VIVA - Anatomy - Cranial Nerves Flashcards
Hypoglossal - where is it’s nucleus?
- Hypoglossal nucleus adjacent midline in medulla on floor 4th ventricle
- Under hypoglossal trigone
Where does Hypoglossal leave the brainstem?
- Leaves medulla via a series of rootlets between the pyramid and the olive
- Rootlets unite to form 2 roots
- Enter hypoglossal canal separately, divided by a septum of dura which occasionally ossifies but unite within
Where does Hypoglossal exit the skull?
- Emerges from skull at Hypoglossal canal
- Medial to ICA / IJV
- Receives a branch from C1 anterior ramus
- Spirals posterior to inferior ganglion of the vagus nerve
- Exchanges branches with vagus / SNS
Describe Hypoglossal’s extracranial course
- Passes between ICA (Deep) and IJV (Superficial), deep to the posterior belly of the digastric and in doing so passes thru the carotid sheath
- Passes deep to IJV in <10%
- It then descends on the carotid sheath, deep to styloid muscles and posterior belly digastric
- It hooks around (under) the origin of the occipital artery (off ECA) and curves forward lateral to the ICA, ECA and Lingual arteries
- Just below the posterior belly of digastric – 3-7mm
- Just above the tip of the greater cornu of the hyoid.
- Deep to digastric tendon and SMG
- Runs forward on lower border hyoglossus deep to Mylohyoid, accompanied by veins draining the tip of tongue.
- Note the lingual artery moves deep to hyoglossus.
- Enters the mouth
- Supplies all tongue muscles except Palatoglossus
- At the anterior border of hyoglossus the trunk breaks into multiple radiating branches
What is Hypoglossal’s relationship to the occipital artery?
Hooks around occipital artery
What muscles does Hypoglossal supply?
Thyrohyoid
Geniohyoid
All tongue muscles except palatoglossus
What are Hypoglossal’s branches?
- All non-lingual branches are derived from C1
- Meningeal branch to posterior cranial fossa enters via hypoglassal canal
- Superior root Ansa Cervicalis (C1) as it crosses ICA, curling around occipital artery
- Joins inferior root
- Run on IJV within the anterior layer of the carotid sheath
- Nerve to Thyrohyoid (Also C1 @ Lingual a)
- Nerve to Geniohyoid (@ mouth above mylohyoid)
- Tongue branches
- Tongue is derived from suboccipital myotomes
- These pass between the carotid vessels deep to the IJV
Drag nerve with them
Tongue deviates towards or away from a Hypoglossal lesion?
Tongue will deviate towards affected side on testing
Where is accessory’s nucleus?
Bulbar (cranial) motor fibres originate in lower nucleus ambiguous
Spinal motor fibres from spinal nucleus of accessory nerve
- Spinal fibres arise from C2/3/4 anterior horn
- Enter posterior fossa via foramen magnum
- Arise from rootlets posterior to the denticulate ligament which unite into a single trunk
Describe accessory’s intracranial component
Bulbar portion travels anterolaterally to exit lateral medulla in post-olivary sulcus inferior to CN IX and X à through basal cistern
Bulbar and spinal portions join within lateral basal cistern
Where does accessory exit the skull?
Pars vascularis of jugular foramen (middle section)
What are the landmarks (name 5) for finding the accessory intraoperatively?
1cm above Erbs point
Enters trapezius muscle 3-5cm above clavicle (lower 1/3)
Under posterior belly of digastric
Crosses the anterior /lateral surface of the IJV
- 70% anterior
- 26.8% posterior
- 3.2% through
Upper branch of occipital artery is a guide to the accessory nerve in front of the upper border of the SCM
How do you tell accessory from the cervical plexus?
Cervical plexus come from deep to fascia
On which muscle of the posterior triangle does accessory run?
Levator scapulae
Between which parts of the SCM does accessory run?
Between cleidomastoid (deep) and remaining parts
If the accessory branches before trapezius, which is the main trunk (upper or lower)?
Lower
What connections does accessory have to the cervical branches in the neck?
Branches from C2 +/- 3 join in posterior triangle
Branches from C3/4 join under trapezius
Which way does the head turn with contraction of the SCM?
Contraction of one muscle produces the ‘wry neck’ position with the ear approaching the tip of the shoulder and the chin rotating to the opposite side
What are the nuclei of the vagus?
Has 3 nuclei within medulla
- nucleus ambiguous – motor nerve
- dorsal nucleus – innervate involuntary muscles
- nucleus of tract solitaries – sensory nerve
Sensory from regional meninges and ear project to spinal nucleus CN5
Where is vagus located in the jugular foramen as it exits the skull?
Pars vascularis (middle component)
Draw the jugular foramen
Name the branches of the vagus from proximal to distal
- Meningeal Branch
- C1/2 fibres which join the vagus as it exits the skull
- Passes up from the superior ganglion
- Supply to the posterior fossa dura below the tentorium
- Auricular Branch (Arnold’s nerve)
- Runs laterally thru a canaliculus in the lateral wall of the jugular foramen between the tympanic and mastoid temporal bones
- Supplies
- Posteroinferior quadrant of outer surface TM
- Adjacent EAC skin
- Corresponding skin behind auricle
- Carotid Body Branch
- Forms a plexus with the carotid sinus branch of the glossopharyngeal nerve
- Pharyngeal Branch
- Passes between ECA and ICA providing motor and sensory fibres to the pharyngeal plexus on middle constrictor muscle
- Runs parallel and below CNIX
- Fibres derived from cranial accessory nerve (nucleus ambiguous)
- Supplies muscles of pharynx except stylopharyngeus and muscles of palate except tensor palati
- Passes between ECA and ICA providing motor and sensory fibres to the pharyngeal plexus on middle constrictor muscle
- Superior Laryngeal Nerve
- Arises at inferior ganglion vagus near jugular foramen
- Passes posterior and deep to ICA – travels medial to ICA and ECA
- Divides into Internal and External laryngeal Nerves at approximately the level of the greater cornu of hyoid – may be before
- Cervical Cardiac Branches
- Recurrent Laryngeal Nerve
What is the Sup laryngeal’s relationship to the carotids?
Medial to both ECA and ICA
What is the Pharyngeal branch’s relationship to the carotids?
Passes between ECA and ICA
What forms the superficial cardiac plexus?
L lower cervical cardiac branch
What cell bodies lie in the Sup ganglion?
Cell bodies for the meningeal (dura of post fossa) and auricular branch – parasympathetic and sensory
What cell bodies lie in the Inf ganglion?
Has cell bodies for other sensory branches
- Receives cranial root of Accessory nerve just above the inferior ganglion
Provides innervation for all striated muscle of the pharynx, soft palate, larynx and oesophagus
What are the branches of glossopharyngeal (in order)?
Tympanic branch (Jacobson’s nerve)
- Leaves nerve at inferior ganglion
- Passes thru tympanic canaliculus between jugular fossa and carotid canal
- Supplies ME, mastoid air cells and bony eustacian tube with sensation as well as parasympathetic branches from the inferior salivary nucleus
Carotid Nerve
- Arises just below the ganglia
- Runs down closely adherent to the ICA within the carotid sheath
- Main supply to carotid sinus and body
- Connections via nucleus of tractus solitarius with vasomotor/autonomic centres
Nerve the Stylopharyngeus (Only muscular branch)
- Cell bodies in nucleus ambiguous
Pharyngeal Branches
- Form pharyngeal plexus with the Vagus (Afferent) on middle constrictor
- Pierce muscle and supply mucous membrane of oropharynx with sensation, taste and parasympathetic innervation from inferior salivary nucleus (relay in small ganglia in mucous membrane of pharynx)
Tonsillar branch
- Supplies mucosa over palatine tonsil with lesser palatine nerve
Lingual branch
- Sensation post 1/3 of tongue and taste
- Sensation over same distribution
- Secretomotor to posterior 1/3 glands - relay in small ganglia of mucous membrane
Describe glossopharyngeal’s extracranial pathway
- Leaves anterior compartment jugular foramen
- Creates a deep notch in the inferior petrous temporal bone via inferior ganglion just below IAM
- Smaller superior
- Contain cell bodies of most sensory fibres within the nerve
- Posterior cranial fossa
- Posterior 1/3 tongue, oropharynx, tonsil
-
Tympanic branch (Jacobson’s nerve)
- Leaves nerve at inferior ganglion
- Passes thru tympanic canaliculus between jugular fossa and carotid canal
-
Carotid Nerve
- Arises just below the ganglia
- Runs down closely adherent to the ICA within the carotid sheath
- Passes down on ICA
- Passes laterally between IJV and ICA then between ICA and ECA
- Curves forward around lateral side of stylopharyngeus then passes parallel to inferior border of sytloglossus, below lower border of superior constrictor
- Gives off Nerve the Stylopharyngeus (Only muscular branch)
- Cell bodies in nucleus ambiguus
- Passes behind posterior border hyoglossus to reach the tongue
- Terminates as pharyngeal, tonsillar and lingual branches
How does glossopharyngeal enter the mouth?
- Curves forward around lateral side of stylopharyngeus then passes parallel to inferior border of sytloglossus, below lower border of superior constrictor
Describe the parasympathetic pathway to the parotid
Pre-ganglionic = Inferior salivary nucleus in medulla
- Via the glossopharyngeal nerve (travels through anterior part of jugular foramen) and petrosal ganglion
- Tympanic branch given off outside skull (jacobsen’s nerve)
- Enters middle ear through inferior tympanic canaliculus
- Gives off hypotympanic branch in 50% (explaining why tympanic neurectomy may not work unless this branch is also sectioned)
- Travels across the promontory (submucosal or bony groove or canal)
- Rejoined by hypotympanic branch, then exits through superior tympanic canaliculus
- Enters middle cranial fossa (outside dura) as lesser superficial petrosal nerve
- Leaves skull through foramen ovale
- Accompanies auriculotemporal nerve before passing to otic ganglion
- Thin serous secretions
Post – Ganglionic = Arise in Otic ganglion, run along auriculotemporal nerve
- Synapses in otic ganglion
- Then rejoins auriculotemporal nerve from where it is distributed to the parotid glandular tissue
What is Abducen’s intracranial course?
- Abducens nucleus situated beneath the facial colliculus in the floor of the 4th Ventricle.
- Axons pass thru the pons in a ventrocaudal direction and emerge at the junction of the pons and the pyramids.
- Some Inter-nuclei neurons are present to oculomotor nucleus to inhibit medial rectus.
- Nerve leaves near ventral midline pontomedullary junction
- Runs upwards thru pontine cistern between the Pons and AICA
- Pierces the dura over the clivus inferolateral to the dorsum sellae.
- Runs forward over the petrous temporal bone, passing over it’s apex à Dorello’s Canal
- Passes into the posterior aspect of the cavernous sinus.
- At this point it is lateral to the internal carotid artery and medial to the inferior petrosal sinus
- Then moves below ICA
- Leaves anterior wall of sinus via SOF
Where does Abducens pierce the arachnoid + dura?
Pierces the dura over the clivus (basisphenoid) inferolateral to the dorsum sellae à to enter Dornello’s canal
Within Dornello’s canal is surrounded by arachnoid
What is Gradenigo’s syndrome?
= Otorrhoea, CN 6 palsy, Retroorbital pain
Likely due to inflammation in Dornello’s canal
Can also get fever, facial palsy, hearing loss, vertigo, meningism
Involvment of V, VII, VI
What form’s Dorello’s canal?
Osseo-fibrous canal between the petrous apex and the petrosphenoidal ligament
Abducens runs within the canal within a meningeal tube à key restriction to movement
Point to Dorello’s canal on the skull
What are Dorello’s canal’s contents?
CN VI
Inferior petrosal sinus
Name the branches of the ophthalmic division and their branches
Name the branches of the maxillary nerve
Before the Pterygopalatine ganglion
- Meningeal
- Anterior MCF sensation
- Zygomatic
- Arises in Pterygopalatine fossa
- Runs above maxillary nerve to enter inferior orbital fissure
- Runs along lower lateral aspect orbital wall and enters zygomatico-orbital foramen where it divides into 2 branches
- Prior to division gives off a communicating branch to lacrimal nerve providing ecretomotor fibres to the lacrimal gland
- Zygomaticofacial Nerve
- Emerges from foramen on outer surface zygomatic bone
- Supplies overlying skin
- Zygomaticotemporal nerve
- Emerges in temporal fossa via fossa on surface zygoma
- Supplies skin over anterior temple at level of upper lid
- Posterior Superior Alveolar Nerve
- Runs thru pterygomaxillary fissure on posterior wall maxilla
Name the branches of the maxillary nerve
From the Pterygopalatine ganglion
- Nasopalatine nerve
- Thru Sphenopalatine foramen
- Crosses roof of nose
- Distributed to septum and incisive gum of hard palate
- Lateral posterior superior nasal nerve
- Pass thru Sphenopalatine foramen
- Supply posterosuperior quadrant of lateral nasal wall
- Greater Palatine Nerve
- Passes down thru greater palatine canal
- Runs forward from greater palatine foramen to supply hard palate mucosa
- Nasal branches supply post/inf lateral nasal wall and medial wall maxillary sinus
- Lesser Palatine Nerves (2)
- Pass down behind greater palatine nerve
- Exit via lesser palatine foramen
- Innervate soft palate and mucosa of palatine tonsil
- Pharyngeal Nerve
- Passes back thru palatovaginal canal
- Emerges at roof of nose
- Supplies mucosa of upper nasopharynx, sphenoid and ethmoid sinuses
Orbital branches supply orbit periosteum
What are the 2 branches of maxillary nerve that accompany the SPA?
Nasopalatine
Lateral posterior superior nasal
Name the branches of the mandibular nerve
What are the unique features of the trochlear nerve?
- Only nerve to emerge from the dorsum of the brainstem.
Describe trochlear nerve‘s pathway
Intracranial
- Trochlear nucleus is inferior to the oculomotor nucleus at the inferior colliculus level.
- Fibres decussate within the midbrain and curve around the PAG and emerge below the inferior colliculus.
- It is the only nerve to emerge from the dorsum of the brainstem.
- Behind the inferior colliculus
- The nerve passes lateral to the superior cerebral peduncle then moves around the midbrain into the middle cranial fossa.
- It runs below the tentorium cerebella between the superior cerebellar arteries and posterior cerebral arteries. (within posterior fossa)
- Lateral to Oculomotor nerve in interpeduncular cistern
- The trochlear nerve then enters the roof of the cavernous sinus
- Enters behind the oculomotor nerve
- Crosses forwards in lateral wall
- Enters SOF above and lateral to oculomotor nerve
Extracranial
- Enters the orbit via the superior orbital fissure superolateral to the tendinous ring.
- Medial to the frontal nerve
- Runs medially above Levator Palpebrae superioris
- Terminates within the superior oblique muscle
- Rotates and depresses the eyeball (Down and In)
In which branch of the oculomotor do the parasympathetics run?
Nerve to inferior oblique from inferior division
Describe oculomotor’s intracranial course
- Nuclei
- Oculomotor Nucleus is situated in the Periaqueductal grey matter of the midbrain
- Ventral to the aqueduct at the level of the Superior Colliculus.
- Edinger-Westphal Nucleus is dorsal to the main oculomotor nucleus.
- Superior rectus fibres appear to be crossed while inferior rectus, medial rectus and Inferior Oblique receive uncrossed fibres.
- Inter-nuclear neurons pass in the medial longitudinal fasciculus to the trochlear and Abducens nuclei to inhibit antagonists
- Oculomotor Nucleus is situated in the Periaqueductal grey matter of the midbrain
- Myelinated axons curve ventrally thru the tegmentum, many passing thru the Red nucleus and emerge as rootlets along the side of the Interpeduncular fossa medial to the cerebral peduncle on the ventral brainstem.
- It passes forward between the PCA and superior cerebellar arteries
- just below and lateral to the posterior communicating artery
- Below the free edge of the tentorium cerebelli,
- Adjacent to the inferior temporal lobe.
- Pierces the dura lateral to the posterior clinoid process to enter the roof of the cavernous sinus (initially on lateral wall).
- As it descends medially it passes over the trochlear nerve and nasociliary branch of the ophthalmic division CN V.
- Passes medial to these nerves
- Gains SNS fibres from ICA Nerve for levator palpebrae superioris
- Divides into superior and inferior divisions at the anterior end of the cavernous sinus.
- Enters the orbit via the medial aspect of the SOF
- As it descends medially it passes over the trochlear nerve and nasociliary branch of the ophthalmic division CN V.
