- A form of movement marked by contractions and relaxations of a muscle, occurring in rapid succession seen with, among other conditions, spasticity and some seizure disorders. SEE ALSO: contraction. [G. klonos, a tumult]- ankle c. a rhythmic contraction of the calf muscles following a sudden passive dorsiflexion of the foot, the leg being semiflexed.- toe c. alternating movements of flexion and extension of the great toe following forcible extension at the metatarsophalangeal joint.- wrist c. rhythmical contractions and relaxations of the muscles of the forearm excited by a forcible passive extension of the hand.
* * *clo·nus 'klō-nəs n a series of alternating contractions and partial relaxations of a muscle that in some nervous diseases occurs in the form of convulsive spasms involving complex groups of muscles and is believed to result from alteration of the normal pattern of motor neuron discharge compare TONUS (2)
* * *n.rhythmical contraction of a muscle in response to a suddenly applied and then sustained stretch stimulus. It is most readily obtained at the ankle when the examiner bends the foot sharply upwards and then maintains an upward pressure on the sole. It is caused by an exaggeration of the stretch reflexes and is usually a sign of disease in the brain or spinal cord.
* * *clo·nus (kloґnəs) [Gr. klonos turmoil] 1. alternate muscular contraction and relaxation in rapid succession. 2. a continuous rhythmic reflex tremor initiated by the spinal cord below an area of spinal cord injury, set in motion by reflex testing. clonic adj
Medical dictionary. 2011.