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  • 1. Lab Activity 19 & 20 Cranial Nerves General Senses Portland Community College BI 232
  • 2. Cranial Nerves
    • Nerves that originate from the brain rather than the spinal cord
    • Part of the peripheral nervous system (not the central nervous system)
    • May contain one or more of the following:
      • Sensory
      • Somatic Motor (voluntary movement)
      • Parasympathetic Motor (involuntary “rest and digest” part of the autonomic nervous system)
  • 3. CN I: Olfactory Nerve
    • Function:
      • Sensory for smell
    • Test: Have patient identify aromatic substances like vanilla or coffee (avoid irritating substances like smelling-salts, cloves, mint)
    • Symptoms of nerve damage: Anosmia: diminished or absent sense of smell
  • 4. CN II: Optic Nerve
    • Function:
      • Sensory for vision
    • Tests:
      • Eye chart
      • Check peripheral vision
      • Funduscopic exam
  • 5. CN II: Optic Nerve
    • Optic chiasm: Fibers from the nasal half of each retina cross over to the opposite side of the brain.
    • Symptoms of nerve damage:
      • Loss of vision (peripheral or central)
      • Abnormal funduscopic appearance
  • 6. CN II: Optic Nerve Pathology Papilledema. Note swelling of the disc, hemorrhages, and exudates, with preservation of the physiologic cup. Proliferative Diabetic Retinopathy. Note the multiple hemorrhages throughout the retina.
  • 7. Cranial Nerves III, IV & VI (Control Eye Movements)
  • 8. CN III: Oculomotor nerve
    • Function:
      • Somatic Motor to extraocular muscles (voluntarily move the eye)
      • Parasympathetic (motor) to iris and lens (pupillary constriction)
    • Tests:
      • Check pupils for size, shape and equality
      • Shine light in each eye and check for pupil constriction
      • Have patient follow an object in all directions to check for symmetric eye movements
    Originates in the midbrain
  • 9. CN III: Oculomotor Nerve Injury
    • Symptoms of nerve damage:
    • Double vision (diplopia): The affected eye turns outward when the unaffected eye looks straight ahead
    • The affected eye can move only to the middle when looking inward and cannot look upward and downward.
    • Ptosis: eyelid droop
    • Pupil may be dilated and sometimes fixed
  • 10. Oculomotor Nerve Injury Right Eye Normal side Injured side
  • 11. Pupillary Reflex Efferent Afferent Consensual reflex: Both pupils should constrict at the same time
  • 12. CN IV: Trochlear Nerve
    • Function:
      • Somatic motor to superior oblique muscle of the eye.
    • Test: Check eye movements
    • Symptoms of nerve damage:
      • Outward rotation of the affected eye
      • Vertical diplopia
    Injured side Normal side Originates in the midbrain
  • 13. CN VI: Abducens Nerve
    • Function:
      • Somatic Motor to lateral rectus muscle of the eye.
    • Test: Check eye movements
    • Symptoms of nerve damage:
      • The affected eye will tend to be deviated inward because of the unopposed action of the medial rectus muscle.
      • Cannot move eyeball laterally beyond the midpoint
    Injured side Normal side Originates in the pons
  • 14. CN V: Trigeminal Nerve
    • 3 Branches
    • Ophthalmic
    • Maxillary
    • Mandibular
  • 15. CN V: Trigeminal Nerve
    • Function:
      • Somatic Motor (mandibular branch) to muscles of mastication (chewing)
      • Sensory (all branches)to face and cornea.
    Originates in the pons
  • 16. CN V: Trigeminal Nerve Test: Have patient bite down while you palpate the masseter muscle Test: Touch patient with an open paperclip and ask “sharp or dull” Test: Touch cornea with a wisp of cotton. Patient should blink
  • 17. CN V: Trigeminal Nerve
    • Symptoms of nerve damage:
    • Inability to firmly bite down (mandibular branch only)
    • Loss of sensation (each branch can be affected independently)
    • Loss of corneal reflex (may indicate brain stem injury)
    • Trigeminal Neuralgia (Tic Douloureux): debilitating intermittent pain on one side of the face
  • 18. CN VII: Facial Nerve
    • 5 Branches
      • Temporal
      • Zygomatic
      • Buccal
      • Mandibular
      • Cervical
    • Function:
      • Somatic Motor to muscles of facial expression
      • Parasympathetic (motor) to lacrimal and salivary glands
      • Sensory taste to anterior 2/3 tongue
    Originates in the pons
  • 19. CN VII: Facial Nerve
  • 20. CN VII: Facial Nerve Testing
    • Tests:
      • Check taste on anterior 2/3 of tongue by having patient taste sugar, salt, sour and bitter
      • Check symmetry of facial muscles:
        • Close eyes, smile, whistle, puff out cheeks (make funny faces)
      • Check tearing with ammonia fumes
  • 21. CN VII: Facial Nerve
    • Symptoms of nerve damage:
      • Mild weakness to total paralysis of facial muscles (may include twitching),
      • Drooping eyelid
      • Drooping corner of the mouth
      • Drooling or dry mouth
      • Impairment of taste
      • Excessive tearing in the eye or dry eye
  • 22. CN VII: Facial Nerve Injury (Bell’s Palsy) Paralyzed facial muscles Patients can still feel their face because sensory is supplied by the trigeminal nerve Injured side Normal side
  • 23. CN VIII: Vestibulocochlear
    • Function: Sensory
        • Vestibular system for balance & equilibrium
        • Cochlea for hearing
    • Tests:
      • Auditory component of the nerve:
        • Hearing test
      • Vestibular control of balance and movement:
        • Romberg test (tests equilibrium)
    Originates in the medulla
  • 24. CN VIII: Vestibulocochlear Tests
    • Simple hearing test:
      • Rub fingers together near the ear and ask “right or left” If there is lateralization (hearing louder on one side) there is a problem
    • Other hearing tests:
      • Performed by an audiologist with special equipment to determine tones, frequencies and degree of hearing loss
  • 25. CN VIII: Vestibulocochlear Tests Romberg Test
    • Have patient stand with arms at side and feet together
    • Have patient stand with their eyes closed
    • Stand close to prevent falls
    • Normally, they should maintain position for 20 seconds with only minimal swaying
      • If they loose their balance, they have failed the equilibrium test.
  • 26. CN IX: Glossopharyngeal
    • Function:
      • Somatic Motor to muscles of pharynx
      • Parasympathetic (motor) to salivary glands
      • Sensory to pharynx and taste to posterior tongue
  • 27. CN IX: Glossopharyngeal
    • Tests:
      • Gag reflex: Touch each side of the throat with the tongue depressor
      • Evaluate swallowing movements
      • Say AHH, and watch the palate and uvula elevate.
      • Evaluate taste on posterior 1/3 of tongue
    • Symptoms of nerve damage:
      • Loss of gag reflex
      • Difficulty swallowing
      • Loss of taste
    Originates in the medulla
  • 28. CN X: Vagus Nerve
    • Function:
      • Somatic Motor to muscles of pharynx and larynx
      • Parasympathetic (motor) fibers of the heart and other viscera
      • Sensory to pharynx and larynx
    Originates in the medulla
  • 29. CN X: Vagus Nerve
    • Test:
      • Inspect palate
      • Test gag reflex
    • Symptoms of nerve damage:
      • Loss of gag reflex
      • Difficulty swallowing
      • Hoarse voice
  • 30. CN XI: Accessory Nerve
    • Function: Somatic Motor to sternocleidomastoid and trapezius muscles
    Originates in the medulla
  • 31. CN XI: Accessory Nerve
    • Test:
      • Shrug shoulders against resistance
      • Turn head against resistance.
  • 32. CN XI: Accessory Nerve
    • Symptoms of nerve damage:
      • Weakness
      • Uneven shoulders
      • Winged scapula
  • 33. CN XII: Hypoglossal Nerve
    • Function: Somatic Motor to tongue
    Originates in the medulla
  • 34. Hypoglossal Nerve Injury
    • Test:
    • Ask patient to stick out tongue
    • Symptoms of nerve damage:
    • When paralyzed, the tongue will point to the damaged side
    Normal side Injured side
  • 35. Lab Activity 20 General Senses
  • 36. General Senses: Receptors
    • Nociceptors: Pain receptors
    • Thermoreceptors: Temperature receptors (free nerve endings)
    • Chemoreceptors: Detect small changes in the concentration of specific chemicals or compounds
    • Mechanoreceptors: Sensitive to stimuli that distort their cell membranes (contain mechanically gated ion channels)
      • Tactile receptors
      • Baroreceptors
      • Proprioceptors
  • 37. Classes of Mechanoreceptors
    • Tactile receptors : sensations of touch, pressure and vibration
      • Free nerve endings
      • Root hair plexus
      • Tactile discs (Merkel’s discs)
      • Tactile corpuscles (Meissner’s corpuscles)
      • Lamellated corpuscles (Pancinian corpuscles)
    • Baroreceptors: Detect pressure changes in the walls of blood vessels and portions of the digestive, reproductive and urinary tracts
    • Proprioceptors: Monitor the positions of joints and muscles.
  • 38. Pancinian Corpuscle (aka: Lamellated Corpuscle)
    • Lie deep in the dermis
    • Respond only when deep pressure is first applied
    • Monitor high frequency vibrations
  • 39. Meissner’s Corpuscle (aka: Tactile Corpuscle)
    • Lie in the dermal papillae of the skin
    • Respond to light touch
  • 40. The End The End