The<unk>  <unk>  is one of two components that make up the nervous system of bilateral animals, with the other part being the central nervous system (CNS). The<unk>  consists of the nerves and ganglia outside the brain and spinal cord. The main function of the<unk>  is to connect the CNS to the limbs and organs, essentially serving as a relay between the brain and spinal cord and the rest of the body. Unlike the CNS, the<unk>  is not protected by the vertebral column and skull, or by the blood–brain barrier, which leaves it exposed to toxins and mechanical injuries. The<unk>  is divided into the somatic nervous system and the autonomic nervous system. In the somatic nervous system, the cranial nerves are part of the<unk>  with the exception of the optic nerve (cranial nerve II), along with the retina. The second cranial nerve is not a true<unk>  nerve but a tract of the diencephalon. Cranial nerve ganglia originated in the CNS. However, the remaining ten cranial nerve axons extend beyond the brain and are therefore considered part of the<unk> . The autonomic nervous system exerts involuntary control over smooth muscle and glands. The connection between CNS and organs allows the system to be in two different functional states: sympathetic and parasympathetic.
Peripheral nervous system
Central nervous system
Nervous system
Cranial nerves
Reproductive system
Enteric nervous system
Urinary system
Integumentary system