The correct option is Synaptic knob.
Explanation
A neuron is the structural and functional unit of the neural system, composed of three major parts: the cell body, dendrites, and the axon. The axon is a long fibre that transmits nerve impulses away from the cell body to a synapse or a neuro-muscular junction.
- Synaptic knob is correct: The distal end of an axon is branched. Each branch terminates as a bulb-like structure called the synaptic knob. These knobs possess synaptic vesicles containing chemicals called neurotransmitters, which are essential for the transmission of nerve impulses across synapses.
- Node of Ranvier is incorrect: The Node of Ranvier refers to the gaps between two adjacent myelin sheaths along the axon. These nodes facilitate the rapid conduction of nerve impulses (saltatory conduction).
- Axon hillock is incorrect: The axon hillock is the cone-shaped region of the cell body (soma) from which the axon originates. It is the site where action potentials are typically initiated.
- Soma is incorrect: The soma (or cell body) is the main part of the neuron containing the nucleus, cytoplasm, and typical cell organelles like Nissl’s granules. It is not the distal end of the axon.
Key Takeaway: The synaptic knob is the terminal, bulbous structure of an axon that contains synaptic vesicles responsible for releasing neurotransmitters.