Jerk Health Dictionary

See REFLEX ACTION.... knee jerk

a deep tendon reflex elicited when the Achilles tendon is stretched and then struck with a tendon hammer. The normal response is reflex contraction of the calf muscles and plantar flexion of the ankle. The ankle jerk may be increased if the spinal cord is compressed above the level of the first sacral spinal nerve (which arises at the level of the second lumbar vertebra). If the nerve itself is cut or compressed the reflex is reduced or absent.... ankle jerk

a deep tendon reflex mediated by the fifth cervical *spinal nerve (C5). The examiner’s thumb or index finger is placed over the patient’s biceps tendon in the elbow crease and struck sharply with a tendon hammer; the normal response is a reflex contraction of the biceps and flexion of the elbow. The jerk is exaggerated in upper *motor neuron lesions, such as a stroke, and reduced or absent in lower motor neuron lesions, such as a disc herniation, peripheral nerve injury, or peripheral neuropathy (e.g. diabetes, alcoholism).... biceps jerk

an abnormal reflex elicited by lightly placing the index finger across the chin of the patient and tapping it with a tendon hammer while the jaw hangs loosely open. A brisk upward movement of the jaw indicates an upper *motor neuron disorder above the brainstem.... jaw-jerk reflex

a tendon reflex that acts at the level of the seventh cervical spinal nerve. With the elbow flexed and relaxed, the triceps tendon is struck just above the elbow, causing contraction of the triceps and extension of the elbow. This reflex is increased in upper *motor neuron lesions and absent in lower motor neuron lesions.... triceps jerk