Reflex arc

A neural pathway that links a stimulus to a rapid, involuntary response. Its signals can produce movement before conscious perception is complete.

Reflex: An automatic response to a stimulus that occurs without deliberate control. The reflex arc is the neural route that generates this broader kind of response.
Stretch reflex: A reflex contraction of a muscle in response to its stretch. It is a classic spinal reflex with a direct sensory-to-motor connection.
Sensory receptor: A specialized cell or nerve ending that detects a stimulus and initiates sensory signaling. A reflex arc begins when a receptor detects the triggering change.
Monosynaptic reflex: A reflex pathway with one synapse between the sensory neuron and motor neuron. It is the simplest arrangement found in the stretch reflex.
Sensory neuron: A neuron that carries information from sensory receptors toward the central nervous system. It carries the stimulus signal into the arc.
Patellar reflex: A knee-extension reflex elicited by tapping the patellar tendon. This familiar test demonstrates the stretch reflex and spinal circuitry.
Afferent nerve fiber: A nerve fiber that carries sensory information toward the central nervous system. It conveys receptor activity toward the spinal cord or brainstem.
Polysynaptic reflex: A reflex pathway in which interneurons create multiple synaptic connections. Many protective reflexes use this more complex arrangement.
Interneuron: A neuron that connects neurons within the central nervous system. In many reflexes, it relays or modifies signals between sensory and motor neurons.
Withdrawal reflex: A protective spinal reflex that pulls a limb away from a harmful stimulus. Its multiple interneurons coordinate a rapid response to pain.

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