Peripheral Nervous System

Peripheral Nervous System

The nervous system is made up of two major parts - the Central and the Peripheral Nervous System. While the former enables us to think, reason, learn, and maintain balance, the latter helps us to carry out voluntary and involuntary actions, and also feel through our senses.
The nervous system is a master system that controls the functions of all different systems of a human body. It is made up of cells called neurons that generate and conduct impulses (messages) between various parts of the body. This system consists of the brain, spinal cord, and nerves. While the brain and spinal cord form the Central Nervous System (CNS), the Peripheral one includes all the nerves outside the CNS. The brain is protected by the skull, and the spinal cord is enclosed within the bony spinal column. However, the Peripheral Nervous System (PNS) does not have any such protective covering, and hence is prone to mechanical injuries.

On the basis of the location of the nerves, PNS consists of the following ones:
  • 31 pairs of spinal nerves that connects the spinal cord with rest of the body.
  • 12 pairs of cranial nerves that connect the brain with the vital organs of the body.
On the basis of the functions of the nerves, the Peripheral Nervous System consists of the following ones:
  • Somatic Nerves carry sensory information from the skin and muscle, and give motor commands to the skeletal muscles.
  • The autonomic nerves carry signals between the CNS and smooth muscles, glands, cardiac muscles, and internal organs.
The nerves of PNS connect the CNS to muscles, glands, blood vessels, and all the organs of the body including the sense organs. The function of this system is to carry messages from the brain to all the other parts of the body, and back from these parts to the brain and the spinal cord.

The PNS is divided into the somatic and the autonomic nervous system.

Somatic Nervous System
It controls voluntary movements of our body, and helps us feel through all our senses. The nerves of this system connect the brain and the spinal cord, to the skeletal muscles and the external receptors. Hence, this system also helps us to move our body around, and feel the touch, smell, sight, taste, and sound.

Autonomic Nervous System
It is also known as the involuntary nervous system, as it controls all the involuntary actions of the body. The nerves connect the CNS to the cardiac muscles, internal organs, and the glands. This system can be further sub-divided into:
  • Sympathetic Nervous System: It is also referred to as the 'flight or fight system', as it prepares our body for emergencies. It results in increased heartbeat, high blood pressure, and also brings about other changes by the release of adrenaline, which prepares us to face danger or stress.
  • Parasympathetic Nervous System: It has a completely opposite effect on the human body, as compared to the sympathetic system. It helps in calming and relaxing the body, and ensures proper functioning of the digestive system. Hence, it is also known as the 'Rest and Digest System'. It dilates the pupil, restores normal blood pressure and heartbeat, etc.
Although diseases or injuries to the CNS can have more serious effects than the PNS; when affected, the trauma or infection to the latter one can be manifested in the form of weakness, loss of control over limbs, slowly progressing sensory loss, and weak bowels. Any disorder related to the nervous system should be referred to a neurologist for proper diagnosis, as proper functioning of the CNS and PNS is important for a healthy life.
Sympathetic nervous system