<Tr> <Td_colspan="2"> Anatomical terms of neuroanatomy (edit on Wikidata) </Td> </Tr> <P> The peripheral nervous system (PNS) is one of the two components of the nervous system, the other part is the central nervous system (CNS). The PNS consists of the nerves and ganglia outside the brain and spinal cord . The main function of the PNS 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 PNS 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 peripheral nervous system is divided into the somatic nervous system and the autonomic nervous system . In the somatic nervous system, the cranial nerves are part of the PNS with the exception of the optic nerve (cranial nerve II), along with the retina . The second cranial nerve is not a true peripheral 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 PNS . The autonomic nervous system is an involuntary control of smooth muscle and glands . The connection between CNS and organs allows the system to be in two different functional states: sympathetic and parasympathetic . </P> <P> The peripheral nervous system is divided into the somatic nervous system, and the autonomic nervous system . The somatic nervous system is under voluntary control, and transmits signals from the brain to end organs such as muscle s . The sensory nervous system is part of the somatic nervous system and transmits signals from senses such as taste and touch (including fine touch and gross touch) to the spinal cord and brain . The autonomic nervous system is a' self - regulating' system which influences the function of organs outside voluntary control, such as the heart rate, or the functions of the digestive system . </P> <P> The somatic system includes the sensory nervous system and the somatosensory system and consists of sensory nerves and somatic nerves, and many nerves which hold both functions . </P>

Which of the following structures is not a part of the peripheral nervous system (pns)