Dr.K.Jaiganesh, MD

Professor of Physiology,

MGMC & RI

Cerebral cortex

Ascending tracts- Sensory

Carrying up sensationsDescending tracts-Motor

Carrying down orders

Motor System

Cerebral cortex

30%

40%

30%

Cerebral cortex

30%30% 40%

Motor Homonculus

Left Right

UMN & LMN Lesion

Motor neuron

UMN & LMN paralysis

UMN Lesion LMN Lesion

Muscle bulk Disuse atrophy Wasting

Muscle tone (spasticity) (flaccidity)

Superficial

reflexes

Lost Lost

Deep reflexes Exaggerated Lost

Plantar reflex Babinski’s sign Normal

Clonus Present Absent

Cause Damage to motor

tracts above the

anterior horn cell

Damage to the

anterior horn

cells and below

UMN & LMN Lesion

Stretch Reflex

Muscle

Spinalcord

Dorsal rootganglion

BASIS-

REFLEX ARC

Muscle

spindle

Sensory nerve

Motor nerve

I

a

α Motor neuron

CS

T

Stretch reflex

G

Cortex

1 a

Role of Higher centers

PF

+

MI

-

ά- γ linkage

γ (Gamma) motor neuron discharge by HC influence

contraction of the ends of the intra fusal fibers

stretching of the intra fusal fibers

Ia afferent impulses to the spinal cord

reflex firing of ά (alpha) motor neuron)

contraction of extra fusal fibers

in muscle tone.

Cortex

Voluntary movement

by cortex

G