Myotatisk

Myotatisk, commonly known in English as the stretch reflex, refers to a muscle contraction produced by a rapid stretch of the muscle. It is a monosynaptic reflex arc that helps regulate muscle length and tone in a dynamic, ongoing way. The reflex is mediated by muscle spindles, which are sensory receptors within the muscle that detect changes in length and rate of lengthening.

The physiological pathway involves sensory Ia afferent neurons from the muscle spindle that transmit a signal directly to the spinal cord. There, they form a synapse with alpha motor neurons that innervate the same muscle, triggering a contraction that counteracts the stretch. The gamma motor system can adjust the sensitivity of the muscle spindle, ensuring the reflex remains responsive during voluntary movement and varying muscle tone. Reciprocal inhibition, mediated by interneurons, also reduces activity in the antagonist muscle during the reflex.

Clinically, the myotatisk reflex is tested during neurological examinations to assess the integrity of the peripheral nerves, spinal cord segments, and upper motor neuron pathways. Common examples include the knee-jerk (patellar) and ankle-jerk (Achilles) reflexes. Normal reflexes are typically brisk and present, while changes can indicate neurological pathology: hyperreflexia may point to upper motor neuron lesions, while hyporeflexia or areflexia can suggest lower motor neuron damage, peripheral neuropathy, or muscle disease.

In summary, the myotatisk reflex is a fundamental nervous system mechanism that helps maintain muscle tone and posture, while serving as a key clinical indicator of neuromuscular health.