Clasp-knife response
Encyclopedia
Clasp-knife response refers to a stretch reflex
with a rapid decrease in resistance when attempting to flex a joint, usually during a neurological examination
. It is one of the characteristic responses of a upper motor neuron lesion. It gets its name from the resemblance between the motion of the limb and the sudden closing of a claspknife after sufficient pressure is applied.
of the antagonistic muscle of that joint, which is an extensor muscle that becomes stretched. In upper motor neuron lesions, muscle tonus may increase and resistance of muscle to stretch increases. However, if sufficient force is applied, limb resistance suddenly decreases.
Stretch reflex
The stretch reflex is a muscle contraction in response to stretching within the muscle. It is a monosynaptic reflex which provides automatic regulation of skeletal muscle length....
with a rapid decrease in resistance when attempting to flex a joint, usually during a neurological examination
Neurological examination
A neurological examination is the assessment of sensory neuron and motor responses, especially reflexes, to determine whether the nervous system is impaired...
. It is one of the characteristic responses of a upper motor neuron lesion. It gets its name from the resemblance between the motion of the limb and the sudden closing of a claspknife after sufficient pressure is applied.
Cause
Although seemingly a stretch reflex when flexing a joint, force from the muscle during the attempt to flex a joint is actually thought to be caused by the tendon reflexTendon reflex
Tendon reflex may refer to:*A stretch reflex, when the stretch is created by a blow upon a muscle tendon. This is the usual definition of the term...
of the antagonistic muscle of that joint, which is an extensor muscle that becomes stretched. In upper motor neuron lesions, muscle tonus may increase and resistance of muscle to stretch increases. However, if sufficient force is applied, limb resistance suddenly decreases.
Mechanism
This reflex is observed in patients with upper motor neuron lesions. It is frequently attributed to the action of the golgi tendon organ, likely because of early studies showing that tendon organs are activated by strong muscle stretch and inhibit motoroneurons of the stretched muscle. It was thought that this was a protective reflex, preventing application of so much force that muscles become damaged. More recent work strongly suggests that tendon organs are not involved in the clasp knife reflex, but that other sensory receptors in muscles are responsible .External links
- http://www.lib.mcg.edu/edu/eshuphysio/program/section8/8ch3/s8ch3_21.htm