Stretchreceptorer

Stretchreceptorer, or stretch receptors, are specialized sensory receptors that detect mechanical stretch in tissues and convert it into neural signals. They provide essential information about body position, limb movement, and the state of internal organs.

In skeletal muscle, the primary stretch receptors are muscle spindles embedded within intrafusal fibers. They house sensory endings of group Ia and II afferent fibers that respond to changes in muscle length and the speed of stretch. Signals from spindle afferents contribute to proprioception and reflex control. Gamma motor neurons adjust the tension of intrafusal fibers to maintain spindle sensitivity during contraction. The stretch reflex is largely monosynaptic, with Ia afferents exciting the homonymous muscle and inhibiting antagonists.

Other stretch-sensitive receptors include Golgi tendon organs in tendons, which respond to muscle tension to regulate force. In the respiratory system, lung stretch receptors sense lung inflation and contribute to reflexive termination of inspiration (the Hering-Breuer reflex). Stretch receptors also occur in the skin, where certain mechanoreceptors respond to sustained skin stretch, and in visceral organs, providing autonomic feedback.

Clinical relevance: impairment of stretch-receptor pathways can affect balance, coordination, and reflexes; assessment of stretch reflexes is used in neurology to evaluate nerve function. Changes in muscle spindle sensitivity can contribute to spasticity after certain spinal or cortical injuries.