A reflex arc defines the pathway whereby a reflex travels—from the stimulus to sensory neuron to motor neuron come reflex muscle movement.

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Key Points

Reflexes, or reflex actions, room involuntary, almost instantaneous activities in solution to a particular stimulus. Reflex arcs the contain just two neurons, a sensory and also a motor neuron, are thought about monosynaptic. Examples of monosynaptic reflex arcs in humans incorporate the patellar reflex and also the Achilles reflex. Many reflex arcs space polysynaptic, definition multiple interneurons (also called relay neurons) interface between the sensory and also motor neurons in the reflex pathway.

Key Terms

motor neuron: A neuron located in the central nervous mechanism that tasks its axon outside the CNS and also directly or indirectly regulate muscles. sensory neuron: this are frequently classified as the neurons responsible for converting various outside stimuli that come indigenous the atmosphere into matching internal stimuli. reflex arc: A neural pathway that controls an activity reflex. In higher animals, most sensory neurons carry out not pass straight into the brain, yet synapse in the spinal cord. This characteristic allows reflex actions to occur reasonably quickly by activating spinal engine neurons without the hold-up of routing signals v the brain, return the brain will obtain sensory input if the reflex action occurs. There are two species of reflex arcs: autonomic reflex arc (affecting inner organs) and also somatic reflex arc (affecting muscles).


A reflex action, likewise known as a reflex, is an involuntary and almost instantaneous activity in an answer to a stimulus. Once a person accidentally touch a hot object, they automatically jerk their hand away without thinking. A reflex does no require any kind of thought input.

The course taken by the nerve impulses in a reflex is referred to as a reflex arc. In higher animals, most sensory neurons do not pass straight into the brain, but synapse in the spinal cord. This characteristic permits reflex actions come occur reasonably quickly by activating spinal engine neurons there is no the hold-up of routing signals with the brain, although the brain will get sensory input when the reflex action occurs.

Most reflex arcs involve just three neurons. The stimulus, such as a needle stick, stimulates the pain receptor of the skin, i beg your pardon initiate an impulse in a sensory neuron. This travel to the spinal cord whereby it passes, by means of a synapse, to a connecting neuron called the relay neuron located in the spinal cord.

The relay neuron subsequently makes a synapse through one or much more motor neurons the transmit the advertise to the muscle of the limb causing them come contract and pull far from the sharp object. Reflexes do not need involvement of the brain, return in some situations the brain can avoid reflex action.

Reflex arc: The route taken by the nerve impulses in a reflex is dubbed a reflex arc. This is shown here in solution to a pin in the paw of an animal, but it is same adaptable to any type of situation and animal (including humans).

Types the Reflex Arcs

There are two species of reflex arcs:the autonomic reflex arc, affecting inner organs, and the somatic reflex arc, affecting muscles. As soon as a reflex arc consists of only two neurons, one sensory neuron, and also one engine neuron, it is characterized as monosynaptic.

Monosynaptic refers to the existence of a single chemical synapse. In the case of peripheral muscle reflexes (patellar reflex, achilles reflex), quick stimulation come the muscle spindle results in the convulsion of the agonist or effector muscle.

By contrast, in polysynaptic reflex arcs, one or an ext interneurons affix afferent (sensory) and efferent (motor) signals.For example, the tap the money reflex (nociceptive or flexor withdrawal reflex) is a spinal reflex plan to protect the body from damaging stimuli. It reasons the stimulation of sensory, association, and motor neurons.

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