Peripheral Nervous System

Its function is to connect the Central Nervous System to other organs in the body and thereby transport information.

It is one of the divisions of the Nervous System, which anatomically is divided into:

• Central Nervous System (CNS): brain and spinal cord;
• Peripheral Nervous System (PNS): nerves and nerve ganglia that connect the CNS to the organs of the body.

Components of the Peripheral Nervous System

The PNS is made up of nerves and ganglia. They are responsible for connecting the CNS to parts of the body.

See below how each of these components acts in the human body.

Nerves

Nerves are bundles of nerve fibers surrounded by connective tissue. They are responsible for connecting the CNS to other peripheral organs and for transmitting nerve impulses .

Nerves are divided as follows:

• Spinal Nerves : made up of 31 pairs, these are the ones that connect to the spinal cord. These nerves are responsible for innervating the trunk, limbs and some specific regions of the head.
• Cranial Nerves : made up of 12 pairs, these are the ones that connect to the brain. These nerves are the ones that innervate the structures of the head and neck.

Nerves have the following types:

• Afferent (Sensitive) Nerves : send signals from the periphery of the body to the central nervous system. This type of nerve is capable of capturing stimuli such as heat and light, for example.
• Efferent (Motor) Nerves : send signals from the central nervous system to muscles or glands.
• Mixed Nerves : formed by sensory fibers and motor fibers, for example, the spinal nerves.

Ganglia

Nerve ganglia are clusters of neurons located outside the central nervous system, spread throughout the body. They commonly form a spherical structure.

See the image below for a summary map of the components of the Peripheral Nervous System.

Divisions of the Peripheral Nervous System

The PNS is divided into the somatic nervous system and the autonomic nervous system, according to its function.

• Somatic Nervous System : regulates actions that are under the control of our will, that is, voluntary actions. It acts on the skeletal muscles of voluntary contraction.
• Autonomic Nervous System : acts in an integrated manner with the central nervous system. Generally, it controls activities that are independent of our will, that is, involuntary actions such as those carried out by internal organs. It acts on the smooth and cardiac muscles.

The Autonomic Nervous System regulates organic activities, ensuring the organism’s homeostasis. It has two subdivisions:

• Sympathetic Nervous System that stimulates the functioning of the organs; it is formed by the spinal nerves of the thoracic and lumbar region of the spinal cord. The main neurotransmitters released are noradrenaline and adrenaline.
• Parasympathetic Nervous System that inhibits the functioning of the organs; it is formed by the cranial and spinal nerves at the ends of the spinal cord. The main neurotransmitter released is acetylcholine.