synaptic transmission and neuromuscular junction

Question 1

describe how a neurotransmitter crosses a synapse to skeletal muscle

Answer 1

when action potential arrives at bulb voltage gated Ca2+ channels open and ca2+ increases causing vesicle to fuse and release neurotransmitter into the synaptic cleft. ach binds to post synaptic receptors causing K+/Na+ channels to open. action potential is generated and propagated causing contraction

Question 2

why is an action potential generated despite the fact that K + is also allowed to diffuse out.

Answer 2

because Na is much farther from ENa value compared to K+ which is relatively close to the Ek. there is therefore a larger conc gradient and the effect of Na+ diffusing will dominate

Question 3

name 2 blockers of Ach receptors and what they are used for

Answer 3

d-tubocurarine and succinylcholine used as anaesthetics during surgery

Question 4

explain how d-tubocurarine works

Answer 4

sits on the binding site of the Ach receptors so it blocked therefore Ach cannot bind. But if the conc is increased enough then it is able to outcompete the inhibitor (competitive block)

Question 5

explain how succinylcholine works

Answer 5

its a depolarising block and is able to bind to the nicotinic receptor to activate them and maintain the depolarisation. The Na+ channels are open but inactive and therefore no conduction is possible

Question 6

what is myasthenia gravis

Answer 6

disease that targets nicotinic Ach receptors and results in weakness especially in the eye muscle after facial exercise. Due to much fewer receptors and loss of action potential amplitude

Question 7

what is organophosphate poisoning

Answer 7

acetylcholine esterase inhibitors form irreversible covalent bods to the enzyme and result is paralysis. recovery takes weeks because synthesis of new acetylcholine esterase is needed