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In neurology, the plantar reflex or Babinski reflex or Babinski sign is a reflex that can identify disease of the spinal cord and brain and also exists as a primitive reflex in infants. When non-pathological it is called the plantar reflex while the term Babinski's sign refers to its pathological form.
The lateral side of the sole of the foot is rubbed with a blunt implement so as not to cause pain, discomfort or injury to the skin; the instrument is run from the heel along a curve to the metatarsal pads. There are three responses possible:
- Flexor: the toes curve inward and the foot everts; this is the response seen in healthy adults.
- Indifferent: there is no response.
- Extensor: the hallux extends upward, and the other toes fan out - the Babinski's sign indicating damage to the central nervous system.
As the lesion responsible for the sign expands so does the area from which the afferent Babinski response may be elicited. The Babinski response is also normal while asleep and after long period of walking.
The Babinski’s sign can indicate upper motor neuron damage to the spinal cord in the thoracic or lumbar region, or brain disease constituting damage to the corticospinal tract. Occasionally, a pathological plantar reflex is the first (and only) indication of a serious disease process, and a clearly abnormal plantar reflex often prompts detailed neurological investigations, including CT scanning of the brain or MRI of the spine, as well as lumbar puncture for the study of cerebrospinal fluid.
- Main article: Primitive reflexes
Infants will also show an extensor response. A baby's smaller toes will fan out, and their big toe will dorsiflex slowly. This happens because the corticospinal pathways that run from the brain down the spinal cord are not fully myelinated at this age, so the reflex is not inhibited by the cerebral cortex. The extensor response disappears and gives way to the flexor response around 12-18 months of age.
Relationship to Hoffmann sign
- Main article: Hoffmann's sign
The Hoffmann's sign is occasionally said[attribution needed] to be the upper limb equivalent of the Babinski's sign because both indicate upper motor neuron dysfunction. Mechanistically, they differ significantly; the finger flexor reflex is a simple monosynaptic spinal reflex involving the flexor digitorum profundus that is normally fully inhibited by upper motor neurons. The pathway producing the plantar response is more complicated, and is not monosynaptic. This difference has led some[attribution needed] neurologists to reject strongly any analogies between the finger flexor reflex and the plantar response.[How to reference and link to summary or text]
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