Ear Flashcards
What are the functions of the ear? (2)
- Hearing
2. Balance
Where is the ear located? What is the exception?
- In temporal bone
2. Apart from cartilaginous auditory tube which is in a groove along the petrosphenoidal suture
What are the 4 components of the ear?
- External ear
- Eardrum (tympanic membrane)
- Middle ear (tympanic cavity)
- Inner ear
What does the inner ear consist of? (3)
- Cochlea
- Vestibule
- Semicircular canals
What is the function of the external ear?
Collection of mechanical sound and vibrations
What is the function of the eardrum? (2)
- Transmission
2. Amplification
What is the function of the middle ear?
- Transmission
2. Amplification
What is the function of the inner ear?
Sensation
How long is the external acoustic canal?
24 mm
What is the lateral 1/3 of the external acoustic canal comprised of?
Cartilaginous substances
What is the medial 2/3 of the external acoustic canal consist of?
Bone
What glands exist in the external acoustic canal? What do these glands produce?
Ceruminous glands
Wax
How is the external acoustic canal oriented?
Medial and slightly slanted anteriorly
What is the shape of the tympanic membrane?
Elliptical, lateral surface concave
What is the tympanic membrane comprised of externally?
Skin
What is the tympanic membrane comprised of internally?
Mucosa
What is the tympanic membrane?
A thickened edge
Where does the tympanic ring fit?
Into tympanic groove in temporal bone
What attaches to the inner surface of the tympanic membrane?
Handle of malleus
What is above and below the eardrum (tympanic membrane) respectively?
Pars flacida
Pars tensa
What is the bottom of handle of malleus? What is it a point of?
Umbo
Point of maximum convexity if viewed from middle ear
How is the middle ear/tympanic cavity oriented?
It is directed anteromedial to psoterolateral length about 15mm, width about 4-6mm
What is the middle ear/tympanic cavity lined with? What is it filled with?
Respiratory mucosa
Air
What does the lateral wall of the middle ear include?
Tympanic membrane
What does the anterior wall of the middle ear include?
Auditory tube
Where does the tensor tympani run?
Tensor tympanic runs in a canal above auditory tube and bends to run along the medial wall.
What does the posterior wall of the middle ear contain?
Epitympanic recess into aditus –> mastoid antrum –> aircells
Where does the facial nerve branch to form the chorda tympani?
Behind the posterior wall of the middle ear.
Where does the facial nerve turn inferiorly?
At aditus
What emerges at the pyramid of the posterior wall?
Tendon of stapedius
What is the roof of the middle ear/tympanic cavity?
Tegmum typani
What is the tegmum tympani?
Thin bone separating middle ear from middle cranial fossa
Where is the tegmum tympani located in relation to the arcuate eminence?
Anterolateral to arcuate eminence on the floor of the middle cranial fossa.
What is the floor of the middle ear/tympanic cavity comprised of? What does it cover?
Thin bone covering jugular fossa/foramen
What is the medial wall of the middle ear/tympanic cavity adjacent to?
Inner ear
What is the majority of the medial wall of the middle ear comprised of? What is the exception?
Bony oval except for oval window
What is the oval window closed by?
Base of stapes
Where is the round window located? What is it closed by?
Inferolateral to oval window and closed by a membrane
What are the other features of the medial wall of the middle ear? (6)
- Promontory inferomedially which overlies cochlea
- Elevation overlying the canal for facial nerve
- Round and oval windows
- Tensor Tympani
- Elevation overlying lateral semicircular canal
- Tympanic plexus - tympanic branch of glossopharygneal and sympathetic from internal carotid plexus
Where does the chorda tympani leave the facial nerve?
About 5mm above styloidmastoid foramen
Where does the chorda tympani travel after leaving the facial nerve?
Arches upwards across posterior wall of middle ear, across upper part of tympanic membrane, then into bone again and down to petrotympanic fissure. Then passes down medial surface of spine of sphenoid and between deep surface of lateral pterygoid and inferior alveolar nerve. Joins lingual nerve at an acute angle, usually deep to lateral pterygoid.
What are the characteristics of the ossicle joints?
Synovial
What are the ossicles covered with?
Mucosa
Where is the head of the malleus?
In epitympanic recess (superior)
What is the handle of the malleus attached to?
Tympanic membrane (and crossed by chorda tympani)
Where do the ligaments attach to?
Anterior and lateral processes of malleus
What does the body of the incus articulate with?
Head of malleus
What does the long crus of the incus articulate with?
Head of stapes
What attaches to the short crus of the incus posteriorly?
Ligamentous
What does the stapes attach to?
Base attaches to oval window
What are the muscles of the ear?
- Stapedius
2. Tensor tympani
Where is the muscular part of the stapedius located?
Muscular part lies in canal in posterior wall
Where does the tendon of the stapedius emerge from?
Pyramid and attaches to neck of stapes
What is the stapedius supplied by?
Facial nerve
Where is the tensor tympani muscle located?
Within a bony canal above cartilagenous auditory tuve
Where does the tendon of the tensor tympani run?
Tendon makes a 90 degree turn as it emerges and runs across middle ear to handle of malleus
What innervates the tensor tympani?
CNV/3 (medial pterygoid branch)
What are the functions of the muscles of the ear?
Muscles usually work together in a reflex response to high intensity sounds. Muscles contract and this reduces vibrations of the ossicles and in turn reduces sound intensity before it reaches the inner ear.
Tensor tympani also pulls the tympanic membrane inward (via malleus) which also reduces sound intensity transmission. Tensor tympani also reduces intensity of sounds produced by chewing.
Where does the auditory tube extend?
Middle ear to nasopharynx
What is the auditory tube posteriorly?
Bony
What is the auditory tube anteromedially? Where does it lie?
Fibrocartilage, lies in a groove on the base of the skull between petrous temporal and posterior greater wing of sphenoid. Groove should run up the narrow opening of the bony part of the auditory tube
What is the auditory tube lined with?
Respiratory epithelium
What is the function of the auditory tube?
Air into middle ear and mucus out
What are the muscles attached to the auditory tube? (4)
- Levator palati (medial)
- Tensory palati (lateral)
- Salpingopharyngeus (superior border at pharyngeal end)
- Tensor tympani (superior)
What does the inner ear consist of? What is it a part of?
Bony labyrinth. Part of petrous temporal bone
What is the labyrinth of the inner ear lined with?
Hard compact bone which is continuous with the spongy bone of the petrous temporal
What is the bony labyrinth filled with?
Perilymph, which separates bony labyrinth from membranous labyrinth
All the chambers of the osseous labyrinth interconnect. True or False?
True
What is the membranous labyrinth? What does it contain?
Separate series of hollow epithelial lined chambers that include sensory tissue. It contains endolymph
Where is the endolymph absorbed?
Via the endolymph duct and sac, ultimately returned to blood in small vessels surrounding endolymph sac)
What does the bony labyrinth consist of?
- Cochlea
- Vestibule
- Semicircular canals
Where is the cochlea located?
Anterior to vestibule
What does the cochlea turn around? What does the first turn produce?
2.5 turns around central bony modiolis with the apex of the cochlea directed laterally.
Promonotary in wall of middle ear
What does the modiolis contain?
Contains spiral ganglion and there are bony channels within modiolis that transmit fibres from ganglion to sensory cells in the chochleal duct
What does the vestibule look like in the bony labyrinth?
Oval and round windows in lateral wall
What are the semicircular canals? Where are they positioned?
3 canals posterosuperior to vestibule which communicate at their bases.
Posterior canal is parallel to edge of middle cranial fossa. Anterior/superior canal is at right angles to edge of middle cranial fossa and vertical. Lateral canal is horizontal.
What does the anterior/superior canal produce in the floor of the middle cranial fossa?
Arcuate eminence
What does the lateral canal cause?
A horizontal bulge on medial wall of middle ear above canal for facial nerve.
What are the 3 interconnecting parts of the membranous labyrinth?
- Cochleal duct
- Vestibule
- Semicircular ducts
What are the characteristics of the cochleal duct?
Blindly ending duct
What are the surrounding scala vestibuli and scala tympani extensions of?
Bony labyrinth and continuous with each other at apex of the chochlea
What does the cochleal duct contain?
Endolymph and incorporates Organ of Corti.
What does the scala vestibuli and tympani contain?
Perilymph
What does the vestibule contain?
Membranous part consists two connected sacs containing endolymph - utricle and saccule - each has a sensory region or macula
What do the semicircular ducts contain?
Endolymph. Each incorporates a dilated region or ampulla at the vestibular end with sensory structure - crista - head movement
Where does the facial and vestibulococlear nerve emerge?
They emerge at inferior border of pons with nervus intermedius between
Where does the facial nerve separate from the vestibulocochlear nerve?
In the medial part of the internal acoustic meatus and passes into a separate facial canal. The vestibular and cochleal parts separate at the lateral end of the internal acoustic canal
Where does the vestibular nerve go through?
Goes through the sensory vestibular ganglion in alteral part of inner ear and then forms five branches