The structural and functional unit of reflex action is the reflex arc. It is the path followed by an impulse, which is unidirectional. It originates in the receptor organ and ends in effector organ via central nervous system.
Simple reflex arc are formed by five components:
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Receptor organ: It is specialized part of body called sense organ that receives the stimulus and converts it into the impulse. E.g. skin, ear, tongue, nasal epithelium, etc.
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Sensory (afferent) neurons: It carries sensory nerve impulse from receptor organ to central nervous system. Its cyton is located in dorsal root ganglion. Its Dendron is long and connected in the grey matter of spinal cord to form a synapse.
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Association or intermediate neuron: It is present in the grey matter of spinal cord. It receives sensory impulse, interprets it and generates motor impulse.
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Motor (effector) neuron: Its cyton is present in the ventral horn of grey matter and axon travels through ventral root. It conducts motor impulse from spinal cord to effector organ.
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Effector organ: It is a specialized part of the body, which is excited by receiving the motor impulse. It gives proper response to the stimulus. E.g. muscles and glands.
Synapse: It is a small gap between axon of one neuron and Dendron of the other neuron. It contains neurotransmitter acetylcholine, which helps in chemical transmission of the impulse.
