Stretch reflex loop

The **stretch reflex loop**—also known as the myotatic or muscle stretch reflex—is a rapid involuntary response triggered when skeletal muscle fibers are stretched. The core elements include: • **Muscle spindle receptors** detect stretching within skeletal muscles. • Sensory afferent neurons transmit signals from these spindles into the dorsal horn of the spinal cord. • In monosynaptic fashion (the fastest human neural response), these sensory neurons synapse directly onto alpha motor neurons innervating the same muscle. • The alpha motor neuron then stimulates contraction of that muscle—counteracting further stretching—and simultaneously inhibits antagonistic muscles via interneurons ("reciprocal inhibition"). • This entire process forms a closed-loop between peripheral tissue and spinal cord without requiring input from higher brain centers—enabling extremely rapid responses essential for maintaining posture and protecting muscles from injury due to excessive force or sudden load changes. • Gamma motoneurons regulate sensitivity by adjusting tension within intrafusal fibers inside each spindle; coactivation mechanisms help maintain responsiveness during voluntary movement. This mechanism underlies clinical tests like the knee jerk/patellar tendon tap used in neurological exams. While critical for normal movement control and safety against injury during sudden perturbations, dysfunctions can manifest clinically as exaggerated ("hyperreflexic") responses after certain types of nervous system damage.

Other names

Stretch reflexMyotatic reflexMuscle stretch reflexDeep tendon reflex (less accurate/older term)

Not applicable for direct targeting. Drugs that reduce spasticity may act by inhibiting excitatory neurotransmission within spinal circuits involved in the stretch reflex.