Neuromuscular transmission

Question 1

What is a motor endplate?

Answer 1

A region in the centre of a muscle fibre from a single branch of a motor neurone

Question 2

How many axon branches normally innervate a muscle fibre?

Answer 2

1

Question 3

What is a motor unit?

Answer 3

The pre-synaptic neurone and the collection of muscle fibres which it innervates

Question 4

How wide is the synaptic cleft?

Answer 4

50-70nm

Question 5

What is a junctional fold and how frequently do they occur down the muscle

Answer 5

A transverse invagination of the muscle membrane

Every 1-2 micrometres

Question 6

What is an active zone?

Answer 6

Regions of thickness in the pre-synaptic membrane above junctional folds where vesicles containing neurotransmitter gather

Question 7

What type of biological ‘glue’ fills the synaptic cleft?

Answer 7

Mucopolysaccharide

Question 8

What is the concentration of ACh in presynaptic vesicles?

Roughly how many molecules are found in a single vesicle

Answer 8

100-200mM

10,000

Question 9

What causes pre-synaptic vesicles to fuse to the membrane?

Answer 9

Rise in intracellular free calcium level in the terminal due to calcium entry via voltage gated channels

Question 10

What suggests that the process of releasing neurotransmitter from vesicles is co-operative?

Answer 10

The amount of release depends on the external calcium concentration

in the frog, release is directly proportional to the calcium concentration to the power 4

Question 11

What is the minimum synaptic delay in a frog at 17 degrees?

Answer 11

500 micro-seconds

Question 12

What is the mean synaptic delay in a frog at 17 degrees?

Answer 12

1 millisecond

Question 13

Where does the majority of synaptic delay occur?

Answer 13

Presynaptic terminal before release

Question 14

How long does is take for ACh to diffuse across the synaptic cleft?

Answer 14

10 micro-seconds

Question 15

Is ACh an anion or cation?

Answer 15

Cation

Question 16

What enzyme synthesises ACh?

Answer 16

Acetyltransferase

Question 17

What enzyme breaks down ACh?

Answer 17

Acetylcholinesterase

Question 18

Where is acetylcholinesterase localised to?

Answer 18

Basal lamina of synaptic cleft

Question 19

What is ACh broken down into?

Answer 19

Acetic acid and choline

Question 20

Where are acetylcholine receptors found?

Answer 20

In the muscle membrane, concentrated opposite active zones

Question 21

How many types of glycoprotein subunits are there in the acetylcholine receptors?

Answer 21

4:

alpha, beta, gamma, delta

Question 22

Where is the binding site for ACh on the AChR?

Answer 22

alpha subunit