1. 1. A “ signal ” is sent from the brain down the axon of a motor neuron . Action Potential!!! Part 1 - Depolarization
2. 2. The signal hits the terminal bud (button) of the axon.
3. 3. The vesicles break open releasing the neurotransmitter , acetylcholine , in to the synaptic cleft .
4. 4. The acetylcholine crosses the synaptic cleft and binds to receptor sites on the sarcolemma .
5. 5. The sarcolemma undergoes a permeability shift from Na + impermeable to Na + permeable .
6. 6. Na + ions rush in to the muscle fiber through channels in the sarcolemma, but they “ overshoot ” equilibrium .
7. 7. Cholinesterase , an enzyme that “ destroys ” acetylcholine, deactivates and removes the acetylcholine from the receptor sites on the sarcolemma.
8. 8. The permeability of the sarcolemma shifts back to Na + impermeable thus trapping the Na + ions inside the muscle fiber.
9. 9. The neuromuscular junction is “ depolarized ” with respect to Na + .
10. 1. A “ signal ” is sent from the brain down the axon of a motor neuron . 2. The signal hits the terminal bud (button) of the axon. 3. The vesicles break open releasing the neurotransmitter , acetylcholine , into the synaptic cleft . 4. The acetylcholine crosses the synaptic cleft and binds to receptor sites on the sarcolemma . 5. The sarcolemma undergoes a permeability shift from Na + impermeable to Na + permeable . 6. Na + ions rush in to the muscle fiber through channels in the sarcolemma, but they “ overshoot ” equilibrium . 7. Cholinesterase , an enzyme that “ destroys ” acetylcholine, deactivates and removes the acetylcholine from the receptor sites on the sarcolemma. 8. The permeability of the sarcolemma shifts back to Na + impermeable thus trapping the Na + ions inside the muscle fiber. 9. The neuromuscular junction is “ depolarized ” with respect to Na + .
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12. 1. K + ions diffuse out of the muscle fiber to help balance the positive charge “imbalance” caused by the Na + being trapped inside the fiber.
13. 2. Na + ions are “pumped” out of the muscle fiber and K + ions are “pumped” back in by the active transport mechanism known as the Na + /K + pump in a ratio of 3 Na + out to 2 K + in .
14. 3. Once the original balance of Na + and K + is restored, the NMJ is said to be repolarized .
15. 1. K + ions diffuse out of the muscle fiber to help balance the positive charge “imbalance” caused by the Na + being trapped inside the fiber. 2. Na + ions are “pumped” out of the muscle fiber and K + ions are “pumped” back in by the active transport mechanism known as the Na + /K + pump in a ratio of 3 Na + out to 2 K + in . 3. Once the original balance of Na + and K + is restored, the NMJ is said to be repolarized .
