Question

An isolated neuron placed in Calcium free medium is given a suprathreshold stimulus. An assay on release of neurotransmitter shows

• A. No neurotransmitter as Ca influx is required for conduction of action potential
• B. Neurotransmitter detected due to suprathreshold stimulus and non-requirement of Ca
• C. No neurotransmitter is detected due to absence of Ca influx into synaptic knob
• D. No prediction possible without knowing whether the neuron was myelinated

Answer 1

The correct option is C No neurotransmitter is detected due to absence of Ca influx into synaptic knob

To transmit the impulse to the next neuron, neurotransmitters are released as chemical messengers by the axon terminals. Therefore these neurotransmitters pass the stimulus from pre-synaptic cell to post-synaptic cell. The amount of neurotransmitters released will depend on the amount of calcium ions that enter from the calcium gated canals at the pre-synaptic terminal. Calcium ions bind to special proteins inside the pre-synaptic membrane at the sites called release sites and hence result in the release of neurotransmitters.

In this statement, it is said that the medium in which the neuron is placed is calcium free, so there will be no calcium influx and hence no neurotransmitters are released.

So the right answer is 'No neurotransmitter is detected due to the absence of Ca influx into synaptic knob'.