Sense of Hearing Ear -important for hearing and equilibrium -made of the outer, inner, and middle ear

Outer Ear Pinna (auricle)-surrounds entrance to the external auditory canal –Made of elastic cartilage –Helps collect sound waves External Auditory Canal –Has ceruminous glands that create ear wax –Wax helps to slow the growth of microorganisms –Small hairs prevent the entry of objects and insects Eardrum (tympanic membrane) –Thin membrane that separates external from middle –Vibrates in response to the change in pressure –Begin of middle ear

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Middle Ear Job-send vibrations onto inner ear Made of the tympanic cavity (air filled) Auditory ossicles: 3 small bones –Malleus, incus, and stapes (smallest bone in body) –Bridge between outer and inner ear –Malleus is attached to ear drum and passes on vibration to incus and then to stapes Stapes’ vibrations will cause inner ear fluid to move –Increase or amplify the vibrations Gating (decrease loudness of sound) and impedance matching (gathering of weak sounds and concentrate it on an area)

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Middle Ear-Auditory Tube (eustachian tube) -connects to nasopharynx -regulates pressure on both sides of the ear drum which is important for normal hearing - allows for drainage of mucus from the middle ear into the throat u Copyright  The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Middle or Outer Ear Issues -middle ear infections (acute otitis media)- caused by mucous infections from auditory tube moving into the middle ear/presence of fluid in the middle ear -ears popping-eardrum moves back to the original position after the change in pressure/auditory tube fixing pressure -ear tubes-fluid forms behind eardrum and help to rid of the fluid -swimmer’s ear-infection in the ear canal-water build up causes bacteria or fungus to grow

Inner Ear-fluid filled Sense of equilibrium and hearing receptors in this region Membranous labyrinth-collection of tubes and chambers –Fluid filled-endolymph (protect receptors) Osseous labyrinth-dense bone that surrounds and protects membranous labyrinth –Contains fluid called perilymph u Copyright  The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Inside bony labyrinth vestibule-receptors here provide sensations of gravity and change of speed/direction Semicircular canals-respond to rotational movements (function in equilibrium) Cochlea-filled with fluid; provide sense of hearing –Covered with tiny hairs on the basilar membrane –Movement creates nerve signals that the brain (temporal lobe) interprets as signals –Round window (membrane) is attached to this –Has organ of corti that has hearing receptors u Copyright  The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

How do we hear? Need to write Organ of Corti has hearing receptors that are stimulated by the fluid vibrating (in cochlea) External acoustic meatus sends sound to ear drum, which vibates ossicles pick up vibraiton (incus, malleus, etc) Oval window transmits vibrations to vestibular membrane Travels to cochlea (has endolymph) Different vibrations in endolymph stimulate receptor cells (organ of corti) Depolarize receptor cell; release nt; signal to temporal lobe

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Sense of Equilibrium Two types of equilibrium The organs of static equilibrium help to maintain the position of the head when the head and body are still. The organs of dynamic equilibrium help to maintain balance when the head and body suddenly move and rotate. u Copyright  The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Static Equilibrium-body position at rest Vestibule is in charge of static equilibrium –Made of chambers called utricle and saccule Chambers have macula –Macula has many hair cells that are sensory receptors –Gel-like substance that hair cells project into –Otoliths-calcium carbonate around gel substance Bend head to side-stimulates hair cells Hairs bend and tilt into gel substance cause action potential to be sent Signal sent to brain to tell what is going on

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Dynamic Equilibrium-motion balance 3 semicircular canals of labyrinth are the important organs Ampulla-swelling in perilymph of bony labyrinth –Contains sensory organs called crista ampullaris Have hair cells and support cells Hairs extend into gel mass called capula –Hairs move opposite of body movement Send signal to brain (cerebellum)

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Deafness Conductive deafness –Middle ear issues –Block the normal transfer of vibrations from the tympanum to the oval window –Caused by scarring or perforation of tympanum or ossicle immobilization Nerve deafness –Cochlea issues –Receptors do not respond or reach their destinations