This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Physiology
Clasp knife rigitidy is also known as: September 2007 
Select and explain. 
A. Inverse stretch reflex, B. Withdrawl reflex, C. Lengthening reaction, D. Crossed extensor reflex
A: Inverse stretch reflex
Answer: A: Inverse stretch reflex 
Explanation: Ans. A: Inverse stretch reflex and C: Lengthening reactionWhen the muscles are hypeonic, the sequence of moderate stretch muscle contraction, strong stretch muscle relaxation is clearly seen. Passive flexion of the elbow, for example, meets immediate resistance as a result of the stretch reflex in the triceps muscle. Fuher stretch activates the inverse stretch reflex. The resistance to flexion suddenly collapses, and the arm flexes. Continued passive flexion stretches the muscle again, and the sequence may be repeated. This sequence of resistance followed by give when a limb is moved passively is known as the clasp-knife effect because of its resemblance to the closing of a pocket knife. It is also known as the lengthening reaction because it is the response of a spastic muscle to lengthening.