4. Cranial Nerves I-VI Flashcards
what are cranial nerves?
Supplying tissues and structures of head and neck region including special sense organs
(Except vagus which supplies other areas too)
Which nervous system are cranial nerves part of?
Peripheral
Where can cranial nerves be damaged?
Cranial nerve during its route outside the CNS
The brainstem where nuclei are located
The tracts within forebrain which communicate with cranial nerves
What are the first 2 cranial nerves?
Extension of the forebrain
Where do the cranial nerves arise from?
2 from forebrain
2 from midbrain
4 from pons
4 from medulla
What is CN1?
Olfactory nerve
- special sense smell
What are the causes for damage to CN1?
Upper respiratory tract infection
Head/facial injury
Anterior cranial fossa tumours
Where do CN1 extensions pass through?
Cribiform foramina in ethmoid bone
What is CNII?
Optic
- special sense vision
How do you test CNII?
Pupillary size and response to light
Visual acuity (Snellen chart) and visual fields
Ophthalmoscopy
What are the signs and symptoms of damage to optic nerve?
Blurred vision involving one eye or complete absence of vision in one eye
On clinical examination: abnormalities in pupillary size and reflex, poor visual acuity, pathology involving optic nerve
What diseases or conditions can involve the optic nerve?
Optic neuritis
Anterior ischaemic optic neuropathy
Papilloedema due to raised intracranial pressure
What is CNIII?
Oculomotor (motor and parasympathetic)
What does CNIII innervate?
Extra ocular muscles
Levator palpebrae superioris
Sphincter pupillae (muscle in iris)
How do you test for CNIII?
Inspection of resting gaze
Eye movements, pupils and pupillary light reflexes, eyelid position
What would be present on examination of CNIII if damaged?
Ptosis
Abnormal position of eye (down and out)
Pupil may or may not be dilated
Double vision
What are the causes of a CNIII lesion?
Micro vascular ischaemia: >50 years, diabetes/hypertension
Compressive: aneurysmal posterior communication artery (headache/retroorbital pain), head injury, tentorial herniation secondary to increased ICP
Where can CNIII be damaged?
Brainstem
By free edge of tentorium cerebelli
Cavernous sinus
What is CNIV?
Trochlear (motor)
What does CNIV innervate?
Superior oblique muscle
How do you test for CNIV?
Inspection of resting gaze, eye movements
What signs or symptoms can you get with CNIV lesion?
Double vision
Abnormal eye position
Head tilt
What can cause CNIV lesion?
Congential
Micro vascular ischaemia (diabetes, hypertension)
Trauma
Tumour
Where can CNIV be damaged?
Midbrain
Cavernous sinus
What is CNVI?
Abducens (motor)
What does CNVI innervate?
Lateral rectus
How do you test for CNVI?
Inspection of resting gaze, eye movements
What can lesion of CNVI present as?
Double vision - worsen in lateral always gaze
Abnormal eye position
Difficulty/unable to move affected eye laterally
What can cause a CNVI lesion?
Micro vascular ischaemia (diabetes/hypertension)
Head injury, tumour
Raised ICP
Which cranial nerves take a very similar pathway and what is the pathway?
Oculomotor
Trochlear
Abducens
Exit brainstem, pass through cavernous sinus, enter into orbit via superior orbital fissure
What is CNV?
Trigeminal (motor and general sensory)
Where does the trigeminal nerve generally supply?
Branches have an extensive distribution supplying skin of the face and scalp and deep structures of the face
Muscles of mastication
Where does the trigeminal nerve originate?
Pons
What are the 3 divisions of the trigeminal nerve?
Ophthalmic
Maxillary
Mandibular
How do you test for CNV?
Light touch on dermatomes, muscles of mastication and corneal reflex
What will patients with trigeminal nerve lesion present with?
Sensory deficits within the dermatomal regions
Weakness in muscles of mastication
Absent corneal reflex
What are some conditions associated with trigeminal nerve lesion?
Trigeminal herpes zosta (shingles) - in subdivisions
Trigeminal neuralgia (compression from blood vessel)
Orbital and mandibular fractures
Posterior cranial fossa tumours
Where do subdivisions of trigeminal nerve run through?
Ophthalmic - cavernous sinus, superior orbital fissure
Maxillary - cavernous sinus, foramen rotundum, infra-orbital foramen
Mandibular - foramen ovale
What are the distal brands of the ophthalmic division of the trigeminal nerve?
Frontal nerve - gives rise to supraorbital/supratrochlear
Nasociliary nerve
Lacrimal nerve
What are the distal branches of the maxillary division of the trigeminal nerve?
Infra-orbital
Superior alveolar nerves
What are the distal branches of the mandibular division of the trigeminal nerve?
Auriculotemporal nerve
Lingual nerve (tongue)
Inferior alveolar nerve and mental nerve
Which nerve is vulnerable in mandibular fractures?
Inferior alveolar nerve
