Ear Flashcards
What occurs in the external ear?
Receives sound waves
What occurs in the middle ear?
Transmits sound waves from air to bone
Amplifies by bone to bone
Transmits sound to inner ear
What occurs in the inner ear?
Sound waves converted to nerve impulses (transmitted to CNS via acoustic nerve)
Contains vestibular organs
What type of epithelium is found on the PINNA?
Stratified keratinised epithelium
What type of cartilage is found on the PINNA?
Elastic - blood supply from overlying dense connective tissue/perichondrium
What type of glands are found in the skin of the lateral 1/3 of the external ear canal and what do they secrete?
Curuminous and sebaceous glands
Modified sweat glands that produce wax
What happens to the hairs as you move medially into the external ear canal?
Hair is thick on the outside and becomes finer
What is the lateral 1/3 of the external ear canal made of?
Skin and cartilage
What is the medial 2/3 of the external ear canal made of?
Skin and bone
No hairs/cilia
No wax
How does the skin grow in the external ear canal?
Grows from umbo of tympanic membrane outwards
How is skin maintained in the external ear canal?
Constantly shed and renewed
Shed in lateral 1/3 of canal and trapped in wax as part of cleaning mechanism
Why is the ear canal prone to infections?
Warm, wet. blinded ended
Can be bacterial or fungal
What is bacterial otitis externa caused by?
Pseudomonas or staph aureus
What are the 3 layers of the tympanic membrane?
Outer - continuous with skin of EAC
Middle fibrous layer
Cuboidal epithelium
What are the contents of the middle ear?
Ossicular chain Oval window Round window Facial nerve (chorda tympani) Eustachian tube opening Mastoid air cells
What are the 3 parts of the ossicles?
Malleus (hammer)
Incus (anvil)
Stapes (stirrup)
What is the function of the ossicles?
Conduct sound waves from tympanic membrane to inner ear via oval window
Amplification of sound
Very important in sound conduction
What can disruption of sound conduction in the ossicles be caused by?
Trauma Bony sclerosis (otosclerosis)
What is the process of hearing?
Direct sound into canal Tympanic membrane vibrates Ossicular chain vibrates Transmitted to oval window of cochlea Detected by hair cells in organ of corti Converted to nerve impulses Transmitted to brainstem via CN VIII
What is the eustachian tube?
Tube that connects middle ear to nasopharynx
What are the functions of the eustachian tube?
Pressure equalisation (gas exchange occurs, vacuum formed in middle ear, vacuum released when eustachian tube opened) Mucus drainage
What is acute otitis media?
Infection of the lining of the middle ear
Can be bacterial or viral
What are the signs of acute otitis media?
Bulging red tympanic membrane
Pus in middle ear
Pain - improves with perforation of TM and pus discharge from ear
What are complications of pus in acute otitis media?
Pus can also be present in the mastoid air cells which leads to mastoiditis
What happens in otitis media with effusion?
Eustachian tube isn’t opening = negative pressure which causes fluid being drawn in middle ear which limits mobility of ossicular chain resulting in hearing loss
Occurs easily in children due to narrow eustachian tube, large adenoids at opening
Why is otitis media with effusion an issue in children?
Needs to be treated because it is an important time for language learning
90% improves in 3 months
If after 3 months a GROMMET may be inserted
What is cholesteatoma?
Negative pressure which sucks in tympanic membrane forms retraction pocket
Retraction pocket enlarges over time which results in skin no longer being able to move out = ball of keratin stuck in middle ear which slowly destroys and invades structures
Can be congenital
What are the complications of otitis media and cholesteatoma?
Problems involving: Meninges Middle cranial fossa Facial nerve Mastoid cavity Inner ear Sigmoid sinus/IJV
What are the 6 segments of the facial nerve?
Intracranial Meatal (internal auditory meatus) Labyrinthine Tympanic Mastoid Extratemporal
What muscles of facial expression does the facial nerve give motor supply?
Stapedius
Posterior belly of digastric
Stylohyoid
What are the 5 branches of the facial nerve?
Temporal Zygomatic Buccal Marginal mandibular Cervical
What is the cochlear?
Organ of corti - involved in hearing
Bony and membranous labyrinth
Membranous labyrinth contains perilymph and endolymph
What makes up the peripheral vestibular apparatus?
Utricle
Saccule
Semicircular canals
What nerve supplies the inner ear?
Vestibulocochlear nerve (CN VIII)
What is the role of the semicircular canals in balance?
Detect head rotation
What is the role of the saccule in balance?
Detects linear acceleration in vertical plane
What is the role of the utricle in balance?
Detects linear acceleration in horizontal plane
What nerve supplies sensation to the middle ear?
Tympanic branch of glossopharyngeal nerve
= Jacobson’s nerve
What nerve supplies sensation to the posterior half of the external auditory canal?
Auricular branch of vagus nerve
= Arnold’s nerve
What nerve supplies the anterior half of the external auditory canal?
Facial nerve
What nerve supplies the pinna?
Mandibular branch of trigeminal nerve
