The plantar reflex is a superficial reflex in which firmly stroking the outer sole of the foot normally makes the toes curl down (a flexor response). An upgoing big toe, often with fanning of the other toes, is the Babinski sign, a classic marker of an upper motor neuron lesion. It is mediated through the L5 and S1 segments.
| Nerve root | L5-S1 |
|---|---|
| Area | Lateral border of the sole, stroked from the heel toward the little toe and across the ball of the foot |
| How to test | With a blunt object, the examiner strokes firmly along the outer sole from the heel toward the little toe and then across toward the big toe, watching the first movement of the big toe. |
| Muscles | |
| Nerve Supply | Tibial nerve (sensory, from the sole); Deep fibular nerve (motor to extensor hallucis longus) |
Shows whether the corticospinal tract is intact; normally it suppresses the primitive extensor response present in infancy.
A Babinski sign in an adult points to damage of the corticospinal tract anywhere from the brain to the spinal cord, for example stroke, multiple sclerosis or cord compression. In infants up to about 1-2 years an extensor response is normal because the corticospinal tracts are still maturing. An equivocal response should be interpreted alongside other signs.
Damage to the corticospinal tract in the brain produces a Babinski sign on the side of the body opposite the lesion.
Compression of the cord from a disc, tumour or myelopathy produces Babinski signs below the level of the lesion.
Demyelinating lesions in the brain or spinal cord commonly produce extensor plantar responses.
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