Reflex Arc – Class 11 | Chapter – 21 | Biology Short Notes Series PDF

Reflex Arc: The reflex arc is the neural pathway controlling the reflexes and acts on an impulse even before it reaches the brain. Some stimuli require an automatic, quick response that does not involve conscious thought. The two types of reflex arcs are:

  • Autonomic Reflex Arc: It affects the functioning of inner organs.

  • Somatic Reflex Arc: It affects the functioning of muscles.

Parts of the Reflex Arc

The reflex arc consists of a receptor, sensory neuron, interneuron, motor neuron, and effector.


It is the part of the reflex arc responsible for detecting the stimulus. A specialized receptor cell or a particular dendrite has this receptor end in a sensory organ. It is highly sensitive to any kind of internal or external change resulting from the stimulus.

Sensory Neuron

It conveys sensory information to the brain or the spinal cord. Dendrite, cell body and axon of a sensory neuron are present to assist it in accomplishing its function. Its function is to transmit nerve impulses from the receptor into the spinal cord or brain.


Also known as relay neurons, it serves as a processing centre and conduct nerve impulses from the sensory neuron to a motor neuron. Interneurons are the central nodes of neural circuits, responsible for communicating between sensory or motor neurons and the central nervous system (CNS). It is the dendrite, cell body, and axon of a neuron within the brain or spinal cord.

Motor Neuron

It conducts motor output to the periphery and it is a nerve cell forming part of the pathway along which impulses travel from the brain or spinal cord to a gland or muscle. It transmits nerve impulses from the brain or spinal cord out to an effector.


Effector cells are muscles, organs, or glands that act in response to a stimulus. It responds to stimulation by the motor neuron and produces a behavioural response called a reflex.

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By Team Learning Mantras