Flashcards in Ear and Auditory Canal (ENT 1) Deck (103):
Where does the outer ear end?
At tympanic membrane
Where is the inner ear?
Embedded in petrous part of temporal bone
What structure is for hearing?
What structure is for balance and equilibrium?
What structures make up the outer ear?
External acoustic meatus
Where is the auricle?
Outside part of ear
What is the function of the auricle?
What is the auricle made of?
What is the tragus?
Little flap of skin over external auditory meatus
What is the external auditory meatus made of?
Lateral 1/3 cartilagenous
Medial 2/3 bony - embedded in temporal bone
What is the innervation of the external auditory meatus?
Posterior and inferior surface innervated by vagus
Anterior and superior surface innervated by auriculotmporal = branch of V3
Where can pain be referred to from the anterior and superior part of the external auditory meatus?
Teeth because of V3 innervation of both
What is the external auditory meatus lined by?
Hairy skin embedded with cerouminous glands
What do cerouminous glands produce?
Cerumen = ear wax
What is the function of cerumen?
Protect skin from water
Where does sound run from the auricle?
Into external auditory meatus > tympanic membrane
Where is the tympanic membrane?
Forms almost complete seal of external auditory meatus into middle ear
What is the bump on the tympanic membrane formed by?
Handle of malleus
Why does shining a light on the tympanic membrane produce a cone of reflected light on it?
Because it's concave
Where is the cone of reflected light on the tympanic membrane?
In antero-inferior quadrant
What is the clinical significance of the position of the cone of light on the tympanic membrane?
Increased pressure in middle ear pushes membrane out a little bit > changes position of cone of light
What is the nerve supply to the mucosa of the middle ear?
Mostly from glossopharyngeal nerve
Where can pain from the middle ear be referred to?
Other areas supplied by the glossopharyngeal nerve, especially tonsils
What is the transmission of sound through the middle ear?
Sound waves make tympanic membrane vibrate > transmitted to middle ear
What is the structure of the middle ear?
Largely a space in petrous part of temporal bone
Made of 2 compartments
What are the two compartments of the middle ear?
Tympanic cavity proper
Where is the tympanic cavity proper?
Medial to tympanic membrane
Where is the epitympanic recess?
Above medial tympanic membrane
What does the epitympanic recess communicated with?
What is the clinical significance of the communication between the epitympanic recess and mastoid sinuses?
Inflammation in epitympanic recess can move to mastoid air cells in mastoid process > pain and further infection
How are infections of the mastoid air cells cleared?
How does the middle ear communicate with the nasal cavity?
Where is the auditory tube?
Projects from anterior and inferior wall of middle ear
What is the function of the auditory tube?
Allows for equalisation of pressure in middle ear and atmosphere
What happens if the middle ear cannot equalise with the atmosphere?
Creates movement in tympanic membrane
If severe, can damage it
How can you get a middle ear infection?
Bacteria from nasal cavity moves up auditory tube to middle ear
What is the clinical significance of the position of the auditory tube?
In adults, auditory tube projects downwards significantly > difficult for bacteria to move up tube, and allows infections to drain down
In infants, tube far more horizontal > easier for bacteria to move to middle ear
By when do chronic middle ear infections tend to resolve in children?
How many ossicles are there?
Where are the ossicles?
In middle ear
What do the ossicles articulate with?
Tympanic membrane laterally
Oval window medially
What is the function of the ossicles?
Transmit sound from middle ear to inner ear
Which ossicle is most lateral?
What does the malleus articulate with?
Handle articulates with tympanic membrane laterally
Head articulates with incus
Which ossicle is in the middle?
What does the incus articulate with?
Head of stapes
Which ossicle is the most medial?
What does the stapes articulate with?
Head with incus
Oval shaped base sits directly over oval window
What kind of joints are the articulations between the ossicles?
What anchors some of the muscles to the walls of the middle ear?
Which muscle articulates with malleus?
Tensor tympani anteriorly
Which muscle articulates with stapes?
Which nerve innervates tensor tympani?
Which nerve innervates stapedius?
What is the role of tensor tympani and stapedius?
Dampen loud sounds to protect inner ear
Is the contraction of tensor tympani and stapedius voluntary?
No, reflexive contraction
How do tensor tympani and stapedius dampen sound?
Muscles pull on ossicles to dampen vibration
What is the clinical significance of damage to the facial nerve in relation to stapedius?
Reflexive mechanism won't work
People more sensitive to sound because can't regulate dampening of energy
Eg: in Bell's palsy people more sensitive to large sounds
What is the landmark for the oval and round windows?
Promotnary formed by basal turn of cochlea
Where is the oval window?
Superior and posterior
Where is the round window?
Inferior and posterior
Which window communicates with the inner ear?
Both oval and round windows
Which nerve goes through the middle ear?
What is the function of chorda tympani?
Taste to anterior 2/3 of tongue
Parasympathetic innervation to some salivary glands
Which cranial nerve is the chorda tympani a branch of?
Where does chorda tympani enter and exit the middle ear?
Enters through posterior wall
Exits through anterior wall
With which nerve does chorda tympani hitchhike to the mouth?
Inguinal nerve - branch of CN V
From which wall does the auditory tube project?
Projects from anterior wall, anteriorly and inferiorly
What is the route of the facial nerve through the middle ear?
Enters through internal auditory meatus
Arches over top of middle ear
Moves posteriorly to exit skull
Exits through stylomastoid foramen
Which artery is very close to the facial nerve?
What is the bony labyrinth?
Oval window opens into series of spaces embedded in petrous part of temporal bone
What is the fluid in the bony labyrinth?
What is suspended inside the bony labyrinth?
What is the membranous labyrinth made of?
Single tube of membrane
What is the fluid in the membranous labyrinth?
What is the shape of the cochlea?
Where are the sensory receptors for hearing?
How many semicircular canals are there?
Where is the vestibule?
Between semicircular canals and cochlea
Into which structure do the oval and round windows open?
How does sound energy enter and exit the inner ear?
Enters through oval window
Exits through round window
Where are the utricle and saccule?
What is the function of the untricle and saccule?
Provide info about static equilibrium
Also provide a little info about dynamic equilibrium
What is knowing head position important for?
Many reflexes around this
What is static equilibrium?
What is dynamic equilibrium?
What nerve carries sound information from the cochlear duct to the brain?
What nerve carries equilibrium information from the ampulla, utricle, and saccule to the brain?
What nerves form CN VIII?
What are the three semicircular ducts?
Why is the orientation of the semicircular ducts important?
What is the orientation of the anterior semicircular duct?
What is the orientation of the posterior semicircular duct?
What is the orientation of the horizontal semicircular duct?
What does the ampulla detect?
In which direction does the cochlear duct project?
Anteromedially along line of petrous part of temporal bone
What is the frequency and amplitude of sound transmitted by the tympanic membrane as compared to that in air?
What is the frequency and amplitude of sound transmitted by perilymph as compared to that in air?
What does perilymph transmit sound energy to?
Membranous labyrinth and sensory receptors
Where are the sensory receptors that respond best to high frequencies?
At base of cochlea
Where are the sensory receptors that respond best to low frequencies?
At apex of cochlea
What is coded by the amplitude of a sound wave?