The correct answer is option 3: nerve endings of nerve cells.

In human beings, when a nerve impulse travels along a nerve cell, it eventually reaches the end of the cell, which is called the nerve ending or synaptic terminal. At this point, the nerve impulse needs to continue to another nerve cell or target tissue.

To accomplish this, certain chemicals called neurotransmitters are released from the nerve endings into the synapse, which is the small gap between the nerve cells. These neurotransmitters then bind to specific receptors on the next nerve cell or target tissue, transmitting the nerve impulse and allowing for communication between cells.

Option 1, the cell body of the nerve cell, is responsible for maintaining the overall function and metabolism of the nerve cell, but it is not directly involved in the release of neurotransmitters.

Option 2, the nucleus of the nerve cell, contains the cell`s genetic material and is responsible for controlling the cell`s activities. It does not have a direct role in releasing neurotransmitters.

Option 4, the axon of the nerve cell, is a long projection of the cell that carries the nerve impulse away from the cell body. While the axon plays a crucial role in transmitting the nerve impulse, it is not where neurotransmitters are released.

Therefore