Peripheral Nervous System (PNS)


Peripheral Nervous System includes all nerve fibers and nerve cells not found in the CNS (spinal and cranial nerves). It conveys sensory information to and from the CNS to the muscles and glands.

Two main divisions of Peripheral Nervous System

1. Somatic Nervous System (SNS)
  • Somatic Nervous System is composed of 43 major pairs of nerves, which includes all the sensory systems and the motor nerves that activates the skeletal muscles responsible for movements. It receives sensory information from the sensory organs and controls the movements of the skeletal muscles. It comprises all voluntary and conscious movements.
    • Cranial nerves (12 pairs) serve the sensory and motor functions of the head and neck region.
    • Spinal nerves (31 pairs) serves the chest, trunk and extremities. Spinal nerves have sensory nevers that give rise to skin sensations and motor nerves involved in the movements of arms, legs, and portions of the trunk. (8 cervical, 12 thoracic, 5 lumbar, 5 sacral, and 1 coccygcal)
2. Autonomic Nervous System (ANS)
  • Autonomic Nervous System is concerned with the regulation of the smooth muscles, glands, and internal organs. It is especially important in emotional behavior.
    • Sympathetic Division is composed of a chain of ganglia (clusters of never cells) located along each sides of the Spinal Cord. It sends our motor fibers to various internal organs of the body. It causes activation and enrgy expenditure. It is dominant in emergency situations and profound body changes.
    • Parasympathetic Division is composed of nerves from the brainstem and the lower parts of the spinal cord. It is system dominant in digestion, elimination, sexual arousal and energy conservation. It slows the heart rate, constricts pupil of the eye and stimulates the flow of saliva.

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