EAR EAR - PARTS

EXTERNAL EAR INTERNAL EAR

MIDDLE EAR EXTERNAL EAR

CONSISTS OF :

1. OR PINNA

2. EXTERNAL AUDITORY CANAL

3. AURICLE OR PINNA IS A FLAP OF ELASTIC CARTILAGE

SHAPED LIKE TRUMPET.

COVERED BY SKIN

RIM OF AURICLE IS

LOWER PORTION IS LOBULE

LIGAMENTS AND MUSCLES ATTACH THE AURICLE TO THE HEAD EXTERNAL AUDITORY CANAL

Is a curved tube

2.5 cm long EXTERNAL AUDITORY CANAL

BONY PART

CARTILAGINOUS PART Collects sound waves and channels them inward TYMPANIC MEMBRANE OR EARDRUM Thin , transparent partition between the external auditory canal and . It is composed of connective tissues and has 3 layers…..

1.Outer surface of tympanic membrane is covered by epidermis ( stratified Squamous keratinised epithelium )

2.Inner surface is lined by simple cuboidal epithelium.

3.Middle layer is composed of collagen, elastic fibers and fibroblasts

Tympanic membrane is the only structure made from all the 3 germ layers ectoderm, endoderm and mesoderm. 3 LAYERS OF TYMPANIC MEMBRANE ARE:

1. CUTICLE LAYER

2. FIBROUS LAYER

3. MUCOUS LAYER

CUTICLE FIBROUS MUCOUS LAYER LAYER LAYER TYMPANIC MEMBRANE

LATERAL PROCESS PARS FLACCIDA OF

Tympanic membrane

UMBO EXTERNAL EAR MIDDLE EAR PARS TENSA Handle of malleus is attached to inner surface of tympanic membrane Point of maximum convexity of tympanic membrane is UMBO Tearing of tympanic membrane is called as PERFORATED EARDRUM

Tympanic membrane may be examined directly by an OTOSCOPE. External auditory canal contains a few hairs and specialized sweat glands called CERUMINOUS GLANDS ( MODIFIED APOCRINE GLAND ) that secrete earwax or cerumen.

The combination of hairs and cerumen helps prevent dust and foreign objects from entering the ear.

The wax secreting sebaceous glands are present in skin of pinna and external auditory canal. MIDDLE EAR PARTS

The middle ear converts air pressure waves to fluid pressure waves. PROPER

EPITYMPANIC RECESS MIDDLE EAR CONTENTS

AIR IS THE REAL CONTENT.

THREE EAR --- , AND MALLEUS

TWO MUSCLES---STAPEDIUS AND TENSOR TYMPANI

BLOOD VESSELS---BRANCHES OF MAXILLARY ARTERY,PTERYGOID PLEXUS OF VEINS.

NERVES-CHORDA TYMPANI AND TYMPANIC PLEXUS

Middle ear is lined by ciliated columnar epithelium except over the posterior part of the medial wall, posterior wall and parts of the medial surface of tympanic membrane , where it is cuboidal or squamous. CONTENTS OF MIDDLE EAR EAR OSSICLES

Ear ossicles increase the efficiency of transmission of sound waves to the .

Malleus is attached to TYMPANIC MEMBRANE and the stapes is attached to the of the . MALLEUS

Resembles a hammer

Largest ossicle

Parts;

head Neck Anterior process Lateral process Handle INCUS OR ANVIL

Parts;

Body

Long process Lentiform nodule STAPES STIRRUP

Smallest ossicle

Parts;

Head

Neck - provides insertion to stapedius

2 limbs or crura

Foot plate EAR OSSICLES (ALL EAR OSSICLES ASSUME ADULT SIZE AT BIRTH)

MALLEUS ( HAMMER )

INCUS ( ANVIL )

STAPES ( STIRRUP )

THE JOINT BETWEEN MALLEUS AND INCUS ( INCUDOMALLEOLAR JOINT ) IS SADDLE JOINT

THE JOINT BETWEEN INCUS AND STAPES ( INCUDO –STAPEDIAL JOINT ) IS BALL AND SOCKET JOINT

The stapedius is the smallest skeletal muscle in the human body.

Just over one millimeter in length.

Its purpose is to stabilize the smallest bone in the body, the stapes.

STAPEDIUS MUSCLE

Tensor tympani and contract simultaneously in response to loud sounds

They restrict the vibrations of the tympanic membrane and the ossicles The tensor tympani muscle tenses the tympanic membrane, thereby damping down the vibrations of the malleus

Paralysis of tensor tympani leads to HYPOACUSIS, which leads to partial deafness for Low pitched sounds.

Paralysis of stapedius produces HYPERACUSIS in which normal sounds appear too loud. The anterior wall of the middle ear contains an opening that leads directly into the Auditory tube or pharyngotympanic tube, commonly known as EUSTACHIAN TUBE.

EUSTACHIAN TUBE helps in equalizing the pressures on either sides of the EAR DRUM.

MIDDLE EAR

Eustachian tube

PHARYNX

AUDITORY TUBE , which consists of both bone and elastic cartilage , CONNECTS THE MIDDLE EAR WITH THE NASOPHARYNX. During swallowing and yawning , it opens , allowing air to enter or leave the middle ear until the pressure in the middle ear equals the atmospheric pressure.

When pressures are balanced, the tympanic membrane vibrates freely as sound waves strike it.

If the pressure is not equalized , intense pain, hearing impairment , ringing in the ears. and vertigo could develop.

The auditory tube also is a route for pathogens to travel from the nose and throat to the middle ear, causing the most common type of ear infection, the OTITIS MEDIA. OVAL WINDOW SEMICIRCULAR CANAL VESTIBULE

COCHLEA MIDDLE EAR INTERNAL EAR or LABYRINTH Lies in petrous part of temporal bone

CONSISTS OF :

BONY LABRYNTH

MEMBRANOUS LABRYNTH INTERNAL EAR MEMBRANOUS LABRYNTH FILLED WITH

SEPARATED FROM BONY LABRYNTH WHICH CONTAINS Is a series of cavities divided into three areas, inside these cavities or channels lies the .

1.

2. Vestibule vestibule 3. cochlea Semicircular canals

cochlea Bony labyrinth contains perilymph Membranous labyrinth contains endolymph

The level of potassium ions ( K+ ) in endolymph is unusually high , and potassium ions play a role in the generation of auditory signals. MEMBRANOUS LABYRINTH

3 PARTS

SPIRAL DUCT OF COCHLEA OR ORGAN OF HEARING

UTRICLE AND ,ORGANS OF STATIC BALANCE

SEMICIRCULAR DUCTS ,ORGAN OF KINETIC BALANCE VESTIBULE Vestibule is the oval central portion of bony labyrinth

The membranous labyrinth in THE VESTIBULE CONSISTS of two sacs called the 1. 2. SACCULE

Projecting above and behind the vestibule are the 3 BONY SEMICIRCULAR CANALS. They are named 1. ANTERIOR 2.POSTERIOR 3. LATERAL

At one end of each canal is a swollen enlargement called the AMPULLA

The portions of the membranous labyrinth that lie inside the bony semicircular canals are called the SEMICIRCULAR DUCTS. These structures connect with the utricle of the vestibule. COCHLEA Resembles shell of snail

Cochlear canal makes two and three quarter turns

Central bony core is called the

MODIOLUS

COCHLEAR DUCT 35 MM COCHLEA COCHLEA IS DIVIDED INTO 3 CHANNELS:

1. COCHLEAR DUCT 2. SCALA VESTIBULI 3. SCALA TYMPANI COCHLEA

MIDDLE EAR COCHLEAR DUCT

The COCHLEAR DUCT OR SCALA MEDIA is a continuation of the membranous labyrinth. It is filled with endolymph. DIAGRAMMATIC REPRESENTATION OF THE SECTIONAL VIEW OF COCHLEA

The transduction of sound waves into action potentials takes place when hair cells are bent against the , causing them to depolarize and release neurotransmitter that stimulates sensory neurons. The channel above the cochlear duct is the scala vestibuli, which ends at the OVAL WINDOW.

The channel below is the scala tympani , which ends at the ROUND WINDOW.

Both the scala vestibuli and scala tympani are part of the bony labyrinth of the cochlea; therefore , these chambers are filled with perilymph. The scala vestibuli and scala tympani are completely separated by the cochlear duct , except for an opening at the apex of the cochlea, the .

The cochlea adjoins the wall of the vestibule, into which the scala Vestibuli opens.

The perilymph in the vestibule is continuous with that of the Scala vestibuli. The or REISSNER’S MEMBRANE separates the cochlear duct from the scala vestibuli.

The separates the cochlear duct from the scala tympani. SPIRAL ORGAN OR lies on the BASILAR MEMBRANE, which are the receptors of hearing.

Spiral organ contains supporting cells and 16,000 hair cells.

There are 2 groups of hair cells: inner hair cells outer hair cells At the apical tip of each hair cell are ( long, hair like microvilli ) that extend into the endolymph of the cochlear duct. Hair cells synapse with cochlear branch of vestibulocochlear nerve. Their cell bodies are located in SPIRAL GANGLION

ORGAN OF CORTI The TECTORIAL MEMBRANE a thin flexible elastic gelatinous membrane, covers the hair cells of the spiral organ.

The ends of the stereocilia of the hair cells are embedded in the tectorial membrane While the bodies of the hair cells rest on the basilar membrane.

INNER HAIR CELLS ARE THE RECEPTORS FOR HEARING.

Outer hair cells do not serve as hearing receptors, instead , they increase the sensitivity of the inner hair cells.

PHYSIOLOGY OF HEARING THE FOLLOWING EVENTS ARE INVOLVED IN HEARING 1. The auricle directs sound waves into the external auditory canal.

2. when sound waves strike the tympanic membrane , the alternating waves of high and low pressure in the air cause the tympanic membrane to vibrate back and forth. tympanic membrane vibrates slowly in response to low –pitched sounds and rapidly in response to high – frequency sounds.

3. The central area of the tympanic membrane connects to the malleus, which vibrates along with the tympanic membrane. This vibration is transmitted from the malleus to the incus and then to the stapes. 4. As the stapes moves back and forth, its oval shaped footplate via a ligament to the circumference of the oval window, vibrates in the Oval window . The vibrations at the oval window are about 20 times more vigorous than those of the tympanic membrane because the auditory ossicles efficiently transmit small vibrations spread over a large surface area.

5. The movement of the stapes at the oval window sets up fluid pressure waves in the perilymph of the cochlea. As the oval window bulges inward, it oushes on the perilymph of the scala vestibuli.

6. Pressure waves are transmitted from the scala vestibuli to the scala tympani and eventually to the round window, causing it to bulge outward into the middle ear. 7. As the pressure waves deform the walls of the scala vestibuli and scala tympani, they also push the vestibular membrane back and forth, creating pressure waves in the endolymph inside the cochlear duct.

8. The pressure waves in the endolymph cause the basilar membrane to vibrate, which move the hair cells of the spiral organ against the tectorial membrane. This leads to bending of the stereocilia and ultimately to the generation of nerve impulses in first - order neurons in cochlear nerve fibers.

9. These impulses are transmitted by the afferent fibres via auditory nerves to the auditory cortex of the brain, where the impulses are analysed and the sound is recognized. EQUILIBRIUM INTRODUCTION

• The ear not only detects sound, but also changes in equilibrium (e-kwi- lib-re-um) or balance.

• Body movements that stimulate the receptors for equilibrium include linear acceleration or deceleration, such as when a car suddenly takes off or stops; tilting the head forward or backward, as if to say "yes";. And rotational (angular) acceleration or deceleration, such as when a rollercoaster takes a quick curve.

• Collectively, the receptor organs for equilibrium are called the VESTIBULAR APPARATUS .These include the utricle and saccule of the vestibule and the semicircular ducts of the semicircular canals. The vestibular apparatus is composed of 3 semi – circular canals and the ( macula is the sensory part of saccule and utricle).

Each semicircular canal lies in different plane at right angles to each other. Each semicircular canal lies in a different plane at right angles to each other. The membranous canals are suspended in the perilymph of the bony canals. The base of canals is swollen and is called AMPULLA, which contains a projecting ridge called which has hair cells. The saccule and utricle contain a projecting ridge called MACULA.

The crista and macula are the specific receptors of the vestibular apparatus responsible for maintenance of balance of the body and posture.

OTOLITHIC ORGANS: UTRICLE AND SACCULE

• The two otolithic organs are the utricle and saccule.

• Attached to the inner walls of both the utricle and the saccule is a small, thickened region called the MACULA

• The two maculae contain the receptors for linear acceleration or deceleration and the position of the head (head tilt).

• The maculae consist of two types of cells: hair cells, which are the sensory receptors, and supporting cells.

• The saccule and utricle contain a sensory projecting ridge called as MACULA Hair cells have on their surface STEREOCILIA (which are actually microvilli) of graduated height, plus one , a conventional cilium that extends beyond the longest stereocilium.

As in the cochlea, the stereocilia are connected by tip links. Collectively, the stereocilia and kinocilium are called a hair bundle.

Scattered among the hair cells are columnar supporting cells that probably secrete the thick, gelatinous, glycoprotein layer, called the , that rests on the hair cells.

A layer of dense calcium carbonate crystals, called (oto- = ear; -liths — stones) extends over the entire surface of the otolithic membrane.

• the maculae of the utricle and saccule are perpendicular to one another.

• when the head is in an upright position, the macula of the utricle is oriented horizontally and the macula of the saccule is oriented vertically.

• because of these orientations, the utricle and saccule have different functional roles.

• the utricle responds to linear acceleration or deceleration that occurs in a horizontal direction, such as when the body is being moved in a car that is speeding up or slowing down.

• the utricle also responds when the head tilts forward or backward. The saccule responds to linear acceleration or deceleration that occurs in a vertical direction, such as when the body is being moved up or down in an elevator. The crista and macula are the specific receptors of the vestibular apparatus responsible for maintenance of balance of the body and posture.

• Because the OTOLITHIC MEMBRANE sits on top of the macula, if you tilt your head forward, the otolithic membrane (along with the otoliths) is pulled by gravity.

• It slides "downhill" over the hair cells in the direction of the tilt, bending the hair bundles.

• However, if you are sitting upright in a car that suddenly jerks forward, the otolithic membrane lags behind the head movement due to inertia, pulls on the hair bundles, and makes them bend in the other direction.

• Bending of the hair bundles in one direction stretches the tip links, which pulls open cation channels, producing depolarizing receptor potentials; bending in the opposite direction closes the cation channels and produces hyperpolarization. • As the hair cells depolarize and hyperpolarize, they release neu- rotransmitter at a faster or slower rate.

• The hair cells synapse with first-order sensory neurons of the vestibular branch of the vestibulocochlear (VIII) nerve.

• These neurons fire nerve impulses at a slow or rapid pace depending on the amount of neurotransmitter present.

• Efferent neurons also synapse with the hair cells and sensory neurons.

• Evidently, the efferent neurons regulate the sensitivity of the hair cells and sensory neurons. SEMICIRCULAR DUCTS

• The three semicircular ducts lie at right angles to one another in three planes.

• The two vertical ducts are the anterior and posterior semicircular ducts, and the horizontal one is the lateral semicircular duct.

• This positioning permits detection of rotational acceleration or deceleration.

• The dilated portion of each duct, the ampulla, contains a small elevation called the CRISTA

• Each crista consists of a group of hair cells and supporting cells. The hair cells contain a kinocilium and stereocilia (collectively known as a hair bundle), and the stereocilia are interconnected via tip links.

• Covering the crista is a mass of gelatinous material called the CUPULA CRISTA • When the head rotates, the attached semicircular ducts and hair cells move with it.

• However, the endolymph within the ampulla is not attached and lags behind due to inertia.

• The drag of the endolymph causes the cupula and the hair bundles that project into it to bend in the direction opposite to that of the head movement.

• if the head continues to move at a steady pace, the endolymph begins to move at the same rate as the rest of the head. This causes the cupula and its embedded hair bundles to stop bending and to return to their resting positions. Once the head stops moving, the endolymph temporarily keeps moving due to inertia, which causes the cupula and its hair bundles to bend in the same direction as the preceding head movement.

At some point the endolymph stops moving and the cupula and its hair bundles return to their resting, unbent positions. Note that bending the hair bundles in one direction depolarizes the hair cells; bending in the opposite direction hyperpolarizes the cells.

The hair cells synapse with first-order-sensory neurons of the vestibular branch of the vestibulocochlear (VIII) nerve.

When hair cells are depolarized, there is a greater frequency of action potentials generated in the vestibulocochlear (VIII) nerve than when hair cells are hyperpolarized EQUILIBRIUM PATHWAYS

• Bending of hair bundles of the hair cells in the semicircular ducts, utricle, or saccule causes the release of a neurotransmitter (probably glutamate), which generates nerve impulses in the sensory neurons that innervate the hair cells. • The cell bodies of sensory neurons are located in the vestibular ganglia. • Nerve impulses pass along the axons of these neurons, which form the vestibular branch of the vestibulocochlear (VIII) nerve .Most of these axons synapse with sensory neurons in vestibular nuclei, the major integrating centers for equilibrium, in the medulla oblongata and pons. • The vestibular nuclei also receive input from the eyes and proprioceptors, especially proprioceptors in the neck and limb muscles that indicate the position of the head and limbs. The remaining axons enter the cerebellum through the inferior cerebellar peduncles. • Bidirectional pathways connect the cerebellum and vestibular nuclei. • The vestibular nuclei integrate information from vestibular, visual, and somatic receptors and then send commands to ….

• (1) the nuclei of cranial nerves—oculomotor (Ill), trochlear (IV), and abducens (VI)—that control coupled movements of the eyes with those of the head to help maintain focus on the visual field; • (2) nuclei of the accessory (XI) nerves to help control head and neck movements to assist in maintaining equilibrium; • (3) the vestibulospinal tract, which conveys impulses down the spinal cord to maintain muscle tone in skeletal muscles to help maintain equilibrium; and • (4) the ventral posterior nucleus in the thalamus and then to the vestibular area in the parietal lobe of the cerebral cortex (which is part of the primary somatosensory area; see areas 1, 2, and 3 in to provide us with the conscious awareness of the position and movements of the head and limbs. DEVELOPMENT

THE FIRST PORTION OF EAR TO DEVELOP IS INTERNAL EAR FROM ECTODERM

DEVELOPS 22 DAYS AFTER FERTILISATION

THE AGE ASSOCIATED PROGRESSIVE LOSS OF HEARING IN BOTH EARS IS CALLED PRESBYCUSIS Sound intensity is measured in units CALLED DECIBELS The hearing threshold – the point at which an average young adult can just distinguish sound from silence is defined as 0 db at 1000 HZ.

Rustling leaves have a decibel level of 15

Whispered speech ,30 The sounds heard most acutely by The human ear are those from Normal conversation,60 Sources that vibrate at frequencies Between 500 and 5000 hertz Vacuum cleaner, 75 The entire audible range extends from 20 to 20,000 HZ. Shouting ,80

Jackhammer or nearby motorcycle,90

Sound becomes uncomfortable for normal year at 120dB

Painful above 140 dB THANK YOU