PNS path

Introduction to the Peripheral Nervous System

  • The nervous system is categorized into the central nervous system (CNS) and the peripheral nervous system (PNS).
  • Today’s focus is on the peripheral nervous system, specifically the diseases associated with it.

Overview of the Nervous System

  • The PNS branches into two further subdivisions:
    • Somatic Nervous System
    • Controls voluntary muscles and sensory perceptions.
    • Autonomic Nervous System (ANS)
    • Regulates involuntary physiological processes, includes:
      • Sympathetic Nervous System
      • Responsible for the 'fight or flight' response.
      • Parasympathetic Nervous System
      • Responsible for 'rest and digest' functions.
Peripheral Nervous System Structure
  • The PNS comprises nerves outside the brain and spinal cord:
    • Motor Nerves
    • Control voluntary muscle movement and have neuromuscular junctions.
    • Sensory Nerves
    • Detect sensations and send signals back to the CNS (via dorsal root ganglion).
Structure of Nerves
  • Nerve structure:
    • Nerves consist of bundles of axons surrounded by:
    • Endoneurium: surrounds individual axons.
    • Perineurium: surrounds a group of axons.
    • Epineurium: surrounds the entire nerve.
Myelination in the PNS
  • Schwann Cells produce myelin sheaths in the peripheral nervous system; essential for fast nerve conduction.
  • Only 20% of fibers in PNS are myelinated:
    • Types of fibers:
    • Aα (Alpha Motor Neurons): myelinated
    • Aβ(Beta fibers): sensory nerves for fine touch; myelinated
    • C fibers: responsible for slow pain; unmyelinated
Aging and Nerve Changes
  • As one ages:
    • The perineurium and epineurium thicken.
    • Reduced myelinated fibers due to decreased protein production, leading to slower nerve conduction.

Classification of Peripheral Nerve Injuries

  • Types of nerve injuries:
    1. Neuropraxia: temporary block of nerve conduction (e.g., “funny bone” injury).
    2. Axonotmesis: loss of continuity of the axon, but the connective tissue remains intact.
    3. Neurotmesis: complete severance of the nerve.
  • Recovery likelihood varies:
    • Neuropraxia has high recovery potential.
    • Neurotmesis has low recovery potential.

Types of Peripheral Nerve Diseases

  1. Neuropathies: pathology confined to the nerve (e.g., diabetic neuropathy).
    • Typologies: mononeuropathy (affects one nerve) and polyneuropathy (affects multiple nerves).
    • Example diseases: diabetic neuropathy, hereditary neuropathies, infections, autoimmune conditions.
  2. Myopathies: pathology of the muscle often linked to neuromuscular junction dysfunction (e.g., myasthenia gravis).
Major Conditions Affecting the PNS
  • Charcot-Marie-Tooth Disease (CMT): inherited disease affecting Schwann cells leading to decreased nerve conduction velocity; affects the peroneal nerve, resulting in sensory loss, muscle weakness, and gait difficulties.
  • Carpal Tunnel Syndrome: median nerve compression at the wrist, causing symptoms like nocturnal numbness and tingling in fingers.
    • Management includes ergonomics education and splinting.
  • Diabetic Neuropathy: symmetrical distal neuropathy due to chronic hyperglycemia; presents as numbness in a glove-and-stocking pattern.
    • Treatment focuses on blood sugar management and physical therapy.
  • Guillain–Barré Syndrome: acute polyneuropathy characterized by rapid ascending paralysis, often following a viral infection.
    • Treatment includes immunotherapy and physical rehabilitation, with prognosis varying.
  • Myasthenia Gravis: autoimmune disorder affecting the neuromuscular junction preventing acetylcholine from binding to receptors, leading to muscle weakness.
    • EMG is a key diagnostic tool; treatment may include anti-cholinesterase medications and energy conservation strategies.
  • Complex Regional Pain Syndrome (CRPS): occurs after injury leading to chronic pain, sensory, and autonomic dysfunction; management is particularly challenging and often multifaceted.
Summary of Symptoms & Management Strategies
  • Common symptoms of peripheral nerve disorders can include:
    • Numbness, tingling, and pain,
    • Weakness or muscle atrophy,
    • Altered reflexes and sensory perceptions.
  • Interventions may include:
    • Physical therapy for strengthening and mobility,
    • Ergonomic modifications,
    • Patient education on management and care.
Conclusion
  • Understanding the peripheral nervous system and its diseases is crucial for proper diagnosis and treatment in physical therapy. Always consider comprehensive assessments and tailored rehabilitation strategies for effective patient care.