Flashcards in Head And Neck Session 6 Deck (115):
In which part of the temporal bone are the cochlear and vestibular organs located?
Petrous part (Otic canal)
What provides venous drainage of the inner ear?
Labyrinthine vein into the sigmoid or inferior petrosal sinuses
What provides arterial supply to the bony labyrinth of the inner ear?
Anterior tympanic branch of the maxillary artery, petrosal branch of MMA and stylomastoid branch of the posterior auricular artery
What provides arterial supply to the membranous labyrinth of the inner ear?
Labyrinthine artery, a branch of the inferior cerebellar artery that divides into one cochlear branch and 2 vestibular branches
What are the components of the inner ear?
Cochlear and vestibular organs
What is the membranous labyrinth?
Series of communicating sacs and ducts that contain endolymph
What fluid is endolymph similar to?
Describe the structure of the utricles.
Contains 5 openings of semicircular ducts and communicates with the saccule via the utriculosaccular duct
Where is the macula of the utricle found?
In the floor, parallel to the base of the cranium
What covers the surface of the macula of the utricle and saccule?
Sensory epithelium with hair cells
What innervates the macula of the utricle and saccule?
Vestibular branch of CNVIII
What do hair cells of the macula of utricle and saccule and hair cells of the crest in the semicircular ducts stimulate?
Primary sensory neurons in the vestibular ganglion of the IAM
What makes the saccule continuous with the cochlear duct?
Where is the macula of saccule located?
Vertically on medial wall
What is the function of the ampullary crest in the semicircular ducts?
Sense movement of endolymph
How is the cochlear duct secured in the inner ear?
Spiral ligament and osseous spiral lamina of modiolus
What is the spiral ligament?
Spiral thickening of the periosteal lining of the cochlear canal
What are the two canals formed by the triangular shape of the cochlear duct?
Scala vestibuli and scala tympani
Describe the passage of excess endolymph from the utricle to its storage reservoir.
Capillaries in membranous labyrinth --> utricle --> endolymphatic duct --> vestibular aqueduct --> endolymphatic sac
Where is the endolymphatic sac located?
Under dura mater on posterior petrous part of the temporal bone
What is Ménière's disease?
Vertigo, low pitched tinnitus and hearing loss due to excess of endolymph causing progressive distension of ducts in inner ear
What forms the lateral wall of the cochlear duct?
What forms the roof of the cochlear duct?
Reissener's membrane (vestibular membrane) between the cochlear duct and scala vestibuli
What forms the floor of the cochlear duct?
Where is the spiral organ of Corti (receptor of auditory stimuli) located?
In basilar membrane overlaid by gelatinous tectorial membrane
Describe the passage of a wave of hydraulic pressure through the inner ear.
Scala vestibuli --> helicotrema --> scala tympani --> secondary tympanic membrane --> tympanic cavity --> deformation of cochlear duct --> disrupted hair cells
What is the internal acoustic meatus?
~1 cm long canal in petrous part of temporal bone, opening in the posteromedial part of the bone in line with the EAM
What closes the IAM laterally?
Thin, perforated plate of bone
What enters the IAM via its lateral end?
CNVII, CNVIII and BV
What happens to CNVIII at the lateral end of the IAM?
Divides into cochlear and vestibular branches
Which fluid is found in the bony labyrinth of the middle ear?
Which fluid is similar to perilymph?
What is the bony labyrinth of the inner ear?
Fluid-filled space surrounded by Otic capsules
How does the bony labyrinth hold the membranous labyrinth?
Delicate filaments (like arachnoid mater) and spiral ligament
Describe the structure of the cochlea.
Starts at vestibule, makes 2.5 turns around the bony mediolus core to form and anterolateral cone shape
What is found at the base of the modiolus?
BV and branches of the cochlear nerve
What type of bone is the modiolus made up of?
What does the cochlea have that is closed by the secondary tympanic membrane?
What is the vestibule of the inner ear?
Small oval chamber containing utricle, saccule and vestibular labyrinth
How is the vestibule of the inner ear continuous with the posterior cranial fossa?
Via vestibular aqueduct
How does the vestibule of the inner ear open posterolateral to the IAM in the posterior petrous part of the temporal bone?
Via vestibular aqueduct
What does the vestibule of the inner ear transmit?
Endolymphatic duct and 2 small BV
Describe the arrangement of the semicircular canals.
Anterior, posterior and lateral lie posterosuperior to the vestibule and at right angles to each other with bony swellings (ampulla) at one end
Why are there only 5 openings into the vestibule of the inner ear when there are three semicircular canals?
Anterior and posterior canals have one common limb
What are lodged within the semicircular canals to facilitate balance?
What are the components of the middle ear?
Ossicles, muscles, eustaschian tube, mastoid air cells and CNVII
What happens in cholesteatoma?
Persistent -ve pressure causes formation of retraction pockets where dead cells accumulate and form a necrotic cell mass (cholesteatoma) that releases lyric enzymes that erode surrounding tissues
How does the tympanic cavity connect anteromedially to the nasopharynx?
Via pharyngotympanic tube
How does the tympanic cavity connect with the mastoid air cells?
Through mastoid antrum
What lines the tympanic cavity?
Mucous membrane that is continuous with the lining of the pharyngotympanic tube, mastoid cells and mastoid antrum
What is the function of tensor tympani?
To reduce the amplitude of sound waves
What gives innervation to tensor tympani?
Which part of stapes does stapedius attach to?
Which part of stapes hits the oval window?
What is the function of stapedius?
Reduce oscillatory range to prevent excessive movement
What gives innervation to stapedius?
What do you suspect has happened if you find O/E a child is missing the crease on the back of their ear?
Acute suppuration with back pressure into the tympanic cavity causing pus to accumulate in the mastoid air cells (mastoiditis)
What forms the roof of the tympanic cavity?
Tegmen tympani below the dura mater of the middle cranial fossa
What forms the posterior wall of the tympanic cavity?
Aditus to mastoid antrum
What forms the medial wall of the tympanic cavity?
Initial part of cochlear plus oval and round windows
What forms the floor of the tympanic cavity?
Layer of bone between cavity and superior bulb of IJV
What forms the lateral wall of the tympanic cavity?
Why can damage to the lateral wall of the tympanic cavity result in loss of taste in the anterior 2/3 of tongue?
Chorda tympani is in close proximity so may be damaged
Which important structure has a groove running close to the posterior wall of the tympanic cavity?
What forms the anterior wall of the tympanic cavity?
Superiorly the opening of the pharyngotympanic tube and canal for tensor tympani
What is tegmen tympani?
Thin plate of bone separating middle cranial fossa and mastoid antrum
Where is the mastoid antrum located?
Mastoid process of temporal bone
How do mastoid air cells communicate with the antrum?
What is the function of the mastoid air cells?
Act as a buffer system by releasing air into the tympanic cavity in low pressure
Where are the mastoid air cells located in relation to the epitympanic recess?
What are the consequence of pneumococcus/Haemophilus/strep infection in acute otitis media?
Inflammation causes a bulging eardrum leading to perforation, CNVII palsy, mastoiditis, meningitis. Can cause secondary prolonged negative pressure and thick effusions to form behind the ear drum leading to conductive hearing loss
Describe the position of the pharyngotympanic tube.
From tympanic cavity posterior to inferior nasal meatus in nasopharynx
How does the pharyngotympanic tube differ in children compared to adults?
Smaller, shorter and narrower in children
Which portion of the eustaschian tube is bony?
What is the function of the pharyngotympanic tube?
Equalise pressure in middle ear by allowing air in and out of the tympanic cavity
What happens if there is dysfunction of the equalisation of pressure by the pharyngotympanic tube?
Negative pressure in middle ear cavity leading to retraction of the eardrum
Which muscles open the pharyngotympanic tube?
Levator veli palatini longitudinally and tensor veli palatini pulling opposite wall
Why do your ears 'pop' when yawning or swallowing?
Muscles opening eustaschian tube are associated with the soft palate
What gives arterial supply to the pharyngotympanic tubes?
Ascending pharyngeal artery from the ECA, MMA and artery of pterygoid canal
Where do the veins of the pharyngotympanic tubes empty?
Pterygoid venous plexus
What gives innervation to the pharyngotympanic tubes?
CNIX via the tympanic plexus and pterygopalatine ganglion
Where does lymph from the pharyngotympanic tubes drain?
Deep cervical nodes
Describe the structure of the auditory ossicles.
Exceptionally dense bone covered in tympanic cavity mucous membrane but no periosteum
Describe the position of the malleus.
Head attaches to tympanic membrane and lies in epitympanic recess. Neck lies on pars flacidda. Handle in tympanic membrane with tip at umbo
In which direction does tensor tympani pull malleus?
Describe the position of the incus.
Large body in epitympanic recess parallel to the handle of malleus. Lenticular process articulates medially with stapes. Short limb is connected by a ligament to the posterior wall of the tympanic cavity
What is the advantage of the base of stapes being smaller than the tympanic membrane?
Decreases amplitude of vibratory force
What are the components of the external ear?
Auricle (pinna), external acoustic meatus (ear canal) and tympanic membrane
How should the auricle be manipulated to examine the ear in adults compared to children?
Up, out and back for adults. Down and back for children
What is the auricle?
Irregularly shaped plate of elastic cartilage covered by thin skin to capture and transmit sound to the EAM
What gives arterial supply to the auricle?
Mainly posterior auricular and superficial temporal
What gives venous drainage to the auricle?
What gives innervation to the auricle?
Cranial aspect, helix, anti helix and lobule = greater auricular nerve. Skin anterior to EAM = auriculotemporal nerve (CNV3)
Where doe lymph drain to from the auricle of the ear?
Laterosuperior position --> superficial parotid lymph nodes. Cranial surface of superior half --> mastoid and deep cervical. Everything else --> superficial cervical
What is the EAM?
Space between tympanic part of temporal bone and tympanic membrane (~2-3 cm in adults)
Compare the structure of the lateral 1/3 and medial 2/3s of the EAM.
Lateral 1/3 = S-shaped and cartilaginous, lined with auricular skin. Medial 2/3s = bony with thin tympanic membrane skin
What forms cerumen in the cartilaginous portion of the EAM?
Ceruminous and sebaceous glands
What is the tympanic membrane?
1 cm diameter, thin, oval, semitransparent membrane oriented at 45 degrees to vertical
How does the internal and external components of the tympanic membrane compare?
Thin skin externally and mucous membrane internally
Why is infection risk increased further in tympanic membrane perforation when using detergents in the shower?
Water tension is lost
What provides innervation to the tympanic membrane?
External surface = auriculotemporal and auricular branch of vagus. Internal surface = glossopharyngeal
How are the collagen fibres arranged in the pars flacidda of the tympanic membrane?
How are the fibres of collagen arranged in the pars tensa of the tympanic membrane?
What can be used on the tympanic membrane to orientate it?
Umbo points to bum. Cone of light points to toes
Why does a patient with lobular/conceal remnant microtia/anotia have some hearing?
Neural portion develops separately
What is a pre-auricular pit?
Squamous epithelium-lined tract near tragus
What is a pre-auricular tag?
Epithelial mound/pedunculated skin near tragus
What is cauliflower ear?
Consequence of pinna haematoma if it collapses
What is otitis externa?
Where obstruction/absence of cerumen, trauma or altered EAM pH allow pseudomonas or staph colonisation
What are the S/S of otitis externa?
Otalgia, hearing loss, tinnitus, discharge
What is the Tx for otitis externa?
Analgesia, remove debris, Abx
How does tympanic perforation arise?
Infection or trauma causes ischaemia
What are the S/S of tympanic perforation?
Whistling in sneezing, reduced hearing
What is pinna haematoma?
Trauma associated with the ear causes formation of a haematoma between cartilage and perichondrium leading to AVN of the cartilage