The Neuromuscular Junction Flashcards
What are alpha motor neurones?
Motor neurones to skeletal muscle of the body
Describe the location and structure of alpha motor neurones
LOCATION: have their cell bodies in the ventral horn of the spinal cord and exit via the ventral roots
STRUCTURE: the terminal boutons contain many mitochondria
What type of calcium channels are present on the presynaptic terminals of the NMJ?
N-type calcium channel
Describe the N-type calcium channel.
these channels have a low activation threshold and a slow inactivation time, they act as the main Ca2+ source for transmitter release in nerve terminals
How may N-type calcium channels be inhibited?
Blocked by w-conotoxin
What type of protein channel does ACh bind to on the sarcolemma?
ligand-gated ion channel
Describe the structure of the cholinergic receptor on the sarcolemma
It’s a ligand-gated ion channel which consists of 5 subunits arranged in a circular cluster, and 2 of these bind ACh .
What happens at the cholinergic receptor on the sarcolemma when ACh binds?
The subunits rotate slightly and open the central channel (which is cation specific) so allows sodium and potassium ions to pass through but no anions. More sodium moves in than potassium out and so the muscle becomes depolarised
What is meant by the ‘end-plate potential’?
when the inward current of sodium produces a depolarisation in the muscle which triggers an action potential when the depolarisation reaches a threshold
Which substrates are required, and which enzyme, in order to produce acetylcholine?
acetyl CoA + choline –> acetylcholine in the presence of acetylase enzyme
Which enzyme stimulates the breakdown of ACh, and what are the products?
acetylcholinesterase. acetylcholine –> choline and acetic acid
How can botox affect muscular contraction?
paralyses muscles as it gets taken up by the vesicles instead of choline and then stops the SNARE protein (which facilitate exocytosis) from working, so the synapse eventually runs out of vesicles
How can curare affect muscular contraction?
acts as a competitive antagonist as it binds irreversibly with ACh receptors and stop ACh acting, paralysing muscle
How can anticholinesterase affect muscular contraction?
these drugs make the synapse hyperactive as the ACh is not broken down and the muscle goes into convulsions
