Réflexes

Réflexes are involuntary, nearly instantaneous movements that occur in response to a stimulus. They are a fundamental part of the nervous system, playing a crucial role in protecting the body from harm and maintaining basic bodily functions. The pathway for a reflex, known as the reflex arc, typically involves a sensory receptor, a sensory neuron, an interneuron (in some reflexes), a motor neuron, and an effector organ like a muscle or gland. When a stimulus is detected, it triggers a signal that travels along the sensory neuron to the spinal cord or brainstem. Here, the signal is processed, and a response signal is sent out via a motor neuron to the effector, causing a rapid action.

There are several types of reflexes. Somatic reflexes involve skeletal muscles and are responsible for actions like withdrawing your hand from a hot object (the withdrawal reflex) or maintaining balance. Autonomic reflexes, on the other hand, control involuntary functions of internal organs, such as the regulation of heart rate, digestion, and pupil dilation. Examples include the pupillary light reflex, where pupils constrict in bright light, and the patellar reflex (knee-jerk reflex), which causes the lower leg to extend when the patellar tendon is tapped. Reflexes are often innate, meaning they are present from birth, but some can be learned and acquired through practice, becoming conditioned reflexes. The speed and automatic nature of reflexes are vital for survival, allowing the body to react to potentially dangerous situations before conscious thought can even process them.