Рефлекстер және олардың механизмдері

Automatic, involuntary response to a stimulus

In biology, a reflex, or reflex action, is an involuntary, unplanned sequence or action and nearly instantaneous response to a stimulus. Reflexes are found with varying levels of complexity in organisms with a nervous system. A reflex occurs via neural pathways in the nervous system called reflex arcs. A stimulus initiates a neural signal, which is carried to a synapse. The signal is then transferred across the synapse to a motor neuron, which evokes a target response. These neural signals do not always travel to the brain, so many reflexes are an automatic response to a stimulus that does not receive or need conscious thought. Many reflexes are fine tuned to increase organism survival and self defense. This is observed in reflexes such as the startle reflex, which provides an automatic response to an unexpected stimulus, and the feline righting reflex, which reorients a cat's body when falling to ensure safe landing. The simplest type of reflex, a short latency reflex, has a single synapse, or junction, in the signaling pathway. Long latency reflexes produce nerve signals that are transduced across multiple synapses before generating the reflex response.

The myotatic or muscle stretch reflexes (sometimes known as deep tendon reflexes) provide information on the integrity of the central nervous system and peripheral nervous system. This information can be detected using electromyography (EMG). Generally, decreased reflexes indicate a peripheral problem, and lively or exaggerated reflexes a central one. A good example of reflex modulation is the stretch reflex. When a muscle is stretched at rest, the stretch reflex leads to contraction of the muscle, thereby opposing stretch (resistance reflex). This helps to stabilize posture. During voluntary movements, however, the intensity (gain) of the reflex is reduced or its sign is even reversed. This prevents resistance reflexes from impeding movements. The underlying sites and mechanisms of reflex modulation are not fully understood. There is evidence that the output of sensory neurons is directly modulated during behavior—for example, through presynaptic inhibition. The effect of sensory input upon motor neurons is also influenced by interneurons in the spinal cord or ventral nerve cord

Breathing can also be considered both involuntary and voluntary, since breath can be held through internal intercostal muscles.