ABSTRACT
The nervous system has two main divisions: the peripheral nervous system (PNS) and the central nervous system (CNS). The PNS is located outside the skull and spine and detects environmental information via sensory receptors. It then transmits this information to the CNS by way of sensory nerves known as afferent nerves (from the Latin for carry information to the CNS). The PNS also transmits information from the CNS to muscles, glands, and internal organs by way of motor nerves known as efferent nerves (from the Latin for carry information away from the CNS). The PNS is subdivided into the somatic and autonomic nervous systems. The somatic division controls skeletal movement, and the autonomic division controls glands and muscles of internal organs. The autonomic division regulates internal bodily processes and consists of the sympathetic (arousal) and parasympathetic (restoration) nervous systems. The CNS is located in the skull and spine and consists of the brain and the spinal cord. Twelve pairs of cranial nerves and 31 pairs of spinal nerves connect the brain and spinal cord to the PNS. As shown in Fig. 1.1, the cranial nerves are located on the ventral surface of the brain and involve numerous functions of the head, neck, and face. The cranial nerves found on the brain stem involve vital functions.
