1.11 Neuromuscular Junction

Question 1

What is a neuromuscular junction?

Answer 1

A neuromuscular junction is a specialised form of synapse, also known as a motor end plate, which refers to the flat disc shaped region in the neuromuscular junction

Question 2

What incorporates acetylcholine into vesicles?

Answer 2

Vesicle Acetycholin transporter = VAch T

Question 3

Give the 6 stages of NMJ synaptic transmission…

Answer 3

1. An impulse causes increased permeability to calcium ions
2. Release of Ach at the end of the motor end plate by exocytosis
3. Ach binds to nicotinic receptors
4. increase in Na input and K output in the motor end plate
5. generation of end plate potential
6. generation of action potential

Question 4

How many nicotinic receptors are there at a motor end plate?

Answer 4

15-40 x 10(6) nicotinic Ach receptor per motor -end-plate

Question 5

How many vesicles are released per impulse?

Answer 5

About 60 -200 vesicles released per impulse

Question 6

How much Ach is there per vesicle?

Answer 6

10’000 Ach molecules vesicle

Question 7

What percentage is the releasable pool and what is its firing frequency like?

Answer 7

20% - low firing frequency

Question 8

What percentage is the reserve pool and what is its firing frequency like?

Answer 8

80% - high firing frequency

Question 9

What is an mEPP…

Answer 9

Leakage - one quantum - not enough to create an AP

Question 10

Define and explain QUANTUM

Answer 10

QUANTUM = amount of neurotransmitter in one vesicle

Question 11

Where does vesicle fusion occur?

Answer 11

Dense bars in the active zone

Question 12

What are the three SNARE proteins involved in vesicle fusion?

Answer 12

Synaptabrevin - vesicle
Snap25 - Membrane
Syntaxin - snap25

Question 13

How many subunits is the nicotinic receptor made up of, name them…

Answer 13

5

2 alpha, beta, delta, gamma

Question 14

Which subunits does Ach bind to?

Answer 14

Alpha subunits

Question 15

Which subunit gets replaced when adulthood is reached and what is it replaced by?

Answer 15

gamma gets replaced by an epsilon

Question 16

Which ions go in and which go out?

Answer 16

Sodium goes and potassium goes out

Question 17

Is the net influx positive or negative?

Answer 17

Positive

Question 18

Where are subjunctional folds found?

Answer 18

membrane of skeletal muscle

Question 19

What are the top of the fold called?

Answer 19

Active zone

Question 20

Explain what is in the ‘active zones’?

Answer 20

Nicotinic receptors at the top, and voltage sensitive sodium are at the base of the folds

Question 21

What can be found within the folds?

Answer 21

Acetylecholinesterase - hydrolyse Ach

Question 22

What is an EPP?

Answer 22

60-200 vesicles released in response to normal action potential at NMJ

Question 23

Explain Myesthenia Gravis?

Answer 23

It is an autoimmune disorder, where antibodies destroy the Ach receptors. It is degenerative, because the antibodies increase over time. This causes EPP to not be sufficient enough to stimulate an action potential. Death usually occurs due to paralysis of respiratory muscles. Treatment through AchE inhibitors

Question 24

Explain Botulin Toxin?

Answer 24

It is made up of a light chain and a heavy chain. The heavy chain allows protein to bind to and enter the neurone, where as the light chain cleaves vesicle docking proteins.

Question 25

Explain curare?

Answer 25

It is an alkaloid poison , derived from a plant and it used to be used as a blow dart poison. It is a competitive antagonist to acetylcholine.