Sensory and motor neurones and spinal reflexes: a narrative review

Neurones are specialised, polarised cells that transmit electrical and chemical signals, underpinning both simple reflexes and complex motor behaviours. Sensory (afferent) neurones relay peripheral information to the central nervous system (CNS), while motor (efferent) neurones convey commands to skeletal muscles. Interneurones within the spinal cord integrate these signals, enabling coordinated motor output. The spinal cord’s dorsal, ventral, and lateral horns support sensory processing, motor execution, and the integration of ascending and descending pathways. Spinal reflexes are rapid, stereotyped responses mediated by organised neural circuits. Monosynaptic reflexes, such as the myotatic (stretch) reflex, involve direct sensory–motor communication, regulated by γ-motoneurones and reciprocal inhibition to maintain muscle length and tone. Polysynaptic reflexes, including the flexor withdrawal reflex, engage interneurones to coordinate synergistic and antagonistic muscle activity, adapting to limb posture, stimulus location, and contextual factors. The inverse myotatic reflex, mediated by Golgi tendon organs, safeguards muscles and ligaments by modulating force during contraction. These reflexes employ reciprocal, non-reciprocal, presynaptic, and recurrent inhibitory mechanisms, collectively ensuring precise, adaptable, and stable motor control. A detailed understanding of sensory and motor neurone organisation and spinal reflex dynamics is essential for elucidating human movement, informing clinical assessment, and guiding neuromuscular rehabilitation.