Peripheral Nervous System (PNS) Overview

Connection and Function

• Definition: Everything outside the central nervous system (CNS) – includes nerves, ganglia, and receptors.
• Role: Connects the CNS to the body and internal environment.

Divisions of the PNS

• Sensory Input and Motor Output: Handled by the PNS.
• Divided into:
  • Sensory (Afferent) Division: Carries signals towards the CNS.
  • Motor (Efferent) Division: Carries signals away from the CNS.

Subdivisions

• Sensory Division:
  • Somatic and visceral sensory divisions based on the origin of information.
• Motor Division:
  • Includes the autonomic nervous system, subdivided into:
    • Sympathetic Division
    • Parasympathetic Division

Autonomic Nervous System

• Will be discussed in detail in chapter 14.
• Involves involuntary reflexes and controls bodily functions.

Anatomy of Nerves

Structure

• Main Organ: Nerves are the primary structure of the PNS.
• Layered Composition:
  • Epineurium: Surrounds the entire nerve.
  • Perineurium: Surrounds each fascicle within the nerve.
  • Endoneurium: Surrounds individual axons within a fascicle.
  • Myelin Sheath: If present, is surrounded by the endoneurium.

Neurons vs. Nerves

• Neurons: Cells that transmit electrochemical signals.
• Nerves: Bundles of axons from multiple neurons.

Classification of Nerves

• Functional Classification:
  • Mixed Nerves: Contain both sensory and motor neurons.
  • Sensory Nerves: Only carry sensory input to the CNS.
  • Motor Nerves: Typically mixed but focus on carrying motor output.

Nerve Plexuses

Structural Classification

• Based on origin:
  • Cranial Nerves: Originate from the brain.
  • Spinal Nerves: Originate from the spinal cord.
• Spinal Nerves:
  • Total: 31 pairs.
  • Divisions: 8 cervical, 12 thoracic, 5 lumbar, 5 sacral, 1 coccygeal.

Path and Structure

• Roots: Connect spinal nerves to the spinal cord.
  • Anterior Roots: Contain motor fibers only.
  • Posterior Roots: Contain sensory fibers only.
• Rami: Branches from spinal nerves.
  • Posterior Rami: Innervate back structures.
  • Anterior Rami: Form nerve plexuses, except for T2-T12.

Importance of Nerve Plexuses

• Function: Allow overlapping of nerve fibers from different spinal nerves.
• Redundancy: Helps maintain function if one spinal nerve is damaged.

Additional Notes

• Regeneration of nerve fibers was skipped in the lecture.
• Upcoming worksheets will cover the peripheral nervous system in more detail.
• Focus on the autonomic nervous system will be detailed in chapter 14.