Which statement correctly describes afferent signaling in the stretch-shortening cycle?

• A. Afferent signals travel from the spinal cord to the brain
• B. Afferent signals travel from the muscle spindles to the spinal cord
• C. Efferent signals travel from the brain to the muscle to contract
• D. Efferent signals travel from the spinal cord to the brain

Answer: (B)

In the stretch-shortening cycle, sensory input comes from the muscle spindle and travels toward the spinal cord. When the muscle is stretched during the eccentric phase, the spindle detects this length change and sends afferent signals to the spinal cord. There, those signals help initiate a rapid, reflexive activation of the same muscle via alpha motor neurons, boosting the subsequent concentric contraction. This spinally mediated afferent feedback is key to the efficiency and timing of force production in the cycle. Some afferent information can also ascend to the brain for perception, but the immediate, functional effect in the SSC comes from signaling to the spinal cord. The other statements describe motor commands traveling from the brain or spinal cord to muscles (efferent pathways), not the sensory signals from muscle spindles.