Ears And Hearing (2nd Ed, 1969)

for [Applause] [Music] come on [Music] no e [Music] the human ear externally a flap of skin and cartilage a gatherer of sound energy at the center of the Gathering organ is a short cartilagenous and bony tube the auditory canal which is sealed off by a flexible membrane sound waves are conducted along the canal and fall on this membrane the eardrum because it is suspended only at its edges to the auditory canal the ear drum can move freely in response to variations in air pressure inward as air pressure Rises outward as air pressure Falls this demonstration show shows the response of a freely moving membrane to Rapid and minute changes in air pressure sound [Music] waves the membrane vibrate sympathetically with the varying frequencies of sound waves the vibrating eardrum acts to transmit the mechanical energy of sound into the skull beyond the eardrum within the skull an airfill chamber the middle ear its major structures are three small bones which further conduct and amplify sound waves at the base of the middle ear chain chamber the ustan tube a duct connected by way of the throat to the outside air this hollow tube serves to equalize the air pressure on both sides of the eardrum so the human eardrum seen here from within the skull and under condition similar to life transmits by its vibrations mechanical sound energy from the environment into the body special lighting is being used to slow slow down the extremely rapid vibrations the vibrating eardrum sets off a chain reaction along the adjacent bones of the middle ear these are the bones of the middle ear the auditory oses the outermost is the malus or hammer it is the bone attached to the eardrum the middle bone is the incus or Anvil the innermost bone is the stapes or stup about as large as a grain of rice the auditory oules are connected in such a way that the slightest pressure on the first of them the hammer will be conducted AC cross the Anvil to the stup Sound Energy conducted from eardrum to hammer to Anvil to Stirrup the stup fits closely over and moves in and out of a small membrane covered opening this opening the oval window is the entrance to the the inner ear because the oval window is much smaller than the eardrum which activates the chain of Bones sound waves are Amplified some 30 times as they are conducted into the inner ear beyond the oval window enclosed within the hardest bones of the skull lies the inner ear this organ is made up of small fluid-filled structures the uppermost is the vestibular apparatus concerned with the sense of balance below the CIA concerned with the sense of hearing in the CIA the mechanical energy of sound is converted into electrochemical energy nerve impulses this specimen of the human CIA has been isolated from the skull it is about the size of a p and has a snail-shaped appearance a cross-section through the Bony exterior reveals that the organ contains one one two parallel tubes these tubes in the living CIA are filled with fluid and the fluid moves in response to sound the movement of cier fluid is crucial to hearing to understand why more information about the internal structures and mechanics of the CIA is necessary this is a simplified transparent model of the CIA along most of its length a partition divides the organ into two parallel canals the upper Canal leads from the sturup covered membrane the oval window the lower Canal ends at another membrane covered opening the right S window which faces back toward the middle ear both canals are filled with a watery fluid at the top of the CIA there is an opening through which the fluid may pass freely between the two canals as the vibrating sta pushes in and out against the oval window waves are set up in the fluid of the upper canal the waves move through this canal toward the top of the CIA here they pass through the opening into the lower Canal the membranous round window at the end of the lower Canal yields to the fluid displaced by the waves as the waves move through the canals the clear partition is set in motion the partition itself is a third fluid filled tube or ducked within the CIA a relatively stiff membrane separates the duct from the upper Canal a more flexible membrane the Basel membrane separates the duct from the lower Canal so the movements of the clear partition are actually movements of the two membranes which make up this duct Research indicates that sounds of various frequencies affect certain portions of the Basel membrane more than others [Music] the movements of the Bassler membrane within the cleia are extremely rapid and complex to show just how complex research scientists visualized the membrane uncoiled into a straight line and with the help of a computer plotted the movements of the membrane as it responds to given sounds the movements have been slowed down 700 [Music] times but these movements cannot be perceived by the brain as sound mechanical energy must somehow be converted into electrochemical energy nerve impulses a cross-section through the CIA reveals that the sensory organ which performs this function is located on the inner surface of the Bassel membrane here a portion of the Bassel membrane and the related organ of Cy covering the entire length of the membrane the organ is made up primarily of thousands of hair cells arranged in two groups inner and outer these hairs touch a stiff overhanging membrane a nerve fiber is associated with each hair cell research suggests that as the Basel membrane moves the cell hairs are bent in a way not completely understood this physical stimulus is converted into nerve impulses the impulses flow along the associated nerve fibers which converge to form the auditory nerve they continue along the nerve which branches to both halves of the brain to some extent then both halves of the brain share the information received by each ear an efficient three-stage process sound waves striking the eardrum are conducted mechanically too and Amplified in the middle ear converted into nerve impulses in the inner ear traveling along the auditory nerve the impulses reach the brain where they are perceived and interpreted as meaningful sound the normal process of hearing however may become impaired one kind of impairment is sensory deafness [Music] [Laughter] [Applause] [Music] sensory deafness occurs when there is damage to the nerve fibers of the inner ear through age disease drugs or prolonged exposure to loud sound at present sensory deafness cannot be treated successfully a second kind of deafness conductive deafness is due to improper movement of the structures of the middle ear conductive deafness can in most cases be corrected a series of standardized tests is given before any attempt a diagnosis or correction is made in one of these tests the subject listens to specially selected words to determine the extent of the hearing loss the words are Amplified to various levels until she can hear and repeat them Greyhound Greyhound stay home hot dog hot dog baseball Iceberg airplane baseball toothbrush toothbrush draw draw bed say the word fail fail say the word s shout say the word white white say the word rain rain say the word which which say the word soap soap in some cases a hearing aid to amplify sound waves is used to bring about sufficient Improvement in many cases of conductive deafness surgery will correct the handicap the patient first came to us complaining of difficulty hearing what people said to him we did a series of tests on him and it turned out that the cause of his hearing problem is a fairly common one the stup is not moving properly against the oval window a calcium deposit has formed and interferes with motion of the little bones much like rust on the hinge examination revealed that the eard drum was normal but hearing tests showed a conductive loss we use a surgical microscope when we operate on the ear because the area we work in is so small first carefully peel back the skin of the ear canal and the eardrum to reach the diseased bone next we take away some bone chips for better exposure we push aside small nerve there are the auditory oses Quick Check of the diagnosis both both a hammer and Anvil seem normal move well but the sterup is pretty well fixed won't move okay let's get it out this is fairly delicate cutting the sterup loose without damaging the Anvil here it comes get out the remaining fragments of the foot plate expose the oval window and there's the fluid of the inner ear we place gel foam over the window gel foam is a light porous material through which new tissue will grow to form a new flexible foot plate within a few days the gel foam dissolves now we must reconstruct the icular chain this wire Loop is a prosthesis an artificial replacement for the stup we put it in place fits nicely over the Anvil secure it looks like it'll hold now another piece of gel foam up here to promote tissue growth over the entire over window check it again prosthesis is free to move okay now we can close things up set the idrum back in place the entire operation takes less than an hour and the patient is usually able to go home the day following surgery in about 85 cases out of 100 hearing will be improved the spoken word is one of the best ways we have of communicating with one another but for 2 million Americans who suffer from conductive deafness this line of communication is to some degree blocked as surgical techniques improve more and more of them will be helped to better hearing for for