Question

Why is the flow of signals in a synapse from axonal end of one neuron to dendritic end of another neuron but not the reverse?​
A. Axons do not have receptors for neurotransmitters.
B. Dendritic ends have receptors for neurotransmitters.
C. No synthesis of neurotransmitters takes place at dendritic end.
D. All of the above

Answer 1

Hint: A single neuron may have thousands of dendrites, so it can communicate with thousands of other cells but only one axon. The axon of the sending neuron does not actually touch the dendrite of the receiving neuron.

Complete Answer:
The place where the axon of one neuron meets the dendrite of another is called a synapse. Synapses are also found between the neurons and other kinds of cells. The axon of the sending neuron does not actually touch the dendrite of the next neuron. There is a tiny gap between them, which is called the synaptic cleft.

The following steps describe what happens when a nerve impulse reaches the end of an axon:
(i) When a nerve impulse reaches the end of an axon, the axon releases chemicals called neurotransmitters.
(ii) Neurotransmitters travel across the synapse between the axon and the dendrite of the next neuron.
(iii) Neurotransmitters bind to the membrane of the dendrite.
(iv) The binding allows the nerve impulse to travel through the receiving neuron.

At chemical synapses, there can be only one–way–information transfer - from a presynaptic neuron to postsynaptic neuron, muscles fiber or gland cell. This is because only synaptic bulbs of presynaptic neurons can release neurotransmitters and only postsynaptic membranes have receptors to recognize and bind that neurotransmitter. In this way, it is ensured that nerve impulses travel in only one direction.

So, the correct answer is option (D) i.e., All of the above.

Note: The axon is covered with a myelin sheath, a fatty layer that insulates the axon and allows the electrical signal to travel much more quickly.