Spierreflex

Spierreflex, or muscle reflex, refers to an involuntary, rapid contraction of a muscle in response to a specific stimulus. These reflexes are organized into reflex arcs that typically involve a sensory receptor, an afferent neuron, a synapse in the central nervous system, an efferent neuron, and the target muscle. They are somatic, not autonomic, and help regulate posture, tone, and movement without conscious effort.

Common examples include the stretch (myotatic) reflex, such as the knee-jerk, where muscle spindle receptors detect stretch and Ia afferents trigger a monosynaptic contraction via alpha motor neurons. The Golgi tendon reflex, or inverse stretch, involves feedback from tendon organs and tends to inhibit muscle contraction to protect tendons, often through a polysynaptic pathway. Other muscle reflexes include flexor (withdrawal) reflexes and the crossed extensor reflex that coordinate limb movements in response to noxious stimuli. The reflex arc operates at the spinal level in many cases, though higher brain centers modulate its gain.

Clinically, testing reflexes is a standard part of neurological examination. Hyperreflexia can indicate upper motor neuron lesions or reduced inhibitory control, while hyporeflexia or areflexia may suggest lower motor neuron disease, peripheral nerve damage, or metabolic disturbances. Reflexes can vary with age, fatigue, medication, or technique. Understanding spierreflex involves basic neurophysiology of muscle spindles, Golgi tendon organs, and spinal interneuronal circuits.