Neural Control and Coordination
Syllabus Unit: Human Physiology
Why it matters
Chapter overview
The nervous system lets the body sense, decide and react in milliseconds. This module builds from a single neuron's anatomy to the impulse racing along it, to the brain and spinal cord that process it, and finally to the eye and ear that feed it raw sensory data — the complete chain NEET tests as one unit.
1Nervous System & Neuron Structure
The neuron is the structural and functional unit of the nervous system — every signal in the body starts here.
Learning Objectives
- Label the dendrites, cell body, axon, myelin sheath and axon terminal of a neuron from memory.
- Distinguish multipolar, bipolar and unipolar neurons by their process count and typical location.
- Explain why myelinated axons conduct impulses faster than unmyelinated ones.
- Differentiate neurons (signal-carrying) from neuroglia (supporting cells like astrocytes and Schwann cells).
Key Terms
A **neuron** is the structural and functional unit of the nervous system: a single specialised cell built to receive a signal at one end, integrate it, and fire it out the other end as an electrical impulse. Everything the nervous system does — reflexes, thought, sensation — is this same basic unit repeated billions of times.
The four parts every neuron shares
- Cell body (soma/perikaryon) — contains the nucleus and Nissl granules; the metabolic centre of the neuron.
- Dendrites — short, branched extensions of the cell body that receive incoming signals.
- Axon — a single long fibre (up to a metre in humans) that carries the impulse away from the soma; may be wrapped in a myelin sheath with gaps called nodes of Ranvier.
- Axon terminal / synaptic knob — the branched end that stores neurotransmitter in synaptic vesicles and passes the signal to the next cell.
Classifying neurons
- Multipolar — one axon, many dendrites; the most common type, found throughout the CNS.
- Bipolar — one axon and one dendrite; found in the retina and olfactory epithelium.
- Unipolar (pseudo-unipolar) — a single process splits into peripheral and central branches; found in dorsal root ganglia.
Neurons never work alone — they are supported by **neuroglia** (glial cells), which do not conduct impulses but nourish, insulate and protect neurons. Schwann cells myelinate PNS axons; oligodendrocytes do the same job in the CNS; astrocytes maintain the blood-brain barrier.