Contraction of the quadriceps muscle

Tapping the patella tendon elicits a reflex contraction of the quadriceps muscle. During the contraction of the quadriceps muscle,

A. The lb afferents from the Golgi tendon organ increase their rate of firing
B. The 1a afferents from the muscle spindle increase their rate of firing 
C. The alpha motoneurons innervating the extrafusal muscle fibers decrease their rate of firing 
D. The gamma motoneurons innervating the intrafusal muscle fibers increase their rate firing

The Answer is A. The Ib afferents innervating the quadriceps muscles are activated when the quadri­ceps contracted in response to tapping the patella tendon. Stretching the patella tendon stretches the intrafusal muscle fibers within the quadriceps muscle and causes an increase in Ia afferent activity. The increase in Ia affer­ent activity causes an increase in alpha motoneuron activity, which results in contraction of the quadriceps muscle. When the muscle contracts, the intra­fusal muscle fibers are unloaded and the Ia afferent activity is reduced.