Ankle jerk

Ankle Jerk (also known as the Achilles Reflex) is a reflex that is tested to assess the integrity of the sacral nerves and the lower motor neuron. It is a type of deep tendon reflex (DTR) that occurs when the Achilles tendon is tapped while the foot is dorsi-flexed.

Mechanism

The ankle jerk reflex is mediated by the S1 and S2 components of the sacral plexus. When the Achilles tendon is struck, it stretches the gastrocnemius muscle, which in turn sends an impulse along the sensory neurons to the spinal cord. This impulse then travels back to the gastrocnemius and soleus muscles via the motor neurons, causing them to contract and the foot to plantar flex.

Clinical Significance

The ankle jerk reflex is used in neurological examination to assess the integrity of the peripheral nervous system and the central nervous system. An absent or diminished ankle jerk reflex may indicate damage to the sacral nerves, lower motor neuron, or the muscle spindle afferents. An exaggerated ankle jerk reflex may suggest an upper motor neuron lesion.

Testing

To test the ankle jerk reflex, the patient should be in a relaxed and semi-recumbent position. The examiner dorsiflexes the foot and taps the Achilles tendon with a reflex hammer. A normal response is the contraction of the calf muscles and plantar flexion of the foot.

See Also

• Knee jerk
• Biceps reflex
• Triceps reflex
• Reflexes