The Ear Flashcards
From the outside inwards, name the different ear structures.
Auricle/pinna -> external acoustic meatus (EAM) -> tympanic membrane (ear drum) -> middle ear -> inner ear -> internal acoustic meatus (IAM) -> CN VIII (vestibulocochlear nerve of brainstem) -> intracranial cavity
What structures come off of the middle ear?
The auditory tube (also called the Eustachian or pharyngotympanic tube) which leads down to nasopharynx
What is the ear?
Organ of hearing, balance + proprioception
Part of upper respiratory tract with direct relations to the nasal cavity + paranasal sinuses
What bone is the inner structures of the ear embedded within?
Temporal bone
The external ear takes in sound i.e. ___ __ and the inner ear converts it into __ __ so your brain can interpret it.
Mechanical signal
Electric signal
What are the three divisions of the ear?
External ear
Inner ear
Middle ear
What is the sensory innervation of the pinna, EAM + tympanic membrane? What does this tell you about referred pain?
From multiple cranial + somatic nerves (C2 + 3 & CN Vc, VII + X)
Referred pain to ear can be from: Mandible + mandibular teeth (CN Vc) Temporomandibular joint (CN Vc) Laryngopharynx (CN X) Cardiac (CN X)
What forms the auricle/pinna and what is its main function?
Formed of elastic cartilage covered with skin + a fleshy lobule
Captures soundwaves directing them into the ear (most effective from inferior-superior/anterior direction)
What is the innervation of the auricle/pinna?
Helix, antihelix, concha + lobule = C2 + C3
Tragus + antitragus = CN Vc, CNVII + CN X
Infection in the auricle/pinna can result in what?
Abscess formation + spread to local node groups
What is the EAM formed of? What is its sensory innervation?
Lateral part is cartilaginous whilst bony part is medial
S- shaped (horizontal in child) anteroinferiorly angled passage 2-3 cm long
Modified sweat glands that produce cerumen (wax) inside
Sensory innervation by CN Vc + CN X
What is an inflamed EAM called?
Otitis externa (sometimes called swimmers ear if due to chlorine for e.g.)
How do you examine the EAM?
In adult: Pull pinna posterior + superior in order to straighten it out to examine it
In child: Pull pinna posterior + inferior in order to straighten it out to examine it (disproportionate different bone structure)
Describe the TM.
Pink thin structure between EAM + middle ear that should reflect a concave of light pointing anterior + inferior (right side)
Handle of malleus is first middle ear ossicle that points posterior + inferior -leads up to flaccid part + down to umbo
Tense + flaccid part for vibration due to sound waves
What is the chorda tympani? How can it go wrong?
Nerve in upper 1/3 of TM but does nothing here, it travels through middle ear + up to tongue conveying taste to anterior 2/3rds of tongue
TM rupture can damage it resulting in loss of taste on anterior 2/3rd of ipsilateral tongue
What can pathology of the TM cause?
Increased concavity, bulging convexity or visible red inflammation + green suppuration -> rupture will provide relief (along with temporary hearing loss)
What are the 3 layers of the TM? What is their sensory innervation?
Outside layer = hairless skin (innervated by CN Vc + X)
Middle layer = mesoderm (innervated by CN Vc + X)
Inside layer: respiratory mucosa (innervation by CN IX)
What is the pain referral of the TM?
Skin + mesoderm layer refer pain from/to mandible + mandibular teeth, temporomandibular joint, laryngopharynx, larynx + cardiac
Inside layer refer pain from/to pharynx (as innervated by glossopharyngeal nerve)
If something is made of respiratory mucosa, what does this mean for it?
It produces mucus so must drain somewhere
What cranial nerve carries sensory from all portions of the pharynx, middle ear, auditory tube + inner side of TM?
CN IX
What is the sensory innervation of the nasopharynx, oropharynx + laryngopharynx?
Naso: CN Vb + IX
Oro: CN IX
Laryngo: CN IX + X
What are the functions of the middle ear?
Space lined with respiratory mucosa with bones in it: maleus, incus + stapes
Ossicles link TM to oval window - in space lined with respiratory mucosa
Bones amplify signal from large TM to small oval window
What can occur if the middle ear ossicles are damaged or if there is middle ear disease?
Mobile synovial joints located between ossicles can dislocate or be subject to disease (but ligaments prevent dislocation) -> conductive hearing loss
What are the 2 muscles of the middle ear that control the oscillatory range of the ossicles?
- Tensor tympani: originate in bony canal above pharyngotympanic tube + insert into neck of malleus - pulls TM medially (taut) reducing amplitude of vibrations (strong noise) (supplied by nerve CN Vc)
- Stapedius: passes from pyramidal eminence to stapes - pulls stapes + limits range of movement in response to large vibrations (loud noise) (supplied by nerve CN VII)
What might happen with a CN VII facial nerve palsy?
Facial nerve passes through inner ear + controls the stapedius muscle of middle ear so this muscle may become paralysed causing hyperacusis (exceptional sensitivity to loud noises which is physically painful)
What are the 6 walls of the middle ear space?
Anterior wall (carotid) Superior wall (tegmen tympani) Lateral wall (membranous) Inferior wall (jugular) Medial wall (labarynthine) Posterior wall (mastoid) (named after their close relations meaning spread of clinical conditions can occur to all kinds of vessels, nerves + inner ear)
Give some examples of clinical conditions occurring from middle ear infections (otitis media).
Affect vestibular system causing dizziness
Spread to mastoid air cells causing mastoiditis
Affect cranial facial nerve VII resulting in ipsilateral facial palsy
What is the only route for air + fluid to escape from the middle ear? What can happen if this gets blocked?
Pharyngotympanic tube which opens into nasopharynx so blockage of the tube prevents drainage of middle ear epithelial secretions + pressure equalization
Describe the pharyngotympanic tube.
1/3rd bone + 2/3 cartilage trumpet-shaped structure lined with respiratory mucosa with opening surrounded by tubal tonsil tissue
Normally closed but opened when swallowing by tensor veli palatine, levator palatine + salpingopharyngeus
What is acute infective (suppurative) otitis media?
Often result of infection spread from nasopharynx to middle ear via pharyngotympanic tube
Pus accumulates in middle ear = pain + swelling of TM (perforation provides relief)
What is chronic secretory otitis media (glue ear)?
Persistent build up of mucoid fluid due to blockage of pharyngotympanic tube
Causes conductive hearing loss + speech/language development problems in young
What 4 structures are involved in the formation of the ear in embryology? What structures do they form + what is their sensory innervation?
- 1st pharyngeal arch: tensor tympani, tensor veli palatini, malleus + incus (CN V)
- 2nd pharyngeal arch: facial expression muscles, stapedius + stapes (CN VII)
- 1st cleft: EAM
- 1st pouch: tubotypanic recess (tympanic cavity, mastoid antrum + auditory tube)
What embryological structures form the TM?
Ectoderm & endoderm 1st pouch + 1st cleft
What can occur as a result of the auricular sinus?
An additional EAM (small/non-functional) can develop in front of pinna
Auricular sinus can be quiescent or become infection, form cysts or discharge
When you examine the ear, what parts would you want to consider?
The ear + EAM for blood, blockage, poly, vesicles (Ramsay-Hunt; latent chicken-pox virus), infection + secretions
The mastoid process as, well as the outside of ear (behind ear)
Test hearing in both ears using a 256 Hz tuning fork (bedside testing-whisper tests)
Explain the Rinne test of the cochlear portion of CN VIII (vestibulocochlear nerve in brainstem).
Tuning fork on mastoid till sound stops then hold in air by EAM;
- Air conduction should be better than bone conduction (Rinne +ve)
- No note at EAM = conduction deafness (Rinne -ve)
Explain the Weber test of the cochlear portion of CN VIII (vestibulocochlear nervein brainstem).
Tuning fork on forehead + ask where patient hears sound/vibrating + if its louder on one lateral side;
- Normally no lateralisation
- Sound loudest in affected ear (conduction deafness)
- Sound loudest in normal ear (sensorineural deafness)
