External and Middle Ear

7/21/2019 External and Middle Ear

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EXTERNAL AND MIDDLE EAR

CLASS: JC3 2013

COURSE: NEUROSCIENCE

CODE: NS 43

LECTURER: DR ROHANA O’CONNELL

DATE: 29/10/13 1600-1700



LEARNING OBJECTIVES

• Structure of external ear

• Tympanic membrane

• Conductive deafness

• Middle ear: ossicles, round and oval

windows

• Tensor tympani and stapedius

• Mastoid air cells





PINNA





NERVE SUPPLY TO PINNA





EXTERNAL AUDITORY CANAL

• 25mm long

• Outer 1/3 –cartilage

• Inner 2/3 – bony

• Apopilosebaceous glands

• Hair follicles

• Sebaceous gland

• Ceruminous gland

•The skin is tightly boundto the underlyingcartilage. Inflammationhere is painful because ofthe limited potential forswelling.



EXAMINING AN ADULT’S EAR



EXAMINING A CHILD’S EAR





TYMPANIC MEMBRANE

• EAC terminates at the tympanic membrane TM

• In newborns the TM is horizontal

• In adults , the TM sits at a 55 degree angle

• Ossification of EAC causes changes in angle of TM

until about age 5 when it reaches adult position



TYMPANIC MEMBRANE

Three Layers of TM

- Ectoderm (cutaneous) - continuous with EAM

- Mesoderm (fibrous) - Radial Fibers

- Concentric Fibers

- Endoderm (mucous) - continuous with TympanicCavity

Pars Tensa contains all three layers.

Pars Flacida DOES NOT contain fibrous layer.



TYMPANIC MEMBRANE



Only epidermal and mucosal layer



MIDDLE EAR



MIDDLE EAR

• Tympanic Cavity

• Ossicles

• Eustachian Tube

• Middle Ear Muscles

• Consists of 4 walls , a ceiling and a floor



OSSICLES







THE CEILING

Tegmen tympani

• Paper thin.

• Separates the tympanic cavity from the middle cranialfossa which houses the temporal lobe.

• Inflammatory conditions of middle ear can pass through

the petrous-squamosal suture in children directly to the

meninges of temporal lobe of cortex.



MEDIAL WALL

• Prominence of lateral semicircular canal

• Prominence of facial canal

• Oval window

• Promontory (basal turn of cochlea)

• Round window



POSTERIOR WALL

• Mastoid wall

• Aditus ad antrum

• Pyramidal eminence

• Jugular wall and jugular vein

• Carotid wall

• Carotid artery

• Eustachian tube

ANTERIOR WALL



LATERAL WALL

• Membranous wall

• Tympanic membrane

• Jugular wall

• Formed by tympanic plate

THE FLOOR





STAPEDIUS

• Smallest muscle

• Nerve to stapedius

• Pyramidal eminence to neck of

stapes• When it contracts, it reduces the

action of the stapes

( it reduces amplification)

• Contracts just before speakingand chewing (can be loud

enough to cause damage)



TENSOR TYMPANI

• Originates from cartilaginous portion

of ET and inserts into the handle of

malleus

• Tense the tympanic membrane

• Reduces the effectiveness of sound

transmission, protecting the inner ear

during louds sounds

•Supplied by V3



EUSTACHIAN TUBE



EUSTACHIAN TUBE

Differences between adults and infants

• Angle of ET

• Adults - about 40 degrees

• Children - more horizontal

• Length

• Adults - about 35 mm

• Children - shorter

• Flaccidity

• More flaccid in children



MUSCLES OF EUSTACHIAN TUBE



EUSTACHIAN TUBE

Function:

• Tensor palatini definitely involved in opening ET.

•Levator palatini role is not clear.

• Clearance of middle ear fluid

• Protect middle ear from nasal secretion

• Equalising middle ear pressure



MASTOID ANTRUM



MASTOID AIR CELLS

• Mastoid air cell system served as an reservoir of air and

serves as buffer system to replace air in the middle ear

cavity temporarily in case of Eustachian tube dysfunction.

• The mean volume of air in the mastoid air cell system could

be about 5-8 ml. CT scan evaluation of temporal bone is

considered to be the best modality to assess mastoid air

cell system.

•Patients with poor pneumatization of mastoid air cell systemare more prone to develop adhesive otitis media following

middle ear infections as the normal buffering system of the

mastoid pneumatization is not adequate in them.



CT TEMPORAL BONE



MASTOID ABSCESS



ROUND WINDOW / OVAL WINDOW





HEARING LOSS



CONDUCTIVE HEARING LOSS

• Is the result of sounds not being able to pass freely to the

inner ear.

•

Usually due to blockage in the outer or middle ear• Ear wax

• Otitis externa

• Stenotic or atretic ear canal

• Perforated tympanic membrane

• Otosclerosis

• Usually can be corrected



SENSORINEURAL

HEARING LOSS

• Sensory, cochlear, neural or inner ear hearing loss.

• Damage to the hair cells within the cochlea or thehearing nerve (or both).

• Causes:

• Presbycusis• Regular and prolonged exposure to loud sounds.

• Ototoxic drugs

• Certain infectious diseases, including Rubella

• Complications at birth

• Injury to the head

• Benign tumours on the auditory nerve

• Genetic predisposition – some people are especiallyprone to hearing loss

Documents

External and Middle Ear