PY10.1-20 | Central Nervous System Physiology — Glossary

The junction between two neurons where signal transmission occurs, consisting of a presynaptic terminal, synaptic cleft (20-40 nm), and postsynaptic membrane.

Chemical messenger released from presynaptic terminals that crosses the synaptic cleft to bind receptors on the postsynaptic membrane, producing excitatory or inhibitory effects.

Dorsal Column-Medial Lemniscus pathway carrying fine touch, vibration, and conscious proprioception; decussates in the medulla.

Ascending pathway carrying pain, temperature, and crude touch; decussates at the spinal cord level via the anterior white commissure.

Theory (Melzack and Wall, 1965) proposing that non-painful input via A-beta fibres closes a 'gate' in the substantia gelatinosa to inhibit pain transmission.

The pyramidal tract from motor cortex to spinal cord anterior horn cells; 85% of fibres decussate at the pyramidal decussation in the medulla.

Neuron with cell body in the motor cortex whose axon descends to synapse on lower motor neurons; lesion causes spastic paralysis and hyperreflexia.

Neuron with cell body in the anterior horn of the spinal cord (or cranial nerve nucleus) whose axon directly innervates skeletal muscle; lesion causes flaccid paralysis and atrophy.

Spinal cord hemisection producing ipsilateral UMN paralysis and DCML loss with contralateral pain and temperature loss below the lesion.

Posterior fossa structure ('little brain') with three functional divisions coordinating movement, balance, and motor learning; lesion causes ataxia without paralysis.

Subcortical nuclei (caudate, putamen, globus pallidus, STN, substantia nigra) that modulate movement via direct (facilitatory) and indirect (inhibitory) pathways.

Paired diencephalic structure containing approximately 50 nuclei that relays and processes nearly all sensory, motor, and limbic information before it reaches the cortex.

Small diencephalic structure controlling homeostasis — temperature, hunger, thirst, circadian rhythm, and autonomic function; links the nervous and endocrine systems via the pituitary.

Interconnected brain structures (hippocampus, amygdala, cingulate gyrus, mammillary bodies) involved in emotion, memory, and motivated behaviour.

Medial temporal lobe structure essential for converting short-term memory into long-term declarative memory; bilateral damage causes anterograde amnesia.

Almond-shaped limbic nucleus mediating fear responses, emotional memory, and the fight-or-flight reaction; bilateral destruction causes Kluver-Bucy syndrome.

Activity-dependent strengthening of synaptic transmission at hippocampal synapses, mediated by NMDA receptor-dependent calcium influx and AMPA receptor insertion — the cellular basis of learning.

Diffuse brainstem network whose ascending projections (ARAS) maintain wakefulness and consciousness; damage causes coma.

Electroencephalogram — recording of cortical electrical activity; key waveforms include beta (alert), alpha (relaxed), theta (drowsy), and delta (deep sleep).

Rapid eye movement sleep characterised by cortical desynchronisation, muscle atonia, dreaming, and irregular autonomic activity; driven by cholinergic pontine neurons.

Non-fluent aphasia from damage to Broca area (areas 44-45) in the dominant inferior frontal gyrus; comprehension preserved but speech is effortful and telegraphic.

Fluent but meaningless aphasia from damage to Wernicke area (area 22) in the dominant posterior superior temporal gyrus; comprehension severely impaired.

Extension (dorsiflexion) of the great toe with fanning of other toes on stroking the lateral sole; indicates UMN lesion in adults (normal in infants under 1 year).

Area of skin supplied by a single spinal nerve root; systematic dermatomal testing helps localise the level of a spinal cord or nerve root lesion.

Crossing of nerve fibres from one side of the CNS to the other; explains why a lesion on one side of the brain produces contralateral clinical deficits.