réflex

A reflex, or reflex action, is an involuntary and nearly instantaneous movement in response to a stimulus. Reflexes are typically mediated by reflex arcs, which are neural pathways that control reflexes. The most basic reflex arc consists of a sensory receptor, a sensory neuron, an interneuron (in many cases), a motor neuron, and an effector. When a stimulus is detected by a sensory receptor, a signal is sent along the sensory neuron to the central nervous system. In most reflexes, the signal is then relayed to a motor neuron via an interneuron, although some reflexes bypass interneurons. The motor neuron then transmits the signal to an effector, such as a muscle or gland, which produces the response.

Reflexes are important for survival as they allow the body to react quickly to potentially harmful stimuli. For example, the withdrawal reflex causes a person to quickly pull their hand away from a hot object, preventing a burn. Another example is the stretch reflex, which helps maintain posture and balance. Reflexes can be classified in various ways, including by the type of stimulus, the location of the reflex arc, or the complexity of the response. Some reflexes are innate, meaning they are present from birth, while others are acquired through learning and experience.

The study of reflexes has been crucial in understanding the nervous system. Early research by scientists like Ivan Pavlov, who studied conditioned reflexes in dogs, laid the groundwork for behavioral psychology. Neurophysiologists continue to investigate reflex pathways to better understand neural circuitry and the mechanisms of motor control. While generally automatic, some reflexes can be modulated by higher brain centers, demonstrating a degree of integration between reflex mechanisms and conscious control.