Q.(i) Draw a labelled diagram of the Human Nervous System. [2]

What is a Neuron? The Intuition

Think of the nervous system as the body's electrical wiring. A neuron is a single wire in that vast network — but a wire that is alive, can receive signals, decide whether to pass them on, and send them over long distances.

The job of a neuron is simple: receive information, process it, and transmit it to the next cell. Every thought, every muscle movement, every heartbeat, every sensation you feel — all of it depends on this one basic task being done by billions of neurons working together.

The Three Essential Parts

A neuron has three distinct regions, each with a specific role. You can remember them by thinking of a tree.

1. Cell Body (Soma) — The Tree Trunk

The cell body is the neuron's command centre. It contains the nucleus and most of the cell's organelles — the machinery that keeps the cell alive. Here, the neuron makes proteins, generates energy, and performs all the housekeeping functions of any living cell.

But the cell body has a special job too: it integrates incoming signals. If enough signals arrive at the same time, the cell body decides "yes, send a message" or "no, stay quiet." This decision is the fundamental basis of all neural activity.

2. Dendrites — The Branches

Dendrites are short, branching extensions that spread out from the cell body like the branches of a tree. Their name comes from the Greek dendron, meaning "tree."

These are the receiving antennas of the neuron. Dendrites pick up chemical signals from other neurons and convert them into tiny electrical changes in the cell. The more dendrites a neuron has, the more inputs it can receive. Some neurons have thousands of dendrites, allowing them to listen to thousands of other neurons at once.

3. Axon — The Long Cable

The axon is a single, long fibre that extends from the cell body, often much longer than the dendrites. In some neurons, axons can be over a metre long — think of the nerve running from your spinal cord all the way down to your big toe.

The axon's job is to carry the electrical signal away from the cell body toward the next neuron or to a muscle or gland. It is the transmission line. Most axons are wrapped in a fatty insulating layer called the myelin sheath, which acts like the plastic coating on an electrical wire — it prevents the signal from leaking out and makes it travel much faster.

At the very end, the axon splits into many tiny branches, each ending in a small swelling called an axon terminal or synaptic knob. This is where the signal gets passed to the next cell.

Putting It All Together

Here is how a signal moves through a single neuron:

1. Reception: Chemical messengers from a neighbouring neuron bind to receptors on the dendrites.
2. Integration: The cell body adds up all the incoming signals. If the total is strong enough, it triggers an electrical impulse.
3. Transmission: The impulse races down the axon, jumping from gap to gap in the myelin sheath for speed. …