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The Senses Hearing and the Vestibular System

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The Senses Hearing and the Vestibular System The Senses Hearing and the vestibular system Jennifer Carbrey Ph.D. Department of Cell Biology Auditory System Sound waves are transmitted through air by the compression and expansion of air molecules in the form of pressure waves. Auditory system detects complex sounds and breaks them into their basic sound frequencies. Sound frequencies are converted to action potentials by the ear and relayed to the brain (auditory areas) for interpretation. image by Pluke, http://commons.wikimedia.org/wiki/File:CPT-sound-pitchvolume.svg, public domain Anatomy of the Ear Pinna and external auditory canal (air filled) focus sound waves on the tympanic membrane, which rocks the malleus, incus, and stapes (air filled), causing ripples in the cochlear fluid (fluid filled) and auditory transduction. image by Dan Pickard (modified), http://commons.wikimedia.org/wiki/File:HumanEar.jpg, public domain Sound Transmission Middle ear amplifies sound waves & couples vibrations of tympanic membrane with oval window. Vibrations at oval window sets off the ripples in the cochlear fluid within the scala vestibuli and scala tympani. These ripples cause the basilar membrane to vibrate. image by Dan Pickard (modified), http://commons.wikimedia.org/wiki/File:HumanEar.jpg, public domain Sound Transmission Middle ear amplifies sound waves & couples vibrations of tympanic membrane with oval window. Vibrations at oval window sets off the ripples in the cochlear fluid within the scala vestibuli and scala tympani. These ripples cause the basilar membrane to vibrate. image by Dick Lyon (modified), http://commons.wikimedia.org/wiki/File:Cochlea.svg, public domain Organ of Corti Stereocilia of hair cells are embedded in the tectorial membrane. As the basilar membrane bounces up & down, stereocilia bend. Bending in one direction depolarizes the cell; in the other direction hyperpolarizes the cell. image by Oarih (modified), http://commons.wikimedia.org/wiki/File:Cochlea-crosssection.png, Creative Commons Attribution 3.0 Unported license Sound Transduction After a hair cell (= receptor) activates the afferent neuron, axons from these neurons join to form the cochlear nerve. The region of the basilar membrane that vibrates the most correlates with the frequency of the sound. The louder the sound, the more vibration and the greater frequency of action potentials produced in the afferent neurons. Sense of Balance: Vestibular System Two receptor organs in the inner ear sense movement of the head. They detect: - angular acceleration (shake or nod your head); - linear acceleration (elevator drops, or body leans to one side). Semicircular canals: respond to changes in head rotation. Otolith organs: saccule detects vertical movement. utricle detects horizontal movement. Sense of Balance: Vestibular System Semicircular canals detect angular acceleration during rotation nodding yes of the head along three perpendicular axes : shaking no tipping ear to shoulder image from The Effects of Space Flight on the Human Vestibular System, an online educational article by the U.S. government’s National Aeronautics and Space Administration (NASA), http://commons.wikimedia.org/wiki/File:Vestibular_organs-_canals,_otolith,_cochlea.jpg, public domain Semicircular Canals image from The Effects of Space Flight on the Human Vestibular System, an online educational article by the U.S. government’s National Aeronautics and Space Administration (NASA), http://commons.wikimedia.org/wiki/File:Inner_ear%27s_cupula_transmitting_indication_of_acceleration.jpg, public domain Otolith Organs OTOLITH ORGANS: sheets of hair cells that detect changes in linear acceleration or position of the head. Since the otoliths are heavier than the fluid around the hair cells, a change in position causes them to move and pull on the stereocilia otoliths – calcium carbonate crystals embedded in gel at the tips of stereocilia UTRICLE detects movement in the horizontal plane (acceleration during take off in a plane or car). SACCULE detects vertical movement (jumping). Cells are at a 90 degree angle compared to utricle. Otolith Organs animation by Rick Melges, Duke University Key Concepts The auditory system detects complex sounds and breaks them into their basic sound frequencies. The fundamental frequency components are transduced into action potentials and transmitted through the auditory pathways to the brain for interpretation. The vestibular system aids in maintaining the body’s balance by detecting the position and motion of the head in space. The sensory cells are in the ampullae of the semicircular canals and in the utricle and saccule. .
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