Clasp-knife response refers to a

Golgi tendon reflex The Golgi tendon reflex (also called inverse stretch reflex, autogenic inhibition, tendon reflex) is an inhibitory effect on the muscle resulting from the muscle tension stimulating Golgi tendon organs (GTO) of the muscle, and hence it is self-indu ...

with a rapid decrease in resistance when attempting to flex a joint, usually during a

neurological examination A neurological examination is the assessment of sensory neuron and motor responses, especially reflexes, to determine whether the nervous system is impaired. This typically includes a physical examination and a review of the patient's medical hist ...

. It is one of the characteristic responses of an

upper motor neuron lesion An upper motor neuron lesion (also known as pyramidal insufficiency) Is an injury or abnormality that occurs in the neural pathway above the anterior horn cell of the spinal cord or motor nuclei of the cranial nerves. Conversely, a lower motor n ...

. 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

When a joint is passively flexed, the resisting force comes from the

stretch reflex The stretch reflex (myotatic reflex), or more accurately "muscle stretch reflex", is a muscle contraction in response to stretching within the muscle. The reflex functions to maintain the muscle at a constant length. The term deep tendon reflex is ...

(or sometimes called tendon reflex) resulting from the extensor muscle being stretched. In

s, muscle tonus may increase and resistance of muscle to stretch increases. However, if sufficient force is applied, limb resistance suddenly decreases, presumably mediated by the

(also call autogenic inhibition).

Mechanism

This reflex is observed in patients with upper motor neuron lesions. It was frequently attributed to the action of the

golgi tendon organ The Golgi tendon organ (GTO) (also called Golgi organ, tendon organ, neurotendinous organ or neurotendinous spindle) is a proprioceptor – a type of sensory receptor that senses changes in muscle tension. It lies at the interface between a musc ...

, 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.Neural mechanisms underlying the clasp-knife reflex in the cat. I. Characteristics of the reflex. Cleland CL, Rymer WZ. J Neurophysiol. 1990 Oct;64(4):1303-18. Spasticity, decerebrate rigidity and the clasp-knife phenomenon: an experimental study in the cat. Burke D, Knowles L, Andrews C, Ashby P. Brain. 1972;95(1):31-48.

Example

Passive flexion of elbow meets immediate resistance due to stretch reflex in the triceps muscle. Further stretch activates inverse stretch reflex. The resistance to flexion suddenly collapses, and the elbow flexes. Continued passive flexion stretches the muscle and the sequence may be repeated. As the muscle tone increases, resistance against flexion of the limb increases as well. However, when flexion is continued, further stretching of the triceps muscle activates an inverse stretch reflex that relaxes the muscle due to autogenic inhibition.

References

External links

Lib.mcg.edu
{{Movement and gait symptoms and signs Somatic motor system Neurophysiology Reflexes

Cause

Mechanism

Example

See also

References

External links