reflexlek

A reflex is an involuntary and nearly instantaneous movement in response to a stimulus. Reflexes are mediated by reflex arcs, neural pathways that control a reflex. These pathways can involve as few as two neurons (a sensory neuron and a motor neuron) or more complex circuits involving interneurons. The purpose of a reflex is to protect the body from harm or to maintain essential bodily functions.

Common examples of reflexes include the patellar reflex (knee-jerk reflex) and the withdrawal reflex. In the patellar reflex, tapping the patellar tendon below the kneecap causes the quadriceps muscle to contract, extending the lower leg. This reflex helps maintain posture and balance. The withdrawal reflex, such as pulling one's hand away from a hot object, is a protective mechanism. When pain receptors in the skin are stimulated, sensory neurons transmit a signal to the spinal cord. Interneurons then activate motor neurons, causing the muscles in the arm to contract and withdraw the hand.

Reflexes can be classified as innate (unlearned) or acquired (learned). Innate reflexes, like the patellar and withdrawal reflexes, are present from birth. Acquired reflexes, such as salivating at the sound of a dinner bell, are learned through association, as demonstrated by classical conditioning. The speed of a reflex is crucial for its effectiveness, and it bypasses conscious processing in the brain to ensure a rapid response. Neurological examinations often test reflexes to assess the integrity of the nervous system.