Applied Anatomy of the Ear Flashcards
List the 3 divisions of the ear.
1 - Outer ear.
2 - Middle ear.
3 - Inner ear.
*This lecture focuses on the outer and middle ear.
Which bone forms the bony layer of the outer ear?
The tympanic part of the temporal bone.
What is the pinna of the ear?
The visible part of the outer ear.
List the functions of the outer, middle and inner ear.
- The outer ear collects sound from the auditory space and funnels it towards the middle ear.
- The middle ear transduces sound energy into movements of joints of the ossicle chain.
- The inner ear transduces movements of the ossicle chain into electrical impulses of hearing.
What is the isthmus of the ear?
The thinnest part of the auditory canal near to the tympanic membrane.
List the embryological structures that give rise to the outer and middle ear.
Are these structures of ectodermal, mesodermal or endodermal origin?
- The outer ear is derived from the first pharyngeal cleft, which is of ectodermal origin.
- The middle ear is derived from the first pharyngeal pouch, which is of endodermal origin.
List the embryological structures from which the mucosa lining the pharynx and auditory tube is derived.
1 - First pharyngeal pouch.
2 - Second pharyngeal pouch.
Which embryological structure gives rise to the inner ear?
Where is this structure located during development?
The otic placode, which is located behind the second pharyngeal arch.
Describe the sensory innervation of the outer ear.
- The upper 1/3 of the outer ear is innervated by the auriculotemporal branch of CN V3.
- The middle 1/3 of the outer ear is innervated by the lesser occipital nerve, which is a spinal nerve of roots C2 - C3.
- The lower 1/3 of the outer ear is innervated by the greater auricular nerve, which is a spinal nerve of roots C2 - C3.
- The central area of the outer ear (and continuing this, the ear canal) is innervated by the auricular branch of the vagus nerve.
Describe the sensory innervation to the middle ear.
1 - The auriculotemporal branch of CN V3.
2 - The tympanic branch of CN IX.
3 - The auricular branch of CN X.
List the embryological structures that give rise to the muscles of the middle ear.
- Tensor tympani is derived from the first pharyngeal arch.
- Stapedius is derived from the second pharyngeal arch.
Which nerve innervates muscles derived from the first pharyngeal arch?
The mandibular branches of CN V.
Which nerve innervates muscles derived from the second pharyngeal arch?
The facial nerve.
What is perichondrium?
What is its function.
- The connective tissue that covers cartilage.
- It supplies the cartilage with nutrients.
What is cauliflower ear?
Necrosis of the cartilage of the ear resulting from separation of the perichondrium from the cartilage due to a haematoma.
What proportion of the external auditory canal is cartilaginous?
What proportion of the external auditory canal is formed by the temporal bone?
- The outer 1/3 is formed of elastic cartilage.
- The inner 2/3 is formed of the tympanic plate of the temporal bone.
How do the innermost regions of the external auditory canal differ in appearance from the outermost regions?
The number of hair cells decreases towards the innermost regions.
What is the ear-cough reflex?
Which afferent nerve is involved?
- Stimulation of the external auditory canal (by touch) excites the auricular branch of the vagus nerve.
- This initiates a reflex, causing a cough.
List the layers of the tympanic membrane?
1 - Outer plate.
2 - Middle plate.
3 - Inner plate.
Give an example of an indication that the tympanic membrane is attached to the ear.
It is concave laterally.
Of which structure is the outer plate of the tympanic membrane a continuation?
The outer plate of the tympanic membrane is a continuation of the skin of the external auditory canal.
Of which structure is the inner plate of the tympanic membrane a continuation?
The inner plate of the tympanic membrane is a continuation of the skin of the lining of the pharynx.
List the cell types that comprise the lateral, middle and medial areas of the tympanic membrane.
- Laterally, the tympanic membrane is composed of keratinised stratified squamous cells.
- In the middle, the tympanic membrane is composed of a fibrous layer.
- Medially, the tympanic membrane is composed of respiratory epithelium (a ciliated columnar epithelium).
Describe the sensory innervation of the tympanic membrane.
- The internal surface is innervated by CN IX.
- The external surface is supplied by the auriculotemporal branch of CN V3, and sometimes by the vagus nerve.
List the surfaces of the middle ear.
1 - Lateral wall, formed by the inner plate of the tympanic membrane.
2 - Medial wall, formed by the outer plate of the oval window.
3 - Roof, formed by the tegmen tympanum.
4 - Floor, formed by the jugular wall.
5 - Posterior wall, formed by the mastoid wall.
6 - Anterior wall, formed by the carotid wall.
List the bones of the middle ear.
1 - Malleus.
2 - Incus.
3 - Stapes.
What is the chorda tympani?
What other structure does it innervate?
Why might this be relevant clinically?
- A sensory branch of CN VII located in the middle ear.
- It also innervates the tongue for taste sensation.
- This means that damage to the ear can result in changes in taste.
What is the name of the canal connecting the middle ear to the mastoid antrum?
What is the mastoid antrum?
- The ‘aditus to mastoid antrum’.
- The mastoid antrum contains air cells that act as a reservoir of air.
Which epithelium lines the middle ear?
Ciliated pseudostratified columnar epithelium similar to respiratory epithelium.
What is the epitympanic recess?
A hollow located on the superior roof of the middle ear containing the aditus to mastoid antrum.
Through which structure does the middle ear communicate with the nasopharynx?
The eustachian tube.
What proportion of the eustachian tube is cartilaginous?
What proportion of the eustachian tube is formed by the temporal bone?
- The posterolateral 1/3 is bony.
- The anteromedial 2/3 is cartilaginous.
Which muscles open the walls of the eustachian tube?
Which section of the eustachian tube is opened by these muscles?
- Palate levator and tensor veli palatini open the walls of the eustachian tube.
- They open the anteromedial 2/3 (cartilaginous part) of the eustachian tube.
What are the primary and secondary functions of the eustachian tube?
- The primary function is to equalise the pressure in the middle ear with the atmospheric pressure.
- The secondary function is the drain the mucus secretions of the middle ear.
What might result from eustachian tube dysfunction?
- Failure to drain mucus secretions of the middle ear, leading to congestion.
- The epithelia of the middle ear begin to remove air from the secretions, producing negative pressure in the middle ear.
- This is known as glue ear.
List 3 contributing factors to otitis media Infection of the middle ear).
1 - Eustachian tube dysfunction.
2 - Infection of the middle ear.
3 - Nasal inflammation.
Why are children more prone to developing otitis media than adults?
Because the eustachian tube in children is more horizontal.
Why might otitis media cause the tympanic membrane to bulge into the external auditory canal?
Because otitis media might cause an inflammatory reaction, producing fluids in the middle ear.
What is the most common pathogen that causes otitis media?
Streptococcus pneumoniae.
What is otitis media with effusion?
- Otitis media where the middle ear become secretory.
- Secretions of the middle ear accumulate with products of inflammation.
Give an example of a complication of otitis media.
- Mastoiditis.
- This occurs when the infection spreads to the mastoid antrum.
List 3 areas other than the mastoid antrum into which infections causing otitis media can spread.
Through which openings can this happen?
1 - The middle cranial fossa via the temporal bone.
2 - Posterior cranial fossa via the mastoid antrum.
3 - The sigmoid venous sinus via mastoid air cells.
What happens in osteosclerosis of the ear?
The stapes fuses to the oval window, resulting in dampened movements of the ossicles.
What is the oval window?
A membrane-covered opening that leads from the middle ear to the inner ear.
Which bone forms the middle and inner ear?
The petrous part of the temporal bone.
List the parts of the temporal bone.
1 - Squamous.
2 - Mastoid.
3 - Petrous.
4 - Tympanic.
