Question

13. Describe the basic sequence of events that occurs as an action potential arrives at the neuromuscular junction and is transmitted to the muscle cell and leads to a contraction. Explain at the end how relaxation of the muscle takes place (include what happens at the neuromuscular junction and in the muscle fiber. You may use some words multiple times. Fill in the blanks with a complete word or words (no abbreviations) of each step.

1. An action potential arrives at the synaptic bulb of a motor neuron causing the exocytosis of vesicles containing ___

2. ____ diffuses across the synaptic cleft to bind to a receptor on the ___ allowing sodium to influx resulting in an action potential.

3. The action potential will spread down the ___ into the center of the muscle fiber.

4. The excitation cause the release of _____ from the ____ into the sarcoplasm.

5. ____ will bind to ___ causing a conformational change.

6. ____ will move___ off the____ of the protein .

7. The ____ will bind to the ____ forming a ____ .

8. The ____ will ___ pulling the ___ . This is called the___ .

9. ____ will attach to the ___causing it to ___from the____ .

10. __ of__ provides the energy to cause the___ of the ___.

11. _____- write out the whole step

Relaxation.

___ cleaves ___

The ___ re-uptakes the ___

___ recovers the so that ___ can no longer bind.

Answer 1

Answer 13

1.An action potential arrives at the synaptic bulb of a motor neuron causing the exocytosis of vesicles containing ACETYLCHOLINE.

2. ACETYLCHOLINE diffuses across the synaptic cleft to bind to a receptor on the MOTOR END PLATE allowing sodium to influx resulting in an action potential.

3. The action potential will spread down the T-TUBULES into the center of the muscle fiber.

4.  The excitation cause the release of CALCIUM from the SARCOPLASMIC RETICULUM into the sarcoplasm.

5. CALCIUM will bind to TROPONIN causing a conformational change.

Explanation: Action potential arrives at the neuromuscular junction then Synaptic vesicles inside the neuron fuse to the membrane and release Acetylcholine (ACh). ACh crosses the synaptic cleft and binds to ACh receptors on the motor end plate. ACh binding to receptors causes an influx of sodium into motor end plate. Sodium entry into motor end plate stimulates action potential via voltage gated sodium channels. Then action potential passes down T-tubule and cause Calcium release from sarcoplasmic reticulum. Calcium then binds to troponin which removes tropomysin from binding sites leading to exposure of myosin binding sites on actin. Cross bridge gets formed which causes muscle Contraction.