Final answer:
The muscle spindle is responsible for sensory reception and inhibition. It detects muscle stretch and initiates a reflex that causes the muscle to contract while inhibiting the antagonist muscle, helping to maintain muscle tension and proprioception.
Step-by-step explanation:
The two primary actions of the muscle spindle are D) Sensory reception and inhibition. Muscle spindles are specialized stretch receptors within muscles that detect changes in the length of the muscle. When the muscle is stretched, the muscle spindle is activated and sends a signal which leads to the muscle contracting in response to the stretch, known as the stretch reflex.
Concurrently, through a process called reciprocal inhibition, it also sends a signal to inhibit the motor neurons of the antagonist muscle, preventing it from contracting and opposing the action of the muscle being stretched. This coordination helps maintain proper muscle tension and proprioception, which is crucial for balance and coordinated movement.