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Flashcards in Nerves 4-5 Deck (26)
1

What type of channel is responsible for the depolarisation in an action potential?

Sodium voltage gated channels

2

What is the usual threshold potential of a nerve cell?

-55mv

3

What is responsible for repolarisation after an action potential?

K+ voltage gated channels

4

Why can't an action potential travel back down the same direction of membrane that it just came from?

The channels are in their refractory state

5

What are the two ways you can increase the speed of action potentials?

Increase the size of the fibre
Myelination

6

Why does increasing the size of axons increase the speed of action potentials?

Bigger axons have a lower axial resistance, depolarisation can spread further and so you can spread your sodium channels further apart. It is the opening of sodium channels that is the rate limiting step of self-propagation.

7

What glial cells are responsible for myelination?

Oligadendrocytes and schwann cells

8

Where are the sodium channels in an axon that is myelinated?

In the nodes (node of raniver)

9

What is the effect of myelination on resistance?

Increases resistance - allows current to spread with little decrement

10

What disease has a lack of myelination in the axons?

Multiple sclerosis

11

What structure is responsible for facilitating the compound action potential?

A bundle of axons (a nerve trunk)

12

Which fibres are most sensitive to anoxia and least sensitive to local anaesthetics?

Proprioception, touch, pressure

These are the fastest nerve fibres

13

What fibres are least sensitive to anoxia and most sensitive to local anaesthetics?

Preganglionic autonomic fibres, heat, slow pain

14

Where is contraction triggered by in the NMJ?

Action potential in the sarcolemma

15

What ion is responsible for the formation of vesicles and release of acetylcholine in the NMJ?

Calcium

16

What are the receptors on the sarcolemma for acetylcholine?

Nicotinic receptors

17

What is the name of the local grade potential produced by activation of ligand gated channels by acetylcholine?

The end plate potential

18

What is the effect of the end plate potential?

Always depolarises the adjacent membrane to threshold, opening voltage gated channels

19

What removes acetyl choline?

Acetylcholinesterase

20

What is the effect of tetrotoxin?

Blocks Na+ channels and so blocks the action potential

21

What is the effect of joro spider toxin?

Blocks calcium channels and so stops the release of transmitter

22

What is the effect of botulinum toxin?

Disrupts the release machinery and so stops the release of transmitter

23

What is the effect of curare?

Blocks acetylcholine receptors and so prevents the end plate potential

24

What is the effect of anticholinesterases?

Block ACh breakdown and so increase the transmission at the NMJ

25

What are the three different types of synapses in the central nervous system?

Axo-somatic
Axo-dendritic
Axo-axonal

26

What are the types of synaptic connectivity?

Convergeance
Divergeance