Lab 14 Continued Cranial Nerves Portland Community College

Lab 14 Continued Cranial Nerves Portland Community College BI 232

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) 2

Cranial nerve origins • First 2 originate from the forebrain • The next 10 pairs originate from the brainstem. • Midbrain-CNIII, CNIV • Pons- CNV, CNVII • Pons/medulla border. CNVIII • Medulla-CNIX, CNX, XII Use Figure 14. 5 to view all CNs 3

Cranial Nerve Passageways • Cranial nerves must leave the cranial cavity by passing through an opening (foramen, fissure, or canal) in the skull. • Identify the openings for the cranial nerves (activity 14. 8) 4

CN I: Olfactory Nerve • Function: • Sensory for smell • Exiting foramen=cribriform plate • Origin forebrain • Test: Have patient identify aromatic substances like vanilla or coffee • Symptoms of nerve damage: Anosmia: diminished or absent sense of smell 5

CN II: Optic Nerve • • Function: • Sensory for vision • Exiting foramen= optic canal • Origin=forebrain Tests: 1. Eye chart 2. Check peripheral vision 3. Funduscopic exam 6

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 7

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. 8

Cranial Nerves III, IV & VI (Control Eye Movements) 9

CN III: Oculomotor nerve • Function: • Somatic Motor to extraocular muscles (voluntarily move the eye) • Parasympathetic (motor) to iris and lens (pupillary constriction) • Exiting Foramen= superior orbital fissure • Origin= midbrain • Tests: 1. Check pupils for size, shape and equality 2. Shine light in each eye and check for pupil constriction 3. Have patient follow an object in all directions to check for symmetric eye movements 10

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 11

Oculomotor Nerve Injury Right Eye Injured side Normal 12 side

Pupillary Reflex Efferent Afferent Consensual reflex: Both pupils should constrict at the same time 13

Originates in the midbrain CN IV: Trochlear Nerve • Function: • Somatic motor to superior oblique muscle of the eye. • Exiting foramen= superior orbital fissure • Origin= midbrain • Test: Check eye movements • Symptoms of nerve damage: • Outward rotation of the affected eye • Vertical diplopia Normal side Injured side 14

Originates in the pons CN VI: Abducens Nerve • Function: • Somatic Motor to lateral rectus muscle of the eye. Exiting foramen=superior orbital fissure Origin= pons • 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 15 side

CN V: Trigeminal Nerve 3 Branches 1. Ophthalmic 2. Maxillary 3. Mandibular 16

Originates in the pons CN V: Trigeminal Nerve • Function: • Somatic Motor (mandibular branch) to muscles of mastication (chewing) • Sensory (all branches)to face and cornea. • Exiting foramen= Ophthalmic branch=superior orbital fissure • Maxillary branch= foramen rotundum • Mandibular branch = foramen oval • Origin= pons 17

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 18

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 19

Originates in the pons CN VII: Facial Nerve 5 Branches 1. Temporal 2. Zygomatic 3. Buccal 4. Mandibular 5. Cervical • Function: • Somatic Motor to muscles of facial expression • Parasympathetic (motor) to lacrimal and salivary glands 20 • Sensory taste to anterior 2/3 tongue

CN VII: Facial Nerve 21

CN VII: Facial Nerve Testing • • • Exiting foramen= enters internal acoustic meatus exits via stylomastoid foramen Origin= Pons Tests: 1. Check taste on anterior 2/3 of tongue by having patient taste sugar, salt, sour and bitter 2. Check symmetry of facial muscles: • Close eyes, smile, whistle, puff out cheeks (make funny faces) 3. Check tearing with ammonia fumes 22

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 23

CN VII: Facial Nerve Injury (Bell’s Palsy) Normal side Injured side Paralyzed facial muscles Patients can still feel their face because sensory is supplied by the 24 trigeminal nerve

Originates in the medulla CN VIII: Vestibulocochlear • Function: Sensory • Vestibular system for balance & equilibrium • Cochlea for hearing • Exiting foramen= internal acoustic meatus • Origin= Pons-medulla border • Tests: • Auditory component of the nerve: • Hearing test • Vestibular control of balance and movement: • Romberg test (tests equilibrium) 25

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 26

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 27 the equilibrium test.

CN IX: Glossopharyngeal • Function: • Somatic Motor to muscles of pharynx • Parasympathetic (motor) to salivary glands • Sensory to pharynx and taste to posterior tongue • Exiting foramen= Jugular foramen • Origin= medulla oblongata 28

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 29

Originates in the medulla 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 30

CN X: Vagus Nerve • Test: • Inspect palate • Test gag reflex • Symptoms of nerve damage: • Loss of gag reflex • Difficulty swallowing • Hoarse voice • Exiting foramen = Jugular foramen • Origin = Medulla oblongata 31

Originates in the medulla CN XI: Accessory Nerve • Function: Somatic Motor to sternocleidomastoid and trapezius muscles 32

CN XI: Accessory Nerve • Exiting foramen = jugular foramen • Origin = medulla oblongata • and spinal cord • Test: • Shrug shoulders against resistance • Turn head against resistance. 33

CN XI: Accessory Nerve • Symptoms of nerve damage: • Weakness • Uneven shoulders • Winged scapula 34

Originates in the medulla CN XII: Hypoglossal Nerve • Function: Somatic Motor to tongue 35

Hypoglossal Nerve Injury • Exiting foramen = hypoglossal canal • Origin = medulla oblongata • 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 36

Lab Activities • Identify cranial nerves on models • Perform cranial nerve tests • Identify cranial nerve passageways on the skulls • Know origins of cranial nerves 37

The End 38