1. 09.12 Function of the Neuromuscular Junction Slide number 1 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 1. An action potential arrives at the presynaptic terminal causing voltage gated Ca 2+ channels to open, increasing the Ca 2+ permeability of the presynaptic terminal. 5. Once ACh is released into the synaptic cleft it binds to the receptors for ACh on the postsynaptic membrane and causes Na + channels to open. 2. Ca 2+ enters the presynaptic terminal and initiates the release of a neurotransmitter, acetylcholine (ACh), from synaptic vesicles in the presynaptic terminal. 3. Diffusion of ACh across the synaptic cleft and binding of ACh to ACh receptors on the postsynaptic muscle fiber membrane causes an increase in the permeability of ligand-gated Na + channels. 4. The increase in Na + permeability results in depolarization of the postsynaptic membrane; once threshold has been reached a postsynaptic action potential results. 6. ACh is rapidly broken down in the synaptic cleft by etylcholinesterase to acetic acid and choline. 7. The choline is reabsorbed by the presynaptic terminal and combined with acetic acid to form more ACh, which enters synaptic vesicles. Acetic acid is taken up by many cell types. Na + Ca 2+ channel Presynaptic terminal Action potential Synaptic cleft Na + ACh Receptor molecule Action potential Action potential Presynaptic terminal Synaptic vesicle ACh Acetic acid Choline Synaptic cleft ACh receptor site Postsynaptic membrane Acetylcholinesterase Na + Acetic acid Choline ACh 1 2 3 4 5 6 7

2. 09.12 Function of the Neuromuscular Junction Slide number 2 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. An action potential arrives at the presynaptic terminal causing voltage gated Ca 2+ channels to open, increasing the Ca 2+ permeability of the presynaptic terminal. Ca 2+ channel Presynaptic terminal Action potential

3. 09.12 Function of the Neuromuscular Junction Slide number 3 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Ca 2+ channel Ca 2+ enters the presynaptic terminal and initiates the release of a neurotransmitter, acetylcholine (ACh), from synaptic vesicles in the presynaptic terminal. ACh Presynaptic terminal

4. 09.12 Function of the Neuromuscular Junction Slide number 4 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Na + Synaptic cleft Na + ACh Receptor molecule Diffusion of ACh across the synaptic cleft and binding of ACh to ACh receptors on the postsynaptic muscle fiber membrane causes an increase in the permeability of ligand-gated Na + channels.

5. 09.12 Function of the Neuromuscular Junction Slide number 5 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. The increase in Na + permeability results in depolarization of the postsynaptic membrane; once threshold has been reached a postsynaptic action potential results. Na + Action potential Action potential Na +

6. 09.12 Function of the Neuromuscular Junction Slide number 6 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Once ACh is released into the synaptic cleft it binds to the receptors for ACh on the postsynaptic membrane and causes Na + channels to open. Synaptic cleft Postsynaptic membrane Na + ACh receptor site

7. 09.12 Function of the Neuromuscular Junction Slide number 7 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. ACh receptor site Acetylcholinesterase Acetic acid Choline ACh ACh is rapidly broken down in the synaptic cleft by acetylcholinesterase to acetic acid and choline.

8. 09.12 Function of the Neuromuscular Junction Slide number 8 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Presynaptic terminal Synaptic vesicle ACh Acetic acid Choline ACh The choline is reabsorbed by the presynaptic terminal and combined with acetic acid to form more ACh, which enters synaptic vesicles.

9. 09.12 Function of the Neuromuscular Junction Slide number 9 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Choline Acetic acid is taken up by many cell types. Acetic acid