The Peripheral Nervous System (PNS) consists of all the nerves branching out of the brain and spinal cord. If you imagine the CNS as the main highway, then the PNS forms all the connecting secondary roads. These allow electrical impulses to travel to and from the furthest regions, or periphery, of the human body.
The peripheral nervous system is divided into the somatic nervous system, and the autonomic nervous system. The somatic nervous system is under voluntary control and transmits signals from the brain to end organs such as muscles. The sensory nervous system is part of the somatic nervous system and transmits signals from senses such as taste and touch to the spinal cord and brain. The autonomic nervous system is a ‘self-regulating’ system that influences the function of organs outside voluntary control, such as the heart rate, or the functions of the digestive system.
Functions of the Peripheral Nervous System
- It connects the brain and the spinal cord to the rest of the body and the external environment.
- Regulates the internal homeostasis.
- It can regulate the strength of muscle contractility.
- It controls the release of secretions from most exocrine glands.
Peripheral Nervous System Divisions
The peripheral nervous system has two divisions:
- Somatic Nervous System
- Autonomic Nervous System
Somatic Nervous System
The main function of the somatic nervous system is to transfer impulses from CNS to skeletal muscles. It consists of:
- Cranial nerves are 12 pairs and they emerge from the brain. Some of the examples of cranial nerves are optic, olfactory, etc.
- Spinal nerves have their point of emergence as the spinal cord. There are 31 pairs of spinal nerves. They emerge from the spinal cords into dorsal and ventral roots. At the junction of these two roots, the sensory fibers continue into the dorsal root and the motor fibers into the ventral root.
Autonomic Nervous System
The autonomic nervous system relays impulses from the central nervous system to the involuntary organs and smooth muscles of the body.
- Sympathetic nervous system: It consists of nerves arising from the spinal cord between the neck and waist region. It prepares the body for violent actions against abnormal conditions and is generally stimulated by adrenaline.
- Parasympathetic nervous system: It is located anterior in the head and neck and posterior in the sacral region. It is mainly involved in the re-establishment of normal conditions when violent action is over.