Reflex arc

In vertebrates, most sensory neurons do not pass directly into the brain, but synapse in the spinal cord.This allows for faster reflex actions to occur by activating spinal motor neurons without the delay of routing signals through the brain.carry the response generated by the spinal cord to effector organs during a reflex action.By contrast, in polysynaptic reflex pathways, one or more interneurons connect afferent (sensory) and efferent (motor) signals.In invertebrates reflex interneurons do not necessarily reside in the spinal cord, for example as in the lateral giant neuron of crayfish.
In a reflex arc, an action potential can bypass the brain for processing and uses dedicated neural pathways for faster processing. When a stimulus (A) is encountered, the signal from that stimulus will travel up the sensory neuron (B, in green) to the spinal column (C). There it will likely pass through a short interneuron (D, in purple) before continuing down a motor neuron (E, in blue) to the origin of the signal. Then, a contraction of the muscles (F, in red) is triggered, moving the bone (G).
Reflex arc demonstrated
(A) Microscopic hairs etched along the tail of the decapod activate a somatic signal (2) in response to the presence of an environmental stimulus (1). (B) The action potential activated by the somatic interneuron (3) relays an impulse to the lateral giant (LG) interneuron (4). (C) The lateral giant interneuron executes a reflex by relaying impulses to various giant motor neurons (5) within the abdomen of the lobster. These muscular contractions result in the decapod being capable of successfully propelling itself through the water, away from the site of stimulus.
neural pathwayreflexvertebratessensory neuronssynapsespinal cordmotor neuronsautonomicsomaticposterior hornanterior hornsensory neuronmotor neuronchemical synapsepatellar reflexachilles reflexmuscle spindleafferentsensoryefferentpatellar tendonaction potentialquadricepsglutamatemotor nervecentral nervous systeminterneuronsneurotransmitterglycineantagonisthamstring muscleslateral giant neuroncrayfishLazarus sign