Question
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A reflex arc in man is best described as movement of stimuli from
A. Receptor cell, sensory neuron, relaying neuron, effector muscles
B. Receptor cell, efferent nerve, relaying neuron, muscles of the body
C. Receptor cell, spinal cord, motor neuron, relaying neuron
D. Receptor cell, synapse, motor neuron, relaying neuron

Answer
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Hint: There are two parts of the human nervous system namely - the central nervous system (CNS) and peripheral nervous system (PNS). The central nervous system consists of the brain and spinal cord while the peripheral nervous system consists of cranial and spinal nerves. The central nervous system is the main site of information processing and control. The nerve fibres of the peripheral nervous system comprise afferent and efferent varieties of nerve fibres.

Complete answer:
The entire process of response to peripheral nerve stimulation that happens involuntarily, without conscious effort or thought and requires the involvement of an element of the central nervous system is termed as a reflex action. Reflex action is a spontaneous, automatic and involuntary mechanical response which is produced by stimulating specific actions.
The reflex pathway is formed of a minimum of one afferent neuron (receptor) and one efferent (effector or excitor) neuron. These neurons are arranged in a series. The afferent neuron receives a signal from the sensory organ and transmits the impulse via a dorsal nerve root into the central nervous system at the level of the spinal cord.
The different neuron then carries the signal from CNS to the effector. This pathway of completion of reflex action is termed as a reflex arc. Sensory fibres carry sensory impulses within the grey matter of the spinal cord. They are converted now into motor impulses and reached to the muscles. These muscles show reflex actions for motor impulses obtained from motor neurons.

Hence, the correct answer is option (A).

Note: The form of animal behaviour in which the stimulation of a sensory organ (receptor) results in the activity of some organ without any voluntary control is called a reflex action. There are various sorts of reflex actions and reflex arcs. Based on previous experiences, conditioned reflex and non conditioned reflex are present and based on the number of synapses formed, monosynaptic and polysynaptic reflexes are present.