Final answer:
Ia spindle afferents exert inhibitory effects on antagonistic muscles as part of the stretch reflex mechanism, which helps maintain muscle length and prevent overstretching.
Step-by-step explanation:
The question, 'Ia spindle afferents exert inhibitory effects on which muscles?' relates to the function of muscle spindles and their role in reflex arcs. Within the muscular system, particularly during a stretch reflex, Ia spindle afferents are sensory neurons that detect the change in muscle length. When a muscle spindle is activated due to a muscle being stretched, it elicits two simultaneous actions:
- It causes the same muscle to contract, being the agonistic muscle.
- It inhibits the motor neurons of the antagonistic muscles, thus reducing their activity.
The reflex action facilitated by the Ia spindle afferents helps maintain constant muscle length and protect muscles from overstretching. Accordingly, the correct response to which muscles the Ia spindle afferents exert inhibitory effects on is b. Antagonistic muscles.