Motor System

THE MOTOR SYSTEM Part of cerebral cortex of frontal lobes which on stimulation gives response to skeletal muscle responses. Motor Area 4-

Area 6

Area 8

AREA 4 : MOTOR AREA Site: Whole length of pre central gyrus. Main region of origin of pyramidal tracts. Body is represented upside down Size of representation of the individual body part is proportional to the skill with which the part is used in fine voluntary movements Large area for hand and face. Supplementary motor area involves involuntary movements that involve planning and are complicated

AREA 6: PREMOTOR AREA Anterior to precentral gyrus. Consist of descending fibers of pyramidal tacts EXTRAPYRAMIDAL FIBRES. FUNCTIONS 1. Complicated motor functions eg. two handed coordination

AREA 8: Anterior to pre motor area Functions Conjugate deviation of the eyes to the opposite side. MOTOR PATHWAYS Pyramidal tracts Corticospinal and corticobulbar tracts. Extra pyramidal tracts. Pyramidal tracts z Origin: motor areas of cerebral cortex. z Termination: last segment of spinal cord. Properties: z z z

Slow conducting pathway Motor area to spinal ventral horn cells- fibers constituting these are called corticospinal tracts. Motor area to motor cranial nuclei in the brain stem; pyramidal tracts constitute corticobulbar tracts.

Note: 1. Pyramidal cells and tracts constitute upper motor neurons. 2. Spinal and cranial motor neurons which innervate muscle directly constitute lower motor neuron.

Course of pyramidal tracts: Internal capsule ↓ Mid brain ↓ Pons ↓ Medulla ↓ Spinal cord Note: 85% of the fibers cross to the opposite side in lower part of the medulla and enter lateral white column and descend down as lateral corticospinal tract. 15% do not cross and enter anterior white column and descend down as anterior corticospinal tract. Functions: 1. Lateral corticospinal tract controls fine voluntary movements 2. Anterior corticospinal tracts. Control of postural movements and gross movements. 3. Corticobulbar tracts control voluntary movements of muscles of pharynx, larynx and jaws and eyes.

EXTRAPYRAMIDAL TRACTS Functions z z z z z

Concerned with postural and muscular movements. Control of tone, posture, equilibrium. Coordinated movements of limbs and body. movements of eyeball Exerts tonic inhibitory control over the lower centers

Applied: Damage to extra pyramidal tracts increase the rigidity of muscles. Tracts that constitute extra pyramidal system: Rubrospinal tracts Tectospinal and tectobulbar tracts Reticulospinal tract Vestibulospinal tract Medial longitudinal fasciculus

Influences Flexor muscle tone Reflex postural movements in response to visual and auditory stimuli Fascilitatory / inhibitory effect on voluntary movements. Fasciculatory effect on extensor muscles Coordination of reflex ocular movements.

Upper motor neuron 1. Involves group of muscles 2. Spastic paralysis; i.e. loss of higher inhibitory control 3. Deep reflexes are hyperactive 4. Babinski’s sign positive

lower motor neuron Involves single muscle Flaccid paralysis; i.e. loss of muscle tone. Deep reflexes are lost. Babinski’s sign not elicited.

Multiple Choice Questions: 1 Pyramidal tract originate in a) Area 4 b) Area 6 c) Area 8 d) None 2 Motor pathways does not include a) Pyramidal tracts b) Corticospinal tract c) Extrapyramidal tract d) Anterior spinothalamic tract

3 About extrapyramidal tract one of following is false a) Concerned with control of tone b) Concerned with control of posture c) Concerned with control of equilibrium d) Concerned with fine touch

4 Upper motor neuron lesion is characterised by a) Hyperreflexia b) Flaccid paralysis c) Loss of Babinski's sign d) All of above