Chapter 45 Synapses (1)

Chapter 45 Synapses (1) - Motor end-plate neuromuscular...

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Motor end-plate – neuromuscular junction A neuromuscular junction is the synapse between a motor neuron and a muscle cell. Acetylcholine (Ach) is the neurotransmitter used by all vertebrate motor neurons.
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A chemical synapse 1. Enzymes for synthesis of neurotransmitter are transported along microtubules. 2. Neurotransmitter is synthesized in the axon terminal and packaged in synaptic vesicles. 3. The pre- and postsynaptic membranes are separated by a synaptic cleft (~10-20 nm) 4. Neurotransmitter is released into the synaptic cleft. What causes its release?
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Neurotransmission (1) When the spike invades the synaptic terminal, (2) it opens voltage dependent Ca ++ channels. (3) The entering Ca ++ triggers fusion of synaptic vesicles, each of which releases thousands of neurotransmitter molecules into the synaptic cleft. (4) Transmitter diffuses across the cleft to bind to receptors on the post- synaptic membrane, causing the dendrite to depolarize or hyperpolarize. (5) Transmitter is cleared by diffusion, re-uptake, and
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Ionotropic (“fast”) acetylcholine channel Ionotropic neurotransmitter receptors are ion channels.
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Metabotropic (“slow”) receptor
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Metabotropic receptors influence the postsynaptic cell through various signal transduction pathways that involve G proteins. These pathways can result in changes in ion channels, alterations of enzyme activity, and/or gene expression. Cascade involving a 2 nd messenger
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EPSP : Excitatory Post Synaptic Potential, fast or slow. The opening of sodium channels (tending to +50 mV) or opening of unselective channels (tending to -15 mV) would depolarize the cell. IPSP
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Chapter 45 Synapses (1) - Motor end-plate neuromuscular...

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