CN VII and VIII

CN VII is also known as…

Facial n.

CN VIII is also known as…

Vestibulocochlear n.

What nerve fibers can be found in CN VIII?

SSA Hearing and balance

What nerve fibers can be found in CN VII?

SM, SS, Para/Pre, Taste

Describe the common pathway before CN VII and CN VIII diverge

Brainstem between pons and medulla, Internal auditory meatus, Petrous portion of temporal bone (CN VII usually found superficial to CN VIII)

Describe the path of CN VIII (starting from the brainstem)

Brainstem between medulla and pons, Internal auditory meatus, Petrous portion of temporal bone, Branch into cochlear and vestibular portions

Which CN mainly innervates the inner ear?

CN VIII

Which CN mainly innervates the external and middle ear?

CN VII

What structures make up the inner ear?

Semicircular canals, vestibule, cochlea

Where do the cochlear portion of CN VIII go?

Cochlea

Where do the vestibular portion of CN VII go?

Semicircular canals and vestibule

What are the 3 semicircular canals?

Horizontal canal, Superior canal, Posterior canal

What type of movement does the horizontal canal sense?

Turning head left and right

What type of movement does the superior canal sense?

Nodding head up and down

What type of movement does the posterior canal sense?

Touching head to shoulder

What is the clinical presentation of damaged semicircular canals?

Vertigo

List the components of the cochlea from the outside → inside

Bony/osseous labyrinth, Perilymph, Membranous labyrinth, Sensory epithelium, Endolymph

List the compartments of the cochlea

Scala vestibuli, Tympanic duct, Cochlear duct

What does the scala vestibuli contain?

Perilymph

What does the tympanic duct contain?

Perilymph

What does the cochelar duct contain?

Endolymph

Where is the organ of corti?

On top of the basilar membrane in the cochlear duct

Function of organ of corti

Transmits fluid displacement to the brain via hair cells

Describe the path of sound (starting from tapping of stapes)

Stapes taps oval window (create pressure waves), Travel through cochlea, Displaces basilar membrane and stimulates cochlear portion of CN VIII, Remaining pressure waves shake into middle ear cavity via round window

What is the place theory?

Stimulation of hair cells in different parts of the basilar membrane results in differences in sound frequencies

Where are high frequency sounds detected?

Close to the middle ear

Where are low frequency sounds detected?

Close to cochlear apex

Where are low frequency sounds processed?

Anterior cochlear nucleus

Where are high frequency sounds processed?

Posterior cochlear nucleus

Prebycusis

Very gradual loss of hearing sensitivity related to aging beginning in young adults

What frequencies are first lost in prebycusis?

> 15-16,000

As you get older, you get less sensitive to _____ frequency sounds

High

Who is at a greater risk for developing prebycusis - males or females?

Males

What device can be used to aid in prebycusis?

Hearing aids

What part of the hearing path do cochlear implants replace?

Hairs of basilar membrane (directly stimulate cochlear n.)

What population typically receives cochlear implants?

Younger individuals

What can cochlear implants help?

Speech development and brain’s processing of speech signals

What does CN VII provide SS to?

Skin of concha of ear and posterior to ear

What does CN VII provide SM to?

Muscles of facial expression, stapedius, posterior belly of digastric, and stylohyoid

What does CN VII provide Para/Pre to?

Lacrimal gland, submandibular gland, sublingual gland, mucous membranes of nasopharynx and hard and soft palate

What does CN VII provide special sensory taste to?

Anterior 2/3 of tongue and hard and soft palate

Describe the path of CN VII (starting from the brainstem)

Brainstem between medulla and pons, Internal auditory meatus, Anteriorly within petrous portion, Geniculate ganglion (angle), Exits stylomastoid foramen

What is within the geniculate ganglion

Collection of sensory neurons

What are the branches of CN VII that come off before it exits the stylomastoid foramen?

Greater (and lesser) petrosal n., N. to stapedius, Chorda tympani

List the branches of CN VII after it exits stylomastoid foramen (superior → inferior)

Temporal, Zygomatic, Buccal, Marginal mandibular, Cervical, Posterior auricular

What does the temporal branch of CN VII innervate?

SM to frontalis and superior portion of orbicularis oculi

What does the zygomatic branch of CN VII innervate?

SM Inferior portion of orbicularis oculi

What does the buccal branch of CN VII innervate?

SM Buccinator and orbicularis oris

What does the cervical branch of CN VII innervate?

SM to platysma

What does the posterior auricular branch of CN VII innervate?

SS occipitalis and most auricular m.

What areas of the face are affected in an UMNL?

Entire face except the forehead

What areas of the face are affected in a LMNL?

Entire face

What can cause an UMNL?

Stroke and subdural hemorrhage

What can cause a LMNL?

Bell palsy and Ramsay Hunt syndrome

Describe the innervation of the forehead

Innervated by facial nucleus in the pons from L and R motor cortex

Describe the innervation of the lower face

Innervated by lower part of facial nucleus in the pons ONLy contralateral side of motor cortex

What are the clinical symptoms of Bell’s Palsy related to oribcularis oculi?

Drooping of eyelid, inability to close eye, cornea drying

What are the clinical symptoms of Bell’s Palsy related to orbicularis oris?

Drooping of mouth and drooling

What are the clinical symptoms of Bell’s Palsy realted to buccinator?

Accumulation of food between cheek and teeth when chewing

List 3 potential causes of Bell’s Palsy

Irritated facial nerve (swollen), Viral infection (HSV1, Lyme dx, Extreme cold), Peripheral n. problem after stylomastoid foramen

Treatment for Bell’s Palsy

Eye-patch, usually spontaneously recover after several days

What muscle does the posterior auricular branch of CN VII run superficial too?

Mastoid

What nerves provide SS to tympanic membrane

CN V3, VII, IX and X

Describe the path of the greater petrosal n. (end at pterygopalatine ganglion)

Branch of geniculate ganglion, Hiatus for the greater petrosal n., Travel under trigeminal ganglion, Cross into foramen lacerum, Pterygopalatine ganglion (in fossa)

What plexus is the deep petrosal n. from?

Tympanic plexus

Greater petrosal n. + deep petrosal n. = ?

N. of the pterygoid canal

Where does the n. of the pterygoid canal synapse at?

Pterygopalatine ganglion

Parasympathetic innervation of the lacrimal gland [increase/decrease] tear production

Increase

Describe the path of parasympathetics innervation of the lacrimal gland

Superior salvatory nucleus, Facial n.m Greater petrosal n., N. of the pterygoid canal, Pterygopalatine ganglion (synapse), Zygomatic branch of V2, Lacrimal branch of V1, Lacrimal gland

Describe the path of sympathetic innervation of the lacrimal gland

Lateral horn T1-4, Ventral root, Spinal n.m Ventral ramus, White communicating ramus, Sympathetic trunk (ascend), Superior cervical chain ganglion (synapse), ICA plexus, Deep petrosal n., N. to pterygoid canal, pterygopalatine ganglion (no synapse), CN V2, CN V1, Lacrimal gland

Sympathetic innervation of the lacrimal gland [increase/decrease] tear production

Decrease

Describe the path of parasympathetics innervation of the nasal mucosa, hard/soft palate

Superior salvatory nucleus, Facial n., Greater petrosal n., N. of the pterygoid canal, Pterygopalatine ganglion (synapse), Greater and lesser palatine n., Nasal and palatine mucosal glands

Describe the path of sympathetic innervation of the nasal mucosa, hard/soft palate via maxillary a.

Lateral horn T1-4, Ventral root, Spinal n.m Ventral ramus, White communicating ramus, Sympathetic trunk (ascend), Superior cervical chain ganglion (synapse), ICA plexus, Maxillary a., Sphenopalatine a./descending palatine a.

Describe the path of sympathetic innervation of the nasal mucosa, hard/soft palate via deep petrosal n.

Lateral horn T1-4, Ventral root, Spinal n.m Ventral ramus, White communicating ramus, Sympathetic trunk (ascend), Superior cervical chain ganglion (synapse), ICA plexus, Deep petrosal n., N. of pterygoid canal, Pterygopalatine ganglion (no synapse), Nasal and palatine mucosal glands

Parasympathetic innervation of the nasal mucosa, hard/soft palate [increase/decrease] mucous secretion

Increase

Sympathetic innervation of the nasal mucosa, hard/soft palate [increase/decrease] mucous secretion

Decrease

Describe the path of parasympathetics innervation of the sublingual and submandibular glands

Superior salvatory nucleus, Facial n. Chorda tympani, Lingal n., Submandibular ganglion (synapse), Sublingual gland OR lingual n. → sublingual gland

Describe the path of sympathetic innervation of the sublingual and submandibular glands

Lateral horn T1-4, Ventral root, Spinal n.m Ventral ramus, White communicating ramus, Sympathetic trunk (ascend), Superior cervical chain ganglion (synapse), ECA plexus, Facial (superior) or lingual (inferior) a. plexus, Submandibular/sublingual gland

Parasympathetic innervation of the sublingual and submandibular glands [increase/decrease] saliva secretion

Increase

Sympathetic innervation of the sublingual and submandibular glands [increase/decrease] saliva secretion

Decrease