This is the difference between a nerve and a neuron

The correct option is "consists of different number of cells".

To understand why this is the correct distinction, let us look at the structural definitions of both a neuron and a nerve:

1. Neuron (A Single Cell):
A neuron (or nerve cell) is the fundamental, individual structural and functional unit of the nervous system. It is a single, microscopically distinct cell consisting of a cell body (soma), dendrites, and a single axon. Because it is an individual cell, a neuron contains exactly one cell.

2. Nerve (A Bundle of Fibers/Cells):
A nerve is a macroscopic, cord-like structure found in the peripheral nervous system. It is not a single cell, but rather an enclosed, cable-like bundle containing the axons of many different neurons. These axons (nerve fibers) are wrapped together in layers of protective connective tissue (endoneurium, perineurium, and epineurium) along with blood vessels. Therefore, a nerve is composed of parts of many cells.

Why the other options are incorrect:
- "one has motor and other has sensory function": Incorrect because both neurons and nerves can have either motor, sensory, or mixed functions. For example, there are sensory neurons and motor neurons, just as there are sensory nerves and motor nerves.
- "nerves are made of grey matter while neurons of white matter": Incorrect because grey matter primarily consists of neuronal cell bodies and dendrites, whereas white matter consists of myelinated axons. Both neurons and nerves are structurally related to these components, but this is not their defining distinction.
- "nerves are present in central nervous system only": Incorrect because nerves are specifically defined as bundles of axons in the peripheral nervous system (PNS). In the central nervous system (CNS), bundles of axons are referred to as tracts.