1.11 Neuromuscular Junction Flashcards Preview

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Flashcards in 1.11 Neuromuscular Junction Deck (25):
1

What is a neuromuscular junction?

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

2

What incorporates acetylcholine into vesicles?

Vesicle Acetycholin transporter = VAch T

3

Give the 6 stages of NMJ synaptic transmission...

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

4

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

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

5

How many vesicles are released per impulse?

About 60 -200 vesicles released per impulse

6

How much Ach is there per vesicle?

10'000 Ach molecules vesicle

7

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

20% - low firing frequency

8

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

80% - high firing frequency

9

What is an mEPP...

Leakage - one quantum - not enough to create an AP

10

Define and explain QUANTUM

QUANTUM = amount of neurotransmitter in one vesicle

11

Where does vesicle fusion occur?

Dense bars in the active zone

12

What are the three SNARE proteins involved in vesicle fusion?

Synaptabrevin - vesicle
Snap25 - Membrane
Syntaxin - snap25

13

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

5
2 alpha, beta, delta, gamma

14

Which subunits does Ach bind to?

Alpha subunits

15

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

gamma gets replaced by an epsilon

16

Which ions go in and which go out?

Sodium goes and potassium goes out

17

Is the net influx positive or negative?

Positive

18

Where are subjunctional folds found?

membrane of skeletal muscle

19

What are the top of the fold called?

Active zone

20

Explain what is in the ‘active zones’?

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

21

What can be found within the folds?

Acetylecholinesterase - hydrolyse Ach

22

What is an EPP?

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

23

Explain Myesthenia Gravis?

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

24

Explain Botulin Toxin?

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.

25

Explain curare?

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.