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External Ear Structures Auricle Pinna Collects sound waves Basically like a funnel! Elastic cartilage and skin composition Auditory canal External acoustic meatus or the external ear canal Guides sound wave to tympanic membrane © 2009 The McGraw-Hill Companies, Inc. All rights reserved Middle Ear Structures Also referred to as the tympanic cavity Tympanic Membrane Ear ossicles Eardrum Vibrates in response to sound waves, transmitting vibrations to middle ear Connective tissue composition Malleus, Incus, Stapes Oval window Ossicles vibrate in response to vibration of tympanic membrane Separates middle ear from inner ear; stapes connected Round Window Vibrates opposite to vibrations entering the inner ear through the oval window © 2009 The McGraw-Hill Companies, Inc. All rights reserved Eustachian Tube ~36 mm in length, ~3 mm in diameter Connects middle ear to throat Closes and opens to equalize pressure on tympanic membrane and within middle ear As you age, tube becomes more upright (45° angle vs. 10°) Child’s tube is shorter in length © 2009 The McGraw-Hill Companies, Inc. All rights reserved Inner Ear Structures Labyrinth of communicating chambers Two Divisions Membranous Labyrinth Semicircular canals (3): detect balance of the body Vestibule: central part of labyrinth; equilibrium Bony Labyrinth Cochlea: coiled canal of dense bone tissue of the skull; shaped like a snail Divided into three fluid-filled parts. Two are canals for the transmission of pressure Third is the sensitive organ of Corti © 2009 The McGraw-Hill Companies, Inc. All rights reserved Cochlea Chambers Pressure Canals: Vestibular canal and tympanic canal Filled with perilymph Almost identical to CSF These canals transmit the movement of air/vibrations from outer/middle ear to cause movement of liquid and the basilar membrane Organ of Corti Contains the fluid endolymph Differs from perilymph in terms of their electrolytes If the membranes are ruptured, mixing of the fluids causes hearing impairment © 2009 The McGraw-Hill Companies, Inc. All rights reserved Organ of Corti “A masterpiece of cellular microarchitecture” Unique strip of epithelial cells allows for transduction of auditory signals into nerve impulses Transduction occurs through vibrations of structures in the inner ear causing displacement of cochlear fluid and movement of “hair” cells at the organ of Corti “Hair” cells = mechanosensory cells © 2009 The McGraw-Hill Companies, Inc. All rights reserved Organ of Corti Projecting from the tops of the hair cells are tiny finger like projections called stereocilia Arranged in a gradated fashion with the shortest stereocilia on the outer rows and the longest in the center. This gradation is thought to be the most important anatomical feature, allowing the sensory cells superior tuning capability © 2009 The McGraw-Hill Companies, Inc. All rights reserved 1. 2. 3. 4. 5. 6. 7. The Hearing Process 35-8 Sound waves collected through external ear canal and funneled to the tympanic membrane Waves cause tympanic membrane to vibrate Ossicles amplify vibrations The mechanical energy from movement of the middle ear bones pushes the oval window in the cochlea. This force moves the cochlea's fluids that, in turn, stimulate tiny hair cells of the organ of Corti Movement of hairs converted into nerve impulses • Length of stereocilia stimulated relays information regarding pitch and amplitude Impulses are transmitted by auditory nerve to the brain for interpretation © 2009 The McGraw-Hill Companies, Inc. All rights reserved 35-9 Equilibrium Position of Body/Movement Above the cochlea are two interconnecting chambers filled with endolymph, the sacculus and utriculus – part of the vestibule On their inner surface are patches of hair cells to which are attached thousands of tiny spheres of calcium carbonate (CaCO3) – ear stones or otoliths Gravity pulls these otoliths downward. As the head is oriented in different directions, the otoliths shift their position. Impulses initiated in the hair cells are sent back to the brain. © 2009 The McGraw-Hill Companies, Inc. All rights reserved Equilibrium (Ctd.) Motion of the body in regards to balance is detected in the semicircular canals Three canals that are found in each body plane (sagittal, transverse, frontal) Contain microscopic hairs, cilia; contain endolymph fluid Whenever the head is moved, the fluid within the canals lags; this stimulates the hair cells to send impulses back to the brain. When the hair cells send messages that are incongruent with what the eyes are seeing and our body is feeling, as may occur in a boat or aircraft during rough weather, motion sickness can result Sensory conflict Some people also suffer severe dizziness because otoliths have become dislodged from their utriculus (following a blow to the head) and settled in a semicircular canal. © 2009 The McGraw-Hill Companies, Inc. All rights reserved Ear Wax Cerumen; naturally produced by your body Produced in sebaceous and modified apocrine glands of the ear Coats the ear canal to moisturize it, fight off infection, keep dust, dirt, and other debris from getting inside ear 20 to 50 percent fat © 2009 The McGraw-Hill Companies, Inc. All rights reserved The Aging Ear External ear larger / earlobe longer Cerumen dryer and prone to impaction Ear canal narrower Eardrum shrinks and appears dull and gray Ossicles do not move as freely Semicircular canals less sensitive to changes in position – affects balance © 2009 The McGraw-Hill Companies, Inc. All rights reserved Hearing Loss Symptom of a disease, not a normal part of aging Conductive hearing loss Interruption in transmission to inner ear Causes Obstruction of ear canal Infection of middle ear Reduced movement of stirrup Sensorineural hearing loss Sound waves not perceived by brain as sound Causes Hereditary Repeated exposure to loud noises / viral infections Side effect of medication © 2009 The McGraw-Hill Companies, Inc. All rights reserved “Cauliflower Ear” Cauliflower ear is medically known as an auricular hematoma. The external ear is made of cartilage and it is the shape of the cartilage that gives the ear its distinctive shell-like shape. The cartilage is lined by perichondrium, a tight layer of connective tissue. Auricular hematoma occurs when the ear cartilage is injured Trauma results in fluid or blood collecting between the perichondrium and the cartilage. This blood or fluid can become permanent and scarred, resulting in the appearance of cauliflower ear. © 2009 The McGraw-Hill Companies, Inc. All rights reserved