Back & Spinal Cord LO 8

8. Understand the major structure of the nervous system. Detail the major structures of the central nervous system (CNS) and peripheral nervous system (PNS).

The nervous system is structured into a central nervous system (CNS) and peripheral nervous system (PNS). These systems are described separately but are functionally and anatomically continuous.

Terminology important to both CNS and PNS:

  • Neuron: main unit of the nervous system
    • Composed of 3 main structures:
      • Cell body
      • Dendrite(s): process(es) that carry impulses to the neuronal cell body
      • Axon: process that carry impulses away from the neuronal cell body
        • Nerve fiber: composed of axon and surrounding connective tissue (CT)

Central Nervous System

  • Composed of: brain and spinal cord
  • Terminology:
    • Nucleus: cell bodies of neurons collection in CNS
    • Tract: nerve fiber collection in CNS
    • Gray matter: composed of cell bodies
    • White matter: composed of systems of interconnection (processes such as axons)

Peripheral Nervous System

  • Composed of: nervous tissue outside of CNS
    • 12 pairs of cranial nerves and 31 pairs of spinal nerves
    • Spinal nerves typically form complex associations, called plexuses, from which named nerves arise
  • Terminology:
    • Nerve: nerve fiber bundles, associated connective tissue, vasculature
    • Ganglion: cell bodies of neurons collection in PNS