15.1.3—Sensory, motor and intermediate neurones

A neurone has a cell body, dendrites that receive input, and an axon that carries an impulse away from the cell body. Myelin made by Schwann cells insulates the axon, leaving nodes of Ranvier between myelinated sections.

• Sensory neurone: carries impulses from a sensory receptor towards the central nervous system (CNS).
• Intermediate/relay neurone: lies within the CNS and connects sensory and motor neurones.
• Motor neurone: carries impulses from the CNS to an effector such as a muscle or gland.

Dendrites provide receiving extensions, the axon provides a long conducting fibre, and myelin helps impulses travel efficiently between nodes. The different neurone types therefore assemble a receptor → CNS → effector route; synaptic transmission and action-potential stages are covered separately.

Axons carry impulses away from their cell body, but the three neurone types are distinguished by their position and connection in the pathway, not simply by whether they have an axon. This card does not explain neurotransmitters or the detailed phases of an action potential.