Anatomy of the ear Flashcards
What % of ENT work is related to the ears?
60-65%
Describe the anatomy of the external ear
pinna and external auditory canal, concha, tragus
Describe the anatomy of the middle ear
tympanic membrane, malleus, incus, stapes
Describe the anatomy of the inner ear
cochlea and semicircular canals
What foreign body would make it a clinical emergency?
Batteries or magnets
Describe the epithelium of the external auditory canal and pinna
Stratified keratinized epithelium
How long is the external ear canal in adults?
4cm
Describe the 3 layers of the tympanic membrane
– Outer layer is continuous with skin of EAC
– Middle fibrous layer
– Inner layer of respiratory epithelium (ciliated columnar epithelium with goblet cells)
What is the diameter of the tympanic membrane?
1cm
What should be seen on inspection of the tympanic membrane?
- Cone of light – if there is a disruption can suggest change of shape
- Pars tensa – tense portion of tympanic membrane
- Pars flaccida – flaccid portion of tympanic membrane
Name the ossicles
Malleus incus and stapes
What can cause disruption of the ossicles?
Disruption can be from trauma or bony sclerosis (otosclerosis)
List the 6 segments of CN VII
6 segments of facial nerve
– Intracranial
– Meatal segment (passes through internal auditory meatus)
– Labyrinthine segment
– Tympanic segment (runs through fallopian tube. 10% of which are dehiscent i.e. nerve passes within mucosa instead of bony canal)
– Mastoid segment
– Extratemporal segment
What muscles receive motor supply from the facial nerve?
– Stapedius
– Posterior belly of digastric
– Stylohyoid
What does the facial nerve innervate?
Motor supply to the muscles of facial expression
– Stapedius
– Posterior belly of digastric
– Stylohyoid
Taste anterior 2/3rds of tongue from chorda tympani
What operation is needed for grommet insertion?
The operation to insert a grommet involves a myringotomy and is performed under local or general anesthesia
Whats the other name for a grommet?
Tympanostomy tube
What is Cholesteatoma?
Abnormal collection/growth of skin in the middle ear
– Keratinized squamous epithelium in the wrong place
Can be congenital or acquired
Cause problems because they grow and are destructive
Can result in the destruction of the ossicles, as well as their possible spread through the skull into the brain
Describe how hearing works specifically in middle and inner ear
- Function of middle ear is transduce vibration into nervous impulses
- Foot of stapes vibrates in oval window
- Causes pressure wave through fluid in cochlear
- This is detected by hair cells in organ of corti
- Transmitted to brainstem (junction of pons and medulla) by CN VIII
What are the semicircular canals responsible for?
• Semicircular canals are responsible for detecting head rotation
vestibulo-ocular reflex
What is the saccule responsible for?
Saccule – detects linear acceleration in vertical plane
What is the utricle responsible for?
Utricle – detects linear acceleration in horizontal plane
What provides sensation to the middle ear?
Tympanic branch of glossopharyngeal nerve (CN IX)
AKA Jacobsons nerve.
What provides sensation to posterior half of EAC?
Auricular branch of vagus nerve (CN X) AKA Arnolds nerve
What is the function of the auricular branch of vagus nerve (CN X) AKA Arnolds nerve?
provides sensation to posterior half of EAC
What is the function of the tympanic branch of glossopharyngeal nerve (CN IX) AKA Jacobsons nerve?
provides sensation to posterior half of EAC
What innervates the anterior half of the EAC?
Facial nerve
What is the function of the facial nerve?
Provides sensation to anterior half of the EAC
What innervates the pinna?
Pinna
