Cranial Nerves

• Peripheral Nervous System (PNS)


  All neural structures outside the brain and spinal cord

  
• Peripheral Nervous System (PNS)

  • Includes sensory receptors, peripheral nerves, associated ganglia, and motor endings
  • Provides links to and from the external environment

  
• Nerve


  Cordlike organ of the PNS consisting of peripheral axons enclosed by connective tissue

  
• Connective tissue coverings of a nerve

  • Endoneurium - loose connective tissue that surrounds axons
  • Perineurium - coarse connective tissue that bundles fibers into fascicles
  • Epineurium - tough fibrous sheath around a nerve

  
• Sensory nerves


  Carry impulses to the CNS
• Motor nerves


  Carry impulses from the CNS
• Mixed nerves


  Carry both sensory and motor fibers to and from the CNS
• Mixed nerves


  • Carry somatic and autonomic (visceral) impulses
  • Four types: somatic afferent and somatic efferent, visceral afferent and visceral efferent
• Cranial nerves


  Twelve pairs of nerves that arise from the brain

  
• Cranial nerves


  • Have sensory, motor, or both sensory and motor functions
  • Each nerve is identified by a number (I through XII) and a name
  • Four carry parasympathetic fibers that serve muscles and glands

  
• Cranial Nerve I: Olfactory


  Carries afferent impulses for the sense of smell
• Cranial Nerve II: Optic


  Carries afferent impulses for vision

  
• Cranial Nerve III: Oculomotor


  Functions in raising the eyelid, directing the eyeball, constricting the iris, and controlling lens shape

  
• Cranial Nerve IV: Trochlear


  Primarily a motor nerve that directs the eyeball

  
• Cranial Nerve V: Trigeminal


  • Composed of three divisions: ophthalmic (V1), maxillary (V2), and mandibular (V3)
  • Conveys sensory impulses from various areas of the face (V1 and V2), and supplies motor fibers (V3) for mastication

  
• Cranial Nerve VI: Abducens


  Primarily a motor nerve innervating the lateral rectus muscle

  
• Cranial Nerve VII: Facial


  • Mixed nerve with five major branches
  • Motor functions include facial expression, and the transmittal of autonomic impulses to lacrimal and salivary glands
  • Sensory function is taste from the anterior two-thirds of the tongue

  
• Cranial Nerve VIII: Vestibulocochlear


  Functions are solely sensory – equilibrium and hearing

  
• Cranial Nerve IX: Glossopharyngeal


  • Motor – innervates part of the tongue and pharynx, and provides motor fibers to the parotid salivary gland
  • Sensory – fibers conduct taste and general sensory impulses from the tongue and pharynx

  
• Cranial Nerve X: Vagus


  • The only cranial nerve that extends beyond the head & neck
  • Most motor fibers are parasympathetic fibers to the heart, lungs, and visceral organs
  • Its sensory function is in tastes

  
• Cranial Nerve XI: Accessory


  Primarily a motor nerve that supplies fibers to the larynx, pharynx, and soft palate, and innervates the trapezius and sternocleidomastoid, which move the head and neck

  
• Cranial Nerve XII: Hypoglossal

  Innervates both extrinsic and intrinsic muscles of the tongue, which contribute to swallowing and speech