Lecture 8 - CN I - V Flashcards
Which 2 cranial nerves arise from the forebrain ?
CN I - Olfactory
CN II - Optic
Purely special sensory cranial nerves
CN I- Olfactory
CN II - Optic
CN VIII - Vestibulocochlear
Motor cervical nerves
CN III - Occulomotor CN IV - Trochlear CN VI - Abducens CN XI - Spinal accessory CN XII - Hypoglossal
Cervical nerves that carry autonomics
CN III - occulomotor
CN VII - facial nerve
CN IX - glossopharyngeal
CN X - vagus
Brain stem
Joins the brain to the spinal cord
Regulates cardio- resp function and maintains consciousness
Contains ascending sensory fibres and descending motor fibres
What makes up the brainstem?
Midbrain
Pons
Medulla
Course of the olfactory nerve
- Olfactory nerve in the roof of the nasal canal
- Enters the cribriform plate of the ethmoid bone
- Olfactory bulbs to olfactory tracts
- To temporal lobe
Function of the olfactory nerve
Olfaction (smell)
CN I test
Change in sense of smell
Anosmia - loss of sense of smell
Commonest cause of anosmia
URTI (cold)
Causes of anosmia
URTI
Head injury - basilar skull fracture
Tumour at base of frontal lobe
Route of the optic nerve
- Retinal ganglion cells at the optic disc have axons that converge into the optic nerve
- Enters the optic canal
- Fibres cross at the optic chiasm
- Optic tracts enter the primary visual cortex in the occipital lobe
Sight when there is a lesion in 1 optic nerve?
Only the ipsilateral eye sight is affected
Sight when there is a lesion in the optic chiasm
Sight in both eyes are affected
What can pituitary tumours course?
Compression on the optic chiasm
- Bitemporal hemianopia
CN II tests
Visual acuity test - Snellen test
Visual field test
Pupillary light response
Optic disc visualised by a opthalmoscope
CN II function
Sight
Afferents of the pupillary light response
Papillodema
Swollen optic disc
Photophobia
The optic nerve carries extensions of the meninges
Raised intracranial pressure can cause disruption to the nerve causing photophobia - trait of meningism
Communication of the optic nerve with the midbrain
Communication from the optic tract with the brainstem midbrain to allow the pupillary reflex to light
- Occulomotor nerve is stimulated to constrict the pupil
Route of the occulomotor nerve
- Midbrain
- Lateral wall of the cavernous sinus
- Superior orbital fissure
- To the extra-ocular muscles except the superior oblique and lateral rectus muscles, levator palbebrae superioris
Muscles that CN III control
Superior rectus
Inferior rectus
Medial rectus
Inferior oblique
Levator palpebrae superioris
Parasympathetic innervation to the sphincter pupillae muscle
CN III role
Eye movements
Raise eyelids
Constrict the pupil
Efferent limb of the pupillary light response
Why is the occulomotor nerve vulnerable to compression
During raised intracranial pressure, the uncus can herniate and compress the nerve.
Between the tentorium cerebelli and uncus
What can happen in CN III external compression
Pupil dilation as the parasympathetic fibres are on the periphery of the nerve that innervate the sphincter pupillae
CNIII tests
Eye movements - follow finger
Inspect eyelids and pupil size
Pupillary light reflex
Presentation of CNIII lesion
Eye in down and out position
Pupil dilation
Complete ptosis
Diplopia
Causes of CN III injury
External compression: Raised intracranial pressure: -tumour -haemorrhage Aneurysm Cavernous sinus thrombosis
Internal compression:
Vascular secondary to:
- diabetes
- hypertension
(pupil sparring)
Route of the trochlear nerve
- Mid brain
- Through the lateral wall of the cavernous sinus
- Through the superior orbital fissure
- To the superior oblique extraocular muscle
Role of CN IV
Eye movement - superior oblique muscle
CN IV test
Eye movement test - follow finger
Why is the trochlear nerve most susceptible to damage
Arises from the dorsal aspect of the brain stem and hooks around therefore has a long intracranial course
Presentation of CN IV lesion
Up and in eye position
Diplopia
3 branches of the trigeminal nerve
Opthalmic
Maxillary
Mandibular
Role of the trigeminal nerve
General sensation to the: - face - part of scalp - paranasal air sinuses - nasal cavity - oral cavity - anterior 2/3rds of tongue meninges
Motor innervation to the muscles of mastication
Opthalmic general sensory structures
Forehead
Upper eyelid
Medial nose
Maxillary general sensory structures
Cheek
Lower eye lid
Lateral nose
Mandibular general sensory structures
Lower lip
Jaw and chin
Lateral head and ear
Route of Va
- Pons
- Trigeminal ganglion
- Va through the superior orbital fissure
- To orbit
Route of Vb
- Pons
- Trigeminal ganglion
- Vb through foramen rotundum
- To the pterygopalatine fossa
Route of Vc
- Pons
- Trigeminal ganglion
- Vc through the foramen ovale
- To the infratemporal fossa
Which branch of the trigeminal nerve supplies motor innervation to the muscles of mastication?
Vc - Mandibular
CN V test
Sensation in dermatomal areas of Va, b and c
Check the function of the muscles of mastication
Check the corneal reflex - blinking (afferent limb)
Conditions involving the trigeminal nerve
Trigeminal neuralgia
Shingles - sight threatening with vesicle scars
Orbital/facial trauma - can affect the inferior orbital and superior alveolar nerve
Branches of the opthalmic nerve
Frontal nerve: - Supraorbital - Supratrochlear Lacrimal nerve Nasociliary
Branches of the maxillary nerve
Infraorbital nerve - cheek and lower eyelid
Superior alveolar nerve - upper lip, teeth and gums
(nerve blocker used by dentists)
Branches of the mandibular nerve
Inferior alveolar nerve - Lower lip, teeth and gums
(continues as the mental nerve)
- Auricotemporal - ear, temples and TMJ
- Lingual - anterior 2/3rds of the tongue
Which nerve is susceptible to damage in a mandibular fracture
Inferior alveolar nerve