Ear Flashcards
The ear is split into 3 sections
The external ear
Middle ear
Inner ear
What is the pinna and whats it made of?
Also called the auricle, its the visible part of the ear residing outside the head.
Its made of elastic cartilage and covered in stratified keratinized epithelium (skin)
Describe the lateral 1/3rd of the external ear canal?
Its made of skin and cartilage like the auricle.
It has ceruminous and sebaceous glands that produce wax
What is the function of the lateral 1/3rd of of the external ear canal and wax?
The lateral 3rd acts as a protective/disinfectant barrier.
Skin gets trapped here in the wax and sheds as a cleaning mechanism
How serious is an external ear obstruction?
Wax or other mechanical obstruction have a minimal effect on hearing loss compared to middle or inner ear problems
What is the tympanic membrane?
A triple layered membrane dividing the external ear canal and the middle ear
Layers of the tympanic membrane?
Outer layer - Continuous with the skin of the EAC, in fact its grows out from the umbo at the centre of the tympanic membrane
Middle layer - Fibrous
Inner Layer - resp. epithelium (Ciliated Columna Epithelium + Goblet Cells)
What can you see through the tympanic membrane?
Handle of the malleus
What are the important parts of the middle ear?
The 3 ossicles:
- Small bones that carry sound from the tympanic membrane -> Inner ear
- Malleus -> Incus -> Stapes
- The stapes foot plate sits against the oval window through to the inner ear
The chorda Tympani comes from the facial nerve and loops around the short process of the malleus.
Describe the epithelium of the middle ear?
Respiratory!
Ciliated Columnar Epithelium + goblet cells
What are the connections of the middle ear?
Mastoid air cells
Nasopharynx via eustachian tube
Whats the clinical relevance of the middle ear?
- The ossicles can be damaged by trauma or osteosclerosis
- Otitis media
- Cholesteatoma
What is a cholesteatoma?
An invasion of keratinized squamous epithelium through the tympanic membrane into the middle ear
What are the important relations of the middle ear?
- Middle Cranial Fossa
- ICA
- Sigmoid Sinus
- IJV
- Meninges
- Facial Nerve
- Mastoid Cavity
- Inner Ear
What are the segments of the facial nerve?
6:
- Intracranial
- Meatal (passing through the internal auditory meatus)
- Labyrinthine segment
- Tympanic Segment
- Mastoid Segment
- Extratemporal segment (section outside the stylomastoi foramen)
What does the facial nerve do?
- Innervates muscles of facial expression
- Special sensory innervation to the ant 2/3rds of the tongue via the chorda tympani
- Parasympathetic innervation of the submandibular/sublingual salivary glands
What makes up the inner ear?
A bony and membranous labyrinth creating sections called the scali vestibuli, tympani & media.
They contain perilymph and endolymph.
Also the organ of corti whch contains hair cells that connect to the cochlear nerve
Also the peripheral vestibular apparatus
How does hearing occur in terms of the inner ear?
Vibration of stapes
- > Transmitted through oval window
- > Produces pressure waves in cochlear fluid
- > Detected by hair cells in organ of corti
- > Transmitted to brainstem via cochlear nerve -> Vestibulocochlear nerve (CN VIII)
What is the peripheral vestibular apparatus?
Utricle: Detects linear Horizontal Acceleration
Saccule: Detects Linear Verticle Acceleration
Semicircular Canals:
- Detect head rotation
- Responsible for vestibulo-ocular reflux
Balance info is then transmitted to the brainstem by the Vestibulocochlear nerve (Cr N 8)
What is the vestibulo-ocular reflex?
The ability to fix vision on an object when the head is moving
What are the key nerves of the ear?
- Trigeminal Mandibular branch (CN V3) supplies pinna
- Facial nerve innervates anterior 1/2 of EAC
- Arnolds nerve is the auricular branch of the vagus and innervates the posterior half of the EAC
- Jacobsons nerve is the tympanic branch of the glossopharyngeal nerve and supplies the middle ear along with the chorda tympani (branch of CN 7)
Why is shared innervation by different parts of the face/head important?
Otalgia can occur with no obvious ear cause, i.e. it may be referred
