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.

Functioning of the peripheral nervous system

The cranial nerves originate from the brainstem and are responsible for the face, heart, digestive system, and airways. The spinal nerves emerge from the spinal cord and contain both motor and sensory nerve fibres. After exiting the spinal canal, they branch into peripheral nerves that extend throughout the body. These peripheral nerves can be very long, running uninterrupted from the spinal cord to the big toe.

Subdivision in 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 the signals from the central nervous system via the motor nerves to the muscles so that movement takes place.

Autonomic nervous system

The autonomic nervous system, as the name suggests, has no conscious control and works automatically. It ensures the functioning of organs and consists only of motor nerve fibres 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 ensures the control of the autonomic nervous system. It activates the sympathetic part during exertion and inhibits the parasympathetic part at rest. In this way, one of the two always predominates.

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

• Increasing the burning of glucose and fats.
• Raising the blood sugar level.
• Raising the heart rate and making the heart muscle contract more strongly.
• Triggering 'goose bumps'.
• Increasing sweat production.
• Airway dilation and reduction of mucus production 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 and digest' state in the body by:

• Narrowing of the airways.
• Bladder emptying, urination.
• Lowering of the heart rate.
• Digestion of food.
• Storage of nutrients.
• Stimulation of bowel movements.