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Ankle clonus. Clonus is a set of involuntary and rhythmic muscular contractions and relaxations. Clonus is a sign of certain neurological conditions, particularly associated with upper motor neuron lesions involving descending motor pathways, and in many cases is accompanied by spasticity (another form of hyperexcitability). [1]
In biology, a reflex, or reflex action, is an involuntary, unplanned sequence or action [1] and nearly instantaneous response to a stimulus. [2] [3] The simplest reflex is initiated by a stimulus, which activates an afferent nerve. The signal is then passed to a response neuron, which generates a response.
exaggerated deep tendon reflexes including spasticity, and clonus (a series of involuntary rapid muscle contractions) Such signs are collectively termed the "upper motor neuron syndrome". Affected muscles typically show multiple signs, with severity depending on the degree of damage and other factors that influence motor control. In ...
Clonus results due to an increased motor neuron excitation (decreased action potential threshold) and is common in muscles with long conduction delays, such as the long reflex tracts found in distal muscle groups. [7] Clonus is commonly seen in the ankle but may exist in other distal structures as well, such as the knee or spine. [8]
The Achilles reflex checks if the S 1 and S 2 [3] nerve roots are intact and could be indicative of sciatic nerve pathology. It is classically delayed in hypothyroidism. This reflex is usually absent in disk herniations at the L 5 —S 1 level. A reduction in the ankle jerk reflex may also be indicative of peripheral neuropathy.
The stretch reflex (myotatic reflex), or more accurately "muscle stretch reflex", is a muscle contraction in response to stretching a muscle. The function of the reflex is generally thought to be maintaining the muscle at a constant length but the response is often coordinated across multiple muscles and even joints. [ 1 ]
These reflexes are believed to be "hard-wired" before birth, and are therefore able to be elicited in the newborn. As the brain matures, certain areas (usually within the frontal lobes) exert an inhibitory effect, thus causing the reflex to disappear. When disease processes disrupt these inhibitory pathways, the reflex is "released" from ...
A list of reflexes in humans. Abdominal reflex; Accommodation reflex — coordinated changes in the vergence, lens shape and pupil size when looking at a distant object after a near object. Acoustic reflex or attenuation reflex — contraction of the stapedius and tensor tympani muscles in the middle ear in response to high sound intensities.