refractory period?

Answer 18

During this period, a neuron cannot generate another action potential regardless of the strength of the stimulus, ensuring a unidirectional flow of nerve impulses.

Question 19

How is the relative refractory period different from the absolute refractory period?

Answer 19

While a stronger-than-usual stimulus can initiate an action potential during the relative refractory period, it requires a higher threshold due to the lingering effects of the previous action potential.