Cranial Nerves

Question 1

Medullary

Cranial Nerves

Answer 1

• Hypoglossal (XII)
• Spinal accessory (XI)
• Vagus (X)
• Glossopharyngeal (IX)

Question 2

Pontine

Cranial Nerves

Answer 2

• Vestibulocochlear (XIII)
• Facial (VII)
• Abducens (VI)
• Trigeminal (V)

Question 3

Midbrain

Cranial Nerves

Answer 3

• Trochlear (IV)
• Oculomotor (III)

Question 4

Hypoglossal nerve

CN XII

Answer 4

General Somatic Efferent (GSE)

Hypoglossal n. → intrinsic & extrinsic musles of tongue.

Unilateral lesion:

Fasciculation, weakness, atrophy of ipsi tongue.

Ipsi deviation of tongue.

Corticobulbar innervation b/l → no sx.

Question 5

Spinal Accessory Nerve

CN XI

Answer 5

Special Visceral Efferent (SVE)

C1-C5 → jugular foramen → ipsi SCN & trapezius

Lesion:

weakness turning head to contralateral side

weakness elevating ipsi shoulder

Question 6

Vagus Nerve

CN X

Answer 6

Two motor components:

1. SVE
   
   • nucleus ambiguus → pharynx & larynx muscles
   • lesion = ipsi paralysis
     • dysphagia & loss of gag
2. GVE
   
   • dorsal motor nucleus of X → thorax and abdomen viscera
     
     • major PNS nucleus of brainstem
   • lesion
     
     • unilateral = no sx
     • bilateral = severe tachycardia

Three sensory components:

1. SVA: taste
   
   • epiglottis → inferior vagal (nodose) ganglion → caudal n. solitarius
   • lesion = minimal loss of taste sensation
2. GVA
   
   • larynx, pharynx, aortic arch, abd and thoracic viscera → inferior vagal (nodose) ganglion → caudal n. solitarius
   • lesion
     
     • hemianesthesia of larynx/pharynx
     • loss of cough reflex (afferent limb)
3. GSA
   
   • meninges, pharynx, ear → inferior & superior vagal (jugular) ganglion → spinal nucleus of V
   • lesion = some loss of sensation from outer ear

Question 7

Glossopharyngeal Nerve

CN IX

Answer 7

Two motor components:

1. SVE
   
   • nucleus ambiguus → stylopharyngeus muscle
   • lesion = dysphagia
2. GVE
   
   • inferior salivatory nucleus → otic ganglion → parotid gland
   • lesion = decreased salivation

Three sensory components:

1. SVA: taste
   
   • posterior 1/3 tongue → inferior (petrosal) glossopharyngeal ganglion → rostral n. solitarius
   • lesion = loss of taste
2. GVA
   
   • pharynx, posterior tongue, middle ear, carotid body → inferior (petrosal) glossopharyngeal ganglion → caudal n. solitarius
   • lesion
     
     • loss of gag (afferent limb)
     • loss of carotid sinus reflex if b/l lesion
3. GSA
   
   • pharynx, posterior tongue, EAC → inferior & superior glossopharyngeal (jugular) ganglion → spinal nucleus of V
   • lesion = loss of sensation from outer ear, pharynx, posterior tongue

Question 8

Gag Reflex

Answer 8

Afferent limb: glossopharyngeal nerve

Efferent limb: vagus nerve

Central connections unclear.

Question 9

Facial Nerve

CN VII

Answer 9

Two motor components:

1. SVE
   
   • motor nucleus of V → muscles of facial expression & stapedius muscle of inner ear
   • lesion:
     
     • ipsi facial paralysis
     • loss of corneal reflex (efferent limb)
     • hyperacusis
   • unilat. corticobulbar lesion = contralateral drooping of mouth
2. GVE
   
   • superior salivatory nucleus (PNS)
     
     • → pterygopalatine ganglion → lacrimal & nasal glands
     • → submandibular ganglion → submandibular & sublingual glands
   • lesion = loss of lacrimation & dry mouth

Two sensory components:

1. SVA: taste
   
   • anterior 2/3 tongue → geniculate ganglion → rostral nucleus solitarius
   • lesion = loss of taste
2. GSA
   
   • ext. auditory canal → geniculate ganglion → spinal nucleus of V
   • lesion = insig. loss of sensation from outer ear

Question 10

Abducens Nerve

CN VI

Answer 10

• General somatic efferent (GSE)
  
  • Abducens n. → lateral rectus muscle
• Lesion to nerve → medial strabismus
• Lesion to nucleus:
  
  • medial strabismus
  • diplopia
  • lateral gaze paralysis of both eyes to ipsilateral side
    
    • damaged internuclear neurons
      
      • normally ascend via MLF
      • controls contralateral oculomotor n.

Question 11

Trigeminal Nerve

CN V

Answer 11

SVE

• motor nucleus of V
  
  • → muscles of mastication
  • → tensor tympani
• lesion = deviation of jaw towards lesion

GSA

From face, mouth, anterior 2/3 of tongue, nasal sinuses, meninges.

V1 = opthalmic

V2 = maxillary

V3 = mandibular

1. Pain & temp → trigeminal ganglion → spinal tract of V → spinal nucleus of V → cross brainstem → STT
   
   • lesion = ipsi loss of protopathic sensation from face
2. Fine touch & proprioception → trigeminal ganglion → chief sensory nucleus of V → cross brainstem → medial lemiscus
   
   • lesion = ipsi loss of epicritic sensation from face
3. Stretch receptors from muscles of mastication → mesencephalic nucleus of V (DRG in brainstem) → motor nucleus of V
   
   • lesion = loss of jaw reflex (afferent limb)

Question 12

Blink Reflex

Answer 12

Afferent Limb:

cornea → V1 of trigeminal nerve → spinal tract of V → spinal nucleus of V

Efferent limb:

spinal n. of V → reficular formation relay → bilateral facial motor nuclei → orbicularis oculi muscles

Question 13

Trochlear Nerve

CN IV

Answer 13

GSE

Trochlear nucleus → cross in superior medullary velus → contralateral superior oblique

Nerve lesion = ipsi diplopia when looking down

Nucleus lesion = contralateral diplopia

Question 14

Oculomotor Nerve

CN III

Answer 14

1. GSE
   
   • oculomotor nucleus → all other intrinsic muscles of eye & levator palpebrae superioris
   • lesion = ipsi opthalmoplegia, diplopia, lateral strabismus, ptosos
2. GVE
   
   • Edinger-Westphal nucleus → ciliary ganglion → pupillary sphincter and cilary msucles
   • PNS component → light and accommodation reflexes
   • lesion:
     
     • loss of accommodation of lens
     • dilated pupillae (mydriasis)

Question 15

Oculomotor Lesion

vs

Horner’s Syndrome

Answer 15

Oculomotor lesion → ptosis and dilated pupil (mydriasis)

Eyelid droop on side of large pupil.

Horner’s syndrome → ptosis, constricted pupil (myosis), and anhidrosis.

Eyelid droop on side of small pupil.