Peripheral Nervous System

Peripheral Nervous System

The peripheral nervous system (PNS) is the part of the nervous system that connects the brain and spinal cord with all the receptors and effectors of the body. It consists of cranial and spinal nerves, which arise from the brain and spinal cord, respectively.

Cranial nerves

12 pairs of nerves depart from various parts of the brain, which innervate mainly the sensory organs, muscles and glands located on the head. These nerves consist of bundles of nerve fibers - axons and dendrites, belonging to both sensory and motor neurons. Like all nerves, cranial nerves are composed of neuronal processes.

One of the most important cranial nerves is the vagus nerve, which forms part of the autonomic nervous system and innervates the internal organs of the chest cavity and upper abdomen.

Spinal nerves

All spinal nerves are mixed, that is, they contain motor and sensory fibers in approximately equal quantities. In humans, they arise from the spinal cord in symmetrical pairs (31 pairs in total), and each pair innervates receptors and effectors in a specific area of ​​the body. Each nerve begins from the spinal cord in the form of two roots, which soon unite to form a spinal nerve.

All sensory fibers enter the spinal cord through the dorsal roots, and all motor fibers exit it through the anterior roots. The thickness of each spinal nerve corresponds to the size of the area of ​​the body that it innervates; In humans, the largest pair of nerves goes to the legs.

Each spinal nerve, soon after the fusion of the anterior and dorsal roots, divides into three branches: the dorsal branch, innervating the skin and muscles of the back, the ventral branch, going to the skin and muscles of the sides and abdomen, and the autonomic branch, serving the viscera.

Ganglia

As for the bodies of nerve cells, the peripheral nervous system contains only the bodies of sensory neurons, forming clusters (the so-called ganglia, or nerve ganglia) near the brain and spinal cord, and the bodies of some motor neurons of the autonomic nervous system.

In conclusion, the peripheral nervous system is important for communication between the brain and the organs and tissues of the body. It consists of cranial and spinal nerves, which innervate various parts of the body, and ganglia, where the bodies of sensory neurons are located. The peripheral nervous system plays an important role in transmitting information about the external environment and internal processes of the body to the brain, as well as in controlling movements and functions of internal organs. Various diseases and damage to the peripheral nervous system can lead to disturbances in sensitivity, movement and function of internal organs.