Ear - Anatomy & Physiology Flashcards
what is Jacobsons nerve and what does it supply?
Tympanic branch of the glossopharyngeal nerve CN IX
- sensation to middle ear
What is arnolds nerve and what does it supply?
Auricular branch of the vagus nerve CN X
- sensation to posterior half of the external auditory canal
what part of the ear does the vagus nerve supply?
posterior half of the EAC
what nerve supplies the pinna?
upper half = CN V3
lower half = greater auricular nerve (C2/C3)
what part of the ear does the facial nerve supply?
the anterior half of EAC
what nerve supplies the inner ear?
vestibulocohlear nerve (CN VIII)
WHAT IS THE LENTGH OF THE EXTERNAL EAR CANAL?
4cm
what is the medial and lateral 1/3rd of the EAC made of?
medial third made of skin and bone
lateral third made of skin and cartilage
what does the skin contain in the lateral 1/3rd of the EAC?
ceruminous and sebaceous glands which produce wax
what are 2 characteristics of the medial 1/3rd of the EAC?
no hairs or cilia
doesn’t produce wax (don’t have ceruminous or sebaceous glands in the skin)
where does the skin of the EAC grow from?
grows from the umbo of the tympani membrane outwards
what type of skin and what type of cartilage is found in the EAC?
Stratified keratinised epithelium
Elastic cartilage
why does minimal hearing loss occur with damage to the EAC?
the pinna isn’t good at sound localisation so if there is wax or disruption this can cause minimal hearing loss
what are the 3 layers of the tympanic membrane?
outer layer - continuous with skin of EAC
middle - fibrous layer
inner layer = respiratory epithelium (ciliated columnar epithelium with goblet cells)
what plays an important role in sound conduction?
ear ossicles found in the middle ear
what does the ossicles attach to?
connects to mastoid system via audits
connects to nasopharynx via eustachian tube
the middle ear receives sensation from the tympanic branch of glossopharyngeal nerve but what nerve runs through the middle ear?
chords tympani - branch of facial nerve
what are important relations of the inner ear?
middle cranial fossa
internal carotid artery
sigmoid sinus and internal jugular vein
apart from running through the middle ear, what else does the chord tympani supply?
taste to the anterior 2/3rds of tongue
what is cholesteatoma?
skin in the middle ear
keratinised squamous epithelium in the wrong place
the skin grows and becomes destructive
what are the collection of tubes and chambers within the inner ear known as?
labyrinth
what type of fluid is within the membraneous labyrinth?
perilymph and endolymph
what part of the inner ear is the the hearing organ?
organ of corti
what forms the peripheral vestibule aparatus in the inner ear?
semi circular canals
utricle
sacculae
what is the function of the semi circular canals in the inner ear?
detects head movement
vestibulo-occula reflex allows us to focus on an object when our head is moving
what is the function of the utricle and saccule in the inner ear?
utricle = detects linear movement in the horizontal plane
saccule - detects linear movement in the vertical plane
describe how we hear.
middle ear traduces vibration into nerve impulses
the foot of stapes vibrates in the oval window which causes a pressure wave through the fluid in the cochlea
the pressure wave is detected by hairs in the organ of corti which is then transmitted to the brain stem via vestibule-cochlear nerve VIII
Otalgia can be secondary to other conditions which cause damage to what nerves which affect the ear?
C2/C3
CN X - vagus
CN V - trigeminal
CN XI - glossopharyngeal
what does the auricular branch of the vagus nerve supply?
the lower part of the pinna
the posterior part of the EAC
what tests can be carried out for assessing hearing ?
clinical testing - hearing threshold test
tuning fork test - webers & rinne
audiometry - pure tone audiometry, visual reinforcement, play audiometry, tymapanometry
how does tympanometry work>
detected pressure within the middle ear
pushes air pressure into the ear canal which causes the tympanic membrane to move back and forth
it measures the mobility of the tympanic membrane which is put into a graph called a typanogram
what can a tympanometry detect?
wax blocking the ear
fluid in the middle ear
perforation of the tympanic membrane
how does are tone audiometry work?
pure tone air conduction test measures the minimum tone a person can hear at selected pitches (frequencies) from low to high
earphones are worn so information can be obtained from each ear
how is hearing loss managed?
surgery of outer and middle ear
sound amplification (hearing aids)
direct stimulus of cochlear nerve (cochlear implant)
what 3 systems does humans use for balance?
vision
vestibular (otolith organs in inner ear)
proprioception (CNS- cerebellum, cerebral cortex and brain stem)
what is the main clinical condition of the inner ear which causes imbalance?
benign paroxysmal positional dysfunction (BPPD)
what commonly causes imbalance? (not from the inner ear)
migraines
what is responsible for imbalance in people with BPPD?
calcium carbonate outwit the utricle into the semicircular canal
where does the cells which detect head movement and stabilisation lie within the inner ear?
the ampulla of the semi circular canals
where is higher frequency picked up and where is lower frequency picked up within the ear?
higher picked up more external
lower picked up more internal
what type of lymph is the cochlear filled with?
endolymph
why is the facial nerve important for surgeons when operating on or near the middle ear?
they have to be aware of the facial nerve and its 6 branches as it passes through the middle ear
a branch
a branch - chord tympani supplies taste to anterior 2/3rds of the tongue
provides motor supply to muscles of facial expression
what helps to stabilise the pressure within the middle ear and how?
eustachian tube - opens during swallowing and yawning to equalise pressure
mastoid air system via audits- releases air into middle ear when pressure gets too low
what can chronic dysfunction of the eustachian tube lead to?
negative pressure which causes retraction of the tympanic membrane leading to otitis media with effusion
