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Flashcards in The NMJ Deck (42)
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1

What is a neuromuscular junction?

A synapse between a motor neurone and a skeletal muscle fibre

2

What signal does a NMJ propagate?

Action potential to muscle contraction

3

How far do presynaptic motor axons terminate from the sarcolemma of a muscle fiber?

30nm

4

How is the motor end plate modified to work as an NMJ?

Invaginations called post-junctional folds, which increase its surface area

5

What lines the sarcolemma of the post synaptic membrane end plate?

Nicotinic acetylcholine receptors (nAChRs)

6

What is the term used to describe the area where vesicles are grouped at the motor nerve terminal membrane?

Active zone

7

How many vesicles are roughly clustered at the active zone?

~50

8

What do vesicles in the motor nerve terminal contain?

ACh

9

How are vesicles in the active zone kept close to the membrane?

Docked by proteins dystrophin and rapsyn.

10

Where are the reserve pool of vesicles docked?

At the cytoskeleton further from the membrane

11

What docks the reserve pool of vesicles?

Actin microfilaments

12

What does the arrival of the action potential cause at the motor presynaptic terminal?

Opens voltage-dependent calcium channels and Ca2+ ions flow from the extracellular fluid into the presynaptic neuron's cytosol.

13

What is the effect of calcium influx into the presynaptic terminal?

Causes several hundred neurotransmitter-containing vesicles to fuse with the presynaptic neuron's cell membrane through SNARE proteins to release their acetylcholine quanta by exocytosis.

14

How do SNARE proteins lead to exocytosis?

The v-SNARES are associated with the vesicle membrane and the t-SNARES with the cell membrane these combine to form a cis-SNARE complex, also known as a "SNAREpin".

15

What is the term used to describe acetylcholine release in packets?

Quanta

16

What does acetylcholine do after exocytosis?

ACh moves across synaptic cleft

The acetylcholine activates acetylcholine receptors, opening their ion channels which permits sodium ions to move into the endplate producing a depolarization

17

Roughly how many nAChRs are bound to from one quanta?

~2000

18

What is the depolarising effect of a single stimulation (single quanta)?

Depolarization of ~0.5 mV known as a miniature endplate potential (MEPP).

19

What is the time interval between the arrival of the nerve impulse in the motor nerve terminals and the first response of the endplate?

0.5 -0.8 msec

20

How many quanta are required to make an EPP?

~200

21

How do quanta need to be released in order to produce an EPP?

Released simultaneously or in rapid series by a nerve impulse

22

What is the EPP?

Chemically induced change in electric potential of the motor end plate.

23

Does an EPP always produce an action potential propagation?

No

24

How does an EPP lead to action potential propagation?

If the EPP depolarizes the cell to a crucial threshold level, it will fully activate sodium channels along the membrane and produce the action potential.

25

What enzyme hydrolyses ACh bound to receptors?

Acetylcholinesterase

26

How long does AChE take to act?

~0.16 ms

27

Where is AChE bound?

Post synaptic membrane

28

What happens to the liberated choline after breakdown?

Taken up again by the pre-synaptic neuron

29

What does AChE break ACh into?

Choline and Acetic acid

30

What happens to reabsorbed choline ?

ACh is synthesized by combining with acetyl-CoA through the action of choline acetyltransferase.