Session 7 - The Ear Flashcards
What are the four components of the temporal bone?
Squamous part
Petromastoid part
Tympanic plate
Styloid process
The petrous parts of the temporal bone contain what parts of the ear?
Middle and inner ear
The internal acoustic meatus transmits what two cranial nerves?
Facial nerve (CN VII) Vestibulocochlear nerve (CN VIII)
What is the mastoid antrum?
A prolongation of the middle ear cavity that extends into the mastoid process and communicates with air cells.
What does the external ear consist of?
Pinna (or auricle)
External acoustic meatus (ear canal)
Describe the structure of the external acoustic meatus.
A cartilaginous tube laterally and bony canal medially lying in the temporal bone. Lined by skin.
What do the skin cells lining the external acoustic meatus secrete?
Cerumen (modified sebum).
Discarded skin cells together with cerumen form the wax.
Are the internal and external acoustic meatus one continuous bony channel?
No, they are separate.
What is another name for the ear drum?
Tympanic membrane
What is another name for the middle ear?
Tympanic cavity
Where are the ossicles found?
Middle ear
What is the role of the ossicles?
Transmit vibrations from the tympanic membrane to the inner ear
Name the ossicles.
Malleus
Incus
Stapes
The apex of the eardrum is attached to what bone?
Malleus
The tympanic cavity is usually air filled and enclosed from the external environment. How can communication between the tympanic cavity and external environment become possible?
Via the pharyngotympanic (Eustachian) tube when it opens.
What is the pharyngotympanic (Eustachian) tube and what is its role?
Tube connecting the nasopharynx to tympanic cavity (middle ear). Important in allowing equalisation of air pressure between the middle ear and the atmosphere. This equalisation is needed to enable efficient transfer of sound energy to the inner ear.
The Eustachian tube provides a potential route for what?
Spread of infection from the nasopharynx to the middle ear.
How does the Eustachian tube open?
Intermittently opened by the pull of attached palate muscles when swallowing or yawning. (Ears ‘popping’)
What are mastoid air cells?
Small air filled cavities within the bone.
The middle ear communicates with mastoid air cells via what?
Mastoid aditus and antrum
How can infection in the middle ear cavity spread to cause mastoiditis?
Mastoid antrum provides a connection between middle ear cavity and mastoid air cells. This provides a potential route for middle ear infections to spread leading to mastoiditis.
What is the function of the ossicles?
To amplify and concentrate sound energy from the eardrum to the oval window.
The stapes articulates with bony labyrinth of the inner ear at what point?
The oval window
What branch of the fascia nerve runs through the middle ear cavity?
Chorda tympani
Why can middle ear pathology potentially cause clinical signs of a facial nerve lesion?
Due to the proximity of the facial nerve to the middle ear (most of the facial nerve runs through the facial canal, which separates it from the middle ear by a very thin bony partition. The chord tympani branch actually runs through the middle ear cavity).
What does the inner ear consist of?
Bony labyrinth - series of canals hollowed out of the petrous temporal bone surrounding the membranous labyrinth
Membranous labyrinth - series of tubes/ducts
What are the names of the ducts forming the membranous labyrinth?
Utricle
Saccule
Semicircular ducts
Cochlear duct
The ducts of the membranous labyrinth are filled with what?
Endolymph
What are the names of the canals forming the bony labyrinth?
Semicircular canal (surround semicircular duct)
Vestibule (surrounding the utricle and saccule)
Cochlear (surrounding cochlear duct)
What is the name of the fluid found between the membranous and bony labyrinths?
Perilymph
Which duct houses the spiral organ of Corti?
Cochlear duct
What is the function of the organ of Corti?
Holds the stereocilia (auditory apparatus). These respond to fluid motion within the cochlear duct (generated by the stapes ‘tapping’ on the oval window) and generate an action potential that is propagated down the cochlear part of the vestibulocochlear nerve to be perceived as sound.
Where in the ear are stereocilia found and what are their functions?
Cochlear (organ of Corti) - sound perception
Utricle and saccule - rotational acceleration and the static pull of gravity
