Control and Coordination

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A stimulus is an agent or an environmental change which can initiate a response in the body. Examples include touch, light, sound, heat, cold, pressure, and chemicals.

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It is a reflex action. The response is automatic and controlled by the spinal cord without conscious thought. The reflex arc carries the message from the skin to the CNS and then to the muscle, which …

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Correct order: Stimulus → receptor in the sense organ → afferent sensory nerve fibre → CNS → efferent motor nerve fibre → muscle to contract or gland to secrete.

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The sensory neuron conveys the impulse from the receptor to the main nervous system. It carries information inward from the body to the CNS for processing.

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Motor neurons carry the impulse from the main nervous system to an effector such as a muscle or gland. This causes the muscle to contract or the gland to secrete.

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Association or connecting neurons are located in the brain and spinal cord. They interconnect sensory neurons and motor neurons and help in communication within the CNS.

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A neuron consists of dendrites, a cell body, and an axon. The cell body contains a well defined nucleus surrounded by cytoplasm. Dendrites receive impulses and the axon transmits them onward.

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The branched dendrites receive the impulse and set off a chemical reaction that creates an electrical impulse. This impulse then moves to the cell body and axon.