Peripheral Nervous System

Peripheral Nervous System (PNS)

Divisions of the Nervous System

  • The nervous system is divided into two main divisions:
    • Central Nervous System (CNS): Discussed in Unit 13.
    • Peripheral Nervous System (PNS): Focus of this unit.

Organs of the PNS

  • The organs of the PNS are called peripheral nerves, or simply nerves.

Types of Nerves Classified by Location

  1. Cranial Nerves:
    • Bring information to and from the brain and the brainstem.
  2. Spinal Nerves:
    • Bring information to and from the spinal cord.

Divisions of the PNS Based on Function

  1. Motor or Efferent Division:
    • Innervates muscle cells and glands.
  2. Sensory or Afferent Division:
    • Innervates the skin, joints,
    • Special sensory organs and other sensory receptors.

Subdivisions of Motor and Sensory Divisions

  1. Somatic Sensory and Somatic Motor Divisions:
    • Serve skin and skeletal muscles, respectively.
  2. Visceral Sensory and Visceral Motor Divisions:
    • Serve smooth muscle, cardiac muscle, and glands.

Autonomic Nervous System (ANS)

  • The visceral motor division is also known as the Autonomic Nervous System (ANS).
  • Controls most of our automatic functions such as:
    • Heart rate,
    • Blood pressure,
    • Digestion,
    • Urine production.

Interwoven Functions of PNS and CNS

  • The functions of the PNS are closely interwoven with the CNS.
  • The branches of the nervous system cannot function independently of one another.

Exercise 14-1: Peripheral Nerve Anatomy

Materials
  • Peripheral nerve models or charts
  • Peripheral nerve slide
  • Light microscope with three objectives
  • Colored pencils
Components and Structure of a Peripheral Nerve
  • Each nerve consists of:
    • Myelinated and unmyelinated axons (nerve fibers).
    • Blood vessels.
    • Lymphatic vessels.
    • Connective tissue sheaths.
Connective Tissue Sheaths
  1. Endoneurium (en-doh-NOOR-ee-um):
    • A connective tissue sheath that covers each individual axon.
    • Superficial to the axolemma (plasma membrane).
  2. Perineurium (pehr-ih-NOOR-ee-um):
    • Another connective tissue sheath that covers bundles of axons called fascicles (FASS-ih-kullz).
  3. Epineurium (ep-ih-NOOR-ee-um):
    • The most superficial connective tissue sheath.
    • Surrounds groups of fascicles, blood vessels, and lymphatic vessels.
Components of a Nerve
  • Nerve
  • Fascicle
  • Blood vessels
  • Epineurium
  • Perineurium
  • Schwann cell (myelin sheath)
  • Axon
  • Endoneurium