H&N 4.1 cranial nerves Flashcards
How many cranial nerves are there?
12 pairs (24)
Where do they arise from?
Mainly the brainstem, some directly off the brain
What’s a difference between the arrangement of the spinal nerves and the cranial nerves?
Spinal nerves arise at regular intervals, cranial nerves do not
Are the cranial nerves part of the central or peripheral nervous system?
peripheral
What are the different types of fibres that cranial nerves carry?
- general sensory
- special sensory
- motor
- autonomics (hitchhike)
What are the parts of the brain stem?
- midbrain
- pons
- medulla
How many cranial nerves come from each part of the brain stem?
forebrain-2
midbrain-2
pons-4
medulla-4
What nerve is CN1?
olfactory nerve
What is the course of the olfactory nerve?
- from the nasal mucosa
- through the cribriform plate of the ethmoid bone
- to the olfactory bulb
- along the olfactory tracts
- to the forebrain
What fibres does CN1 carry?
Therefore, what is it’s function?
Special sensory- conveys the sense of smell.
How would you test CN1?
test one nostril at a time, to see if the patient could smell certain smells, such as coffee.
Not formally tested
What is the result of damage to the olfactory nerve?
Anosmia
What are some different causes of anosmia?
- temporary eg due to a virus
- degenerative- for example alzhaemiers
- permanent (eg if there has been trauma which has damaged the olfactory nerve)
- congenital (eg Kallman’s syndrome)
What is Kallmann’s syndrome?
a chromosomal abnormality leading to malformation of the hypothalamus which leads to lack of GnRH release, and also anosmia.
How can trauma lead to damage of the olfactory nerve?
blunt trauma will cause movement of the brain within the cranial cavity, which may cause the cribriform plate to shear the olfactory nerves, leading to anosmia.
What nerve is CN2?
optic nerve
What is the route of the optic nerve?
From the retina
optic canal
through the optic chiasm
optic tracts
forebrain
What’s anatomically important about the optic chiasm?
It lies very close to the pituitary gland, so any tumour etc can compress the optic chiasm and affect sight.
What nerve fibres are contained in CN2?
What is its function?
- special sensory
- sight.
How would you test the optic nerve?
Visual acuity (letter charts)
visual fields
pupillary reflex.
Describe the pupillary reflex.
When bright light is shone in the eye, the optic nerve conveys this to the brain, this stimulates the parasympathetic nerve fibres on the occulomotor nerve to carry a signal to cause pupilalry constriction.
Why do patients with meningitis suffer from photobia?
meningitis causes inflammation of the meninges, the covering of the brain.
The optic nerve is a direct extension of the brain, so the inflammation will cause impingement of the nerve, so sight will be affected. light causes irritation, becuase the signals have to travel down an injured nerve.
How can you visually see the optic nerve?
Via a fundoscope, seen as the optic disc.
What nerve is CN3?
Occulomotor nerve.
What is the route of CN3?
arises from the midbrain
through the cavernous sinus
travels through the superior orbital fissue to enter the orbit.
What nerve fibres does the occulomotor nerve carry?
What’s its function?
Motor
(autonomics hitchhike)
movement of the eyeball (and constriction of the pupil in response to light)
What muscles are innervated by the occulomotor nerve?
- medial rectus
- superior rectus
- inferior rectus
- inferior oblique
- levator palpabrae superioris
How can you test the occulomotor nerve?
Test eye movement asking the patient to follow a H shape.
Also test the pupillary light reflex.
ask patient to open eyes against resistance.
What’s the function of levator palpabrae superioris?
to elevate the superior eyelid.
What happens when there is damage to the occulomotor nerve?
- down and out position
- diplopia
- dilated pupil
- ptosis of the eye
What is ptosis?
How can it be further classified?
dropping of the upper eyelid.
Full ptosis- closed eye
partial ptosis- partially closed.
What are some causes of occulomotor lesions?
trauma
raised ICP
cavernous sinus thrombosis
diabetes
In raised ICP, what changes to the eye would you see first and why?
Blown pupil (excessive dilation). The parasympathetics run on the outside of the occulomotor nerve, so will be affected first.
What nerve is CNIV?
trochlea nerve
What is the route of the trochlea nerve?
Comes from the midbrain, but dorsally, so has a long course. (longest CN)
through the cavernous sinus,
What fibres does the trochlea nerve carry?
What’s it’s function?
motor only
movement of the eye
What muscle(s) does the trochlea nerve innervate?
The superior oblique muscle.
How do you test the trochlea nerve?
eye movements, using the H shape.
What would you see in a patient with trochlea nerve damage?
What would the patient complain of?
Slight tilt of the head to compensate for the loss of innervation to the superior oblique.
Patient would complain of diplopia thats worse when reading/going down stairs.
How can damage to the trochlea nerve occur?
trauma or raised ICP common (due to long course of nerve it’s commonly affected)
congenital palsies.
What nerve is CNV?
Trigeminal nerve
What’s are the 3 main branches of the trigeminal nerve?
opthalmic
maxillary
mandibular
What’s the route of the 3 branches of the trigeminal nerve?
opthalmic- through the cavernous sinus and through the superior orbital fissure
maxillary- through the cavernous sinus and then through the foramen rotundum
Mandibular- through the foreamen ovale.
What fibres are carried by the trigeminal nerve?
What’s it’s function
Mainly general sensory- provides mostof the sensation over the face
Motor- along the mandibular nerve, innervate the muscles of mastication
How do you test the trigeminal nerve?
Test light touch over the areas of the face (the forehead, the cheeks and the chin).
Ask pateint to clench teeth and feel for the muscles of mastication, or observe them chewing something.
corneal reflex
What is trigeminal neuralgia?
sudden severe facial pain that comes in attacks for brief periods. Often caused by compression of the trigeminal nerve,
What is the corneal reflex?
A rapid protective reflex which causes blinking when the eye detects a threat.
Afferent limb- opthalmic branch of CNV.
Efferent- facial nerve.
What nerve is CN VI?
Abducens nerve
What is the route of abducens nerve?
Arises from the pons,
Goes through the cavernous sinus
Enters orbit through superior orbital fissure
What fibres are carried on abducens nerve?
What’s it’s function?
motor only.
Innervates a muscle involved in movement of the eye.
What muscle is innervated by abducens nerve?
lateral rectus muscle
How can you test abducens nerve?
test eye movements.
How could abducens nerve be damaged?
Raised ICP
runs under the surface of the pons so is suceptible to stretching
What would be the features of damage to abducens nerve?
diplopia
one eye would drift towards the midline (obvious deformity)
What nerve is CNVII?
Facial nerve
What is the route of the facial nerve?
Very complex!
Involves travelling through the internal accoustic meatus, going through the petrous part of the temporal bone and through the styloid foreamen, before braching.
What nerve fibres are carried on the facial nerve?
motor- muscles of facial expression, stapedius
special sensory- taste (anterior 2/3 of tongue)
autonomics- lacrimal glands
What are the 3 major intracranial branches of the facial nerve?
greater petrosal nerve
nerve to stapedius
chorda tympani
What nerve is CN VIII?
Vestibulocochlea nerve
Whats the route of the vestibulocochlea nerve?
Through the internal accoustic meatus.
What fibres run with the vestibulocochlear nerve?
What’s it’s function?
Special sensory fibres only
Allow us to hear sound, and balance.
How do we test the vestibularcochlear nerve?
Test hearing (Rinne and webers test)
Test balance
What will damage to CNVIII lead to?
Hearing loss
loss of balance,
vertigo, tinnitus
What is an accoustic neuroma?
a benign growth within the IAM/on the vestbiulocochlear nerve, and cause changes to hearing and balance.
What nerve is CN IX?
Glossopharyngeal nerve.
What is the route of the glossopharyngeal nerve?
Runs through the jugular foreamen.
What nerve fibres are within the glossopharyngeal nerve?
motor- stylopharyngeus
special sensory- taste to posterior 1/3 tongue
general sensory-soft palate, tonsils, oropharynx, tympanic membrane, Carotid body and sinus.
autonomic- parotid gland.
What is the function of the stylopharyngeus muscle?
elevates the larynx and pharynx and allows swallowing.
How can you test the function of CN IX?
could test the gag reflex (not formally tested)
Could test taste (not formally tested)
describe the gag reflex.
contraction of the back of the throat evoked by toushing posteior tongue, uvular, tonsils, back of throat.
Afferent- glossopharyngeal
Efferent- motor nerves of vagus nerve to contract.
What nerve is CN X?
Vagus nerve
What is the route of the vagus nerve?
Travels through the jugular foreamen,
Goes through the carotid sheath, into the neck.
What fibres are carried on the vagus nerve?
general sensory- laryngopharynx, larynx, small part of ear
motor- muscles of larynx, pharynx and soft palate
autonomic- parasympathetic to thorax and abdominal viscera.
How can you test the vagus nerve?
Test speech
test the gag reflex
test swallowing
test coughing
What would be a visible finding of a damaged vagus nerve/
deviated uvula when saying ahhh.
Uvula would be deviated away from lesion.
What is the signifance of the recurrent laryngeal nerve in the neck?
It’s a branch of the vagus nerve on the right side.
It loops under the right subclavian artery and ascends to the larynx, where it innervates most of the intrinsic muscles, including the vocal chords]
How could you tell if the recurrent laryngeal nerve was damaged
There’s be a hoarseness of voice, due to loss of innervation of the vocal cords.
What’s the course of the left recurrent laryngeal nerve?
Turns underneith the arch of the aorta.
What nerve is CN XI?
the spinal accessory nerve
What is the course of the spinal accessory nerve?
Courses through the jugular foreamen and then travels down through the posterior triangle.
What is the function of the spinal accessory nerve.
What nerve fibres does it carry?
motor nerves, innervates the trapezius and sternocleidomastoid muscles.
How can you test CN XI?
By asking patient to turn head against resistnace and shrug shoudlers against resistnace.
What nerve is CN XII?
hypoglossal nerve.
What is the route of the hypoglossal nerve?
through the hypoglossal canal, then runs medial to the angle of the mandible, and crosses the internal and external carotid arteries.
What nerve fibres does the hypoglossal nerve carry?
What’s it’s function?
motor fibres to innervate the muscles of the tongue.
What would be seen in damage to the hypoglossal nerve?
wasting of the tongue on teh affected side and deviation towards the affected side.
When is the hypoglossal nerve at risk of damage?
When doing surgery on the carotid arteries.
