Repeated Medical PG Question- 11

You are testing knee jerk reflex in a patient. The afferents in deep tendon reflexes are carried by:

A. Dynamic intrafusal fibers

B. Golgi tendon organ

C. Nuclear bag and static chain fibers

D. Both Golgi tendon and muscle spindle

Answer is A. Dynamic intrafusal fibers

▪️Dynamic nuclear bag fibers are highly sensitive to the rate of change in muscle length, providing velocity sensitivity to

muscle stretch.

▪️Nuclear bagfibers can be divided into nuclear bagfibers type I and nuclear bagfiber Ope 2. 

▪️The sum of these difference renders: 

(l) the nuclear bag type I fibers with littte elasticity in their polar regions making them sensitive to dynamic changes (velocity of length-change); and 

(2) nuclear bag type 2 with significant elasticity in their polar region making

them sensitive to the changes in length (but not to the velocity of length change) 

Hence, nuclear hag fibers type I are also

called dynanmic nuclear big fibers and nuclear bag fibers type II fibers are also called static nuclear bag fibers.