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Lecture 4 Neuromuscular Junction

Lecture 4 Neuromuscular Junction - Lecture 4 Neuromuscular...

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Lecture 4 Neuromuscular Junction I. NMJ Anatomy A.) Endplate – where nerve meets muscle Starts at center of muscle cell Aα neurons go to muscle cell 1 NMJ/muscle cell NMJ at center of muscle cell Aα motor neurons touch many muscle cells B.) Vesicles are made of: Lipid bilayer ~300,000/terminal ~10,000 Ach/vesicle II. Function of NMJ A.) NMJ convert Nerve Action Potential Muscle AP (MAP) Specifically: EPP is not an AP, it is a graded potential and can change its size based on Ach amount coming across and amount of receptors opening up It is a localized kind of event. EPP does not change like an AP, it has a change in potential and dissipates as it spreads away In most cases for humans, enough Ach comes out to make NMJ 100% effective. It is not necessarily the case for frogs B.) Stop transmission – because you don’t want your muscle to be always firing and contracting 1.) Stop exocytosis a.) Ca ++ diffuses away from active zones b.) [Ca ++ ] in [Ca ++ ] out by ATPase pumps because it is against a concentration gradient 2.) Remove Ach a.) diffuses away b.) breakdown by enzymes recycling new Ach new vesicles AchE = Acetylcholine esterase (fast acting) CAT = choline acetyltransferase
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vAchT = vesicle Ach transporter C.) Fatigue ability Store ~300,000 vesicles (in pre-synaptic terminal)
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