What is the ear?
The organ of hearing and balance
Where is the ear found?
Within the petrous part of the temporal bone
What does the petrous part of the temporal bone constitute?
\A large portion of the lateral area of the skull
What does the petrous part of the temporal bone house?
The cavities of the ear
What are the components of the temporal bone?
- Squamous part
- Petromastoid part
- Tympanic plate
- Styloid process
What does the petromastoid part of the temporal bone contain?
The middle and inner ear
What does the upper surface of the petromastoid part of the bone form?
Part of the floor of the middle and posterior cranial fossae
What is the part of the petromastoid part that forms the posterior cranial fossa is pierced by?
The internal acoustic meatus
What does the internal acoustic meatus transmit?
Facial and vestibulocochlear cranial nerves
Describe the inferior surface of the petromastoid part of the temporal bone?
What does the inferior surface of the petromastoid part of the temporal bone contain?
The carotid canal
What is the purpose of the carotid canal?
Transmits the internal carotid artery
What is the mastoid process?
A large palpable landmark to which several muscles are attachedf
What is the cavity of the mastoid antrum?
A prolongation of the cavity of the middle ear
What extends into the mastoid process?
The cavity of the mastoid antrum, by intercommunicating air cells
What is the clinical significance of the communication between the mastoid antrum and the mastoid process?
Middle ear disease can spread by this route to cause mastoiditis
What does the tympanic plate consist?
Most of the external acoustic meatus
What does the free outer border of the tympanic plate do?
Provides attachment for the cartilage of the external ear
What does the tympanic plate do medially?
Fuses with the petrous part of the temporal bone
What does the external ear consist of?
- External acoustic meatus (ear canal)
- Lateral surface of tympanic membrane
What is the functional of the external ear?
Collects, transmits, and focuses sound waves onto the tympanic membrane
What does the action of the external ear on the tympanic membrane cause?
The membrane to vibrate
Draw a picture of the pinna/auricle
Describe the pinna
Cartilaginous and covered with skin
What is true of the elastic cartilages of the pinna?
They are arranged in a number of curved ridges
What is the outer rim of the ear called?
What is the small flap of cartilage of the ear called?
What does the tragus do?
Guards the external acoustic meatus
What is the earlobe?
A fatty structure
What is the external acoustic meatus?
A skin-lined cul-de-sac
What shape is the external acoustic meatus?
What is the clinical relevance of the sigmoid shape of the external acoustic meatus?
Need to pull ear up and back to straighten when examining
How long is the external acoustic meatus?
Describe the external acoustic meatus
- Outer 1/3 cartilaginous tube
- Inner 2/3 bony canal
Where does the external acoustic meatus lie?
In the temporal bone
What is the external acoustic meatus lined by?
What is the purpose of the self cleaning function of the external acoustic meatus?
Keep pathway clear
What facilitates the self cleaning function of external acoustic meatus?
Arrangement of hairs and production of wax by the cartilaginous part
What does the cartilaginous part of the external acoustic meatus secrete?
What is cerumen?
What does cerumen do?
Affords protection to the delicate meatal skin
What forms wax?
Discarded cells of the skin together with cerumen
What is the function of wax?
- Prevents objects entering deeper into the ear canal
- Aids desquamation and skin migration out of canal
How can the external ear be visualised?
What does the fibrous tympanic membrane mark?
The border between the external and middle ear
How is the tympanic membrane arranged?
As a shallow cone with its apex pointing medially
Is the fibrous tympanic membrane transparent or opaque?
Neither, it is translucent
What is the result of the tympanic membrane being translucent?
It allows visulisation of some structures within the middle ear, including the malleus
What is attached to the malleus?
The apex of the eardrum
What is the pars tensa?
The taut surface area of the tympanic membrane
Draw a diagram of the tympanic membrane
What is the result of the pars tensa being stretched?
It vibrates in relation to airwaves as they hit the eardrum
What is the pars flaccida?
The loose connective tissue above the malleus
What is the handle of malleus?
Where the first ossicle is attached to the tympanic membrane
What does the middle ear, or tympanic cavity contain?
What do ossicles do?
Transmit vibrations from the tympanic membrane to the inner ear in the petrous part of the temporal bone
What are the names of the ossicles?
What is the handle of the malleus attached to?
The tympanic membrane
What does the body of the malleus articulate with?
That of the incus
What does the incus articulate with?
What do the stapes articulate with?
The bony labyrinth of the internal ear
Where does the stapes articulate with bony labyrinth of the internal ear?
At the oval window
What are the articulations of the ossicles by?
What do the articulations of the ossicles of the ear serve to do?
Relay vibrations encountered by the tympanic membrane to the internal ear
What is the function of the ossicles?
Amplify and concentrate sound energy from the eardrum to the oval window
What does the oval window run into?
The epitympanic cavity
What does the middle ear communicate with anteriorly?
How does the middle ear communicate with the nasopharynx?
Via the pharyngotympanic (Eustachian) tube
What is the Eustachian tube part of?
The upper respiratory tract
What is the clinical relevance of the Eustachian tube?
It is a potential route for infection to spread to the middle ear
What does the Eustachian tube allow for?
- Equalisation of air pressure between middle ear and atmosphere
- Important in ventilation and drainage of mucus from the middle ear
What is the equilisation of air pressure between middle ear and atmosphere necessary for?
Transfer of sound energy to internal ear
What state is the Eustachian tube usually in?
How is the Eustachian tube intermittently opened?
By the pull of attached palate muscles when swallowing
What does the middle ear communicate with posteriorly?
Mastoid air cells
What is the inner ear also known as?
What does the inner ear consist of?
A series of channels hollowed out of the petrous temporal bone surrounding the membranous labyrinth
What does the membranous labyrinth contain?
Fluid called endolymph
What does the perilymph seperate?
The bony and membranous labyrinths
What does the labyrinth contain?
- Semicircular ducts and canals
- Spiral organ of Corti
What is the vestible involved in?
Maintaining our sense of position and balance
What does the vestible contain?
- Three semicircular canals
What do the utricle and saccule contain?
Receptors that respond to rotational acceleration and static pull of gravity
What are the semicircular ducts and canals?
Components of the balance system
What does the semicircular ducts and canals communicate with?
How are the semicircular ducts and canals arranged?
Perpendicular with each other
What do the semicircular ducts and canals contain?
Receptors that respond to rotational acceleration in three different planes
What is the cochlea?
A fluid filled tube
What sets up movements of fluid into the coclear?
Movements at the oval window
What do waves of fluid cause in the cochlea?
Movement of special sensory cells within the cochlear duct which fire action potentials
What is the cochlea the clinical site of?
Sensorineural hearing loss
What does the cochlear contain?
The cochlear duct
What does the cochlear duct accommodate?
The spiral organ of Corti
What is the cochlear concerned with?
How is the cochlear duct associated with hearing?
It converts sound vibration into electrical signals (action potentials) which is perceived as sound
What does the spiral organ of Corti contain?
The receptors of the auditory apparatus
How is vibration created by sound waves at the tympanic membrane translated into electrical signal in the vestibulocochlear nerve?
- Vibration of the ossicles (stapes at the oval window) sets up vibrations/movement in the cochlear fluid
- Sensed by nerve cells in the cochlear duct (part called the spiral organ of Corti)
- Movement of these receptors in organ of Corti trigger action potentials in CN VIII
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