The Peripheral Nervous System (PNS) consists of 12 cranial nerves, 31 pairs of spinal nerves, and Sensory Organs, for example: eyes, ears, tongue, nose, skin, and other sense organs, for example: vestibular system, proprioception system.
There are 31 pairs of spinal nerves. Again, they are named according to where they each exit in the spine (see figure below).
Each spinal nerve is attached to the spinal cord by two roots: a dorsal (or posterior) root which relays sensory information and a ventral (or anterior) root which relays motor information. Therefore, once the two roots come together to form the spinal nerve, the nerve carries a combination of both sensory and motor information (i.e. it contains mixed fibers).
The spinal nerves are named according to where it emerges and passes through the bones in the spinal vertebrae.
The nervous system is divided into two systems:
The Central Nervous System (CNS) consists of the brain and the spinal cord. The spinal cord is the continuation of the brain which lies protected within the bones of the spine. You can think of the CNS as the control center for the body. It allows us to think, create memories, speak, move, run, etc.
The Peripheral Nervous System (PNS) consists of 12 cranial nerves, and 31 pairs of spinal nerves. The PNS acts as the system of electrical wires that allows for communication between the CNS and the body’s muscles and sensory receptors. They also control the automatic functions of the bowel, bladder, respiratory (breathing), and heart function.
Essentially, the PNS sends signals from the brain to the muscles of our body so that they can contract, which leads to movement. The PNS also relays information regarding sensation from the sensory receptors of our body to our brain, so we can feel and interact with the environment around us.
The spinal nerves are named according to where in the spine they emerge i.e. they are named in accordance with the level of the spine they exit from. E.g. the C2 nerve exits between the C1-2 vertebrae, the L4 nerve exits between the L4-5 vertebrae.