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January 13 Lecture - Special Senses Hearing and Equilibrium...

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January 13, 2009 Special Senses: Hearing and Equilibrium - Ear is the mechanical receptor involved in hearing and equilibrium - Both dependent on basic receptor mechanism, o Hearing receptor o Mechanical Receptor o Ear External ear/Outer ear Middle ear (location where large amount of hearing is located) Inner ear (involved in both hearing and equilibrium) The Ear - Consists of three parts o External ear/Outer ear Directs sound waves to middle of ear o Middle ear Located behind temporal bone (as is the inner ear)) Converts sound waves from external ear into tiny vibrations and transmits them into the inner ear As the sound waves are moved through the middle ear it is magnified o Inner ear Sensory organs transmit signals to nerve impulses which then move the impulse to the appropriate areas of the brain for interpretation The External Ear - Two regions o Expanded portion is known as the auriple or pinna Made up of elastic cartilage, small slips of muscle, and skin o Short canal running to the middle ear is the external auditory meatus About an inch in length, ending at the tympanic membrane ( ear drum ) Contains a waxy material known as cerumen which is secreted by ceruminous glands which is excreted onto the sides of the external auditory meatus Serves to protect ear from intruders (bugs, dirt, dust) o Tympanic membrane represents the division between the external ear and middle ear The Middle Ear - Structures are contained within a cavity known as the tympanic cavity or middle ear cavity - Region is filled with air along with three small bony ossicles o Extremely important for sense of hearing, stretch along the length of the middle ear cavity o Three Ossicles are:
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Malleus : attaches directly to the tympanic membrane ( Hammer ) Incus: articulates with the malleus ( Anvil ) Stapes: articulates with the medial portion of the incus and the fenestra ovalis (or oval window) which is the opening to the inner ear ( Stirup ) The malleus and incus attached to roof of tympanic cavity by means of tiny ligaments which suspend them within the cavity o Ossicles transmit vibrations in to the inner ear - A narrow tube extends from the tympanic cavity to the nasal pharynx, called the e ustachian tube o Functions: allows cavity of the ear to be equalized by atmospheric pressure
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