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The PNS comprises cranial and spinal nerves, peripheral ganglia, and sensory and motor endings. Its structural divisions describe the direction of information flow: afferent pathways carry sensory input to the CNS, while efferent pathways carry motor commands outward. Functionally, somatic pathways govern voluntary skeletal muscle activity, and autonomic pathways regulate involuntary functions involving viscera, cardiac and smooth muscle, and glands. Spinal nerves form from sensory dorsal roots and motor ventral roots, then divide into rami; plexuses redistribute fibers into peripheral nerves. The autonomic system uses preganglionic and postganglionic neurons, with sympathetic and parasympathetic divisions. The enteric nervous system also regulates gut activity and is modulated by the autonomic system.