Clonus (from the Greek for "violent, confused motion") is a series of involuntary muscular contractions due to sudden stretching of the muscle. Clonus is a sign of certain neurological conditions, and is particularly associated with so-called upper motor neuron lesions such as stroke, multiple sclerosis or spinal cord damage. Unlike the small, spontaneous twitching known as fasciculations (usually caused by lower motor neuron pathology), clonus causes large motions that are usually initiated by a reflex. Upper motor neurons, or Betz cells, are motoneurons located in the primary motor cortex. ... Jump to: navigation, search A stroke or cerebrovascular accident (CVA) occurs when the blood supply to a part of the brain is suddenly interrupted by occlusion (called an ischemic stroke -- approximately 90% of strokes), by hemorrhage (called a hemorrhagic stroke -- about 10% of strokes) or other causes. ... A fasciculation is a small, local involuntary muscle contraction (twitching) visible under the skin arising from the spontaneous discharge of a bundle of skeletal muscle fibres. ... Lower motor neurons are the motoneurons connecting the spinal cord to the muscle fibers, bringing the nerve signals from the upper motor neurons out the spine to the muscles. ...

Clonus is most common in the ankles, where it is tested by rapidly flexing back (dorsiflexing) the relaxed ankle. It can also be tested in the knees by rapidly pushing the patella towards the toes. Human anatomy In human anatomy, the knee joint is a complex, compound, condyloid variety of a synovial joint. ... Jump to: navigation, search Left patella - anterior aspect Left patella - posterior aspect The patella or kneecap is a thick, triangular bone which articulates with the femur and covers and protects the front of the knee joint. ...

See also:

• Tonus