Auditory Apparatus Flashcards
What is the External Ear composed of?
Composed of the shell-like auricle (pinna) that collects sound and the external acoustic meatus which conducts sound to the tympanic membrane.
What is the auricle composed of?
Composed of an irregularly shaped plate of elastic cartilage covered by thin skin.
Concha of auricle:
o Deepest depression
Helix:
o Elevated margin of the auricle
Lobule:
o Consists of fibrous tissue, fat and blood vessels
Tragus:
o Tongue like projection overlapping the opening of the external acoustic meatus
Arterial supply of the auricle:
o Posterior auricular and superficial temporal aa.
Innervation of the auricle: (3)
o Great auricular nerve supplies
- Back of the ear
- Posterior aspect of the front of the ear
o Auriculotemporal nerve (from mandibular n. (CN V3))
- Anterior aspect of the front of the ear
o Auricular br. of vagus nerve (with contribution from facial n.)
- Skin of the concha
External acoustic meatus: (2)
- Ear canal leading inward through the tympanic part of the temporal bone from the auricle to the tympanic membrane
- 2-3 cm in adults
External acoustic meatus:
* Lateral third: (3)
o Slightly S-shaped and cartilaginous
o Lined with skin that is continuous with the auricular skin
o Ceruminous and sebaceous glands in the subcutaneous tissue produce cerumen (ear wax)
External acoustic meatus:
* Medial 2 thirds:
o Bony and lined with thin skin that is continuous with the external layer of the tympanic membrane
External acoustic meatus:
* Innervated by…
- Innervated by auriculotemporal n. (superior & anterior walls) and vagus n. (posterior & inferior walls)
What is the Tympanic Membrane? (4)
- Approximately 1cm in diameter
- Thin, oval, semitransparent membrane at the medial end of the external acoustic meatus
- Forms a partition between the external acoustic meatus and the tympanic cavity of the middle ear
- Covered with skin externally and mucosa of the middle ear internally
Tympanic Membrane
* Umbo-
- Umbo- peak of central depression
Tympanic Membrane
* Pars flaccida-
- Pars flaccida- thin membrane superior to lateral process of malleus
Tympanic Membrane
* Pars tensa-
- Pars tensa- remainder of the membrane
Tympanic Membrane
* Innervation: (3)
o Auriculotemporal n. (external supero-anterior 2 thirds)
o Auricular branch of vagus n. (external postero-inferior
o Glossopharyngeal n. (internal surface)
What is the middle ear (Tympanic Cavity)?
- Narrow air-filled chamber in the petrous part of the temporal bone
Middle Ear
Tympanic Cavity:
* Has 2 parts:
o Tympanic cavity proper- space directly internal to the tympanic membrane
o Epitympanic recess- space superior to the tympanic membrane
Middle Ear
Tympanic Cavity:
* Communications: (2)
o Anteromedially- nasopharynx by the pharyngotympanic tube (Eustachian tube)
o Posterosuperiorly- mastoid cells through the mastoid antrum
What is the middle ear lined with?
- Lined with mucosa that is continuous with the pharyngotympanic tube, mastoid cells and mastoid antrum
- Walls of the tympanic cavity:
1. Tegmental wall (roof):
o Thin plate of bone (tegmen tympani) separating tympanic cavity from middle cranial fossa
- Walls of the tympanic cavity:
2. Jugular wall (floor)
o Bone separating tympanic cavity from superior bulb of jugular vein
- Walls of the tympanic cavity:
3. Membranous wall (lateral)
o Convex tympanic membrane with bony wall of epitympanic recess superiorly
- Walls of the tympanic cavity:
4. Labyrinthine wall (medial): (2)
o Promontory of labyrinthine wall formed by initial part of cochlea
o Has oval and round windows
- Walls of the tympanic cavity:
5. Mastoid wall (posterior): (2)
o Has aditus to mastoid antrum connecting it to the mastoid cells
o Canal for facial nerve descends between the posterior wall and the antrum medial to the aditus
- Walls of the tympanic cavity:
6. Carotid wall (anterior): (2)
o Separates tympanic cavity from carotid canal
o Superiorly- opening for pharyngotympanic tube and canal for the tensor tympani
What is the Mastoid antrum? (4)
o Cavity in the mastoid process of the temporal bone
o Separated from the middle cranial fossa by tegmen tympani
o Common cavity into which the mastoid air cells open
o Lined by mucosa
Contents of the middle ear: (4)
o Auditory ossicles
o Stapedius and tensor tympani muscles
o Chorda tympani (branch of facial nerve)
o Tympanic nerve plexus
What is the Pharyngotympanic Tube? (4)
- Connects the tympanic cavity to the
nasopharynx - Opens posterior to the inferior nasal meatus
- Posterolateral third is bony and the rest is
cartilaginous - Lined by mucosa that is continuous posteriorly
with the tympanic cavity and anteriorly with the
nasopharynx
What is the function of the Pharyngotympanic Tube?
o Equalizes pressure in the middle ear with the atmospheric pressure to allow for free movement of the tympanic membrane
Pharyngotympanic Tube:
- The walls of the _________ part are normally in apposition (the tube is closed)
- The tube is opened by _______ veli palatini and ______ veli palatini
cartilaginous
levator
tensor
Pharyngotympanic Tube:
* Blood supply: (3)
o Ascending pharyngeal artery from the external carotid artery
o Middle meningeal artery from maxillary artery
o Artery of pterygoid canal from maxillary artery
How is the Pharyngotympanic Tube drained?
- Drained by pterygoid venous plexus
Pharyngotympanic Tube:
* Innervation: (2)
o Nerves from the tympanic plexus (glossopharyngeal nerve fibers)
o Nerves from pterygopalatine ganglion
What are Auditory Ossicles?
- Form a mobile chain of small bones across the tympanic cavity from the tympanic membrane to the oval window
Oval window-
o Oval window- opening on the labyrinthine wall of the tympanic cavity leading to the vestibule of
the bony labyrinth
Auditory Ossicles:
- First bones to ______
- Covered with mucosa but lack ________
ossify
periosteum
What is the 1. Malleus? (3)
o Attaches to the tympanic membrane
o Moves with the membrane
o Functions as a lever
- Malleus
o Head: (3)
- Round and superior
- Lies in the epitympanic recess
- Articulates with incus
- Malleus
o Neck: (2)
- Lies against the flaccid part of the tympanic membrane
- Chorda tympani crosses the medial surface
- Malleus
o Handle: (3)
- Embedded in the tympanic membrane
- Tendon of tensor tympani inserts into the handle near the neck
- Tip at the umbo
What is the 2. Incus? (2)
o Between the malleus and stapes, and articulates with them
o Has a body and 2 limbs
- Incus
o Body: (2)
- Lies in the epitympanic recess
- Articulates with the head of the malleus
- Incus
o Long limb: (2)
- Parallel to the handle of the malleus
- Interior end articulates with stapes with its
medial lenticular process
- Incus
o Short limb:
- Connected by a ligament to the posterior wall of the tympanic cavity
What are 3. Stapes? (2)
o Smallest ossicle
o Has a head, 2 limbs and a base
- Stapes
o Head: (2)
- Directed laterally
- Articulates with incus
- Stapes
o Base: (3)
§ Fits into the oval window on the medial wall of the tympanic cavity
§ Attached to the margins of the oval window by an anular ligament
§ Considerably smaller than the tympanic membrane
* Vibratory force is increased 10 times
* Increases the force but decreases the amplitude of vibrations
- Associated muscles:
o Tensor tympani: (3)
- Short muscle that pulls the handle of the malleus medially
- Tenses the tympanic membrane and reduces amplitude of its oscillations
- Prevents damage to internal ear when exposed to loud sounds
- Associated muscles:
o Tensor tympani
Innervation:
- Innervation- mandibular nerve
- Associated muscles:
o Stapedius: (4)
- Tiny muscle inside the pyramidal eminence (hollow prominence on the posterior wall of the
tympanic cavity) - Inserts onto the neck of the stapes
- Pulls the stapes posteriorly and tilts its base in the oval window
- Reduces excessive movement of the stapes and reduces its oscillatory range
- Associated muscles:
o Stapedius
Innervation:
- Innervation- nerve to stapedius from facial nerve
What is the Internal Ear? (3)
- Contains the vestibulocochlear organ buried in the petrous part of the temporal bone
- Membranous labyrinth contains endolymph
- Bony labyrinth surrounds membranous labyrinth and contains perilymph
What is the Bony Labyrinth? (2)
- Series of cavities (cochlea, vestibule and semicircular canals)
- Contained within the otic capsule of the petrous part of temporal bone
- Cochlea: (2)
o Shell-shaped part of the bony labyrinth that contains the cochlear ducts
o Part of the inner ear concerned with hearing
Where does the Spiral canal of the cochlea begin?
- Begins at the vestibule and makes 2.5 turns around a bony core
- Cochlea:
o Modiolus: (3)
- Cone-shaped core of spongy bone around which the spiral canal turns
- Contains canals for blood vessels and the distribution of the cochlear nerve
- Apex is directed laterally, anteriorly and inferiorly
- Cochlea:
o Promontory of the labyrinthine wall:
- Produced by the large basal turn of the cochlea
- Cochlea:
o Cochlear aqueduct:
- Communication between the bony labyrinth and the subarachnoid space superior to the
jugular foramen at the basal turn
- Cochlea:
o Round window:
- Closed by the secondary tympanic membrane
What is the vestibule? (3)
o Small oval chamber 5mm long
o Contains the utricle and saccule
o Continuous with the bony cochlea anteriorly and the semicircular canals posteriorly
- Vestibule:
o Vestibular aqueduct: (4)
- Communication between the posterior cranial fossa and the vestibule
- Extends to the posterior surface of the petrous part of the temporal bone
- Opens posterolateral to the internal acoustic meatus
- Transmits the endolymphatic duct and 2 small blood vessels
- Vestibule:
o Oval window:
- Found on the lateral wall, occupied by the base of the stapes
What are the 3. Semicircular canals? (4)
o Communicate with the vestibule of the bony labyrinth
o Lie posterosuperior to the vestibule
o Set at right angles to each other
o Each canal forms 2 thirds of a circle and 1.5mm in diameter (except for the bony ampulla)
How many openings do the semicircular canals have?
o The canals only have 5 openings
- The anterior and posterior canals have one limb common to both
o Lodged within the canals are the semicircular ducts
What is Membranous Labyrinth? (2)
- Consists of a series of communicating sacs and ducts suspended in the bony labyrinth
- Contains endolymph
What is endolymph?
o Watery fluid similar in composition to intracellular fluid
What are the two divisions of the Membranous Labyrinth? (2)
- Composed of 2 functional divisions- vestibular labyrinth and cochlear labyrinth
- The 2 divisions are connected via the ductus reuniens between the saccule and cochlear duct
- Vestibular labyrinth:
o Semicircular ducts:
- Open into the utricle through 5 openings
- Vestibular labyrinth:
o Utriculosaccular duct: (2)
- Communication between the utricle and saccule
- The endolymphatic duct arises from here
- Vestibular labyrinth:
o Endolymphatic duct: (3)
- Traverses the vestibulocochlear aqueduct
- Emerges through the bone of the posterior cranial fossa
- Expands into a blind pouch- the endolymphatic sac
- Vestibular labyrinth:
o Endolymphatic sac: (3)
- Located between the 2 layers of dura mater on the posterior surface of the petrous part of
the temporal bone - Storage reservoir for excess endolymph
- Formed by the blood capillaries in the membranous labyrinth
- Vestibular labyrinth:
o Maculae: (5)
- Specialized sensory epithelium in the utricle and saccule
- In the utricle- found on the floor, parallel to the base of the cranium
- In the saccule- vertically placed on the medial wall
- Sensitive to gravity and linear acceleration or deceleration
- Hair cells in the maculae are innervated by fibres of the vestibular division of the vestibulocochlear nerve
- Vestibular labyrinth:
o Ampullae: (4)
- Each semicircular duct has an ampulla at one end
- Ampullary crest- area in the ampullae that have hair cells sensitive to rotational motion
- Hair cells record movements of the endolymph in the ampullae resulting from head rotation
- Hair cells in the ampullary crests are innervated by fibers of the vestibular division of the vestibulocochlear nerve
What is the cochlear duct? (2)
o Spiral tube closed at one end and triangular in cross-section
o Firmly suspended across the cochlear canal between the spiral ligament on the external wall of the canal and the osseous spiral lamina of the modiolus
Cochlear duct:
o The duct divides the canal into 2 channels: (3)
- Scala vestibuli
- Scala tympani
- The 2 channels are filled with perilymph and join at the apex of the cochlea- the helicotrema
- Cochlear duct:
o Roof of duct-
o Floor of duct-
o Roof of duct- vestibular membrane
o Floor of duct- basilar membrane
What is the spiral organ of corti in the cochlear? (4)
- Receptor of auditory stimuli on the basilar membrane
- Overlaid by tectorial membrane
- Contains hair cells embedded in the tectorial membrane
- Hair cells innervated by cochlear division of the vestibulocochlear nerve
Conduction of sound through the ear: (7)
What is the Internal Acoustic Meatus? (2)
- Narrow canal that runs laterally for 1cm within the petrous part of the temporal bone
- It opens in the posteromedial part of the bone
Internal Acoustic Meatus:
* Closed laterally by a thin, ________ plate of bone that separates it from the internal ear
* Facial nerve, _________ nerve and blood vessels pass through the plate of bone
perforated
vestibulocochlear
- The vestibulocochlear nerve divides near the lateral end of the internal acoustic meatus into: (2)
o Cochlear nerve
o Vestibular nerve
Applied Anatomy
Otitis Media: (5)
- Infection of the middle ear
- Inflammation and swelling of the mucosa lining the tympanic cavity may cause blockage of the
pharyngotympanic tube - Scarring of the ossicles limits their ability to move in response to sound
- Due to continuity of the middle ear and mastoid antrum, mastoiditis can result as a complication
- Facial nerve can be affected the infection spreads beyond the middle ear and will result in facial nerve palsy
