Final answer:
The appropriate response to a stimulus is selected by the somatic nervous system or the brain. Reflexes are controlled by the spinal cord.
Step-by-step explanation:
The appropriate response to a given stimulus is selected by the somatic nervous system or the brain. The somatic nervous system is responsible for voluntary or conscious responses, such as contraction of skeletal muscles. Conversely, the brain processes the information and sends commands to initiate motor responses. The spinal cord plays a crucial role in reflexes, which are quick and unconscious movements controlled by local synaptic connections.