Neurons

Question 1

What are neurons?

Answer 1

Nerve cells - present in the nervous system

Question 2

What are neurons specialised for?

Answer 2

communication

Question 3

What do neurons connect with?

Answer 3

• Each other and with other ‘excitable cells’ e.g. muscles, glands

Question 4

Name 6 different types of neuron?

Answer 4

• Purkinje cell
• Spinal interneuron
• Sensory neuron
• Pyramidal cell
• Motor neuron
• Bipolar cell

Question 5

What is the resting membrane potential?

Answer 5

A potential difference existing across the membrane of all cells

Question 6

What is the range of values for a resting membrane potential?

Answer 6

• 20-90mV

Question 7

How are charged distributed across the membrane?

Answer 7

• The inside is negative with respect to the outside
• There are approximately equal numbers of positive and negative charges on each side of the membrane, but they are not evenly distributed

Question 8

What is resting membrane potential determines by?

Answer 8

• Diffusion of K+ from cell interior through K+ channels

- The sodium potassium pump also continuously moving unequal amounts of Na & K (3 Na out to 2 K in)

Question 9

What can the membrane potential be altered by?

Answer 9

• By applying an electric current (stimulus) to the cell

Question 10

Explain the process of an action potential?

Answer 10

• If the MP is raised to around -55mV, a large depolarisation occurs
• The MP ‘overshoots’ zero, so that the polarisation is reversed
• This large change in MP is called the ‘action potential’
• The action potential is an ‘all or none’ event
• The AP amplitude is independent of the stimulus intensity

Question 11

What happens ‘at threshold’ of an action potential?

Answer 11

• Voltage-gated Na+ channels open

- Na+ diffuse in –> depolarisation

Question 12

What happens at the ‘peak’ of an action potential?

Answer 12

• Na+ channels close
• Voltage-gated K+ channels open
• K+ diffuse out –> repolarisation

Question 13

What does local anaesthetic do?

Answer 13

Stops nerve conduction by blocking the Na+ channels (so will not allow the activity of pain)

Question 14

What is the refractory period?

Answer 14

• After an AP is initiated, the neuron cannot regenerate another AP until the first one has ended
• This period of inexitability is called the refractory period

Question 15

What causes the refractory period?

Answer 15

• It is due to the inactivation of voltage-gated sodium channels

Question 16

What is action potential propagation (a wave of depolarisation)?

Answer 16

• An AP in one section of an axon depolarises adjacent ‘resting’ parts of the axon
• The AP is regenerated further along the axon
• Action potentials travel along the axon as waves of depolarisation

Question 17

What increases the speed of AP propagation?

Answer 17

• Increasing the axon diameter
• Large axons conduct impulses more rapidly than small ones
• But rapid conduction is achieved only with very large axons

Question 18

What can greatly increase the AP conducting speed of an axon?

Answer 18

• Wrapping a layer of myelin around the axon (myelin sheath)

Question 19

What is myelin and how is it formed?

Answer 19

• Myelin is a fatty layer
• Formed by wrapping the membranes of ‘glial’ cells around the axon
• This in effect ‘insulates’ the axon, and improves conduction

Question 20

What is a ‘node of Ranvier’?

Answer 20

• Intervals that interrupt the myelin sheath (areas with no insulation - exposure of membrane to ECF)
• Here, the axon membrane is exposed to the ECF, and ion flow can occur

Question 21

What is Saltatory conduction?

Answer 21

• The rapid passage of an electric potential between the nodes of Ranvier in myelinated nerve fibres, rather than along the full length of the membrane