GLOSSARY

The stretch (myotatic) reflex is the automatic contraction of a muscle in response to being stretched quickly, initiated by the muscle spindle, which helps maintain muscle length, posture, and joint stability; it is the only monosynaptic reflex in the human body.

Mechanism

• Rapid muscle stretch → spindle activation → Ia fibres → direct synapse with the alpha motor neuron of the same muscle in the spinal cord → muscle contraction.
• Reciprocal inhibition: at the same time, via an inhibitory interneuron, the antagonist muscle relaxes.

Components

• Phasic response: fast and brief (as with a tendon tap).
• Tonic response: slower and more sustained, maintaining muscle tone and posture.

Examples and Clinical Testing