Anatomy of Ear Flashcards
What are the parts of the ear?
- External
- Middle
- Inner
Look at the parts of the external ear
What is the epithelium of the pinna/auricle?
Stratified keratinized epithelium - skin
What is the cartilage of the pinna and external auditory canal?
Elastic cartilage
What is the lateral and medial portions of the external ear made from?
- Lateral 1/3rd made of skin and cartilage
- Medial 1/3rd made of skin and bone
What glands are contained within the later portion of the external ear?
Ceruminous and sebaceous glands- produce wax
What is the hair distribution in the external ear?
Lateral portion - thick hairs on the outside , become finer inside
Medial portion - no hairs or cilia
Does the medial ear produce wax?
No
What ist he function of the hair and wax in the middle ear?
–Protective barrier and disinfectant
Where does the skin of the external ear grow from?
From the umbo of the tympanic membrane outwards
How is skin shed in the external ear?
Shed in the lateral 1/3rd of canal and trapped in wax as part of cleaning mechanism
Why does wax or other mechanical obstructions cause minimal hearing loss when compared with problems in other parts of the ear?
•The human pinna is not very good at sound localisation
What are the following parts of the tympanic membrane?
What are the three 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 and thickness of the tympanic membrane?
- 1cm in diameter
- 1/10th of a millimeter thick
What are the ossicles?
Malleus
Incus
Stapes
What is the function of the ossicles?
Conduct sound waves from tympanic membrane to the inner ear
What causes disruption of sound conduction by the ossicles?
–Disruption can be from trauma or bony sclerosis (otosclerosis)
What is the epithelium of the middle ear?
•Lined with same continuous respiratory epithelium that forms inner layer of tympanic membrane
–Capable of producing mucous (glue ear)
What does the middle ear connect to?
Mastoid system via aditus and nasopharynx via Eustachian tube
What nerve does the middle nerve contain?
Facial nerve
- chorda tympani
Chorda tympani is also involved in providing taste to the anterior part of the tongue, sensory supply to anterior portion of the tongue is also supplied by mandibular branch of the trigemnial nerve. (CNV3)
What are the important relations of the middle ear?
–Middle cranial fossa
–Internal carotid artery
–Sigmoid sinus and internal jugular vein
Also: Meninges, mastoid cavity, Inner ear
What are the 6 segments of the facial nerve?
–Intracranial
–Meatal segment (internal auditory meatus)
–Labyrinthine segment
–Tympanic segment (Fallopian tube. 10% of which are dehiscent. i.e within mucosa)
–Mastoid segment
–Extratemporal segment
What does the facial nerve do to the face?
•Motor supply to the muscles of facial expression
–Stapedius
–Posterior belly of digastric
–Stylohyoid
Chorda tympani also supplies taste to the anterior two thirds of the tongue
What is cholesteatoma?
Skin in the middle ear - –Keratinized squamous epithelium in the wrong place
The inner ear contains a bony and membranous labyrinth, what does the membranous labyrinth contain?
–contains fluid – perilymph and endolymph
What is the hearing organ?
The cochlear - contains nerve endings that transmit sound vibrations to the auditory nerve
Organ of corti
What is the purpose of the peripheral vestibular apparatus?
Controls balance
What is the vestibular system composed of?
3 semicircular canals and 2 otolith sensors
What do the semicircular canals detect?
angular accelerations (head rotations)
What do the otolith organs detect?
Sensitive to linear straight line accelerations
How are the semi - circular canals arranged?
as a set of 3 mutually orthogonal sensors - each canal is at a right angle to another. Each canal is maximally sensitive to rotations that lie in the plane of the canal
What are the otolith organs?
The utricle and the saccule
What is the function of the utricle and the saccule?
The utricle senses motion in the horizontal plane (eg, forward-backward movement, left-right movement, or a combination thereof). The saccule senses motions in the sagittal plane (eg, up-down movement).
Which nerve is responsible for both hearing and balance?
Vestibuocochlear nerve (CN V111)
What is the mechanism of hearing?
- 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 makes you able to fix your vision on an object even when your head is moving?
Vestibulo-ocular relfex - semicircular canals
What provides sensation to the middle ear?
Tympanic branch of glossopharyngeal nerve (CN IX) AKA Jacobsons nerve
What provides sensation to the posterior half of the EAC?
•Auricular branch of vagus nerve (CN X) AKA Arnolds nerve
What supplies the anterior half of the EAC ?
Facial nerve
What supplies the pinna?
Mandibular branch of the trigeminal nerve
