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What effect does the monkey grip have on the patellar stretch reflex?

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Pediatrician, Infectious Diseases
Practicing since : 2005
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What effect did the monkey grip have on the patellar strecth reflex?Why?
Posted Tue, 22 May 2012 in General Health
Answered by Dr. Hema Yadav 6 hours later
hb Hello ,
Thanks for posting your query.
The patellar stretch reflex is a XXXXXXX tendon reflex and the monkey grip( or jendrassic manoeuvre ) reinforces the reflex making it a stronger, more visible response , hence used to confirm it if the reflex seems to be weak or absent.
Let me explain you the basics of the reflex so that you can understand the reason for it.Though difficult if you are unaware of the medical terminologies I will try my best so that your doubts are resolved .
Normally our muscles naturally stretch and recoil to accomodate various movements.
Imbedded in each muscle is bundle of fibers called the muscle spindles that "keep watch" of:
1 the length of the muscle and
2 how fast the length of the muscle is changing

By monitoring these things the spindle fibers prevent the muscle from being damaged by over stretching. If the muscle starts to become over stretched (or if stretching is occurring really really fast, and therefore the body is anticipating that it is about to be over stretched), then the muscle spindle causes the muscle to contract to place resistance against the overstretching.
In the knee-jerk reflex (also known as patellar tendon reflex) a tap is applied to the tendons of the quadriceps muscles, which stretches the muscles and their muscle spindles. A brisk tap excites the afferent fibers, because of their velocity sensitivity, ultimately causing the muscle to contract.

The phenomenon of effect of monkey grip that you are referring to is called the Jendrassik manoeuver.
When your arms are clenched , there will be slightly increased tone in the rest of your body, and therefore the receptors on your muscle spindles.

When the patellar tendon is tapped, the body thinks it must contract the muscle even harder than normal, because the muscle spindles were already experiencing some tone,
and yet they were still stretched durring the tap.
The result is a reinforced reflex which is seen as an exaggerated knee jerk.
Similar reinforcement also can be seen with clenching of teeth ,infact any motor activity increasing the tone of muscles which is not related to legs can trigger such reinforcement.
Hope I have answered your query to your satisfaction.

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