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Hair Cells Are Bent Against the Tectorial Membrane , Causing Them to Depolarize and Release Neurotransmitter That Stimulates Sensory Neurons

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Hair Cells Are Bent Against the Tectorial Membrane , Causing Them to Depolarize and Release Neurotransmitter That Stimulates Sensory Neurons EAR EAR - PARTS EXTERNAL EAR INTERNAL EAR MIDDLE EAR EXTERNAL EAR CONSISTS OF : 1. AURICLE OR PINNA 2. EXTERNAL AUDITORY CANAL 3. EARDRUM AURICLE OR PINNA IS A FLAP OF ELASTIC CARTILAGE SHAPED LIKE TRUMPET. COVERED BY SKIN RIM OF AURICLE IS HELIX 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 middle ear. 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 MALLEUS 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. TYMPANIC CAVITY PROPER EPITYMPANIC RECESS MIDDLE EAR CONTENTS AIR IS THE REAL CONTENT. THREE EAR OSSICLES--- STAPES,INCUS 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 inner ear. Malleus is attached to TYMPANIC MEMBRANE and the stapes is attached to the OVAL WINDOW of the cochlea. 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. TENSOR TYMPANI MUSCLE STAPEDIUS MUSCLE Tensor tympani and stapedius muscle 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 ROUND WINDOW INTERNAL EAR or LABYRINTH Lies in petrous part of temporal bone CONSISTS OF : BONY LABRYNTH MEMBRANOUS LABRYNTH INTERNAL EAR MEMBRANOUS LABRYNTH FILLED WITH ENDOLYMPH SEPARATED FROM BONY LABRYNTH WHICH CONTAINS PERILYMPH BONY LABYRINTH Is a series of cavities divided into three areas, inside these cavities or channels lies the membranous labyrinth. 1. Semicircular canals 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 SACCULE ,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. UTRICLE 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 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 tectorial membrane , 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 HELICOTREMA. 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 VESTIBULAR MEMBRANE or REISSNER’S MEMBRANE separates the cochlear duct from the scala vestibuli. The BASILAR MEMBRANE separates the cochlear duct from the scala tympani. SPIRAL ORGAN OR ORGAN OF CORTI 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 STEREOCILIA ( 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.
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