Peripheral nervous system

The peripheral nervous system is the part of the nervous system consisting of the nerves that emerge from the brainstem and spinal cord and extend to the head, arms, legs, and trunk. These nerves serve as the connection between the brain and all organs, muscles, and blood vessels.

Anatomy

The peripheral nervous system consists of 12 pairs of cranial nerves, 31 pairs of spinal nerves, and an extensive network of branches.

Function of the peripheral nervous system

The cranial nerves arise from the brainstem and are responsible for functions of the face, heart, digestive system, and airways.

The spinal nerves arise from the spinal cord and contain both motor and sensory nerve fibers. After leaving the vertebral canal, they branch into peripheral nerves that travel throughout the body. These peripheral nerves can be very long and run from the spinal cord to the big toe without interruption.

Subdivision of the peripheral nervous system

The peripheral nervous system consists of two parts:

• Somatic nervous system.
• Autonomic nervous system.

Somatic nervous system
The somatic nervous system is under conscious control of the central nervous system and has a dual role.

• Receiving information from the senses and conducting it via the sensory nerves to the central nervous system.
• Carrying signals from the central nervous system via the motor nerves to the muscles so that movement takes place.

Autonomic nervous system
As the name suggests, the autonomic nervous system is not under conscious control and works automatically. It regulates organ function and consists only of motor nerve fibers that control the muscles of the organs, such as the heart, lungs, and blood vessels.

The autonomic nervous system itself also consists of two parts:

• Sympathetic nervous system.
• Parasympathetic nervous system.

The hypothalamus is part of the brain and controls the autonomic nervous system. It activates the sympathetic division during exertion and inhibits the parasympathetic division at rest. In this way, one of the two always predominates.

The sympathetic nervous system provides the 'fight' state of the body by:

• Increasing the burning of glucose and fats.
• Raising the blood sugar level.
• Increasing the heart rate and making the heart muscle contract more strongly.
• Triggering 'goose bumps'.
• Increasing sweat production.
• Dilating the airways and reducing mucus formation in the airways.
• Inhibiting bladder emptying, holding urine.
• Inhibiting digestion by decreasing bowel movements.
• Contracting the sphincter around the anus.
• Stimulating the production of adrenaline by the adrenal gland.

The parasympathetic nervous system provides the 'rest' state in the body by:

• Narrowing the airways.
• Emptying the bladder, urination.
• Lowering the heart rate.
• Digesting food.
• Storing nutrients.
• Stimulating bowel movements.