Cranial Nerves I-VI Flashcards
How many cranial nerves do we have?
12 pairs
What is the brainstem?
The brainstem adjoins the brain to the spinal cord and is continuous with the spinal cord caudally.
It has a vital role in the regulation of cardio-resp functions and maintaining consciousness.
Ascending sesory and descending motor fibres between brain and rest of the body run through brainstem
Location of majority of cranial nerve nuclei
What are the three parts of the brainstem?
Midbrain
Pons (transverse fibres - connects to cerebellum)
Medulla
What are structures called if they arise from above brianstem?
Forebrain
What is cranial nerve I?
Olfactory nerve
What type of nerve is the olfactory nerve I?
A special sensory nerve
What does the olfactory nerve do?
Olfaction (sense of smell)
What is the course of the olfactory nerve?
Olfactory neurones to roof of nasal cavity
Through olfactory foramina in the cribriform plate of the ethmoid bone
Olfactory bulb (where cell bodies are)
Olfactory tract
Temporal lobe
What is anosmia?
Loss of sense of smell
How do you test CN I?
Not formaly tested - ask about changes smell and taste. (can also rise smelling salts).
Must test one nostril at a time because we have two nerves,
When is anosmia significant?
Head injury - secondary to shearing forces and / or a basilar skull fracture.
Also tumours at the base of the frontal lobes (within the anterior cranial fossa) may also involve CN I and cause anosmia.
What is CN II?
Optic nerve
What does CN II do?
Helps you see - part of the visual pathway
What is the visual pathway?
Impulses generated by cells within the retina in response to light: generates action potentials which propagate along the optic nerve,
Via other components of the visual pathways, they reach primary visual cortex where they are perceived as vision.
What is the pathway of CN II?
Retinal ganglion cells
Axons form optic nerve
Exit back of orbit via optic canal
Fibres cross and merge at optic chiasm
What kind of visual field loss do you get if there is optic nerve damage?
One sided because usually one one optic nerve is damaged.
What kind of visual field loss do you get if there is optic chiasm damage?
Bilateral (bilaterally anywhere after chiasm) - follow different patterns depending on where about in the visual pathway the damage is.
How can a pituitary tumour affect vision?
Compress optic chiasm and therefore cause bilateral visual symptoms (bitemporal hemianopia)
How day uni test the function of CN II?
Visual acuity tests (opticians) - Snellen chart, checking visual fields, testing pupillary responses,
It is also the only nerve you can see directly with an ophthalmoscope - The optic disc is the point at which the nerve enters the retina.
What is papilodema?
Swelling of optic disc due to raised ICP
This occurs because the optic nerve carries an extension of the meninges.
You can see this in a fundoscopy.
Why is there communication from the optic tracts with the brainstem?
To allow for visual reflexes - pupillary light reflexes
What is CN III?
Oculomotor nerve
What type fo nerve is CN III?
Motor and it also carries some autonomic parasympathetic fibres
What is the route of the oculomotor nerve?
Midbrain
Lateral wall of cavernous sinus
Superior orbital fissure
What does the oculomotor nerve do?
Innervates most of the muscles that move the eyeball (extra-ocular muscles)
Innervates the muscles of the eyelid (LPS)
Innervates the sphincter pupae muscle which constrict pupil (autonomic)
Innervates ciliary muscle (autonomic)
Where is the oculomotor nerve vulnerable to compression?
Between the tentorium cerebelli and part of the temporal lobe when the intracranial pressure is raised.
Tested by seeing if the pupil is blown - see if they are equal and reactive.
How do you test function of CN III?
Inspect eyelid and pupil size, test eye movements and pupillary reflexes
What can pathology of the oculomotor nerve cause?
Pupillary dilation and / or double vision (diplopia)
Down and out position with severe ptosis is the key sign.
What could cause injury or pathology of the CN III?
Raised intecranial pressure, Aneurysms, Cavernous sinus thrombosis - as there all cause compression of the external nerve
Vascular - secondary to diabetes or hypertension, Typically pupil sparing.
What is CN IV?
Trochlear nerve
What type of nerve is CN IV?
Purely a motor nerve
What does CN IV do?
Innervates one of the muscles that moves the eyeball (extra-ocular muscles)
- Superior oblique
What is the route of CN IV?
Midbrain
Cavernous Sinus
Superior orbital fissure
(same as CN III)
It has the longest intracranial course and is the only nerve to emerge from the dorsal aspect of the brainstem.
How do you test the function of CN IV?
You test the function bu testing eye movements - This tests III,IV,VI at the same time
How does a patient this CN IV pathology present?
Diplopia (double vision) - worse on downwards gaze e.g. when reading, walking downstairs
What is CN V?
Trigeminal nerve
What are the three branches of CN V?
Ophthalmic (Va)
Maxillary (Vb)
Mandibular (Vc)
Where does CN V come from?
Midbrain
Route of Va?
Cavernous Sinus
Superior orbital fissure
Orbit
Route of Vb?
Cavernous sinus
Foramen rotundum
Pterygopalatine fossa
Route of Vc?
Foramen vale
Infratemporal fossa
What type of nerve is V?
Both general sensory and motor
What does V do?
- Main sensory nerve supplying skin of face and part of scalp
- Sensory to deeper structures within the head e.g. paranasal air sinus, nasal and oral cavity, anterior part of tongue (general sensation, not taste), meninges
- Motor to muscles of mastication (Vc only)
How do you test CN V?
Sensation in dermatomes, test muscles of mastication (jaw jerk), and corneal reflex (blinking)
Why are corneal ulcer painful?
There are lots of fibres on the cornea so a lot of pain receptors.
What are the branches of the maxillary division of the trigeminal nerve?
Infraorbital nerve - runs through floor of the orbit and carries sensory information from areas of the cheek and lower eye lid. It is susceptible to injury in orbital floor fractures.
Superior alveolar nerve - Carries sensory information from the upper teeth and gums. It is the nerve in which nerve blocks are inserted by dentists.
What are the branches of the mandibular division of the trigeminal nerve?
Inferior alveolar nerve - goes through bony canal in mandible and exits as mental nerve (via mental foramen). It carries sensory information from area of mental protuberance (chin), lower lip and gum. It is susceptible to injury in mandibular fractures.
Lingual nerve - general sensory from anterior 2/3rd of tongue.
Auriculotemporal nerve - general sensory from part of ear, temple / lateral head and scalp and TMJ.
What is CN VI?
Abducens nerve
What is the route of CN VI?
Lower pons (junction between pons and medulla)
Runs upwards before being able to pass into cavernous sinus
Enters into orbit via superior orbital fissure.
What type of nerve is the abducens?
Motor
What does CN VI do?
Innervates one muscle that moves the eye (extra ocular muscle) - lateral rectus
How do you test CN VI?
Eye movements (tests III, IV, VI)
What is CN VI susceptible to injury in raised intercranial pressure?
As it emerges anterior, at ponto-medullary junction before running under the surface of the pons upwards towards cavernous sinus.
Patients present with diplopia
