1. How is an action potential passed from the motor neuron to a muscle fiber? Ar
ID: 3476608 • Letter: 1
Question
1. How is an action potential passed from the motor neuron to a muscle fiber? Arrange the labels in the order in which they would occur, beginning at the presynaptic membrane. (Note: ACh = acetylcholine).
- Ach is released into the synaptic cleft and binds to receptors.
- Calcium moves into the nerve terminal of the presynaptic cell.
- Influx of Na+ initiates an action potential in the muscle fiber.
- Signal from the motor neuron arrives at the nerve terminal of the presynaptic cell.
What is the correct order?
2. What step is responsible for the release of actin by the myosin head?
a) binding of ATP to the actin filament
b) binding of ATP to the myosin head
c) binding of Ca2+
d) split of ATP into ADP + Pi
Explanation / Answer
1. Answer :
Step 1 : Signal from the motor neuron arrives at the nerve terminal of the presynaptic cell.
Step 2 : Calcium moves into the nerve terminal of the presynaptic cell.
Step 3 : Ach is released into the synaptic cleft and binds to receptors.
Step 4 : Influx of Na+ initiates an action potential in the muscle fiber.
Action potential depends on presynaptic and postsynaptic cell. Presynaptic cell is the site where action potential arrives causing voltage gated Calcium channels to open and then calcium enters the cell to make the vesicles to release neurotransmitters (Acetylcholine). The neurotransmitters reaches the synaptic cleft and binds the receptors of the postsynaptic cell. Then it causes influx of sodium ions and action potential is propagated over the muscle cell membrane.
2. Answer : b) binding of ATP to the myosin head
In the absence of ATP, myosin head cannot detach from the actin. When ATP is bound to myosin head, actin detaches from it. Then ATP is hydrolyzed by ATPase activity of myosin to ADP and Pi and this makes the myosin head again to bind to actin for movement. Again, ATP binds to myosin and this process repeats until ATP is available.
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