Lecture 6: Neuromuscular Junction

Question 1

component of an axon that is anchored to the presynaptic membrane, but we do not know it’s true function.

Answer 1

dense bars

Question 2

axon synaptic vesicles contain…..

Answer 2

ACH

Question 3

another term for local potential

Answer 3

end plate potential

Question 4

where is the synaptic gutter located

Answer 4

groove indented in the sarcolemma surface

also called a trough

Question 5

small clefts in bottom of synaptic trough

Answer 5

Subneural clefts

Question 6

synaptic cleft

Answer 6

20-30nm wide = very narrow

between axolemma and sarcolemma

Question 7

where are the ACH ligand gated channels located?

Answer 7

the sarcolemma

Question 8

how many ACH must attach before the channels can open?

Answer 8

2

Question 9

enzyme responsible for ACH breakdown

Answer 9

acetylcholinesterase

found on sarcolemma, breaks ACH into —- choline + acetate

Question 10

ACH binding sites

Answer 10

binds to alpha subunits of the ligand channel

Question 11

where is ACH synthesized

Answer 11

cytosol of axons

Question 12

synaptic vesicle creation/transport/filling

Answer 12

formed in golgi (40nm)
carried via axonal transport to terminus
then filled with ACH

Question 13

how many vesicles fuse to the synaptic membrane?

Answer 13

~125 vesicles

releasing thousands of ACHs

Question 14

what ions could be responsible for drawing synaptic vesicles closer to the V-gates of the neurolemma?

Answer 14

Ca ions

Question 15

when an AP reaches an axon terminus, what 2 events follow on the axon?

Answer 15

Ca voltage gates open

Ca enters the axon

Question 16

a sarcolemma AP is activated by the flux of what ions?

Answer 16

influx of Na ions from the ACH ligand gates

causes Na V-gates to open allowing further influx

Question 17

calcium’s role in a skeletal muscle contraction

Answer 17

Ca binds to troponin C
conformational change in troponin
tropomyosin then pulls away from active sites on actin

Question 18

ATP is required for myosin ……?

Answer 18

for myosin heads to release the actin active sites

Question 19

after each AP ______ appears in the axon terminal

Answer 19

clathrin coated pits

which refill as new synaptic vesicles

Question 20

how is ACH removed from the synaptic cleft after an AP?

Answer 20

acetylcholinesterase degrades ACH into choline + acetate

clathrin pits re-uptake the choline

acetate diffuses away from site

Question 21

what is another term for excitation-contraction coupling?

Answer 21

electro-mechanical coupling

Question 22

what is meant by excitation-contraction coupling?

Answer 22

we are converting electrical energy into mechanical energy

voltage —> induces muscle contraction

Question 23

methacholine
carbachol
nicotine

Answer 23

drugs that mimic ACH, but are not broken down by ACHase

cause spasms

Question 24

neostigmine
physostigmine
diisopropyl fluorophosphates

Answer 24

drugs that inactivate ACHase

cause spasms

Question 25

effect of ‘curare’ on skeletal muscle contraction

Answer 25

prevents passage of impulses from axon to muscle

results = total muscle relaxation

Question 26

how can total muscle relaxation be dangerous?

Answer 26

too much curare?

relax muscles that we need to be alive
diaphragm, heart

Question 27

myasthenia gravis

Answer 27

autoimmune disease
antibodies attack ACH receptors

thus no receptor available to accept ACH to induce a muscle contraction ==== very weak contractions

Question 28

drug that can help alleviate myasthenia gravis and how

Answer 28

neostigmine

can be used to inactivate ACHase, leaving excess ACH in the cleft allowing a relatively normal contraction