The Neuromuscular Junction

Question 1

Where is the neuromuscular junction?

Answer 1

• Between a motor neurone and a muscle cell.

- At the neurovascular hilum / nerve entry point of a muscle.

Question 2

What triggers fusion of vesicles with the presynaptic membrane?

Answer 2

Ca2+ influx into presynaptic terminal.

Question 3

What is the name of the Ca2+ sensor?

Answer 3

Synaptotagmin

Question 4

What is another term for ligand-gated ion channels?

Answer 4

Ionotropic channels

Question 5

Give examples of excitatory ionotropic receptors.

Answer 5

Glutamate Receptors:

• AMPA Receptors
• NMDA Receptors
• Kainate Receptors

ACh Nicotinic Receptors

Question 6

What do excitatory receptors cause at the postsynaptic membrane?

Answer 6

Na+ influx

Excitatory postsynaptic potential (EPSP)

Question 7

What are the specialised features of the postsynaptic membrane?

Answer 7

Junctional folds:

• Allow for high density of nACh receptors - the receptors of the NMJ.
• Allow for high density of voltage gated of Na+ channels.

Question 8

What are quanta?

Answer 8

Packaged vesicles containing neurotransmitters released into a synapse.

Question 9

What is the major amino acid excitatory neurotransmitter?

Answer 9

Glutamate

Question 10

What is the major amino acid inhibitory neurotransmitter?

Answer 10

GABA

Question 11

Are nicotinic ACh receptors excitatory, inhibitory or both?

Answer 11

All nicotinic AChRs are excitatory.

Question 12

Are muscarinic ACh receptors excitatory, inhibitory or both?

Answer 12

Muscarinic AChRs can be either excitatory or inhibitory.

Question 13

List 4 monoamine neurotransmitters

Answer 13

1 - Adrenaline.

2 - Noradrenaline.

3 - Dopamine.

4 - Serotonin.

Question 14

What is another term for G-protein coupled receptor?

Answer 14

Metabotropic

Question 15

What are the two receptor signalling mechanisms?

Answer 15

Ionotropic and metabotropic.

Question 16

What do inhibitory receptors cause at the postsynaptic membrane?

Answer 16

Cl- influx

Inhibitory post synaptic potential (IPSP)

Question 17

Give 2 examples of inhibitory ionotropic receptors.

Answer 17

GABA(a) Receptors

Glycine Receptors

Question 18

What is the end plate potential?

Answer 18

The end plate potential initiates an action potential in the muscle. These are 2 different electrical events.

EPP decays as it moves away from the end-plate.

Question 19

What is an end plate?

Answer 19

The postsynaptic terminals of the NMJ. So called for large, saucer-like appearance.

Question 20

How does the voltage of an EPP differ from that of most other synaptic potentials?

What causes this?

What is the advantage of this?

Answer 20

• An EPP is much larger than most other synaptic potentials.
• This is because there are many NAChRs at the NMJ, triggering the opening of many Na+ channels.
• This ensures that the threshold for AP generation in the muscle is easily passed.

Question 21

What is the function of T tubules?

Answer 21

They allow for transmission of AP deep into the muscle fibre (to individual myofibrils)

Question 22

What are the levels of organisation of a muscle?

Answer 22

Sarcomere < Myofilament < Myofibril < Myocyte (Fibre) < Fascicle < Muscle

Question 23

When very frequent action potentials are summated, what happens to muscle contraction?

Answer 23

Contraction is sustained.

Question 24

What is ACh hydrolysed by in the synaptic cleft?

Answer 24

Acetylcholinesterase (AChE)

Question 25

Name a symptom of myesthenia gravis.

Answer 25

Muscle weakness during sustained activity.

Question 26

What is the cause of myesthenia gravis?

Answer 26

Autoimmune disease of nAChR that causes a reduced number of nAChRs at the NMJ.

Question 27

What is a treatment of myesthenia gravis?

Answer 27

AChE inhibitors, e.g. neostigmine.

This will prolong the signal.