What are the 12 Cranial Nerves?
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Olfactory Optic Oculomotor Trochlear Trigeminal Abducens Facial Vestibulotrochlear Glossopharyngeal Vagus (Spinal) Accessory Nerve Hypoglossal
Which nerves are motor, sensory, or both?
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What is the route of the Olfactory Nerve?
Temporal Lobe Olfactory Tract Olfactory Bulb Cribriform Plate and Foramina Olfactory Nerves
Olfactory Nerve Injury
Causes?
Complications?
Test?
Upper respiratory tract infection (cold) is most common Head injury (basilar skull fracture) or frontal lobe tumour compressing nerve
Anosmia (Loss of smell)
Test each nostril’s sense of smell individually
What is the route of the Optic Nerve?
Retinal ganglion cells generate APs due to light
Travel along axons
Exit via the optic canal (2 nerves)
Merge at the Optic Chiasm (2 nerves merged)
Optic Tract
Primary visual cortex in the Occipital Lobe of the brain
What is the significance of the location of damage to the development of Bitemporal Hemianopia?
What can cause the damage?
Bitemporal Hemianopia is blindness in both eyes
For this to occur, a lesion must take place at the places where the two optic nerves meet, otherwise blindness would be in one eye
= Optic Chiasm or Tract
Causes = Pituitary Tumour, Optic Neuritis (inflammation)
How can the optic nerve be examined microscopically?
With an ophthalmoscope
Examines the optic disc (point where nerve enters retina)
This nerve is the only nerve that can be examined
How does meningitis cause photophobia?
Optic nerves have an extension of meninges surrounding them, as they are considered as extensions of the brain itself
In meningitis, these become inflamed due to raised ICP
= Swollen optic nerve and disc
= Papillodema of the disc (swelling)
= Compression = PHOTOPHOBIA
Describe and explain what allows the pupillary reflex to occur?
The optic tract is connected to the brainstem (midbrain)
This allows pupil reflex to occur depending on the level of light seen (dilate or constrict)
What is the route of the Oculomotor Nerve?
Midbrain
Cavernous Sinus
Superior Orbital Fissure
What are the 2 functions of the Oculomotor Nerve?
1) Motor
Innervates muscles that move the eyeball (extra-ocular muscles)
Muscles of eyelid (Levator Palpebrae Superioris)
2) Autonomic
Innervates Sphincter Pupillae Muscles that constrict pupil
How can the Oculomotor Nerve become compressed, and what signs can a patient present with to indicate this?
It can compress by an increase in ICP, causing an Uncal Herniation of the Temporal Lobe onto the Tentorium Cerebelli.
This will affect the autonomic function of the nerve, which is to constrict the pupil (parasympathetically) , and therefore the patients pupils will dilate!
Oculomotor Nerve Injury
Causes?
Complications/Signs?
Tests?
Cavernous Sinus Thrombosis
Raised ICP
(both compress nerve)
Pupil Dilation
Diplopia
Down/out eye position, severe ptosis (eyelid droop)
Inspect eyelid and test light reflex
What is the route of the Trochlear Nerve?
Midbrain
Lateral wall of Cavernous Sinus
Superior Orbital Fissure
Function of Trochlear Nerve
Innervates Superior Oblique Muscle (abducts, depresses and internally rotates eye)
Trochlear Nerve Injury
Causes?
Complications/Signs?
Tests?
Only nerve to emerge from dorsal brainstem so it has longest intracranial route (susceptible to damage)
Diplopia, Congenital Palsies in children
Test nerves 3,4 and 6 together
What is the route of the Trigeminal Nerve?
Pons
Trigeminal ganglion
Splits into the 3 trigeminal nerves
- Ophthalmic - Sup. orbital fissure - Orbit
- Maxillary - Foramen Rotundum - Pterygopalatine Fossa
- Mandibular - Foramen Ovale - Infratemporal fossa
Function of Trigeminal Nerves?
Sensory:
Dermatomes
Paranasal air sinuses, anterior tongue (touch, not taste), and meninges
Motor: Muscles of mastication
Trigeminal Nerve Injury
Causes?
Complications/Signs?
Tests?
Trigeminal Neuralgia
Shingles
Shingles on Ophthalmic dermatome can run on eye and cause scarring of eye, leading to blindness and corneal ulcers
Trigeminal Neuralgia causes sharp shooting pains in jaw
Test dermatomes
Test muscles of mastication (Jaw Jerk)
Corneal reflex (no touch feeling)
Branches of Ophthalmic Nerve Division
1) Frontal
- Exits front of orbit as Supraorbital and Supratrochlear Nerves that pass up onto anterior forehead
2) Lacrimal
3) Nasociliary
Branches of Maxillary Nerve Division
1) Infraorbital
- Runs through floor of orbit so if this fractures can injure nerve
- Sensory: Cheek and lower eyelid
2) Superior Alveolar Nerves
- Sensory: Nasopharynx, nasal cavity, upper teeth etc.
Branches of Mandibular Nerve Division
1) Inferior Alveolar Nerve
- Runs via mandibular foramen, exits as Mental Nerve via mental foramen, INJURED IN MANDIBULAR FRACTURES
- Sensory: Chin, lower lip, gum
2) Lingual Nerve
- Sensory: Ant. tongue
3) Auriculotemporal Nerve
- Sensory: Ear, temple, scalp, TMJ
What is the route of the Abducens Nerve?
Lower pons
Runs up to Cavernous Sinus
Sup. Orbital Fissure
Function of Abducens Nerve?
Innervates Lateral Rectus of eye (abducts eye)
