Definition of Plantar Reflex
The plantar reflex assesses motor neuron function. To test the reflex, the lateral, or outside, sole of the foot is stroked with a thumbnail or blunt instrument. Based on the foot's reaction, an analysis of motor neuron health is postulated.
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Theory
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Stimulating a specific area of the foot should cause an instant, involuntary withdrawal response from a correlating part of the body. This is a natural defense mechanism against a foreign stimulus.
Troubleshooting
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If no response follows stimulation, progressively sharper tools may be used on the foot until a response is generated. Reasons for a possible lack of response include previous nerve damage, or, especially thick, calloused skin.
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Features
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In a "normal" plantar reflex response, the big toe flexes, and the other toes may flex and adduct (move away), indicating healthy motor neuron function. The muscles of the leg, knee, and hip might flex as well.
Babinski sign
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When the big toe extends instead of flexes, and the other toes spread into a fan shape, it is called a Babinski sign. This is considered an abnormal response, and may indicate upper motor neuron damage or brain disease.
Considerations
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Infants will always generate a Babinski reflex as the neuron pathways are not yet fully formed. At 12 to 18 months of age, infants should generally start demonstrating a normal response.
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References
- Photo Credit Image by Flickr.com, courtesy of Nicholas
