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Unformatted text preview: 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 vAchT = vesicle Ach transporter C.) Fatigue ability • Store ~300,000 vesicles (in pre-synaptic terminal)...
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This note was uploaded on 07/21/2008 for the course BIPN 105 taught by Professor Armour during the Winter '08 term at UCSD.
- Winter '08