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A clonus ( Greek κλόνος klonos , German 'violent movement' ) is understood to mean involuntary, rhythmic contractions of muscles or muscle groups. (See also cramp )

The term “clonic spasm ” is used synonymously .


To a certain extent, the clonus represents the extreme form of a muscle reflex . It is triggered by a stretching stimulus, for example by passive stretching of a joint . The stretching stimulus is perceived by the muscle spindles and transmitted to the spinal cord via afferent nerve fibers . There it is monosynaptically connected to a motor neuron in the reflex arc and then played back as excitation to the muscle via efferent fibers.

This process is usually controlled by fibers from the pyramidal tract . In the clonus, this control is defective, so that instead of the brief excitement that occurs in the physiological reflex, the muscle is permanently excited. The clonus is therefore a pyramidal orbit sign .

According to the duration of the clone, two forms can be distinguished:

  • Inexhaustible clonus
  • Exhaustible clonus (only pathological if there are side differences)

See also