Medsci 142 Lectures 3 & 4 – Sensory and Motor Systems Vocabulary

Vocabulary flashcards covering key sensory and motor terms from Medsci 142 Lectures 3 & 4.

Discriminative sensation

Touch and pressure information that can be precisely located and graded in intensity.

Non-discriminative sensation

Crude pain and temperature signals with poor spatial resolution.

Dorsal column-medial lemniscal system

Ascending pathway for discriminative touch/pressure that crosses in the lower medulla and relays in the thalamus.

Spinothalamic tract

Ascending pathway conveying pain and temperature that crosses in the anterior white commissure of the spinal cord.

Decussation

The crossing of nerve fibres from one side of the central nervous system to the other.

Dorsal funiculus

Posterior white-matter column of the spinal cord containing gracile and cuneate fasciculi.

Gracile fasciculus

Medial part of dorsal column carrying lower-limb and trunk touch/pressure signals.

Cuneate fasciculus

Lateral part of dorsal column carrying upper-limb and trunk touch/pressure signals.

Medial lemniscus

Brain-stem tract formed by internal arcuate fibres that carries touch/pressure to the thalamus.

Internal arcuate fibres

Axons from gracile and cuneate nuclei that cross the midline to form the medial lemniscus.

Nucleus proprius

Spinal dorsal-horn region receiving sensory input, part of the pain/temperature pathway.

Substantia gelatinosa

Superficial dorsal-horn layer that processes pain and temperature information.

Monosynaptic (myotatic) reflex

Stretch reflex with a single synapse between sensory and motor neuron, e.g., knee-jerk.

Polysynaptic (withdrawal) reflex

Protective reflex using interneurons to withdraw from painful stimuli.

Convergence

Many primary afferents synapsing onto fewer second-order neurons to economize spinal wiring.

Brown-Séquard syndrome

Hemisection of spinal cord causing ipsilateral touch/pressure loss and contralateral pain/temperature loss.

Associative sensory loss

Brain-stem lesion causing loss of both touch/pressure and pain/temperature on the body side opposite the lesion.

Ventral white commissure

Region where spinothalamic fibres cross the spinal midline.

Dorsolateral tract (Lissauer’s tract)

Entry zone where pain/temperature fibres ascend or descend before synapsing.

Primary somatosensory cortex

Post-central gyrus area mapping the body surface; enlarged areas for hands, lips, and face.

Somatotopy

Ordered, point-to-point representation of the body within a neural structure.

Corticospinal (pyramidal) tract

Major descending pathway from motor cortex to spinal cord controlling voluntary movement.

Pyramidal decussation

Lower-medulla crossing where ~85 % of corticospinal fibres form the lateral corticospinal tract.

Lateral corticospinal tract

Crossed corticospinal fibres controlling fine, distal (appendicular) movements.

Anterior corticospinal tract

Uncrossed or bilaterally crossing corticospinal fibres controlling axial muscles.

Upper motor neuron (UMN)

Neuron originating in cortex or brain-stem projecting to lower motor neuron.

Lower motor neuron (LMN)

Spinal or cranial motor neuron that directly innervates skeletal muscle.

Flaccid paralysis

Loss of tone and reflexes due to LMN damage.

Spastic paralysis

Increased tone and reflexes with loss of voluntary control owing to UMN damage.

Basal ganglia

Subcortical nuclei (striatum, globus pallidus, subthalamic nucleus, substantia nigra) that modulate movement.

Striatum

Input nucleus of basal ganglia composed of caudate nucleus and putamen.

Globus pallidus internal segment (GPi)

Basal-ganglia output nucleus sending inhibitory signals to the thalamus.

Subthalamic nucleus

Excitatory glutamatergic nucleus within basal-ganglia circuitry that influences GPi activity.

Substantia nigra pars compacta (SNc)

Dopaminergic nucleus that ‘primes’ striatal neurons for movement control.

Dopamine

Neurotransmitter made in SNc; excess causes psychosis, deficiency causes Parkinson’s disease.

Parkinson’s disease

Neurodegenerative loss of SNc dopamine neurons producing bradykinesia, tremor, and rigidity.

Bradykinesia

Slowness of movement typical of Parkinson’s disease.

L-DOPA (Levodopa)

Dopamine precursor that crosses the blood–brain barrier and is used to treat Parkinson’s.

Pallidotomy

Surgical lesion of GPi to reduce its inhibitory output in Parkinson’s therapy.

Deep brain stimulation

Implanted electrodes (e.g., in STN or GPi) delivering pulses to alleviate Parkinsonian symptoms.