Final answer:
The reflex arc consists of an afferent branch, an integrating center, and an efferent branch, facilitating a quick response to stimuli through sensory input, processing, and motor output.
Step-by-step explanation:
The reflex arc consists of several key structures that facilitate a quick and involuntary response to a stimulus. The arc involves a sensory input and motor output, or an afferent branch and an efferent branch, as well as an integrating center to connect these two branches. The afferent branch begins with a sensory receptor that responds to a specific sensation and sends a nerve impulse along a sensory neuron to the spinal cord. Within the spinal cord, the nerve impulse usually passes to an interneuron. The integrating center, for many reflexes, is located within the spinal cord and is responsible for processing the sensory input and initiating an appropriate response. Finally, the efferent branch begins with the projection from the central neuron along the preganglionic fiber, which makes a synapse on the ganglionic neuron that projects to the target effector, such as a muscle or gland, causing it to react accordingly.