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)