Cranial nerves Flashcards
How do cranial nerves exit in relation to their corresponding vertebra? Which cervical nerve is somewhat of an exception and why?
Cervical spinal nerves emerge above their corresponding vertebral body EXCEPT C8 which emerges below the C7 vertebra (between C7 and T1) as there is no C8 vertebra
Where are the cell bodies of cranial nerves and where are the nerves themselves located? kind of nerves are the cranial nerves?
Cell bodies in the brain but actual nerves are peripheral nerves (not part of CNS)
What are the collections of cell bodies called in the CNS and PNS?
CNS: Nuclei
PNS: Ganglia
Which cranial nerves are atypical and why?
CN I and II which are part of the brain tract, so they are an extension of the brain
Which cranial nerves are autonomic?
Autonomic: CN III, VII, IX, X
Why is the accessory nerve sometimes called the spinal accessory nerve?
As it has a cranial portion/root which joins VAGUS and provides part of its motor component
Which general location do all (non atypical) cranial nerves originate from? Which specific cranial nerves originate from where?
The brain stem (midbrain, pons and medulla)
Midbrain: III and IV
Pons: V, VI, VII, VIII
Medulla: IX, X, XI, XII
What is the function of CN I and where is it located?
Sensory: detects sense of smell
Starts at the olfactory mucosa (superior portion of nasal cavity) where the olfactory receptors neurones are
Ascends through cribriform plate of ethmoid bone
Forms the olfactory bulb (swelling of olfactory nerve) -> Olfactory tract
What is the term given for a sense of bad smell not related to a specific odour?
Kakosmia
Name four things that can damage CN I
- Trauma (i.e fractures to cribriform plate)
- Meningitis
- Upper resp tract infection
- Nasal polyps/rhinosinusitis
Define rhinosinusitis
Inflammation of nasal cavity and sinuses
What three things could you use to test one’s sense of smell?
Vanilla, coffee and orange
*test each nostril separetely!
Which of the cranial nerves are purely sensory?
CN I, II, VIII
What is the function of CN II? Briefly describe its course
Sight
Retina -> optic canal -> optic chiasma -> optic tract -> primary visual cortex (occipital lobe)
What structure is the optic chiasma directly superior to? Which major blood vessel runs below and lateral to it?
The pituitary gland is immediately below
The ICA is below and lateral
Name five ways to examine the integrity of the optic nerve, what specific tools might be used to test them if any?
- Visual acuity: snellen chart
- Color vision
- Visual fields
- Papillary reflexes
- Fundoscopy: looking in back of eye at optic disc (i.e for swelling/papilloedema)
Which cranial nerves are involved in papillary reflex?
CN II: afferent nerve sensing sensory info from retina-> brain
CN III: efferent nerve
Which cranial nerves are purely motor?
CN III, IV, VI, XII
What does CN III originate from and which foramen does it pass through to exit the skull? Which muscles does it provide somatic and visceral motor innervation?
Goes from the oculomotor nucleus (in the midbrain) -> superior orbital fissure ->
Somatic: 4/6 Oculomotor muscles
a) Moving the upper eyelid: levator palpabrae superioris
b) Moving the eyeballs: Superior, inferior, medial rectus. Inferior oblique
Visceral/Parasympathetic: sphincter pupillae (constricts during PS stimulation) and ciliary muscle of the eye (changes the lens)
Name the extra ocular muscles and work out how each muscles will move the eye if moving individually. Which cranial nerve supplies the majority of them?
Superior rectus: up
Medial rectus: medial
Inferior rectus: down
Lateral rectus: lateral
Inferior oblique: up, out and external rotation
Superior oblique: down (depression), in (ABduction) and internal rotation
Levator Palpebrae superioris: lifts the upper eyelid
Majority supplied by CN III
Which extraocular muscles does CN III NOT supply? Which cranial nerves do supply these muscles?
Superior oblique (CN IV) and the lateral rectus (CN VI)
What is the classical presentation of a damaged oculomotor nerve?
- Eye is down and out
- Ptosis: droopy eyelid
- Mydriasis: Lone dilated pupil
How can the function of CN III be tested and which reflexes would be absent in a lesion?
- By testing the eye motor movements: ask patient to follow ‘H’ drawn with finger
- Absent pupillary light reflex (paralysis of constrictor muscles)
- Absent accommodation reflex (paralysis of ciliary muscles)
What might cause damage to CN III
- Aneurysm
2. Increased intracranial pressure
What does CN IV supply and what is its course?
Just supplies superior oblique muscle; helps eye look down (and in) on its own
Extends from the trochlear nucleus -> dorsal midbrain -> cavernous sinus -> enters orbit of eye through superior orbital fissure -> superior oblique muscle
Which CN is the only one to emerge from the brain dorsally?
Trochlear: CN IV
Which structures travel through the cavernous sinus?
Therefore, name one pathology that can affect any one of these structures
Cavernous sinus thrombosis can affect any of these structures
IT OAT Trochlear nerve CN IV Abducens nerve CN VI Oculomotor nerve CN III Trigeminal V1 and V2 Internal carotid artery
Generally, what two symptoms should you look out for that may indicate a lesion with a cranial nerve?
Diplopia: difficulty walking down stairs (due to vision problems)
Very subtle head tilt: trying to realign their eyes
What does CN VI do/innervate and where is it?
Lateral eye movement (abducts-Abducens nerve)
Goes from Abducens nucleus (in the pons) -> SOF -> to the lateral rectus muscle of the eye
How would someone with a lesion in CN VI present? Why might a patient have a false localizing sign?
Cross eyed and can’t draw ‘H’: Can’t abduct their eye
‘False Localising Sign’: problem may be on the opposite side than expected as the nerve has a very long course and the brainstem is small (so compression from one side may affect structures on both of the brainstem’s sides)
What should you suspect in a child with a CN VI lesion until proven otherwise?
A brain tumour
Which cranial nerves are mixed sensory and motor nerves
CN V, VII, IX, X
Where is CN V and what does it innervate?
Supplies muscles of mastication and general face sensation
From the Pons: trigeminal sensory nuclei -> trigeminal ganglion -> branches V1,2,3
Which foramina does each of the three branches of CN V use?
Include the names of the branches (other than just numbers)
V1 Ophthalmic: Superior orbital fissure
V2 Maxillary: Foramen rotundum
V3 Mandibular: foramen ovale
Which of the branches of CN V are sensory and which are motor? Which sensations and/or motor abilities do they supply if any?
Sensory:
V1 - around the eye and forehead
V2: sensation to rest of face (including cheek area)
V3: sensory and motor
- sensory to the chin
- Motor: muscles of mastication
What is characteristic of trigeminal Neuralgia?
Sharp pain from the jaw which may be due to light touching or without any stimuli
What happens in a corneal reflex and which cranial nerves supply the afferent and efferent branches of the reflex?
Blinking in response to cornea stimulation
Afferent: CN V1
Efferent: CN VII
What might a dentist do before working on someone’s mouth and why?
Inferior alveolar nerve block: Anaesthetic to the Mandibular foramen to anesthetize the mandibular nerve (and teeth, jaw, etc)
Name three ways a patient with a CN V lesion may present
- Clenched jaw muscles
- Jaw jerk reflex: temporalis and masseter should contract in response to lower jaw tapping
- Sensory deficits
What is the function of CN VII? (special sensory, somatic motor, visceral motor, somatic sensroy, visceral sensory, etc?
Special sensory: anterior 2/3 of tongue for taste and small sensory branch to the ear/stapedius
Somatic sensory: Posterior auricular supplies sensation to external ear canal
Somatic motor: muscles of facial expressions
Parasympathetic:
- salivation: submandibular and sublingual glands
- nasal, palatine and pharyngeal mucous glands
- Lacrimal glands
Describe the pathway of CN VII
Pons -> internal acoustic meatus (1cm opening in the petrous part of temporal bone) -> Facial canal:
Inside the facial canal:
- Nerve forms the geniculate ganglion
- Nerve gives rise to
- greater petrosal n: parasympathetic fibres to mucous glands and lacrimal glands
- nerve to stapedius: motor fibres to stapedius muscle of middle ear
- chorda tympani: anterior 2/3 of tongue and parasympathetic to salivary glands
Exits facial canal and cranium via the stylomastoid foramen -> turns superiorly and runs anterior to the outer ear
Gives Off
- posterior auricular: motor innervation to some muscles around the ear
- Nerves to digastric (posterior belly)
- Nerves to stylohyoid
Continues anterior and inferior into the parotid gland and terminates by splitting into 5 branches: To Zanzibar by motor car
- temporal
- zygomatic
- buccal
- marginal mandibular
- cervical
Which structures pass through the internal acoustic meatus?
CN VII and CN VIII
What is the most common condition arising from a lesion of CN VII and what presentation is it characterized by?
Bell’s palsy: idiopathic one-sided facial paralysis
Name four general causative agents you could consider when diagnosing Bell’s palsy
- reminder: it’s a diagnosis of exclusion
1. Surgery
2. Tumours
3. Fractures
4. Infection
How would you examine someone with suspected Cbn VII lesion? (i.e Bell’s palsy?)
- Look for facial asymmetry
- Can test taste
- Tear production
Which branches of the CN VIII are responsible for which functions?
Vestibular branch: balance
Cochlear branch: hearing
Describe the course of CN VIII
- Both branches (vestibular and cochlear) combine in the pons to form the vestibulocochlear nerve
- Emerges from the brain at the cerebellopontine angle
- Exits the cranium via the internal acoustic meatus (with CN VII), and within the distal aspect of IAM it splits to form the vestibular and cochlear nerve -> semicircular canals in inner ear and cochlea respectively
Describe the course of CN IX. What is its function? (special sensory, somatic motor, visceral motor, etc..)
Medulla oblongata -> leaves cranium via jugular foramen
- Somatic sensory: tympanic nerve to middle ear
- Visceral motor; Auriculotemporal nerve to parotid
Extracranial: descends down neck
3. Somatic motor:
stylopharyngeus
4. Visceral sensory: carotid sinus nerve to carotid sinus and body
Enters pharynx and terminates by giving off 3 branches (lingual, tonsil and pharyngeal branches)
5. Special and somatic sensory to the posterior 1/3 tongue
Which structures pass through the jugular foramen?
CN IX, X, XI and the internal jugular vein
Which nerves compose the afferent and efferent branches for the carotid sinus?
Carotid sinus:
Afferent: IX
Efferent: VAGUS
What symptom might a patient with a lesion in CN IX present with?
Dysphagia - as the pharynx is affected
What is the function of CN X? (somatic motor, visceral motor, etc)
Somatic sensory: auricular branch to external ear
Somatic motor: soft palate, larynx and pharynx (pharyngeal branches and R/L recurrent laryngeal)
Special sensory: taste over epiglottis
Visceral motor: bronchoconstriction, peristalsis (branches to esophagus, stomach, small/large bowels), vomiting and bradycardia (cardiac branches)
Visceral sensory: aortic arch/body (cardiac branches)
Where on the brainstem is the CN X nucleus? Where in the skull does this cranial nerve exit?
Nucleus is in the Medulla
Exits cranium via the jugular foramen
At which point of the intestines does innervation from the Vagus nerve stop?
The splenic flexure
Clinically, what nerves would you test VAGUS with?
CN IX
Which nerves contribute to the gag or pharyngeal reflex?
How should the palate appear normally and how might it appear if there is a lesion on one side (R/L recurrent laryngeal)
Afferent: CN IX
Efferent: CN X
Palate should be symmetrical, if there is a lesion the uvula will move AWAY from the lesion side as the muscles on the other side are functional and pull it
What two symptoms might indicate a lesion in the recurrent laryngeal nerves?
Hoarseness and bovine cough
What would happen if you performed a carotid sinus massage in a patient with a CN X lesion?
Vasovagal syncope
Where anatomically do the L and R recurrent laryngeal nerves branch off VAGUS?
L: aortic arch
R: R subclavian artery
Describe the course of CN XI, which muscles does it innervate?
Spinal portion (C1-C5/6 roots) travels superiorly through cranial cavity and through foramen magnum to meet with short cranial portion
Exit skull together through jugular foramen
Supplies trapezius and sternocleidomastoid
What would a patient with a lesion in CN XI be unable to do? How might they appear on examination?
Shrug shoulders (trapezius) Rotate head against resistance (sternocleidomastoid)
May have wasting of SCM and trapezius on examination
Where does CN XII run from and what does it supply?
Hypoglossal nucleus in medulla -> through hypoglossal canal to tongue -> extrinsic and intrinsic tongue muscles
How might a patient with a CN XII present on examination?
Atrophy and fasciculations of the tongue, tongue will deviate TOWARDS the lesion
Why might a fractured cribriform plate lead to a loss of sense of smell and a runny nose? What are the clinical terms for these symptoms?
Damage to the olfactory nerves in the cribriform plate as they enter the floor of the anterior cranial fossa and CSF may leak from the nose.
Rhinorrhea: runny nose
Anosmia: loss of sense of smell
What do the carotid sinus and body detect?
Sinus: Monitors BP
Body: Changes in arterial Oxygen
Where does the spinal root of CN XI contain fibres from?
C2,3,4
Which muscle of the tongue does CN XII NOT supply?
Palatoglossus muscle
What forms ansa cervicalis and where are these fibres distributed to?
Some cervical nerves from C1,2,3 are looped onto the hypoglossal nerve to form ansa cervicalis, these fibres are distributed to the strap muscles of the neck
