outter and middle ear

cerumen

A sticky and unpleasant smelling substance •The amount, texture, coloration can vary depending on the individual and how long the wax has been in the ear •Excessive cerumen can cause problems

Middle Ear Function: The Area Ratio Advantage

The TM has a vibrating area ~________ greater than the oval window • Allows the sound pressure to be collected on the TM and then concentrated on the oval window • Examples • Water hose • Hammer/nail

Outer Ear: External auditory canal (2)

The external auditory canal is essentially a tube with effective acoustic characteristics. •The adult ear canal amplifies sound at a resonance frequency within the region of 2500-3000Hz, depending on the diameter and length of the canal. •This frequency region is very important in the perception of consonants and speech sounds. •resonance frequencies are considerably higher for the smaller ear canals of infants and young children

Middle Ear: Ossicles (2)

The first of the three ossicles is the malleus which is usually visible through the tympanic membrane. •The malleus connects with the short process of the incus which is the second ossicle. •The lenticular process of the incus connects with the head of the stapes which is the innermost stirrup-shaped ossicle. •The stapes is the smallest and lightest bone in the body.

Middle Ear: Muscles

The mallidus muscle is connect to the malleus and is innervated by the fifth or trigeminal cranial nerve. • The muscle contracts during self-generated sounds such as chewing and reduces the interference of self-generated sounds with hearing of external sounds. •The Stapedius muscle inserts into the neck of the stapes and is innervated by a branch of the seventh or facial cranial nerve. • This muscle stabilizes the stapes bone in quiet conditions.

Middle Ear: Borders

The middle ear consists of the tympanic membrane and a space behind it. •The middle ear space is enclosed within the temporal bone. •Laterally, the tympanic membrane separates the middle ear space from the external ear canal. •The medial border of the middle ear space includes the promontory round window and the oval window

middle ear functions

The middle ear system serves the important function of matching the low resistance of the air in the external ear canal to the high resistance or impedance of the fluid within the inner ear. •Resistance will occur in the auditory system because the sound waves are moving from the air (outer ear) to a solid (middle ear) to a fluid (inner ear) • As a result, more energy is required to make the transfer •The impedance matching middle ear system is important for normal hearing. •Three factors contribute to increased energy related to sound pressure as it passes from the ear canal through the middle ear to the inner ear: • The tympanic membrane is considerably larger in area than the stapes footplate • The ossicles connecting the tympanic membrane to the inner ear fluid function as a lever • The shape of the tympanic membrane contributes to an increase in the sound pressure reaching the inner ear

Middle Ear Function: Lever Action (leverage)

The ossicular chain pivots back and forth on an axis which acts as a lever • The lever takes the input force and amplifies it, providing a greater output force • Using leverage, the force the stapes receives is greater than that applied to the malleus

localization

orientation of ears to sound source, crease a slight time difference in the sound waves arrival between the 2 ears head shadow effect

Auricle/Pinna

visible part of ear

parts of temporal bone

zygomatic process, sqaumus portion mastoid process external auditory meatus styloid process mandibular fossa

•Middle Ear Function: Curved Membrane of the TM

• The TM is not flat but cone-shaped • This shape increases the __________ of the vibrations on the TM (speaker) and increases the _________ of the malleus • This enhances the impedance matching property of the middle ear

effect of middle ear on pressure

• pressure stronger than without the middle ear • Results in pressure increase; the same amount of energy that would be lost without the middle ear!

Middle Ear: Borders (2)

•The superior region is comprised of two air-filled spaces called the aditus ad antrum and the epitympanic recess which is also know as the attic. •The posterior region consists of air cells within the mastoid region of the temporal bone and the pyramidal eminence. •The Eustachian tube is located toward the inferior and anterior border of the middle ear.

Outer Ear: External ear canal (3)

•sebaceous and ceruminous glands lining the external ear canal secrete a substance called cerumen. •The word cerumen is from the Latin word cera and Greek word keros for "wax". It's commonly called earwax. •Cerumen is a sticky, unpleasant-smelling substance that helps to protect the ear by catching debris before it reaches the delicate tympanic membrane •Cerumen also helps to minimize bacteria and fungus from infecting the ear canal

The peripheral auditory system consists of the

Outer ear Middle ear Inner ear Auditory nerve that leads from the ear to the brainstem within the central auditory nervous system (CANS)

Outer Ear: External ear canal

An S-shaped tube that carries sound from the auricle to the tympanic membrane •Walls of the lateral or outer 2/3 of the ear canal consist of cartilage, whereas walls of the medial or inner 1/3 of the external ear canal of bone. •The curvy course of the external ear canal helps to protect the delicate tyrannic membrane located at the medial end of the canal. •The volume of the adult external ear canal is about 1.0ml

outer ear function

Concave shape helps to collect and amplify sound and to funnel the sound into the external ear canal. •The bowl-shaped concha increases sound levels by up to 10-15 dB in the frequency region of 4500 Hz. •Outer ear enhances the detection of sounds coming from the direction a listener is facing. •It enhances localization which is the process of determining where a sound is coming from.

wax management

Exits the ear naturally via shedding of skin cells and the distortion of the EAC with jaw movement Can be completed by an audiologist, ENT, GP, or PA with training If additional resources are needed: Softening Agents Manual removal Suction Irrigation Candling (not)

Middle Ear: Tympanic Membrane (2)

The tympanic membrane consists of three different layers of tissue. The outer epidermal is distinguished from the other two layers because it renews itself, Old cells in the epidermal layer migrate outward through the ear canal and new cells form in their place.

Middle Ear: Tympanic Membrane

The tympanic membrane is the outermost structure of the middle ear system. •The tympanic membrane separates the external ear canal from the middle ear space. •With illumination, the tympanic membrane typically reflects cone of light. •The extent of vibration/displacement of the tympanic membrane is very small.

Middle Ear: Ossicles

Three tiny bones that form a chain which connects the tympanic membrane to the inner ear. • They are the smallest bones in the human body • The three ossicles are called the: malleus, incus, stapes

annulus, pars flaccida, pars tensa

________The outer rim of the tympanic membrane, where it connects to the bony wall of the external ear canal The _______, which is the most flexible region of the tympanic membrane, is near the edge in the anterior-superior quadrant. The______ is the largest and tightest portion of the tympanic membrane and contributes mostly to hearing.

eustatian tube

allows for fluid drainage and air pressure equalization

EAC

external auditory canal outer portion= cartilgae metting place= osteocartiliagenous junction inner portion= bone

landmarks of auricle

helix, triangular fossa, scaphoid fossa, crux of helix, concha, tragus, intertragal notch, anti-tragus, lobe

pars flaccida

most flexible portion of tympanic membrane

pars tensa

most stiff region of tympanic membrane