The impact of primary motor cortex, spinal cord, and sciatic nerve cooling on spinal reflex activity in the rat: a reversible deactivation study
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The influence of spinal reflex arcs on lower limb movement cannot be understated, but the individual contribution of various parts of the reflex pathway, namely the primary motor cortex, spinal cord, and sciatic nerve, are incompletely known. This study aims to consider each of these to develop a better understanding of how spinal cord reflexes and the relationship between the central and peripheral nervous systems, particularly in terms of motor control. In the anesthetized rat, recording electrodes were placed in the tibialis anterior muscle of the hindlimb to record both the direct muscle response (M-wave) and the muscle reflex response (H-wave) in response to electrical stimulation of the sciatic nerve. After baseline recordings, thermal deactivation was used to selectively silence the primary motor cortex, spinal cord, or sciatic nerve in the rat and test the hypothesis that different locations exerted different effects on the excitability and timing of the spinal cord reflexes. Deactivation of motor cortex produced a faster or more excitable spinal cord reflex, whereas sciatic nerve deactivation produced a profound attenuation of both the M and the H waves. This study strongly supports the contention that the motor cortex, through pathways that travel through the spinal cord, normally serves to inhibit the excitability of spinal cord reflexes.