Question

question 12 (1 point)
an impulse arrives at an axon terminal that synapses with a muscle cell. record the processes in the order that they occur at the synapse.
cholinesterase breaks down acetylcholine and the sodium gates close.
acetylcholine binds to the receptors on the muscle cell.
acetylcholine is released from the axon terminal.
muscle fibers contract when sodium gates open allowing sodium ions to diffuse into the muscle cytoplasm.
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Explanation:

To solve this, we analyze the sequence of events at a neuromuscular synapse:

Step 1: Neurotransmitter Release

When an impulse reaches the axon terminal, the neurotransmitter (acetylcholine) is released into the synaptic cleft. So the first event is: Acetylcholine is released from the axon terminal.

Step 2: Neurotransmitter Binding

Next, acetylcholine diffuses across the synapse and binds to receptors on the muscle cell membrane. So the second event is: Acetylcholine binds to the receptors on the muscle cell.

Step 3: Ion Channel Activation and Contraction

Binding of acetylcholine opens sodium gates, allowing \( \text{Na}^+ \) ions to enter the muscle cell. This triggers muscle fiber contraction. So the third event is: Muscle fibers contract when sodium gates open allowing sodium ions to diffuse into the muscle cytoplasm.

Step 4: Termination of Signal

After the signal is transmitted, cholinesterase (an enzyme) breaks down acetylcholine to stop the signal, and sodium gates close. So the fourth event is: Cholinesterase breaks down acetylcholine and the sodium gates close.

Final Order (from first to last):

1. Acetylcholine is released from the axon terminal.
2. Acetylcholine binds to the receptors on the muscle cell.
3. Muscle fibers contract when sodium gates open allowing sodium ions to diffuse into the muscle cytoplasm.
4. Cholinesterase breaks down acetylcholine and the sodium gates close.

(If ordering via numbering the dropdowns, assign 1 to "Acetylcholine is released...", 2 to "Acetylcholine binds...", 3 to "Muscle fibers contract...", and 4 to "Cholinesterase breaks down...".)

Answer:

To solve this, we analyze the sequence of events at a neuromuscular synapse:

Step 1: Neurotransmitter Release

When an impulse reaches the axon terminal, the neurotransmitter (acetylcholine) is released into the synaptic cleft. So the first event is: Acetylcholine is released from the axon terminal.

Step 2: Neurotransmitter Binding

Next, acetylcholine diffuses across the synapse and binds to receptors on the muscle cell membrane. So the second event is: Acetylcholine binds to the receptors on the muscle cell.

Step 3: Ion Channel Activation and Contraction

Binding of acetylcholine opens sodium gates, allowing \( \text{Na}^+ \) ions to enter the muscle cell. This triggers muscle fiber contraction. So the third event is: Muscle fibers contract when sodium gates open allowing sodium ions to diffuse into the muscle cytoplasm.

Step 4: Termination of Signal

After the signal is transmitted, cholinesterase (an enzyme) breaks down acetylcholine to stop the signal, and sodium gates close. So the fourth event is: Cholinesterase breaks down acetylcholine and the sodium gates close.

Final Order (from first to last):

1. Acetylcholine is released from the axon terminal.
2. Acetylcholine binds to the receptors on the muscle cell.
3. Muscle fibers contract when sodium gates open allowing sodium ions to diffuse into the muscle cytoplasm.
4. Cholinesterase breaks down acetylcholine and the sodium gates close.

(If ordering via numbering the dropdowns, assign 1 to "Acetylcholine is released...", 2 to "Acetylcholine binds...", 3 to "Muscle fibers contract...", and 4 to "Cholinesterase breaks down...".)