Peripheral Nervous System (Extension from Central Nervous System and includes All other systems. Motor and Sensory Neurons, nerves and ganglia outside the brain and spinal cord)
<p>the PNS is not protected by the <a title="Vertebral column" href="https://en.wikipedia.org/wiki/Vertebral_column">vertebral column</a> and <a title="Skull" href="https://en.wikipedia.org/wiki/Skull">skull</a>, or by the <a title="Blood–brain barrier" href="https://en.wikipedia.org/wiki/Blood%E2%80%93brain_barrier">blood–brain barrier</a>, which leaves it exposed to <a title="Toxin" href="https://en.wikipedia.org/wiki/Toxin">toxins</a> and mechanical injuries</p>
<p>The main function of the PNS is to connect the CNS to the limbs and <a title="Organ (anatomy)" href="https://en.wikipedia.org/wiki/Organ_(anatomy)">organs</a>, essentially serving as a relay between the brain and spinal cord and the rest of the body.<sup id="cite_ref-2" class="reference"><a href="https://en.wikipedia.org/wiki/Peripheral_nervous_system#cite_note-2">[2]</a></sup> Unlike the CNS, the PNS is not protected by the <a title="Vertebral column" href="https://en.wikipedia.org/wiki/Vertebral_column">vertebral column</a> and <a title="Skull" href="https://en.wikipedia.org/wiki/Skull">skull</a>, or by the <a title="Blood–brain barrier" href="https://en.wikipedia.org/wiki/Blood%E2%80%93brain_barrier">blood–brain barrier</a>, which leaves it exposed to <a title="Toxin" href="https://en.wikipedia.org/wiki/Toxin">toxins</a> and mechanical injuries. The peripheral nervous system is divided into the <a title="Somatic nervous system" href="https://en.wikipedia.org/wiki/Somatic_nervous_system">somatic nervous system</a> and the <a title="Autonomic nervous system" href="https://en.wikipedia.org/wiki/Autonomic_nervous_system">autonomic nervous system</a>. In the somatic nervous system, the <a class="mw-redirect" title="Cranial nerve" href="https://en.wikipedia.org/wiki/Cranial_nerve">cranial nerves</a> are part of the PNS with the exception of the <a title="Optic nerve" href="https://en.wikipedia.org/wiki/Optic_nerve">optic nerve</a> (cranial nerve II), along with the <a title="Retina" href="https://en.wikipedia.org/wiki/Retina">retina</a>. The second cranial nerve is not a true peripheral nerve but a tract of the <a title="Diencephalon" href="https://en.wikipedia.org/wiki/Diencephalon">diencephalon</a>.<sup id="cite_ref-3" class="reference"><a href="https://en.wikipedia.org/wiki/Peripheral_nervous_system#cite_note-3">[3]</a></sup> <a title="Cranial nerve ganglia" href="https://en.wikipedia.org/wiki/Cranial_nerve_ganglia">Cranial nerve ganglia</a> originated in the CNS. However, the remaining ten cranial nerve <a title="Axon" href="https://en.wikipedia.org/wiki/Axon">axons</a> extend beyond the brain and are therefore considered part of the PNS.<sup id="cite_ref-White2008_4-0" class="reference"><a href="https://en.wikipedia.org/wiki/Peripheral_nervous_system#cite_note-White2008-4">[4]</a></sup> The autonomic nervous system is an involuntary control of smooth <a title="Muscle" href="https://en.wikipedia.org/wiki/Muscle">muscle</a> and <a title="Gland" href="https://en.wikipedia.org/wiki/Gland">glands</a>. The connection between CNS and organs allows the system to be in two different functional states: <a title="Sympathetic nervous system" href="https://en.wikipedia.org/wiki/Sympathetic_nervous_system">sympathetic</a> and <a title="Parasympathetic nervous system" href="https://en.wikipedia.org/wiki/Parasympathetic_nervous_system">parasympathetic</a>.</p>