describe the structure and function of a sensory neurone and a motor neurone and state that intermediate neurones connect sensory neurones and motor neurones
Control and Coordination in Mammals – Sensory and Motor Neurones
Control and Coordination in Mammals
Learning Objective
Describe the structure and function of a sensory neurone and a motor neurone and state that intermediate neurones connect sensory neurones and motor neurones.
Sensory Neurone (Afferent Neurone)
A sensory neurone carries information from peripheral receptors towards the central nervous system (CNS). Its structure is specialised to detect and transmit specific types of stimuli.
Dendrites (or sensory endings): highly branched or specialised endings (e.g., hair‑cell bundles, free nerve endings) that receive the stimulus.
Cell body (soma): located in a dorsal root ganglion (spinal) or a cranial nerve ganglion; contains the nucleus and organelles.
Axon: usually a single, long fibre that projects centrally into the spinal cord or brainstem.
Myelin sheath: many sensory fibres are myelinated, allowing rapid conduction of action potentials.
Synaptic terminals: form connections with interneurones in the CNS, releasing neurotransmitters such as glutamate.
Motor Neurone (Efferent Neurone)
A motor neurone transmits impulses from the CNS to effectors (muscles or glands) to produce a response.
Cell body (soma): located in the ventral grey matter of the spinal cord or in cranial nerve nuclei.
Dendrites: receive input from interneurones and other motor neurones.
Axon: a single, often very long fibre that exits the CNS via the ventral root and travels to the target muscle or gland.
Myelin sheath: typically heavily myelinated (except for the smallest motor fibres), enabling fast conduction.
Interneurones are neurones whose cell bodies lie entirely within the CNS. They receive input from sensory neurones and, after processing, transmit signals to motor neurones. Thus, they form the essential link that allows sensory information to be integrated and appropriate motor responses to be generated.
Comparison of Sensory and Motor Neurones
Feature
Sensory Neurone (Afferent)
Motor Neurone (Efferent)
Direction of impulse
Peripheral → CNS
CNS → Peripheral
Cell body location
Dorsal root or cranial ganglion (outside CNS)
Ventral grey matter or cranial nerve nuclei (inside CNS)
Primary function
Detect and transmit sensory information (e.g., touch, pain, temperature)
Yes – receptors such as mechanoreceptors, thermoreceptors, etc.
No – terminal branches form synapses with muscle fibres or glands
Suggested diagram: A schematic showing a sensory neurone entering the dorsal horn, an interneurone within the spinal cord, and a motor neurone exiting the ventral horn to a muscle fibre.