Anatomy of the Ear Flashcards
External ear: where is it? function?
from the pinna to the ear drum (tympanic membrane)
receives sound waves
What parts make up the middle ear and what is its function?
ear drum + chamber including eustachian tube (ossicular chain, oval window, round window, facial nerve, mastoid air cells)
Transmits sound waves from air to bone
Amplifies bone to bone
Transmits sound to inner ear
What makes up the inner ear and what is its function?
Made up of the semi-circular canal and cochlea
sound waves converted to nerve impulses
Transmitted to CNS via acoustic nerve CN VIII
Vestibular organs - contributes to sense of balance and spatial orientation
What is the Pinna lined with?
stratified keratinised epithelium - normal skin
This overlies the framework of elastic cartilage
Where does the cartilage in the ear get its blood supply from?
Overlying dense connective tissue/perichondrium
Describe the external ear canal
made up of 2 parts:-
- lateral 1/3 is made of skin and cartilage
In this part, the skin contains modified sweat glands that produce a protective wax layer (ceruminous and sebaceous glands). Also has thick hairs on outside
- medial 2/3 is made of skin and bone
There are no hairs or cilia here and no wax is produced
How does the skin grow in the ear
from the umbo of the tympanic membrane outwards and it then sheds in the lateral 1/3 of the canal - this is trapped in the wax and cleared by conveyor belt system
What is otitis media?
inflammation of the external ear
It can be bacterial (pseudomonas or staph aureus) or fungal.
Treatment for otitis media: what is important to remember when treating bacterial otitis media
pseudomonas need specific antibiotic treatment e.g ciprofloxacin
some medication that would work for staph aureus has no effect on pseudomonas bacteria
Describe what you would see through an otoscope of a right ear drum?
Handle of malleus is slightly anterior along with the cone of light and the temperomandibular joint
The cone of light may not be present in otitis media remember
Describe the structure of the tympanic membrane
Has 3 layers
outer layer is continuous with the skin of the external ear
Middle is a fibrous layer
Cuboidal epithelium
1cm diaemter
1/10th mm thick
what is the function of the ossicles?
3 bones that play a very important role in sound conduction (more so than tympanic membrane).
Conduct sound waves from the TM to the inner ear via the oval window
what are the names of the ossicles (3)
Malleus (hammer)
Incus (anvil)
Stapes (stirrup)
What role does the external ear play in hearing?
TRANSDUCES THE VIBRATION INTO NERVOUS IMPULSES
Directs sound into the canal TM vibrates Ossicular chain vibrates Transmitted to oval window of cochlea Detected by hair cells in organ of corti converted into nerve impulses and then transmitted to the brainstem
which cranial nerve transmits nerve impulses to the brain stem
CN VIII
what connects the middle ear to the nasopharynx?
the eustachian tube
functions of the eustachian tube?
pressure equalisation
mucus drainage
it doesn’t always work well
What is acute otitis media
Infection of the lining of the middle ear
- can be bacterial or viral
often caused by respiratory infections that spread via the eustachian tube
You get a red TM and pus in middle ear
Pain can improve if the TM perforates but if not it builds up and can spill over into the mastoid air sacs and cause mastoiditis - this requires a procedure to remove the pus
What is otitis media with Effusion
This can occur when the eustachian tube is not opening so there is a negative pressure in the ear - fluid is drawn in which limits the mobility of the ossicular chain - this causes hearing loss
occurs easily in children - narrow E tube
What can be put in place if an ear hasn’t gone back to normal after 3 months of OM with effusion?
grommets - do the same job as eustachian tube would (presssure etc) - they should fall out over time
What is a cholesteatoma?
benign condition - abnormal skin growth
Negative pressure in the ear sucks in the TM which creates a retraction pocket where skin grows into
keritinase - eats into inner ear or into middle cranial fossa - slowly destroys structures
can be congenital
What are the 6 segments of the facial nerve (CN VII)
Intracranial Meatal segment Labyrinthine segment Tympanic segment Mastoid segment Extratemporal segment
Where does the facial nerve start
at the cerebellopontine angle
What does the facial nerve innervate
Gives motor supply to the muscles of facial expression
- stapedius, posterior belly of digastric and stylohyoid
Special sensory - taste - to the anterior 2/3 of the tongue
also gives parasympathetic innervation to the submandibular, sublingual and lacrimal glands
What are the 5 branches of the facial nerve
Temporal Zygomatic Buccal Marginal mandibular Stylohyoid
Two Zombies Bit My Cat
How can you tell if it patient has upper motor neurone facial palsy?
the forehead is unaffected - innervation from contralateral side
What is the cochlear?
sense organ that translates sound into nerve impulses to be sent to the brain. Has 3 compartments.
Organ of corti sits in one of these.
It is a bony and membranous labyrinth. It contains fluid called perilymph and endolymph
Which cranial nerve is involved in the transmission of nerve impulses from the cochlea to the brain?
vestibulocochlear nerve (CN VIII)
What are the most common head and neck cancers?
Pharyngeal
Laryngeal
Nasopharyngeal
What innervates the middle ear
Glossopharyngeal nerve (CN IX)
What innervates the posterior part external ear
auricular branch of vagus nerve (CN X)
What innervates the anterior part of external ear
Facial nerve
What innervates the Pinna?
Mandibular branch of the trigeminal nerve (CN V3)
