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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

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lab 14 continued

Lab 14 Continued

Cranial Nerves

Portland Community College

BI 232

cranial nerves
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)
cranial nerve origins
Cranial nerve origins
  • First 2 originate from the forebrain
  • The next 10 pairs originate from the brainstem.
  • Midbrain-CNIII, CNIV
  • Pons- CNV, CNVI, CNVII
  • Pons/medulla border- CNVIII
  • Medulla-CNIX, CNX, XI, XII

Use Figure 14.5 to view all CNs

cranial nerve passageways
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)
cn i olfactory nerve
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
cn ii optic nerve
CN II: Optic Nerve
  • Function:
    • Sensory for vision
    • Exiting foramen= optic canal
    • Origin=forebrain
  • Tests:
    • Eye chart
    • Check peripheral vision
    • Funduscopic exam
cn ii optic nerve1
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
cn ii optic nerve pathology
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.

cn iii oculomotor nerve
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:
    • 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
cn iii oculomotor nerve injury
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
oculomotor nerve injury right eye
Oculomotor Nerve Injury Right Eye

Injured side

Normal side

pupillary reflex
Pupillary Reflex



Consensual reflex: Both pupils should constrict at the same time

cn iv trochlear nerve
Originates in the midbrainCN 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

cn vi abducens nerve
Originates in the ponsCN 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 laterallybeyond the midpoint

Normal side

Injured side

cn v trigeminal nerve
CN V: Trigeminal Nerve

3 Branches

  • Ophthalmic
  • Maxillary
  • Mandibular
cn v trigeminal nerve1
Originates in the ponsCN 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
cn v trigeminal nerve2
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

cn v trigeminal nerve3
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
cn vii facial nerve
Originates in the ponsCN 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
cn vii facial nerve testing
CN VII: Facial Nerve Testing
  • Exiting foramen= enters internal acoustic meatus exits via stylomastoid foramen
  • Origin= Pons
  • 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
cn vii facial nerve2
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
cn vii facial nerve injury bell s palsy
CN VII: Facial Nerve Injury (Bell’s Palsy)

Paralyzed facial muscles

Normal side

Injured side

Patients can still feel their face because sensory is supplied by the trigeminal nerve

cn viii vestibulocochlear
Originates in the medullaCN 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)
cn viii vestibulocochlear tests
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
cn viii vestibulocochlear tests romberg test
CN VIII: Vestibulocochlear TestsRomberg 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.
cn ix glossopharyngeal
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
cn ix glossopharyngeal1
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
cn x vagus nerve
Originates in the medullaCN X: Vagus Nerve
  • Function:
    • Somatic Motor to muscles of pharynxand larynx
    • Parasympathetic (motor) fibers of the heart and other viscera
    • Sensory to pharynx and larynx
cn x vagus nerve1
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
cn xi accessory nerve
Originates in the medullaCN XI: Accessory Nerve
  • Function:Somatic Motor to sternocleidomastoid and trapezius muscles
cn xi accessory nerve1
CN XI: Accessory Nerve
  • Exiting foramen = jugular foramen
  • Origin = medulla oblongata
  • and spinal cord
  • Test:
    • Shrug shoulders against resistance
    • Turn head against resistance.
cn xi accessory nerve2
CN XI: Accessory Nerve
  • Symptoms of nerve damage:
    • Weakness
    • Uneven shoulders
    • Winged scapula
hypoglossal nerve injury
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

lab activities
Lab Activities
  • Identify cranial nerves on models
  • Perform cranial nerve tests
  • Identify cranial nerve passageways on the skulls
  • Know origins of cranial nerves
the end
The End

The End