5. Pyramidal system, examination of muscle strength, lesion syndromes of central and peripheral motor neuron

Explains the pyramidal (corticospinal) tract, from its origin in the precentral gyrus through the internal capsule, brainstem and medullary decussation to the anterior horn cells, and its role in voluntary and fine distal movement. Covers how muscle strength is graded on the MRC scale and which movements are tested in each limb. Sets out upper and lower motor neuron syndromes with their causes, clinical features and distribution patterns, closing with a comparison table of UMN versus LMN lesions.

Inside: 3 sections · 2 labelled pictures · 2 tables · 15 flashcards · 2 min

Topic 5 of 88 in the MU Sofia syllabus for Neurology (Medicine, Year 4). The free AceMed note covers it in 3 sections, about 240 words (2 min of reading), with 15 flashcards.

Pyramidal system. Examination of muscle strength. syndromes of the central and peripheral motor neruon

Pyramidal System: The pyramidal system (corticospinal tract) is the main voluntary motor pathway controlling precise and skilled movements.

Anatomy

Origin: Primary motor cortex (precentral gyrus, Brodmann area 4)

Fibers pass through: Corona radiata. Internal capsule. Cerebral peduncles. Pons. Medullary pyramids

80–90% cross in the lower medulla (pyramidal decussation).

Continue as the lateral corticospinal tract and terminate on anterior horn cells.

Function

Initiation and control of voluntary movements
Fine motor movements, especially of distal limbs

Examination of Muscle Strength

Muscle strength is assessed by asking the patient to perform movements against resistance and comparing both sides.

Medical Research Council (MRC) Scale

Commonly Tested Movements

Upper Limb: Shoulder abduction. Elbow flexion/extension. Wrist extension. Finger abduction. Hand grip
Lower Limb: Hip flexion. Knee extension. Ankle dorsiflexion. Plantar flexion

Central Motor Neuron (Upper Motor Neuron) Syndrome

Results from lesions of the motor cortex, internal capsule, brainstem, or corticospinal tract.

Causes: Stroke. Multiple sclerosis. Brain tumors. Spinal cord lesions

Clinical Features: Weakness or paralysis. Spasticity (increased muscle tone). Hyperreflexia. Clonus. Positive Babinski sign. Minimal muscle atrophy (disuse atrophy). No fasciculations

Distribution

Hemiparesis (one side)
Paraparesis (both legs)
Quadriparesis (all limbs)