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BIOL 153
Robert Harris

Biology 153/155 Notes Parveen Kaur Sarana May 28 , 2012 - Hearing and balance basically use the same mechanism - Special Senses: Hearing and Balance Tympanic membrane: ear drum is the boundary between the outer ear and the inner ear Middle ear: three small bones that articulate with each other but are not attached with other bones.they basically articulate with the ear bone and take all the vibrations from the ear drum. The last bone (smallest) connects to a membrane that is between middle and inner ear. This bone transfers the vibrations to the inner ear Middle ear is filled with air because water has a lot more mass than air does. Vibrations can easily be sent via air but it would be much more difficult if it was filled with water. Mucus sometimes fills up the auditory tube causing fluid to fill up with fluid which is why it is hard to hear when you are sick The auditory tube is connected to the phaynx where there is air coming in at Po. This helps keeps the pressure constant at either side of the drum. When we change altitude quickly sometimes it takes the pharyx time to catch up. The outside of the ear drum is much lower pressure so the ear drum buldges out. = painful The inner ear is covered in boning and is filled with fluid. Inner ear is where we see the actual “hearing” and sense of balance. “Snail shell” = cochlea = sense of hearing Middle ear bones – smallest bones in the body 1. Malleus (looks like a hammer) Incus Sterup = they are held into place by ligaments to the inner ear and the bone-y portion The ear drum is directly attached to the malleus so that if there is any vibrations we get the ear drum vibrating in and out = vibration in malleus = vibration in the incus that is amplified due to hinge like structure of malleus = leaver of the incus transfers to the stapes. We see a mechanical amplification as these small bones move together to make sound bigger Skeletal muscle: Stapedis musle and Tensor tympani muscle act as protection from really loud noises. Loud noise = these muscles contract and when they do they limit the degree of motion of the bones in the middle ear. They protect the chochlea because it limites the transmission of the sound waves = basically mutes Prolonged exposure to loud noise will still be damaging because these muscles cannot stay contracted because they cannot maintain protection max 30 minutes due to fatigue Round/Oval Window = very thin membranes, dispurses sound waves/ make them die out so that there is no echoing with the cochlea Inner Ear Two types of structures 1. Central chamber = Utricle = a common area where fluid can enter into the semicircular canals (3 on each side oriented in 90 degrees to each other – each in a different axis of rotation = one that senses up/down, side/side, rolling = basically senses how our body rotates in 3D space). Maculae = how our head is oriented/how its moving Notice: the utricle is connected to the cochlear duct which is all filled with the same fluid = endolymph = unique compared to other extracellular fluids in the body because it is high in K and low in Na. Any other fluid filled compartment in the body is basically relatively high Na and low K. We compartmentalize K and Na/K ATPase keeps Na out and K in. Extracellular fluid compartments are generally the same Na/K ratio. Endolymph is the opposite of that ratio. Completely different that any other fluid filled compartments WHY? Along the cochlear duct = region of epithelial cells Hair cell = epithelial cells = has a synaptic connection with the receptor cells Endolymph surrounds the modified cilia. The surface of the hair cells is not symmetrical that on one side there is a very thick and long cilium (kinocilium) as you progress away from that we get smaller cilia (middle = stereocilia there are not as big as kinocilium and internally they do not In between the ciliums we have glycoproteins that connect the ciliums. If you move one you end up moving them all. The cilia stick out into the endolymph. They hav
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