Peripheral nervous system

PERIPHERAL NERVOUS SYSTEM

  • Comprised of Central Nervous System (CNS) and Peripheral Nervous System (PNS).
  • PNS divided into Sensory (afferent) and Motor (efferent) divisions.
  • Motor division has Somatic Nervous System and Autonomic Nervous System (ANS).
    • ANS further divided into Sympathetic and Parasympathetic divisions.

NERVE ANATOMY

  • Nerves are bundles of axons surrounded by connective tissue.
  • Categories of nerves: Afferent (Sensory), Efferent (Motor), Mixed.

CRANIAL NERVES

  • Total of 12 cranial nerves, each with specific functions:
    • I: Olfactory - smell (sensory)
    • II: Optic - vision (sensory)
    • III: Oculomotor - eye movement (motor & parasympathetic)
    • IV: Trochlear - eye movement (motor)
    • V: Trigeminal - facial sensation and muscles of mastication (mixed)
    • VI: Abducens - eye movement (motor)
    • VII: Facial - facial expression and taste (mixed)
    • VIII: Vestibulocochlear - hearing and balance (sensory)
    • IX: Glossopharyngeal - taste, swallowing, salivary gland (mixed)
    • X: Vagus - regulates organs in the body (mixed)
    • XI: Accessory - movement of neck and shoulders (motor)
    • XII: Hypoglossal - tongue movement (motor)

SPINAL NERVES

  • Total of 31 pairs, including cervical, thoracic, lumbar, sacral, and coccygeal nerves.
  • Each spinal nerve has dorsal root (sensory) and ventral root (motor).
  • Dorsal root ganglion contains cell bodies of afferent neurons; ventral horn contains motor neuron cell bodies.

REFLEXES

  • Reflex arcs allow for rapid responses to stimuli, involving:
    1. Receptor
    2. Sensory neuron
    3. Integration center (spinal cord)
    4. Motor neuron
    5. Effector (muscle/gland)
  • Types of reflexes: Intrinsic (inborn) and Acquired (learned); also Somatic and Autonomic.

REFLEX EXAMPLES

  • Muscle Stretch Reflex (e.g., Patellar Reflex):
    • Activation of muscle spindles due to stretch causes contraction of affected muscles and inhibition of antagonist muscles.
  • Flexor Reflex: Response to noxious stimuli causing withdrawal of affected limb (ipsilateral) and simultaneous activation of extensor muscles on the opposite side (contralateral).