The Peripheral Nervous System
The peripheral nervous system refers to the nervous structures outside of the central nervous system (CNS). The CNS consists of the brain and spinal cord, while the peripheral nervous system encompasses all neural structures that lie outside these central components 1.
Anatomical Structure of the Peripheral Nervous System
The peripheral nervous system includes:
- Cranial nerves: 12 paired nerves emerging directly from the brain and brainstem, primarily innervating the head and neck region 1
- Spinal nerves: Nerves that form major plexuses including the brachial plexus (supplying upper extremities) and lumbosacral plexus (supplying lower extremities) 1
- Peripheral nerves: Branches of cranial and spinal nerves that extend throughout the body 1
Functional Divisions
The peripheral nervous system can be functionally divided into:
Sensory (afferent) division:
- Transmits sensory information from the periphery to the CNS
- Includes general sensory, special sensory, and visceral sensory components
- Provides tactile, pain, temperature, and other sensations 1
Motor (efferent) division:
- Carries signals from the CNS to effector organs
- Includes somatic motor components (innervating skeletal muscles) and autonomic motor components (innervating viscera) 1
Comparison with the Central Nervous System
While the peripheral and central nervous systems have similarities in neuronal structure and function, they differ in several key aspects:
- Glial cell types: Different supporting cells exist in the PNS (Schwann cells) versus the CNS (oligodendrocytes, astrocytes) 2
- Barrier protection: The CNS is protected by the blood-brain barrier, while the PNS has the blood-nerve barrier with different properties 3
- Regenerative capacity: The PNS generally has greater regenerative potential than the CNS 2
Clinical Relevance
Understanding the distinction between the peripheral and central nervous systems is crucial for:
- Diagnosing neurological disorders: Determining whether symptoms originate from PNS or CNS pathology
- Neuroimaging interpretation: Different imaging techniques may be required for PNS versus CNS structures
- Treatment approaches: Therapeutic strategies differ for peripheral versus central nervous system disorders 1
The peripheral nervous system serves as the critical interface between the central nervous system and the rest of the body, facilitating bidirectional communication that enables both sensory perception and motor control of bodily functions.