Question

1. when an impulse arrives at the synaptic knob of the motor neuron, calcium a) exits through ligand - gated channels and triggers neurotransmitter uptake. b) enters through voltage - gated channels and triggers the release of transmitter. c) exits through active transport pumps and brings neurotransmitter with it. d) is released from synaptic vesicles.

Explanation:

When an impulse reaches the synaptic knob of a motor neuron, calcium enters through voltage - gated channels. This influx of calcium triggers the release of neurotransmitter from synaptic vesicles into the synaptic cleft. Ligand - gated channels are not involved in calcium entry here. Neurotransmitter uptake is a different process and not triggered by calcium in this way. Calcium does not exit through active transport pumps to release neurotransmitter, and calcium is not released from synaptic vesicles.

Answer:

None of the above options are correct. The correct process is that calcium enters through voltage - gated channels and triggers the release of neurotransmitter from synaptic vesicles.