Anatomy Of The Ear Flashcards
What components make up the external ear?
Pinna
External auditory meatus
Lateral surface of tympanic membrane
What is another name for pinna?
Auricle
What bone of the skull houses the ear?
Temporal
What are the components of the temporal bone?
Squamous
Petromastoid
Tympanic plate
Styloid process
What part of the temporal bone contains the middle and inner ear?
The petrous part
What is the auricle made of?
Elastic cartilage covered by skin
What is the outer rim of the auricle called?
Helix
What does the tragus guard?
The external acoustic meatus
What shape is the external acoustic meatus?
Sigmoid- need to pull ear up and back to straighten when examining
The external acoustic meatus has a cartilaginous outer third and…
Bony inner third
Which part of the external acoustic meatus has hairs and produces wax?
Cartilaginous part
How long is the EAM?
2.5cm
The EAM is lined with skin secreting cerumen - what is this?
Modified sebum
What is wax made of?
Discarded cells of skin and cerumen
What is the function of the auricle?
Capture and direct sound waves towards the EAM
What is the only part of the external ear not supported by cartilage?
The lobule - fat
What is the second innermost curvature of the auricle called?
The antihelix
The antihelix divides into…
Two cura - inferoanterior crus and superoposterior crus
In the middle of the auricle is a hollow depression called the …
Concha - continues into skull as EAM
What lies opposite to the tragus?
Antitragus
The external ear is supplied by branches of what artery?
External carotid artery
What branches of the external carotid artery supply the external ear?
Superficial temporal
Posterior auricular
Occipital
Maxillary - deep auricular branch
What supplies the upper lateral surface of the auricle?
Auriculotemporal nerve (branch of CNV mandibular division)
What innervates the lower lateral and medial surface of auricle?
C3 greater auricular nerve
What innervates the superior medial surface of auricle?
C2/3 lesser occipital nerve
What innervates the EAM?
Auricular branch of vagus
What is another name for ear drum?
Tympanic membrane
What shape is the tympanic membrane?
A shallow cone, with apex pointing medially
The apex of the tympanic membrane is attached to what bone?
The malleus
Is it possible to see structures in the middle ear during otoscopy?
Yes the tympanic membrane is translucent
The malleus attaches to the tympanic membrane at a point called…
The umbo
How should a normal tympanic membrane appear?
An intact, translucent, pearly grey membrane
The middle ear is an air filled cavity between tympanic membrane and inner ear. How many ossicles does it contain?
3
What is the role of the ossicles?
Amplify and concentrate vibration from tympanic membrane to the cochlea via the oval window
The ossicles transmit vibration from air medium to…
Fluid medium in inner ear
What are the 3 ossicles called (from outer to inner)
Malleus
Incus
Stapes
What connects the 3 ossicles together?
Synovial joints
The vibrations of the ossicles is tampered by what two muscles?
Tensor tympani
Stapedius
Muscles contract if potentially excessive vibration due to loud noise
How can the middle ear communicate with the external environment?
Via the pharyngotympanic (Eustachian) tube, when it is open
What is the role of the Eustachian tube?
Equalisation of air pressure between middle ear and atmosphere - necessary for efficient transfer of sound energy to the internal ear
Where does the pharyngotympanic tube arise from?
Nasopharynx (upper respiratory tract)
The mucous membrane of middle ear continuously reabsorbs air in middle ear. This causes…
Negative pressure - so need Eustachian tube to establish equilibrium
Is the Eustachian tube usually open or closed?
Usually closed
Intermittently opened by the pull of attached palate muscles when swallowing or yawning
What does the middle ear communicate with posteriorly?
The mastoid air cells via the mastoid aditus and antrum
The connection between the middle are and nasopharynx provides a potential route…
For infection to spread
What are mastoid air cells?
Small air filled cavities within the bone
What nerve runs through the middle ear?
Facial nerve in its own bony canal
A branch of facial nerve - chorda tympani runs through the cavity on the inner surface of tympanic membrane
Stapedius nerve (another branch) also runs in this cavity to innervate stapedius muscle
As well as equilibration of the middle ear, what else does the Eustachian tube do?
Allows for drainage of mucus from middle ear
What is the inner ear also called?
The labyrinth - series of canals
What part of the temporal bone does the inner ear reside in?
Petrous part
The inner ear can be divided functionally into two parts…
The vestibule and semicircular canals = vestibular apparatus
The cochlea
What is the membranous labyrinth filled with?
Endolymph
What is the membranous labyrinth surrounded by?
Perilymph contained within the bony labyrinth
What does the perilymphatic system communicate with?
The subarachnoid space and CSF via the cochlear aqueduct
What does perilymph fluid resemble?
CSF
What does endolymph fluid resemble?
Intracellular fluid
The bony shapes of the inner ear are called canals, the membranous shapes are called…
Ducts
What is the bony labyrinth surrounding the utricle and saccule called?
The vestibule
How many semicircular canals are there?
3 - anterior, lateral and posterior
The semicircular canals exist at how many degrees to each other?
90 degrees
What part of the inner ear is responsible for the perception of hearing?
The cochlea
What is the bony core of the cochlea called?
The modiolus
How many turns does the cochlea have?
2.5
Give an overview of the process of hearing
Auricle and external auditory canal focuses and funnels sound waves towards the tympanic membrane which vibrates.
Vibration of the ossicles occurs and stapes, at the oval window, sets up vibrations in the cochlear fluid
Vibrations / movement in the cochlear fluid sensed by stereocilia in the cochlear duct - particularly the spiral organ of Corti
Movement of stereocilia in organ of corti triggers action potentials in cochlear part of CNVIII
CNVIII sends signal to primary auditory cortex to make sense of the input
What part of the inner ears does the stapes articulate with?
Oval window - causes movement of perilymph and a pressure change, which is compensated by the round window
Where about in the cochlea is low and high frequency sound detected?
Low - at apex
High - base
Movement of the tectorial membrane in the inner ear causes movement of what?
Hair cells and subsequent depolarisation of neuronal fibres
What is the organ of corti?
The receptor organ for hearing
It rests on the basilar membrane and contains hair cells which transduce vibrations into electrical impulses
The vestibular system is responsible for…
Balance
What do the stereocilia in the utricle and saccule respond to?
Rotational acceleration and the static pull of gravity
What do the stereocilia in the semicircular canals respond to?
Rotational acceleration in 3 different planes
What type of movement does the utricle detect?
Linear / horizontal movement - hair cells point UP
What type of movement does the saccule detect?
Vertical movement - hair cells stick out to the SIDE
Is the saccule or utricle closer to the cochlea?
Saccule
Balance requires input from the vestibular system to be integrated centrally with…
Proprioceptive and visual inputs
The APs generated by the vestibular system are transmitted via what nerve?
Vestibular part of CNVIII - vestibulocochlear nerve
