L17: Neurons

Question 1

What is the function of Purkinje cells (found in the cerebellum, heart)?

Answer 1

Conduct nerve impulse for contraction

Question 2

What is a spinal interneuron?

Answer 2

• Important for reflexes;

- Form motor responses without the cortex.

Question 3

What is a sensory neuron?

Answer 3

Receive nerve impulses

Question 4

What is a motor neuron?

Answer 4

Relay nerve outputs

Question 5

Describe resting membrane potential (RMP)

Answer 5

A potential charge difference across the membrane of all cells

Question 6

What is RMP in nerve cells?

Answer 6

-70mV

Question 7

At RMP, what is the difference in charges across the membrane?

Answer 7

Inside (ICF) is NEGATIVE to outside (ECF) i.e. polarised

Question 8

How is RMP maintained?

Answer 8

Na-K pump contributes by moving 3 Na+ OUT and 2 K+ IN

Question 9

What does a hyperpolarising current do?

Answer 9

Moves the membrane potential further from 0

Question 10

What does a depolarising current do?

Answer 10

Moves the membrane potential closer to 0, i.e. leads to depolarisation of neuron

Question 11

What is the intensity of the output dependent on?

Answer 11

Action potential frequency

Question 12

What is the threshold potential?

Answer 12

-55mV

Question 13

What happens at threshold potential?

Answer 13

• Opening of voltage-gated sodium channels;

- Influx of sodium.

Question 14

What does an influx of sodium cause?

Answer 14

Depolarisation

Question 15

When do voltage-gated sodium channels close?

Answer 15

+35mV

Question 16

What happens at +35mV?

Answer 16

• Voltage-gated sodium channels close;
• Voltage-gated potassium channels open;
• K+ leave, taking positive charge with it;
• Start of repolarisation (ICF becomes more negative).

Question 17

What is repolarisation?

Answer 17

Rebalance of ions back to -70mV MP

Question 18

What is the refractory period?

Answer 18

When a membrane repolarises, no action potentials can be generated in this period (inactivation of Na+ channels)

Question 19

Why can nerve impulses only move in one direction?

Answer 19

Refractory period

Question 20

How do local anaesthetics work?

Answer 20

By blocking the Na+ channels, so no action potentials can be generated

Question 21

How does the speed of action potentials differ with the diameter and width of an axon?

Answer 21

Longer or wider axons conducti

Question 22

How does myelination effect the conduction speed?

Answer 22

Increases

Question 23

How do nodes of Ranvier (intervals within the myelin sheath) speed up electrical impulses?

Answer 23

• Axon is exposed to ECF;
• NOR are rich in ion channels where quick exchange can happen;
• Action potentials ‘jump’ (conduct) between NOR rather than along entire length of axon.