ICL 6.4: Anatomical and Clinical Pearls of Cranial Nerves V & VII Flashcards
what is the name of CN V?
trigeminal nerve
what information does CN V convey?
it’s the sensory nerve of the face
it’s a a MIXED nerve containing general somatic afferent (GSA) and special visceral efferent components (SVE)
- touch, pain, temperature, and proprioceptive information (GSA) from the face
- motor innervation (SVE) to the muscles of mastication, which are derived from branchial arch mesoderm
what are the divisions of CN V and what type of information is conveyed by each?
V1 = sensory only
V2 = sensory only
V3 = sensory and motor
all of these stem out from the ganglion which sits in Mekel’s cave
how do V1, V2, and V3 enter the face and what are they called?
V1 = supraorbital nerve once entering supraorbital notch
V2 = infraorbital nerve once entering infraorbital foramen
V3 = mental nerve once entering mental foramen
what formamina do V1, V2 and V3 pass through after branching from the trigeminal ganglia?
V1 = ophthalmic division passes through the superior orbital fissure and innervates the upper portion of the face
V2 = maxillary division exits the skull through the foramen rotundum and innervates the midface
V3 = mandibular division joined by the motor root, exits through the foramen ovale and innervates the lower portion of the face
what are the 3 nuclei of CN V?
- mesencephalic nuclei in the midbrain
- chief sensory nuclei in the pons
- spinal tract in the medulla
these are all in the dorsal part of the brainstem, not ventral
each of these nuclei are in the brainstem and receive different information
sidenote: the trigeminal ganglion are outside the CNS while the nuclei are part of the CNS
what information do each of the nuclei of the trigeminal nerve receive?
- mesencephalic nucleus = proprioception
- chief sensory nucleus = touch/pressure
- spinal tract nucleus = pain/temperature
where are the first and second order neurons of the nuclei of CN V?
the first order neurons that convey touch/pressure and pain/temperature that are going to the chief sensory nucleus and spinal tract nucleus, respectively, first pass through the trigeminal ganglia before going to their respective nuclei
however the first order neurons that convey proprioception and are headed to the mesencephalic nucleus do NOT stop in the trigeminal ganglion and instead go directly to the mesencephalic nucleus
then second order neurons from all these nuclei ascend and meet up and cross the brain stem in something called the trigeminothalamic tract where they then synapse in the ventral posteromedial nucleus of the thalamus
slide 6
what is the trigeminothalamic tract?
when the second order neurons from all 3 CN V nuclei leave and they travel together and cross the midline of the brainstem and extend to the thalamus through the trigeminothalamic tract
these fibers synapse in the VPM nucleus of the thalamus, where third-order neurons send axons to the parietal lobe
what is the pathway of the fibers that convey pain and temperature through the trigeminal nuclei?
pain and temperature fibers do not synapse in the chief sensory nucleus but turn caudally and descend down through the dorsolateral medulla and upper 3 or 4 segments of the cervical spinal cord as the spinal tract of the V
axons in this tract synapse on cell bodies of second-order neurons in the underlying nucleus of the spinal tract of V
then second-order fibers from the spinal nucleus of cranial nerve V cross to the opposite side of the medulla and ascend to the thalamus as the ventral trigeminothalamic tract which is near the medial lemniscus
these fibers synapse in the VPM nucleus of the thalamus, where third-order neurons send axons to the parietal lobe
what is the pathway of the fibers that convey proprioception through the trigeminal nuclei?
proprioceptive fibers in the trigeminal nerve, unlike all other first-order sensory neurons, arise from cell bodies located in the central nervous system
these cell bodies form the mesencephalic nucleus of CN V and lie along the lateral border of fourth ventricle and cerebral aqueduct
the peripheral axons of these neurons travel WITHOUT synapse through the trigeminal ganglion and they just go directly to the mesencephalic nucleus of CN V
what is the function of the efferent neurons of the trigeminal nerve?
what happens is that the special visceral efferent (SVE) fibers that innervate the muscles of mastication arise from cell bodies in the motor nucleus of cranial nerve V which is located medial to the principal (Chief) sensory nucleus
then the axons exit from the lateral surface of the pons as the motor root and join the mandibular V3 division and exit the skull through the foramen ovale
they then go and innervate the temporalis, masseter, medial and lateral pterygoid, and tensor tympani muscles
which muscles do the special visceral efferent fibers of the trigeminal nerve innervate?
the muscles of mastication!
- temporalis
- masseter
- medial and lateral pterygoid
- tensor tympani
temporalis, masseter, and medial pterygoid muscles close the jaw
the lateral pterygoid muscles open the jaw and facilitate its lateral movement
what is the function of the tensor tympani muscle?
a small muscle in the middle ear that dampens vibration of the eardrum
what deficits would be present if there was a lesion on the ventral trigeminothalamic tract?
contralateral loss of sensory information from the head
this is because the tracts have already crossed over once they’re at the VTT tract
what deficits would be present if there was a lesion on the ventral trigeminothalamic tract and the anterolateral system of the spinothalamic tract?
contralateral loss of sensory information from the head
and
contralateral loss of pain/temp from the body
what deficits would be present if there was a lesion on the chief sensory nucleus?
ipsilateral loss of fine touch/pressure from the head
what deficits would be present if there was a lesion on the spinal nucleus and tract of V?
ipsilateral loss of pain/temperature from the head
what deficits would be present if there was a lesion on the spinal nucleus and tract of V and the anterolateral system of the spinothalamic tract?
ipsilateral loss of pain/temp from the head
contralateral loss from the body
what structures are located in the cavernous sinus vs. the wall of the cavernous sinus?
CN 6 and the internal carotid are in the cavernous sinus; the ophthalmic artery comes off the internal carotid while it’s in the cavernous sinus
CN 3, 4, V1 and V2 are in the wall of the cavernous sinus
what is the pathway and branches of the opthalmic division of the trigeminal nerve?
V1 branches from the trigeminal ganglion in Mackles cave then passes through the wall of the cavernous sinus and then the superior orbital fissure to enter the orbit
it then branches into the:
- lacrimal nerve
- frontal nerve
- nasociliary nerve
what is the function of the lacrimal nerve?
it’s a branch of V1 after it has passed through the superior orbital fissure
it conveys sensory information from the temple and upper eyelid
it also carries parasympathetic to the lacrimal and nasal glands for secretomotor functionalists
what are the branches and function of the frontal nerve?
the frontal nerve is a branch of V1 after it has passed through the superior orbital fissure
the frontal nerve then branches into the supraorbital nerve and the supratrochlear nerve
the supraorbital nerve then passes through the supraorbital foramen to exit the orbit
these nerves are responsible for conveying sensory information from the forehead, scalp and upper eyelid
what are the branches of the nasociliary nerve?
the nasociliary nerve is a branch of V1 after it has passed through the superior orbital fissure and passed through the common tendinous ring
the nasociliary nerve gives of the following branches:
- long ciliary nerves
- infratrochlear nerve
- anterior ethmoidal nerve –> external nasal nerve
what is the function of the long ciliary nerve?
it’s a branch of the nasociliary nerve which is a branch of V1
the long ciliary nerves carry some of the sympathetics to dilate the pupils and the mueller’s muscles/tarsal muscle for elevating the upper eyelid
what is the function of the infratrochlear nerve?
it’s a branch of the nasociliary nerve which is a branch of V1
it carries sensory information from the root of the nose and upper eyelid
what is the function of the anterior ethmoidal nerve?
it’s a branch of the nasociliary nerve which is a branch of V1
the anterior ethmoidal nerve conveys sensory information from the mucosa of nasal cavity and paranasal sinuses
the anterior ethmoidal nerve turns into the external nasal nerve and it conveys sensory from external nose
what is the pathway of the maxillary division of the trigeminal nerve? what are the branches that are given off?
V2 comes out of the trigeminal ganglia and passes through the wall of the cavernous sinus then through the foramen rotundum to enter the pterygopalatine fossa
within the pterygopalatine fossa there’s the pterygopalatine ganglion –> two branches come out of the pterygopalatine ganglion and that is the greater and lesser palatine nerves which pass through the greater and lesser palatine foramen!
once V2 exits the pterygopalatine fossa through the inferior orbital fissure it becomes the infraorbital nerve which conveys sensory information from the face and nose
there’s other branches of V2 but we don’t need to know them (:
what is the function of the greater palatine nerve?
the greater palatine nerve is a branch that descends from the pterygopalatine ganglion of V2 via the greater palatine foramen and then enters the palatine canal
the greater palatine nerve innervates the gingivae, mucosa and glands of the hard palate and communicates with the nasopalatine nerve
what is the function of the lesser palatine nerve?
the lesser palatine nerve is a branch that descends from the pterygopalatine ganglion coming from V2
it innervates the uvula, tonsils and soft palate
so when you gag, you’re stimulating your lesser palatine nerve
what is the pathway and function of the infraorbital nerve?
it’s the terminal branch of the maxillary nerve (V2)
it exits the pterygopalatine fossa and enters the orbit via the inferior orbital fissure –> it then exits the skull via the infraorbital foramen – it’s not the infraorbital nerve until it enters the infraorbital foramen!!!
the infraorbital nerve supplies sensory branches to the lower eyelid, the side of the nose, and the upper lip
what does the mandibular division of the trigeminal nerve receive afferent sensory information from?
general somatic afferent neurons receive information from:
- lower face
- lower lip
- lower teeth
- anterior 2/3 of the tongue (NOT taste)
- EXTERNAL tympanic membrane (tympanic membrane is dually innervated)
- auditory canal
- upper ear
- dura matter
what nerve innervates the tympanic membrane?
V3 innervates the external tympanic membrane
some other nerve innervates the internal side
so it’s dually innervated!
what is the pathway and branches of the mandibular nerve?
V3 exits the trigeminal ganglion and goes through the foramen oval where it then gives off:
- motor branches to the muscles of mastication
- long buccal nerve
- lingual nerve + chorda tympani –> submandibular ganglion
- inferior alveolar nerve –> branches into mental nerve and nerve to mylohyoid
- auriculotemporal nerve –> otic ganglion
which division of the trigeminal nerve is the chorda tympani nerve related to? what is the function of the chorda tympani?
the chorda tympani nerve is a branch coming from the facial nerve (CN 7) but then it swoops down and hitches a ride with the lingual nerve which is a branch of V3
the chorda tympani innervates the anterior 2/3 of the tongue for taste!!
what is the function of the long buccal nerve?
it’s a branch of V3 after it exits the foramen ovale
it conveys sensory information from the skin of the cheek and the buccal mucosa of the oral cavity and buccal gingiva
what is the function of the lingual nerve?
it’s a branch of V3 after it exits the foramen ovale
it conveys general sensory information from the anterior 2/3 of the tongue and floor of the mouth
it also carries parasympathetics from CN 7 via the chorda tympani to the submandibular ganglion to the submandibular and sublingual glands for secretomotor function!
it also carries taste from the anterior 2/3 of the tongue via the chorda tympani nerve!
what is the function of the articulotemporal nerve?
it’s a branch of V3 after it exits the foramen ovale
it conveys sensory information from the TMJ, side of the head and external ear
it also carries parasympathetic fibers to the partotid gland for secretomotor function –so it helps the parotid gland secrete fluid
it also has a tight connection with the MMA which comes off the maxillary artery then goes through the foramen spinosum so they’re good landmarks for each other!
which muscles does the lingual nerve travel on top of?
the lingual nerve travels on the muscle tissue of the medial and lateral pterygoid muscles
what does the V3 give off somatic visceral efferent neurons too?
- muscles of mastication
temporalis, masseter, medial and lateral pterygoids
- mylohyoid
- digastric (anterior belly)
- tensor veli palatini
- tensor tympani
which nerves will be effected if there’s a tumor that’s coursing towards the internal acoustic meatus?
CN 7/8
what is the pattern of tumor spread in the trigeminal nerve?
the tumor can be confined to one compartment of the nerve!!
these are the 3 compartments:
- preganglionic = confided to the cerebellopontine angle before Meckel’s cave
- ganglionic = in in Meckel’s cave between the dura and the petrous portion of the temporal bone
- postganglionic = in the cavernous sinus or extending into the respective skull foramina
what color is a lesion on a T2 weighted MRI?
white
what is the histopathology involving a trigeminal nerve tumor?
usually they’re slow growing encapsulated tumors composed of schwann cells
the tumor stretches the nerve roots, whose fibers are spread along the surface of the tumor and later incorporated within its capsule
with trigeminal neuralgia, it’s usually because of compression on the nerve that’s causing the pain so surgeons go in a relieve the pressure
microscopically on an H&;E stain you’ll see narrow elongated bipolar cells with little cytoplasm, rod shaped nuclei arranged in elongated drift, whorls or characteristic palisades
where does the facial nerve originate from?
the facial nucleus which is located in the lateral tegmentum of the pons
the special visceral efferent (SVE) fibers that innervate the muscles of the face arise in the facial nucleus!
axons from the facial nucleus loop around the abducens nucleus before proceeding to the lateral surface of the caudal pons
the looping of the facial nerve fibers around the abducens nucleus causes a slight bulge called the facial colliculus, on each side of the midline in the floor of the fourth ventricle
so the facial colliculus is made of the nerve fibers of the facial nerve and the abducens nucleus –> imagine what a 4th ventricle enlargement would do to these structures
what is the pathway of the facial nerve?
it originates from the facial nucleus is the pons and wraps around the abducens nucleus to form the facial colliculus then it continues to the lateral surface of the caudal pons and exits the brainstem at the cerebellopontine angle
it then traverses the posterior cranial fossa and enters the internal acoustic meatus where it passes through the auditory canal of the petrous temporal bone together with CN 8
the nerve fibers then take a turn posteriorly and inferiorly in the temporal bone = genu
the facial nerve then descends via the facial canal which is very close to the mastoid air cells –> the motor branch passes through the stylomastoid foramen
facial canal = canal running through the temporal bone from the internal acoustic meatus to the stylomastoid foramen
what is the geniculate ganglion?
it lies in the genu of the facial nerve (the genu is the sharp nerve that CN 7 takes when entering into the facial canal)
it contains primary sensory neurons for taste sensation and SVE (near external auditory meatus, auricle)
slide 27
what are the 3 major branches that CN 7 gives off?
while traversing the facial canal in the petrous portion of the temporal bone, CN 7 gives off:
- greater petrosal nerve
- nerve to the stapedius muscles of the ear
- chorda tympani nerve
what is the function of the chorda tympani? where do its first and second order neurons synapse?
it’s a branch of CN 7 in the facial canal that is a specialized visceral afferent neuron
it innervates taste in the anterior 2/3 of the tongue
the cell bodies of the first-order neurons of this component are located in the geniculate ganglion –> the central axons from this ganglion enter the pons and synapse, along with other taste fibers, in the rostral aspect of the nucleus solitarius in the medulla
slide 33 (red)
how does the facial nerve exit the skull?
it exits skull at stylomastoid foramen and enters the parotid gland
in the parotid is where the facial nerve branches into it’s 5 motor branches! To Zanzibar By Motor Car = temporal, zygomatic, buccal, mandibular, cervical
this is why dentists have to be careful when doing stuff with the parotid gland or you could end up with Bell’s Palsy
what do the specialized visceral efferent fibers of the facial innervate?
the muscles of facial expression!
- temporal
- zygomatic
- buccal
- marginal mandibular
- cervical
which spinal tract innervates the facial nerve?
the corticobulbar tract dually innervates the facial nuclei of CN 7
so when the corticobulbar pathway fibers are coming down, some cross while some don’t and this tells you that the facial nuclei are bilaterally inervated!
this is important because yo could knock out one side and still have communication to the nuclei form the other side
what is the function, nucleus of origin, ganglion, foramen and signs of disfunction associated with the SVEs of the CN 7?
aka the motor root nerves that pass through the sylomastoid foramen to innervate the facial muscles
SVEs are responsible for innervating the motor muscles of the facial expression and stapedius muscle of the ear
they originate from the facial nucleus and there is no associated ganglion
they pass through the internal auditory meatus and stylomastoid foramen
signs of disfunction would be facial weakness and hyperacusis
what is the function, nucleus of origin, ganglion, foramen and signs of disfunction associated with the GVEs of the CN 7?
aka the parasympathetic fibers that innervated the glandular tissue
GVEs of CN 7 innervate the parasympathetic lacrimal gland and originate from the superior salivatory nucleus –> they are associated with the sphenopalatine ganglion and pass through the internal auditory meatus –> signs of dysfunction would be decreased tearing
GVEs of CN 7 also innervate the salivary glands and originate from the superior salivary nucleus –> they’re associated with the submandibular ganglion and pass through the internal auditory meatus –> signs of dysfunction would be decreased salivation
what is the function, nucleus of origin, ganglion, foramen and signs of disfunction associated with the SVAs of the CN 7?
aka the chorda tympani
the SVAs of CN 7 are responsible for conveying taste in the anterior 2/3 of the tongue
they terminate in the nucleus solitarius and are associated with the geniculate ganglion
they pass through the internal auditory meatus and signs of dysfunction would be decreased taste
what are the GVEs associated with CN 7?
the parasympathetic GVEs of the facial nerve go to glandular tissue
the preganglionic parasympathetic fibers from the salivatory nucleus in the pons travel in the greater petrosal and synapse in the pterygopalatine ganglion –> then the postganglionic fibers innervate the lacrimal gland
the other pathway is that the preganglionic parasympathetic fibers from the salivatory nucleus in the pons travel through the facial canal and synapse in the submandibular ganglion –> then the postganglionic fibers innervate the sublingual and submandibular gland
slide 33 (blue)
what is the pathway and branches of CN 7?
the motor and sensory fibers of CN 7 enter through the internal acoustic meatus and then there’s the geniculate ganglion in the facial canal
the greater petrosal nerve exits the temporal bone from the facial canal and once it passes through the foramen lacer it becomes the nerve of the pterygoid canal – once the nerve of the pterygoid canal enters the pterygopalatine fossa it ends as as the pterygopalatine ganglion
from the geniculate ganglion are 2 branches:
- once the first branches passes through the styloid foramen it then passes through the parotid gland and there it will give off the motor branches to the muscles of facial expression(to zanzibar by motor car)
- the other branch will pass through the petrotympanic fissure and enter the infra temporal fossa where it will become the chordates tympani – it will be joined by the lingual nerve from V3 and they will both go to the mouth area to innervate the tongue and submandibular/sublingual glands
what is Bell’s palsy?
facial weakness is caused by damage to CN 7 affecting the branches innervating the muscles of facial expression
so the motor branches of CN 7 exiting from the parotid gland will be damaged
just remember, if the patient says that their taste is fine, then that means the location of the lesion is DISTAL to where the chordates tympani branches off of CN 7 aka somewhere distal to the stylomastoid foramen
however, if the patient says that she has lost taste in the tip of her tongue, this means the chordates tympani has also been affected so the lesion must be PROXIMAL to the branching of the chordates tympani such as within the temporal bone –> at this point you might also have CN 8 problems such as unilateral hearing loss of tinnitus because CN 8 also passes through the internal acoustic meatus
what are the potential causes of Bell’s palsy?
- Vascular insufficiency (Basilar, AICA)
- Extreme Cold
- Trauma to the side of the face
- Surgical intervention of the parotid gland
- Middle ear infection/Labyrinthine (VII/VIII)
- Tumor in the IVth ventricle (VI/VII)
- Cerebellopontine tumor (acoustic neuroma)
what are the signs/symptoms of Bell’s palsy?
- Paralysis of upper and lower face on affected side
- Muscle atrophy
Loss of corneal (blink) reflex - Loss of taste from anterior 2/3 of tongue
- Hyperacusis (stapedius)
- Difficulty shaving due to loss of input to platysma
- Patient can’t whistle or hold food in mouth
- Loss of salivation and lacrimation
how can you differentiate between an upper motor neuron lesion vs. a lower motor neuron lesion involving the facial nerve?
with an UMN, since the facial nucleus at the level of the pons is receiving bilateral innervation from the corticobulbar tract then you would still have innervation from the other side of the corticobulbar tract and you’d still be able to wrinkle your forehead –> so you’d only have paralysis of the contralateral lower face
however with a LMN lesion, you’d be knocking out the facial nucleus as a whole because now it’s a problem with the postganglionic fibers leaving the facial nucleus and innervation from the contralateral corticobulbar tract wouldn’t be of help since it’s already synapsed in the facial nucleus so you wouldn’t be able to wrinkle the forehead at all –> this is Bell’s palsy!
slide 38
selective damage to CN 7 tumor locations; slide 39
slide 39
what is the pneumonic for whether a cranial nerve is sensory, motor or both?
CN 1-12 if it’s sensory, motor or both
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