Action Potentials

Question 1

What causes multiple sclerosis (MS) ?

Answer 1

Axonal neurotransmission failure

Degeneration of myelin and development of scar tissue disrupts and eventually blocks neurotransmission along myelinated axons

Question 2

What is temporal summation?

Answer 2

From a single neurone

When one presynaptic neurone releases neurotransmitter many times over a period of time to achieve the threshold on the postsynaptic neurone.

Question 3

What is spatial summation?

Answer 3

From multiple neurones

When multiple presynaptic neurones together release enough neurotransmitter to exceed the threshold of the postsynaptic neurone

Question 4

What do excitatory neurotransmitters do?

Answer 4

• Depolarise the cell membrane
• Increase probability of an action potential being elicited
• Causing an Excitatory Post Synaptic Potential (EPSP)

Question 5

What do inhibitory neurotransmitters do?

Answer 5

• Hyperpolarise the cell membrane
• Decrease probability of an action potential being elicited
• Causing an Inhibitory Post Synaptic Potential (IPSP)

Question 6

What is the threshold of excitation?

Answer 6

-60mv

Question 7

How does Ouabain work?

Answer 7

Dart poison for hunting

Selectively blocks the Sodium/Potassium Pump so that the neurones cannot restore resting potential following an action potential

Question 8

What is lidocaine and how does it work?

Answer 8

Local anaesthetics

Blocks voltage gate sodium ion channels which stops action potentials from being generated

Question 9

What is the role of the myelin sheath?

Answer 9

Insulates sections of the axon leading to faster and more accurate transmission

Question 10

What is saltatory conduction?

Answer 10

Decremental conduction between nodes of ranvier increasing velocity of action potential

Question 11

Describe synaptic transmission

Answer 11

• Calcium ion channels open when action potential reaches pre-synaptic terminal
• Ca+ ions cause vesicles to move to release sites, fuse with the cell membrane and discharge their contents through exocytosis
• Neurotransmitter diffuses across synaptic cleft
• Attach to receptor sites on dendrites of post-synaptic membrane

Question 12

What are the 3 ways that excess neurotransmitter is removed from the synaptic cleft?

Answer 12

1. Diffuses out and is destroyed by surrounding tissues
2. Transmitter re-uptake into the pre or postsynaptic terminal for reuse
3. Enzymatic Degradation