Peripheral Nervous System and Reflex Activity: BIOL 2111

Importance of Peripheral Nervous System (PNS)

  • PNS is essential for diagnosing and treating nerve damage.

Structure of the Peripheral Nervous System

  • Composed of neural structures linking the body to the external environment.
  • Divided into four components:
    • Sensory Receptors
    • Transmission Lines (Nerves and Structure)
    • Motor Endings and Activities
    • Reflex Activity

Sensory Processing

  • Sensation: Awareness of environmental changes.
  • Perception: Conscious interpretation of sensory stimuli.
  • Processed in three levels:
    1. Receptor Level: Sensory reception and transmission to CNS.
    2. Circuit Level: Processing in ascending pathways.
    3. Perceptual Level: Processing in cortical sensory areas.

Types of Sensory Receptors

  • Classified by:
    • Type of Stimulus:
    • Mechanoreceptors: Touch, pressure.
    • Thermoreceptors: Temperature changes.
    • Photoreceptors: Light energy (e.g., retina).
    • Chemoreceptors: Chemicals (e.g., taste).
    • Nociceptors: Pain signals.
    • Location:
    • Exteroceptors: External stimuli (skin).
    • Interoceptors: Internal stimuli (organs).
    • Proprioceptors: Body positioning and movement.

Pain Perception

  • Visceral Pain: Vague, aching sensation from internal organs.
  • Referred Pain: Pain perceived in areas other than the source due to shared nerve pathways.
  • Pain tolerance varies among individuals, affected by genetic factors.

Nerves and Their Structure

  • Nerves consist of bundles of axons with connective tissue coverings:
    • Endoneurium: Encloses individual axons.
    • Perineurium: Bundles axons into fascicles.
    • Epineurium: Outermost layer enclosing entire nerve.

Regeneration of Nerve Fibers

  • PNS can regenerate if soma is intact; CNS cannot regenerate effectively.
  • Regeneration involves:
    1. Wallerian degeneration of axon.
    2. Macrophages clean debris.
    3. Schwann cells create a regeneration tube.
    4. New axon and myelin sheath formation occurs.

Cranial Nerves Overview

  • 12 pairs of cranial nerves, mainly mixed but some purely sensory or motor.
  • Functions include sensory perception, motor control, and autonomic responses.

Summary of Cranial Nerve Functions

  • I: Olfactory - Smell (Sensory)
  • II: Optic - Vision (Sensory)
  • III: Oculomotor - Eye movement (Motor)
  • IV: Trochlear - Eye movement (Motor)
  • V: Trigeminal - Sensation of face; chewing (Mixed)
  • VI: Abducens - Eye movement (Motor)
  • VII: Facial - Facial expressions; taste (Mixed)
  • VIII: Vestibulocochlear - Hearing, balance (Sensory)
  • IX: Glossopharyngeal - Taste; swallowing (Mixed)
  • X: Vagus - Autonomic control (Mixed)
  • XI: Accessory - Neck movement (Motor)
  • XII: Hypoglossal - Tongue movement (Motor)