Many of the neurons inside nerves form the somatic nervous system (or somatic division of the PNS). Information carried by somatic neurons allows the CNS to voluntarily (or consciously) monitor the world around us and regulate the activity of the skeletal muscles. The process begins when receptors in the skin, joints, sense organs, and skeletal muscles detect changes in the environment. Somatic sensory neurons, in response, carry action potentials (= impulses) into the CNS. In the CNS, the sensory information is imaged, interpreted, and integrated (except with with reflexes). CNS neurons then plan an appropriate response (except with reflexes). The respone information is transmitted to somatic motor neurons, which carry action potentials out to the effectors, the skeletal muscles, causing them to contract.