A reflex arc defines the pathway through which 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, practically instantaneous movements in solution to a particular stimulus. Reflex arcs that contain just two neurons, a sensory and a motor neuron, are thought about monosynaptic. Examples of monosynaptic reflex arcs in humans include the patellar reflex and the Achilles reflex. Many reflex arcs space polysynaptic, definition multiple interneurons (also called relay neurons) interface in between the sensory and motor neurons in the reflex pathway.

Key Terms

motor neuron: A neuron situated in the main nervous mechanism that jobs its axon external the CNS and directly or indirectly regulate muscles. sensory neuron: this are generally classified as the neurons responsible for converting various exterior stimuli the come indigenous the atmosphere into equivalent internal stimuli. reflex arc: A neural pathway that controls an action reflex. In higher animals, many sensory neurons perform not pass directly into the brain, however synapse in the spinal cord. This characteristic enables reflex actions to occur reasonably quickly by activating spinal engine neurons there is no the hold-up of routing signals v the brain, although the mind will get sensory input while the reflex activity occurs. There are two species of reflex arcs: autonomic reflex arc (affecting within organs) and also somatic reflex arc (affecting muscles).


A reflex action, additionally known together a reflex, is one involuntary and almost instantaneous movement in response to a stimulus. Once a person accidentally touches a hot object, they immediately jerk your hand far without thinking. A reflex does no require any thought input.

The route taken by the nerve impulses in a reflex is referred to as a reflex arc. In greater animals, most sensory neurons do not pass directly into the brain, yet synapse in the spinal cord. This characteristic allows reflex actions to occur reasonably quickly by activating spinal engine neurons there is no the delay of routing signals v the brain, although the brain will receive sensory input if the reflex action occurs.

Most reflex arcs involve only three neurons. The stimulus, such together a needle stick, stimulates the pain receptor of the skin, i m sorry initiate an impulse in a sensory neuron. This travel to the spinal cord where it passes, by way of a synapse, to a connecting neuron referred to as the relay neuron situated in the spinal cord.

The relay neuron subsequently makes a synapse v one or much more motor neurons that transmit the advertise to the muscles of the limb resulting in them to contract and also pull away from the sharp object. Reflexes do not require involvement the the brain, return in some situations the mind can protect against reflex action.

Reflex arc: The path taken by the nerve impulses in a reflex is dubbed a reflex arc. This is presented here in solution to a pen in the paw of one animal, yet it is same adaptable to any kind of situation and animal (including humans).

Types of Reflex Arcs

There are two varieties of reflex arcs:the autonomic reflex arc, affecting within organs, and also the somatic reflex arc, affect muscles. When a reflex arc is composed of just two neurons, one sensory neuron, and one motor neuron, it is characterized as monosynaptic.

Monosynaptic refers to the presence of a solitary chemical synapse. In the case of peripheral muscle reflexes (patellar reflex, achilles reflex), brief stimulation to the muscle spindle results in the contraction of the agonist or effector muscle.

By contrast, in polysynaptic reflex arcs, one or more interneurons attach afferent (sensory) and also efferent (motor) signals.For example, the withdrawal reflex (nociceptive or flexor tap the money reflex) is a spinal reflex intended to defend the body from damaging stimuli. It reasons the stimulation the sensory, association, and also motor neurons.

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