3.3 Anatomy of the ear Flashcards
The auricles (pinna) are paired structures on the lateral aspects of the head, involved in the collection of sound and transmission to the external auditory meatus:
• Mostly cartilaginous (except the lobule)
• Vascular supply: posterior auricular, superficial temporal, occipital
• Innervation: ________________ (C2 – C3; from cervical plexus), ______________ nerve (branch of posterior division of CN V3)
Structure
- Helix: Outer curvature of the ear (folded inwards)
- __________: Ends superiorly as the inferior anterior crus and superior posterior crus
- _________: Continues into the skull as the external acoustic meatus (directs sound)
- _______: Elevation of tissue anterior to the external meatus
- Antitragus: Opposite to the tragus (not present in everyone)
greater auricular nerve;
auriculotemporal;
Antihelix;
Conchae;
Tragus
The external acoustic meatus conducts sound to the tympanic membrane (eardrum):
• Canal extends from the concha to the tympanic membrane (through the tympanic part of the temporal bone) →
~2 – 3cm long in the average adult
Part Characteristics
- Lateral 1/3: _________ (lined with skin) → involved in earwax (cerumen) production
- Medial 2/3: Bony (lined with thin skin) → continuous with external layer of tympanic membrane
Cartilaginous;
The tympanic membrane forms a partition between the external ear and the tympanic cavity of the middle ear:
• Forms the medial end of the external acoustic meatus (~1cm in diameter)
• Consists of three layers: __________________
• Translucent → middle ear structures (particularly __________) are visible through the tympanic membrane
In the otoscopic view, several features of the tympanic membrane may be seen:
• Concavity of the tympanic membrane is towards the ____________ → cone of light (reflection of light anteroinferiorly from otoscope) implies healthy ear
• Handle of malleus is attached to the __________ on the inner surface of membrane → continues superiorly as the _______________
• Anterior and posterior malleolar folds stretch from the lateral process
The chorda tympani nerve (CN VII) carrying taste sensation is related to the eardrum:
• Exits the cranial cavity via the internal acoustic meatus (along with CN VII) → travels through middle ear (posterior to anterior) → between ________________ on medial surface of neck of malleus → across the tympanic membrane
Perforation of tympanic membrane: causes reduced hearing and whistling sounds during sneezing and nose blowing
- Most commonly caused by trauma and infections (otitis –> pus and fluid build up causes increased pressure and rupture
- Treatment: mainly conservative (small perforations resolve on their own), surgical (for large)
thin modified skin (outer) → fibrous (middle) → mucous membrane of middle ear (inner);
malleus;
external auditory meatus ;
umbo;
lateral process of malleus;
malleus and incus
The middle ear lies within the _________________, and begins at the tympanic membrane to the lateral wall of the internal ear:
• Consists of the ______________ (air chamber in the temporal bone) and the ________________ → contains air
• Involved in transmission of vibrations (via the auditory ossicles)
petrous part of the temporal bone;
tympanic cavity;
epitympanic recess
what are the relations of the middle ear?
- Roof: thin petrous temporal bone (separates from middle cranial fossa)
- floor (jugular wall); thin piece of bone (separates middle ear from IJV)
- lateral (membranous wall): contains of tympanic membrane + epitympanic recess
- medial (labyrinthine wall): lateral wall of inner which contains bulge (CN VII), oval window, round window
- anterior carotid wall): Thin bony plate with 2 openings (for auditory tube and tensor tympani muscles) which separates middle ear from the ICA
- posterior (mastoid wall): Separates middle ear from the mastoid air cells:
• Aditus (opening in wall) to mastoid antrum allows communication between the middle ear and mastoid air cells
The 3 auditory ossicles (malleus, incus, stapes) link the tympanic membrane to the ______________, helping to mechanically amplify the vibrations of the tympanic membrane:
• Transmits the vibrations to the cochlear (inner ear) → interpreted as sound
• Connected via _________________ (allows for movements)
Malleus: Largest and most lateral ossicle
• Attached to the tympanic membrane via the __________________
• Head of malleus lies in ___________________ and articulates with incus
Incus: Connects the malleus to the stapes
• Body articulates with the head of malleus
• Short limb attaches to the __________; long limb articulates with the ______
Stapes: Smallest bone in the human body and the most medial ossicle
• Stirrup-shaped (head, 2 limbs, base)
• Head of stapes articulates with long limb of incus
• Base joins to the oval window of the inner ear
oval window;
tiny synovial joints;
handle of malleus;
epitympanic recess;
posterior wall of middle ear;
stapes
The mastoid air cells (within mastoid antrum) are air-filled spaces in the mastoid process of the temporal bone lying posterior to the epitympanic recess:
• Communicates directly with the middle ear via the _____________
• Function: release air into tympanic cavity when the pressure is too low
Mastoiditis: infection of the mastoid antrum and mastoid cells
= Caused by spread of otitis media
- Risk of spread into middle cranial fossa (resulting in meningitis ) –> pus requires drainage (be careful due to proximity of _____)
aditus to mastoid antrum;
CN VII
The auditory (pharyngotympanic/Eustachian) tube is both bony (posterolateral) and cartilaginous (remaining), and connects the tympanic cavity with the nasopharynx:
• Opens posterior to the _______________ → pathway for spread of URTI
• Allows air to enter/leave the tympanic cavity (equalisation of pressure between the middle ear and atmospheric pressure) → free movement of tympanic membrane
o Cartilaginous part of tube must be actively opened (normally in apposition) → involves soft palate muscles
o Equalising pressure/popping of ears associated with yawning/swallowing (modified Valsalva + Toynbee manoeuvre)
• _____________________ overlies the tube (controls opening/closing)
Otitis media (middle ear infection): secondary to URTI
- Presents with ___________________
- Risk of blockage of Eustachian tube (causes pain), scarring of ossicles causing impaired hearing (if left untreated), and tympanic membrane perforation
Paediatric Eustachian tube dysfunction: may occur due to blockage of Eustachian tube (by _______________) or natural more horizontal position in children
- Presents with a _________________
- Tends to get better with age (as the Eustachian tube becomes more oblique)
inferior meatus of nasal cavity;
Salpingopharyngeus muscle;
bulging, red tympanic membrane with pus/fluid , pain and ear popping;
enlarged pharyngeal tonsils;
depression in the tympanic membrane
tensor tympani and stapedius muscles have protective functions in the acoustic reflex:
• Acoustic reflex: loud noise causes muscles to contract → reduces ossicle vibrations → reduces sound transmission to inner ear (prevents damage)
Tensor tympani
- Origin: _______________
- Insertion: Handle of malleus
- Innervation: ________
- Function: Pulls handle to malleus medially (tenses tympanic membrane and dampens vibrations)
Stapedius
- Origin: ______________
- Insertion: Neck of stapes
- Innervation: ________
- Function Pulls neck of stapes (dampens vibrations)
The middle ear also contains 2 nerves (__________________), mucosal folds and ligaments, and various blood vessels.
Eustachian tube;
CN V3;
Wall of pyramidal eminence;
CN VII;
chorda tympani and tympanic plexus
INNER EAR
The inner ear also lies within the _______________ (between the middle ear and inner acoustic meatus)
• Contains vestibulocochlear organs which convert mechanical signals from the middle ear into electrical signals (to auditory pathways in brain) and maintains balance
• Innervation: ____________________ → enters inner ear via the internal acoustic meatus (vestibular nerve → balance; cochlear nerve → hearing)
Bony labyrinth
- Within petrous part of temporal bone
- Consists of the cochlear, vestibule, 3 semicircular canals (superior, horizontal/lateral, posterior)
- Contains ___________
Membranous labyrinth
- Lies within the _______________
- Hearing: mediated by cochlear duct
- Balance: mediated by _______________
- Contains _____________)
petrous part of temporal bone;
vestibulocochlear nerve (CN VIII);
perilymph (fluid);
bony labyrinth;
semicircular ducts (contains otoliths), utricle, saccule;
endolymph (fluid
The windows are membrane-covered outlets connected to the air-filled middle ear:
• Oval window: filled by the _____________ → vibrates in response to vibrations of the tympanic membrane (moves the fluid in the inner ear)
• Round window: pressure valve (increased inner ear pressure causes it to bulge out)
plate of stapes;
The internal acoustic meatus is a narrow canal (~1cm) within the petrous temporal bone:
• Closed laterally by a thin plate of perforated bone (separates it from inner ear)
• Relations: _____________________
Meniere’s disease: disorder of the inner ear which occurs due to excess endolymph in the membranous labyrinth –> progressive distension of cochlear duct, utricle, saccule
- Damage to the membranes of ear which detect sound and balance
- Presents with the triad of ___________________
- Accompanied by sense of pressure in ear and distortion of sound/sensitivity to noise
CN VII, CN VIII, blood vessels (pass through it);
vertigo, tinnitus, hearing loss
