INTRODUCTION TO AUDIOLOGY (SPHS 1100) WEEK 3 POWER POINT TOPICS ANATOMY OF EAR PHYSIOLOGY OF EAR

GOALS and OBJECTIVES GOAL Learner will understand the different topics related to Audiology. OBJECTIVES TLW understand the anatomy and physiology of the ear. (cognitive)

Ear Diagram

ANATOMY OF EAR Parts Of the Ear The Human ear is divided in to three main parts Outer Ear Middle Ear Inner Ear

Outer Ear The outer ear is the visible part of the ear. The outer ear comprises a shell like-protrusion from each side of the head, a canal through which sounds travel, and the eardrum membrane. Eardrum membrane is called as Tympanic membrane. It consists of three parts 1. The Auricle (pinna ). 2. The External Auditory Canal. 3. The Tympanic Membrane

The Human Pinna and its landmarks (auricle)

Outer Ear The Auricle The auricle is the most visible part in the outer-ear mechanism. It varies in size and shape from person to person. The funnel-like shape plays an important role on gathering sound waves from the environment. The auricle is made of cartilage, with a number of twists, turns and indentations. The cartilage is covered with skin. The bottom-portion of the auricle is lobule or ear lobe.

Outer Ear The outer rim of the auricle folds outwardly forming helix. Antitragus is above the lobule. Antihelix is the elevation which is close to the center of auricle. A small triangular protrusion which points backwards and forms the anterior portion of the auricle is called the tragus. Depression of the tragus in to the opening of the external ear canal is an efficient means of blocking sounds.

Outer Ear The occlusion is more efficient than plugging the ear with a finger, clasping the hands over the auricle, and even using some earplugs specifically designed for sound attenuation. The middle portion of the outer-ear, before opening the head is called the concha. Concha is bowl shaped and it is divided in to the lower cavum concha and the upper cyber concha. The auricle is more efficient at delivering high- frequency sounds than low-frequency sounds. It helps on localization of sounds delivered to head.

Outer Ear The External Auditory Canal (EAC) The external auditory canal is a tube formed in the side of the head, which begins at the concha and extending inward at a slight upward angle for approximately 1 inch in adults. EAC is elliptical in shape and averages about 9mm in height and 6.5 mm in width. The outer portion of the external auditory canal passes through cartilage. The skin of EAC supports several set of glands such as sebaceous glands.

Cross section of the external ear

Outer Ear Sebaceous glands secrete an oily and fatty substance which is called sebum. The major product of these secretions is earwax, or cerumen. Cerumen exists the ear naturally when the walls of the EAC are distorted by movement of the jawbone during chewing and speaking. The outer third of the EAC contains a number of hair follicles. Cerumen and hairs helps to keep foreign objects from passing into the inner two-thirds of the canal.

Outer Ear The inner area of the EAC passes through tympanic portion of the temporal bone. There are no glands and hair in this area. The two portions of the EAC meet at the osseocartilaginous junction. The condyle which a protrusion of mandible comes to rest just below the osseocartilaginous junction when the jaw is closed. If the mandible override its normal position ,the condyle will press into the junction causing pain and this pain is called TemporoMandibularJoint (TMJ).

Outer Ear The angle of EAC is different in small children compared to adults. The canal angles downward, rather than upward and it is a more acute angle. Children’s ear can be examined from above the head because of the above reason.

Tympanic Membrane

Outer Ear Tympanic Membrane The external auditory canal ends in a concave disk- like structure called the tympanic membrane. It is also called as Ear Drum. The tympanic membrane acts as border between outer ear and middle ear. The total area is about 63.3 mm2 (Harris, 1986). It is constructed of three layers. The outer layer is osseous. The middle layer is tough, fibrous, connective tissue,

Outer Ear which contributes most of the membrane’s ability to vibrate with impinging sound. The middle ear space behind the tympanic membrane is lined with mucous membrane, including the third layer of the tympanic membrane. The tympanic membrane is thin averaging about 0.07mm. According to Harris (1986) movement of one-billionth of a centimeter is sufficient to produce a threshold response in normal hearing individuals in the 800 to 6000HZ range.

Middle Ear

Middle Ear  The middle ear is a space behind the eardrum and it is roughly 2 cm3. The roof of the middle ear is a thin layer of bone, separating the middle-ear cavity from the brain. Jugular bulb is below the floor of the middle ear and behind the anterior wall is the carotid artery. The labyrinth of the inner ear lies behind the medial wall . Mastoid process is beyond the posterior wall. The space in the middle ear above the tympanic membrane is called epitympanic recess.

Middle Ear Middle ear is separated from the external auditory canal by the tympanic membrane. It is connected to nasopharynx via the eustachian tube. Middle-Ear Cleft comprises of the eustachian tube and middle ear. The middle-ear cleft is lined with mucous membrane. The mucous membrane is ciliated and topmost cells contain cilia. The motion of cilia creates a wiping action which helps to cleanse the middle ear by moving particles down and out of Eustachian tube.

Middle Ear The Eustachian Tube The Eustachian tube enters middle ear anteriorly at a 30 degree angle and passes down in to nasopharynx for a distance of about 36 millimeters. The Eustachian tube opens during yawning, sneezing, or swallowing and when excessive air pressure is applied from the nose. Eustachian tube opens about once per minute when we are awake and an average of once every five minutes during sleep. The Eustachian tube is shorter and wider in length in children compared to adults.

Middle Ear The orifice of the Eustachian tube in the nasopharynx remain to open in infants till 6 months of age. The air pressure of middle ear must match that of the external auditory canal to keep the pressure equal on both sides of the tympanic membrane in order to increase its mobility. The major reason for the need of pressure equalization system is the absorption of air by middle-ear tissues.

Middle Ear The Mastoid Some of the bones of the skull which surround the ear are not solid and they are honeycombed with hundreds of air cells. Each of these cells is lined with mucous membrane and they are similar to that of the middle-ear cleft. These cells form the pneumatic mastoid of the temporal bone. The middle ear opens up, back and upward in an area called audits ad antrum. The mastoid process is the bony process behind the auricle .

Middle Ear Windows of the Middle Ear There are two windows in middle ear . 1. Oval window 2. Round Window The section of the bony portion of the inner ear extends to the middle ear space and this protrusion is called the promontory. The promontory separates two connections between the middle and inner ear. Oval window is above promontory and below is the round window.

Middle Ear The round window is covered by a very thin, tough and elastic membrane. The oval window is filled by a membrane which supports the base of stapes.

Middle Ear Bones in the Middle Ear Middle ear contains three small bones which are called as ossicles. 1. Malleus 2. Incus 3. Stapes The manubrium of the malleus is embedded in the fibrous layer of the tympanic membrane. Manubrium extends from the upper portion of the tympanic membrane to its approximate center.

Middle Ear The head of malleus is connected to the body of the incus. The incus has a long process or crus which turns abruptly to a very short crus, the lenticular process. The end of lenticular process sits on stapes. The stapes consists a head, neck, and two crura. The posteriors crus is longer and thinner than the anterior crus. The base or footplate of the stapes occupies the space in oval window.

Middle Ear The inward and outward movement of the umbo of the tympanic membrane causes malleus and incus to rotate, which transfers this force to the stapes. This movement in turn results in the inward and outward motion of the oval window. Vibrations of the tympanic membrane are conducted along the ossicular chain to the oval window. The chain acts like a single unit when transmitting sounds above 800HZ.

The Middle-Ear Impedance Matcher The average adult tympanic membrane is 85 to 90 mm2,but the effective vibrating area is only 55mm2. The vibrating area is 17 times that of the oval window. The sound pressure collected over the larger area of the tympanic membrane is focused on the oval window. The mass of the ossicular chain is poised to take advantage of the physical laws of leverage. The ossicular chain rocks back and forth on an axis and the action of the stapes in the oval window is like a pivot.

The Middle-Ear Impedance Matcher The combined effects of increased pressure and the action of the malleus result in a pressure increase at the oval window 23 times what it would be if airborne sound impinged on it directly.

Inner Ear

Inner Ear The inner ear contains the sensory organs for hearing and balance. It is made up of two parts, the cochlea and the vestibular system.  The cochlea deals with hearing where as the vestibular system affects balance. The bony shaped structure like a snail in the inner ear is cochlea. It is filled with endolymph and perilymph fluids.  The organ of corti is the sensory receptor inside the cochlea which holds the hair cells.

Inner Ear The vestibular Mechanism The membranous sacs with in the vestibule are called the utricle and the saccule. These two sacs are surrounded by perilymph and contain fluid called endolymph. The saccule is smaller than the utricle. The end organ for balance is located at the bottom of the utricle. The end organ within saccule is located on side on the side.

Inner Ear Semicircular canals arise from utricle. They are membranous, containing endolymph and surrounded in a larger bony cavern by perilymph. Three semicircular canals returns to the utricle through enlarged areas called ampullae. Each ampulla contains an end organ for the sense of equilibrium. The semicircular canals are arranged per-pendicular to one another to cover all dimensions in space. The semicircular canals are the receptors for angular acceleration.

Inner Ear The Auditory Mechanism Vestibule communicates with a snail-like shelled called the cochlea. Cochlea is made up of a twisting bony shell about 1cm wide and 5 mm from base to apex in humans. Scala vestibule is a part behind the oval window. At the bottom of the cochlea, the scala tympani is visible which begins at round window. Both of these canals contains perilymph which is continuous through a small passageway at the apex of the cochlea called the helicotrema.

Inner Ear The canal between scala vestibule and scala tmypani is scala media. Scala media is filled with endolymph and it is continuous through the ductus reuniens with the endolymph contained in the saccule, utricle, and semicircular canals. The scala media is separated from the scala vestibule by Reissners’ membrane and from the scala tmypani by the basilar membrane. The organ of corti which is the end organ of hearing extends along the full length of the scala media.

Inner Ear Basilar Membrane It is about 35 mm long and varies in width from less than 0.1 mm at the basal to turn about 0.5 mm at the apical turn . Three to five parallel rows of 12,000 to 15,000 outer hair cells and one row of 3,000 inner hair cells are located on the basilar membrane. Cortis’ arch separates outer and inner hair cells. The auditory nerve endings are located on the basilar membrane.

References Images https://www.studyblue.com/notes/note/n/final/deck/492 5488 https://ostranderbellepoint.wordpress.com/2013/03/30/e ars-are-strange/ http://biology- forums.com/index.php?action=gallery;sa=view;id=6155 http://news.stanford.edu/news/2013/august/ear-bone- conduction-080513.html http://patient.info/health/dizziness