Anatomy of the Outer and Middle Ear

What are the 3 main components of the ear

outer ear

middle ear

inner ear

Label this diagram

Which structure marks the boundary between the outer ear and the middle ear

the tympanic membrane/ eardrum

Which structures mark the boundary between the middle ear and the inner ear

round window and oval window

General function fo the outer ear

collects sound from auditory space

funnels sound towards the middle ear

General function of the middle ear

transduces sound energy (pressure) into movements of joints of the ossicle chain

General function of the inner ear

converts movements of the ossicle chain into electrical impulses of hearing

General function of the brain in relation to the ear

interprest signals from the ear into a meaningful special sense

Explain the process of hearing

1. ear canal (external acoustic meatus) catch sound waves and funnel them to the tympanic membrane

2. sound waves cause the eardrum to vibrate causing movement of the ossicles which amplify the vibrations

3. the stapes pushes on the oval window transmitting the vibrations to the cochlear, creating waves in the cochlear fluid

4. this causes hair cells in the cochlear to move and convert the mechanical energy into electrical signals

5. the auditory nerve carries these signals to the brain

What is another factor excluding function that explains why we can separate the ear into those 3 categories

they have disorders or pathologies unique to each division

they have different embryological derivations

Consequence of diseases to the outer ear

conductive deafness- usually occurs when sound waves are physically blocked from reaching the eardrum

What is the general definition of conductive deafness

soundwaves are blocked from reaching the inner ear due to issues in the outer or middle ear

Consequences of diseases to the middle ear

conductive deafness- usually caused by the middle ear becoming filled with fluid

Consequences of disorders of the inner ear

sensorineural deafness- eaither sensorial (problem with the transduction of mechanical to electrical energy by the heair cells) or neural (damage to the actual nerves themselves)

Embryological origin of the outer ear

first pharyngeal cleft (ectoderm)

Embryological origin of the middle ear

first pharyngeal pouch (endoderm)

Embryological origin of the mucosa lining the pharynx and eustachian tube

first and second pharyngeal pouch

Neural innervation of the outer ear

-sensory dupply shared between the trigeminal and facial nerves (1st and 2nd pharyngeal arch nerves)

What are the 2 muscles found in the middle ear

tensor tympani- attached to the malleus

stapedius- attatched to the stapes

both protect the inner ear from damage caused by loud noises (e.g. chewing, shouting)

Motor supply to the tensor tympani

develops formt he 1st pharyngeal arch so its motor supply comes from the motor division of the trigeminal nerve (mandibular division of the trigeminal)

Motor supply to the stapedius

-develops from the 2nd pharyngeal arch so its motor supply comes from the motor division of the facial nerve

What is the outer ear also known as

the external ear

What is the outer ear further divisible into

the pinna/ auricle and the external auditory canal

What is the auricle/pinna of the era

external visible part of the ear

What is the structure of the pinna

-its skeleton is made form elastic cartilage and it is covered by skin

What is the main function of the pinna

to collect sound from the auditory space

What causes cauliflower ear

blunt force trauma/ repeated friction to the outer ear which causes a blood clot to form between the skin and cartilage cutting off nutrients to the cartilage causes it to harden, scar and deform

Label this image

Auricle/pinna of the ear

Which nerves provide sensory innervation to the skin covering the ear

lesser occipital nerve- innervates the skin of the auricle

greater auricular nerve

auricotemporal nerve (branch of CNV3)- innervates skind of auricle and external auditory meatus

auricular branch of the facial nerve- innervates deeer aspect of auricle and EAM

auricular branch of vagus nerve- innervates deeer aspect of auricle and EAM

Shape of the external auditory canal

sinuous S-shaped canal ensures that the velocity of the air slows so bacteria/dust etc doesn’t travel further into the ear to the tympanic membrane

what are the 2 main parts of the external auditory canal

outer 1/3- made of elastic cartilage

inner 2/3- made of the tympanic plate of the temporal bone

What lines the EAC

lined by skin throughout which then also covers the outer plate of the tympanic membrane

Features of the skin lining the outer 1/3 of the external auditory canal

-many hairs (trpas dust etc)

-has ceruminous glands that secrete bactericidal wax (prevents bacteria developing)

-has sabaceous glands

How do the features of the skin change as you go deeper into the external auditory canal

fewer hairs as you travel deeper into the canal

What is the ear-cough reflex

• triggered by activation of the auricular branch of the vagus nerve which triggers the cough reflex mechanism

Label this image, which structure is shown

tympanic membrane

What are the 3 layers of tissues of the tympanic membrane

outer/lateral plate layer- lined by skin (keratinised stratified squamous cells

middle plate layer- fibrous layer

inner plate layer- respiratory epithelium (low columnar epithelium)

Which bone does the tympanic membrane adhere to

malleus

Function of the ossicular chain

-act as an impedence matching device

-sound has to travel from air into the cochlear fluid and most of it would bounce back

-however the ossicles are able to increase pressure at the oval window by acting as a lever and due to the oval window having a much smaller surface area than the eardrum

-this makes the sound ensuring it is strong enough tot move the fuid in the cochlea properly

Sensory nerve supply to the external surface of the tympanic membrane

auriculotemporal nerve (branch ov CNV3)

small branch of the vagus nerve

Sensory nerve supply of the internal surface of the tympanic membrane

glossopharyngeal nerve

Label this image

Features of the middle ear

bi concave compartment

aroudn 15mm diamete

normally filled with air

has 6 walls

Lateral wall of the middle ear

inner plate of the tympanic membrane

Medial wall of the middle ear

outer plate of the oval window

Roof of the middle ear

tegmen tympani

Flood of the middle ear

jugular wall

Posterior surface of the middle ear

mastoid wall

Anterior usrface of the middle ear

carotid wall

What are the 2 compartments that the middle ear is separated into by this line

epitympanic recess- above the line

tympanic cavity- below the line

How does the middle ear communicate with the nasopharynx

via the auditory/eustachian tube

How does the middle ear communciate with the mastoid air cells

via the epitympanic recess and mastoid antrum

Contents of the middle ear

tympanic membrane

auditory ossicles

auditory tube

muscles of the ossicles

branches of facial and glossopharyngeal nerves

epitympanic recess

mastoid air cells

upper respiratory epithelium

Function of the eustachian/pharyngotympanic tube

passes between the tympanic cavity and the nasopharynx and equalizes pressure across the membrane (keeps air pressure on both sides of the eardrum the same)

drains contents of middle ear cavity (epithelium secretes miucus)

Consequences of eustachian tube dysfunction

failure to drain mucuous secretions of the middle ear leading to congestion

What is an otoscopy

medical examination using an otoscope (light magnifying device to inspect the ear canal, tympanic membrane and outer ear