AN7.1-8 | Introduction to the nervous system — Glossary

The brain and spinal cord; covered by meninges and bathed in CSF; contains upper motor neurons, interneurons, and sensory relay nuclei

All nervous tissue outside the CNS including 12 cranial nerve pairs, 31 spinal nerve pairs, and peripheral ganglia

The division of the PNS controlling involuntary visceral functions; divided into sympathetic (thoracolumbar) and parasympathetic (craniosacral)

A neuron with its cell body in the motor cortex whose axon descends through the pyramidal tract to synapse on the LMN; lesion causes spastic paralysis

A neuron with its cell body in the anterior horn of the spinal cord whose axon exits via the ventral root to innervate skeletal muscle; lesion causes flaccid paralysis

A cluster of pseudounipolar sensory neuron cell bodies on the posterior root of each spinal nerve; no synapses within the ganglion

A mixed nerve formed by the union of a dorsal (sensory) root and ventral (motor) root at the intervertebral foramen; divides into dorsal and ventral rami

The posterior branch of a spinal nerve supplying the deep muscles and skin of the back

The anterior branch of a spinal nerve supplying the anterior and lateral body wall and limbs; forms nerve plexuses

A connecting branch between a spinal nerve and the sympathetic chain; white (myelinated preganglionic, T1-L2) or grey (unmyelinated postganglionic, all levels)

An area of skin supplied by the sensory fibres of a single spinal nerve; used clinically to localise the level of a nerve or spinal cord lesion

A group of muscles innervated by a single spinal nerve segment; used for motor level testing in neurological examination

The nerve supplying a joint also supplies the muscles acting on that joint and the skin over those muscles

A junction where signal transmission occurs via neurotransmitter release across a synaptic cleft; unidirectional with 0.5 ms delay

A junction where signal transmission occurs via gap junctions allowing direct ionic flow; bidirectional with no delay

A synapse between an axon terminal and a dendrite; the most common synapse type in the CNS; usually excitatory

A synapse between an axon terminal and a neuronal cell body; often inhibitory

A ganglion in the paravertebral chain or collateral position containing multipolar neurons where preganglionic sympathetic fibres synapse

Upgoing great toe (extension) on stroking the lateral sole; normal in infants, pathological in adults indicating UMN lesion

Visible spontaneous twitching of muscle fibres caused by denervation of the motor unit; a sign of LMN disease

Dissolution and dispersal of Nissl substance from the neuronal cell body following axon injury; indicates shift to regenerative mode

The neural pathway mediating a reflex: receptor → afferent neuron → integration centre (interneuron in CNS) → efferent neuron → effector