ANATOMY

Detailed explanation-1: -(i) Sudden reaction in response to the stimulus is called reflex action. (ii) Sensory neurons carry signals from the spinal cord to muscles. (iii) Motor neurons carry signals from receptors to spinal cord. (iv) Reflex arc is the process in which the nerve impulse is carried and the response is generated.

Detailed explanation-2: -Spinal cord reflexes are simple behaviors produced by central nervous system (CNS) pathways that lie entirely within the spinal cord. The sensory afferent fibers that evoke these reflexes enter the spinal cord and activate spinal motor neurons directly or through a chain of one or more spinal interneurons.

Detailed explanation-3: -Spinal Cord is the center that controls reflex action. Reflex actions are actions that are carried out quickly in response to a stimulus and thus do not involve any thinking, and thus are under the control of spinal cord.

Detailed explanation-4: -Most reflex arcs involve only three neurons. The stimulus, such as a needle stick, stimulates the pain receptors of the skin, which initiate an impulse in a sensory neuron. This travels to the spinal cord where it passes, by means of a synapse, to a connecting neuron called the relay neuron situated in the spinal cord.