Action Potentials

Question 1

What is the resting membrane potential and describe what happens to the neurone?

Answer 1

RMP~70mV
Na+/k+ ATPase pumps
3Na+ out and 2K+ in
Na+ can’t go back in (stay outside)
K+ channels allow K+ to diffuse out
Inside is more negative than outside

Question 2

What is threshold level and what happens when its exceeded?

Answer 2

Action potential whem threshold level exceeds 55mV
Ligand and voltage gated Na+ channels open
Na+ ions move into neurone, becomes more positive inside
Depolarization

Question 3

When does repolarisation take place and what happens?

Answer 3

+30mV
Voltage gated Na+ channels inactivate, Na+ influx stops
Voltage gated K+ channels open, K+ moves out of neurone
If open too long, hyperpolarisation occurs (below -70)
Rectified back to normal

Question 4

When is the absolute refractory period and what happens in it?

Answer 4

When Na+ close

No further AP no matter how strong the stimulus is

Question 5

When is the relative refractory period and what does happens?

Answer 5

Until membrane returns to resting potential
Below threshold level
Can have AP but needs bigger stimulus

Question 6

The refractory periods mean…..

Answer 6

Impulses travel unidirectionally and do not overlap

Question 7

What is myelin made up of?

Answer 7

70% lipid

30% protein

Question 8

What cells myelinate the CNS and how many axons do they myelinate?

Answer 8

Oligodendrocytes
1 oligodendrocyte = myelinate many axons
Branch to form myelin for as many as 40 axons

Question 9

What cells myelinate the PNS and how many axons do they myelinate?

Answer 9

Schwann cells

1 cell = 1 myelinated axon

Question 10

What are the spaces between the myelinated sections called?

Answer 10

Nodes of ranvier

Question 11

What does myelin do to conduction?

Answer 11

Increases the speed of conduction along axons

Question 12

What are myelinated axons particularly needed for?

Answer 12

Long distances

Question 13

Myelinated axons are…..

Where are myelinated axons found?

Answer 13

Thicker

Somatic nerves, muscle & spinal systems, fast sensory/motor systems

Question 14

Unmyelinated axons are…..

Where are unmyelinated axons found?

Answer 14

Thinner

Post ganglionic autonomic fibres, olfactory neurones, hypothalamus

Question 15

When AP jump from one node to the next along a myelin fibre, what is this called?

Answer 15

Saltatory conduction

Question 16

What 2 diseases are caused by damage to the myelin sheath?

Answer 16

Multiple sclerosis

Guillain Barré syndrome

Question 17

What happens in MS?

Answer 17

Degeneration of myelin amd development of scar tissue
Disrupts and eventually blocks neurotransmission along myelinated axon

Symptoms:
• Uncontrolled eye movements - seeing double • Slurred speech
• Partial/complete paralysis
• Tremor
• Loss of co-ordination
• Weakness
• Sensory numbness, prickling, pain

Question 18

What happens in guillain barré syndrome?

Answer 18

Damage to PNS myelin, muscle weakness and pain