Cranial Nerves I and II

Question 1

Cranial Nerve I

Answer 1

Olfactory Nerve

• ​SVA: Special Visceral Afferent: Senses SMELL in this case
• Foramen: Cribriform plate (ethmoid bone)
• Main Structures innervated:
  
  • Olfactory nasal mucosa (smell)
• CN I or the olfactory nerve has only a special sensory component
  
  • Functions in the special sense of smell or olfaction
• Route: Olfactory nerves –> Cribiform plate –> olfactory bulb –> olfactory tract

Structures to know:

• Ethmoid bone (cribiform plate)
• Crista Galli
• Foramen Cecum

Question 2

Cranial Nerve II

Answer 2

Optic Nerve

• Foramen: Optic Foramen (canal)
• Compartments: SSA (Special Somatic Afferent). Vision in this case.
• Innervation: Rods and Cones of retina. (vision)
• Nasal fibers cross in the optic chiasm, temporal do not!
• Optic nerve (CN II) enters the orbit via the optic canal
• Route: Retina –> Optic nerve –> optic canal –> optic chiasm –> optic tract
• Sella turcica (Hypophyseal fossa)
  
  • ​Pituitary gland rests here
    
    • Would see and optic chiasm hit (bitemporal hemianopsia) with a pituitary tumor

Question 3

Cranial Nerve III

Answer 3

Oculomotor Nerve

• Foramen: Superficial orbital fissure
• Components: GVE (General visceral efferent –> Parasympathetic) and GSE (General somatic efferent)
  
  • GSE innervates Superior rectus, inferior rectus, medial rectus, inferior oblique and levator palpebrae. It DOES NOT innervate the Lateral rectus or superior oblique
• Innervation:
  
  • (via ciliary ganglion) to sphincter pupillae and ciliary muscles
  • Superior, medial, and inferior recti and inferior oblique eyeball muscles and levator palpebrae superioris
• Route: Brainstem –> Cavernous sinus –> Superior obital fissure –> orbit

Question 4

Cranial Nerve IV

Answer 4

Trochlear Nerve

• Foramen: Superior orbital fissure
• Components: GSE: General somatic efferent
• Innervation: Superior oblique eyeball muscle –> responsible for eye movement
• Unique features:
  
  • ​Only nerve to exit from the dorsal surface of the brain
  • Only nerve in which all the lower motor neuron fibers decussate
  • Has the longest intracranial course
  • Has the smallest number of axons
• Route: Posterior brainstem –> cavernous sinus –> superior orbital fissure –> orbit

Question 5

Cranial Nerve V

Answer 5

Trigeminal Nerve

• 3 Divisions:
  
  • ​Ophthalmic (V1)
  • Maxillary (V2)
  • Mandibular (V3)
• Foramen:
  
  • ​Superior orbital fissure (V1)
  • Foramen rotundum (V2)
  • Foramen ovale (V3)
• Components:
  
  • ​GSA: General somatic afferent
  • SVE: Somatic visceral efferent
• Innervation:
  
  • ​V1: skin of upper part of face
  • V2: Skin of mid face, upper teeth, nasal and palatal mucosa
  • V3: skin of lower face and jaw, floor of mouth, mucosa of anterior 2/3 of tongue, lower teeth and gums, ear pinna and canal
  • Motor to muscles of mastercation, anterior belly of digastric, tensor tympani, mylohyoid, tensor palatini (first arch)
• Routes:
  
  • ​V1: Superior orbital fissure –>
    
    • ​Nasociliary nerve –> ethmoids, ciliary, infratrochlear
    • Frontal nerve –> supraorbital (lateral) –> supratrochlear (medial)
    • Lacrimal
  • V2: Foramen rotundum –> zygomatic, superior alveolar, infraorbital, palatine, nasopalatine, pharyngeal nerve
  • V3: Foramen ovale –> meningeal branch, buccal nerve, ariculotemporal, inferior alveolar (–> mental), lingual
    
    • ​Inferior alveolar nerve goes INTO mandible (emerging as mental nerve)
    • Lingual nerve goes UNDER mandible to tongue (TOUCH anterior 2/3 of tongue)

Question 6

Divisions of the Trigeminal nerve (CN V)

Answer 6

1. Ophthalmic
2. Maxillary
3. Mandibular

Question 7

CN V1

Answer 7

Ophthalmic Nerve

• Innervates and provides GSA (sensory) to the skin of the upper part of the face (upper orbit and above)
• NFL: NFL refers to the nasocilliary nerve, the frontal nerve, and the lacrimal nerve—all these nerves are SENSORY (GSA)

Question 8

CN V2

Answer 8

Maxillary Nerve

• Innervates and provides sensory information to the skin of the midface, upper teeth, nasal and palatal mucosa
• V2 (maxillary division) is sensory to the upper teeth via the superior alveolar nerves and terminates as the infraorbital nerve which is sensory below the eye. The greater and lesser palantine nerves give sensation to the palate.

Question 9

CN V3

Answer 9

Mandibular Nerve

• Innervates and provides sensory information to the skin of the lower face and jaw, floor of the mouth, mucosa of anterior 2/3 of tongue, lower teeth and gums, ear pinna and canal
• V3 is sensory to the lower teeth, tongue. And lower face and skin in front of ear. (GSA)
• V3 contains the only motor branches of the trigeminal. (SVE)!
  
  • Provides motor to muscles of mastication, anterior belly of digastric, tensor tympani, mylohyoid, tensor palatini (first arch muscles)

Question 10

Cranial Nerve VI

Answer 10

Abducens Nerve

Question 11

Name the nerve you use to see

Answer 11

CN II: optic

Question 12

Name the nerve you use to focus

Answer 12

CN III: Occulomotor –> Ciliary muscle

Question 13

Name the nerve you use when looking at bright light

Answer 13

CN III: Oculomotor: Sphincter Pupillae

Question 14

Name the nerve you use to open your eyes

Answer 14

CN III: Occulomotor: levator palepbrae

Question 15

Name the nerve you use to force your eyes closed

Answer 15

CN VII: Facial Nerve

Question 16

Cranial Nerve VII

Answer 16

Facial Nerve

• Foramen: Internal auditory meatus
• Components:
  
  • GVA
  • SVA
  • GSA
  • GVE
  • SVE
    *