ICL 6.4: Anatomical and Clinical Pearls of Cranial Nerves V & VII

Question 1

what is the name of CN V?

Answer 1

trigeminal nerve

Question 2

what information does CN V convey?

Answer 2

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)

1. touch, pain, temperature, and proprioceptive information (GSA) from the face
2. motor innervation (SVE) to the muscles of mastication, which are derived from branchial arch mesoderm

Question 3

what are the divisions of CN V and what type of information is conveyed by each?

Answer 3

V1 = sensory only

V2 = sensory only

V3 = sensory and motor

all of these stem out from the ganglion which sits in Mekel’s cave

Question 4

how do V1, V2, and V3 enter the face and what are they called?

Answer 4

V1 = supraorbital nerve once entering supraorbital notch

V2 = infraorbital nerve once entering infraorbital foramen

V3 = mental nerve once entering mental foramen

Question 5

what formamina do V1, V2 and V3 pass through after branching from the trigeminal ganglia?

Answer 5

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

Question 6

what are the 3 nuclei of CN V?

Answer 6

1. mesencephalic nuclei in the midbrain
2. chief sensory nuclei in the pons
3. 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

Question 7

what information do each of the nuclei of the trigeminal nerve receive?

Answer 7

1. mesencephalic nucleus = proprioception
2. chief sensory nucleus = touch/pressure
3. spinal tract nucleus = pain/temperature

Question 8

where are the first and second order neurons of the nuclei of CN V?

Answer 8

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

Question 9

what is the trigeminothalamic tract?

Answer 9

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

Question 10

what is the pathway of the fibers that convey pain and temperature through the trigeminal nuclei?

Answer 10

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

Question 11

what is the pathway of the fibers that convey proprioception through the trigeminal nuclei?

Answer 11

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

Question 12

what is the function of the efferent neurons of the trigeminal nerve?

Answer 12

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

Question 13

which muscles do the special visceral efferent fibers of the trigeminal nerve innervate?

Answer 13

the muscles of mastication!

1. temporalis
2. masseter
3. medial and lateral pterygoid
4. tensor tympani

temporalis, masseter, and medial pterygoid muscles close the jaw

the lateral pterygoid muscles open the jaw and facilitate its lateral movement

Question 14

what is the function of the tensor tympani muscle?

Answer 14

a small muscle in the middle ear that dampens vibration of the eardrum

Question 15

what deficits would be present if there was a lesion on the ventral trigeminothalamic tract?

Answer 15

contralateral loss of sensory information from the head

this is because the tracts have already crossed over once they’re at the VTT tract

Question 16

what deficits would be present if there was a lesion on the ventral trigeminothalamic tract and the anterolateral system of the spinothalamic tract?

Answer 16

contralateral loss of sensory information from the head

and

contralateral loss of pain/temp from the body

Question 17

what deficits would be present if there was a lesion on the chief sensory nucleus?

Answer 17

ipsilateral loss of fine touch/pressure from the head

Question 18

what deficits would be present if there was a lesion on the spinal nucleus and tract of V?

Answer 18

ipsilateral loss of pain/temperature from the head

Question 19

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?

Answer 19

ipsilateral loss of pain/temp from the head

contralateral loss from the body

Question 20

what structures are located in the cavernous sinus vs. the wall of the cavernous sinus?

Answer 20

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

Question 21

what is the pathway and branches of the opthalmic division of the trigeminal nerve?

Answer 21

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:

1. lacrimal nerve
2. frontal nerve
3. nasociliary nerve

Question 22

what is the function of the lacrimal nerve?

Answer 22

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

Question 23

what are the branches and function of the frontal nerve?

Answer 23

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

Question 24

what are the branches of the nasociliary nerve?

Answer 24

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:

1. long ciliary nerves
2. infratrochlear nerve
3. anterior ethmoidal nerve –> external nasal nerve

Question 25

what is the function of the long ciliary nerve?

Answer 25

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

Question 26

what is the function of the infratrochlear nerve?

Answer 26

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

Question 27

what is the function of the anterior ethmoidal nerve?

Answer 27

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

Question 28

what is the pathway of the maxillary division of the trigeminal nerve? what are the branches that are given off?

Answer 28

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 (:

Question 29

what is the function of the greater palatine nerve?

Answer 29

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

Question 30

what is the function of the lesser palatine nerve?

Answer 30

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

Question 31

what is the pathway and function of the infraorbital nerve?

Answer 31

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

Question 32

what does the mandibular division of the trigeminal nerve receive afferent sensory information from?

Answer 32

general somatic afferent neurons receive information from:

1. lower face
2. lower lip
3. lower teeth
4. anterior 2/3 of the tongue (NOT taste)
5. EXTERNAL tympanic membrane (tympanic membrane is dually innervated)
6. auditory canal
7. upper ear
8. dura matter

Question 33

what nerve innervates the tympanic membrane?

Answer 33

V3 innervates the external tympanic membrane

some other nerve innervates the internal side

so it’s dually innervated!

Question 34

what is the pathway and branches of the mandibular nerve?

Answer 34

V3 exits the trigeminal ganglion and goes through the foramen oval where it then gives off:

1. motor branches to the muscles of mastication
2. long buccal nerve
3. lingual nerve + chorda tympani –> submandibular ganglion
4. inferior alveolar nerve –> branches into mental nerve and nerve to mylohyoid
5. auriculotemporal nerve –> otic ganglion

Question 35

which division of the trigeminal nerve is the chorda tympani nerve related to? what is the function of the chorda tympani?

Answer 35

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!!

Question 36

what is the function of the long buccal nerve?

Answer 36

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

Question 37

what is the function of the lingual nerve?

Answer 37

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!

Question 38

what is the function of the articulotemporal nerve?

Answer 38

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!

Question 39

which muscles does the lingual nerve travel on top of?

Answer 39

the lingual nerve travels on the muscle tissue of the medial and lateral pterygoid muscles

Question 40

what does the V3 give off somatic visceral efferent neurons too?

Answer 40

1. muscles of mastication

temporalis, masseter, medial and lateral pterygoids

2. mylohyoid
3. digastric (anterior belly)
4. tensor veli palatini
5. tensor tympani

Question 41

which nerves will be effected if there’s a tumor that’s coursing towards the internal acoustic meatus?

Answer 41

CN 7/8

Question 42

what is the pattern of tumor spread in the trigeminal nerve?

Answer 42

the tumor can be confined to one compartment of the nerve!!

these are the 3 compartments:

1. preganglionic = confided to the cerebellopontine angle before Meckel’s cave
2. ganglionic = in in Meckel’s cave between the dura and the petrous portion of the temporal bone
3. postganglionic = in the cavernous sinus or extending into the respective skull foramina

Question 43

what color is a lesion on a T2 weighted MRI?

Answer 43

white

Question 44

what is the histopathology involving a trigeminal nerve tumor?

Answer 44

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

Question 45

where does the facial nerve originate from?

Answer 45

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

Question 46

what is the pathway of the facial nerve?

Answer 46

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

Question 47

what is the geniculate ganglion?

Answer 47

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

Question 48

what are the 3 major branches that CN 7 gives off?

Answer 48

while traversing the facial canal in the petrous portion of the temporal bone, CN 7 gives off:

1. greater petrosal nerve
2. nerve to the stapedius muscles of the ear
3. chorda tympani nerve

Question 49

what is the function of the chorda tympani? where do its first and second order neurons synapse?

Answer 49

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)

Question 50

how does the facial nerve exit the skull?

Answer 50

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

Question 51

what do the specialized visceral efferent fibers of the facial innervate?

Answer 51

the muscles of facial expression!

1. temporal
2. zygomatic
3. buccal
4. marginal mandibular
5. cervical

Question 52

which spinal tract innervates the facial nerve?

Answer 52

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

Question 53

what is the function, nucleus of origin, ganglion, foramen and signs of disfunction associated with the SVEs of the CN 7?

Answer 53

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

Question 54

what is the function, nucleus of origin, ganglion, foramen and signs of disfunction associated with the GVEs of the CN 7?

Answer 54

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

Question 55

what is the function, nucleus of origin, ganglion, foramen and signs of disfunction associated with the SVAs of the CN 7?

Answer 55

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

Question 56

what are the GVEs associated with CN 7?

Answer 56

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)

Question 57

what is the pathway and branches of CN 7?

Answer 57

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:

1. 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)
2. 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

Question 58

what is Bell’s palsy?

Answer 58

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

Question 59

what are the potential causes of Bell’s palsy?

Answer 59

1. Vascular insufficiency (Basilar, AICA)
2. Extreme Cold
3. Trauma to the side of the face
4. Surgical intervention of the parotid gland
5. Middle ear infection/Labyrinthine (VII/VIII)
6. Tumor in the IVth ventricle (VI/VII)
7. Cerebellopontine tumor (acoustic neuroma)

Question 60

what are the signs/symptoms of Bell’s palsy?

Answer 60

1. Paralysis of upper and lower face on affected side
2. Muscle atrophy
   Loss of corneal (blink) reflex
3. Loss of taste from anterior 2/3 of tongue
4. Hyperacusis (stapedius)
5. Difficulty shaving due to loss of input to platysma
6. Patient can’t whistle or hold food in mouth
7. Loss of salivation and lacrimation

Question 61

how can you differentiate between an upper motor neuron lesion vs. a lower motor neuron lesion involving the facial nerve?

Answer 61

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

Question 62

selective damage to CN 7 tumor locations; slide 39

Answer 62

slide 39

Question 63

what is the pneumonic for whether a cranial nerve is sensory, motor or both?

Answer 63

CN 1-12 if it’s sensory, motor or both

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