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Bio-Psych: Four Senses:_Hearing Balance Taste Smell.doc

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PSYC 280
Neil Watson

Biological Psychology 7edition Website-sourced Study Questions Chapter 9: Hearing, Vestibular Perception, Taste, & Smell Hearing BOX 9.1 The Basics of Sound Study questions: 1) The auditory system is highly sensitive and can rapidly detect changes in intensity, measured in decibels (dB), and in frequency, measured in hertz (Hz). The decibel scale is logarithmic and is calculated from the ratio of the sound pressure level of the source being measured (say, a jetliner) to a reference level. This reference level is the human threshold intensity for hearing a 1000-Hz tone and is calculated to be 0.0002 dyn/cm2 in amplitude. Each Part of the Ear Performs a Specific Function in Hearing • The external ear captures, focuses, and filters sound • The middle ear concentrates sound energies • The cochlea converts vibrational energy into waves of fluid • Active mechanical processes in the cochlea enhance frequency discrimination Study questions: 2) The external ear consists of the fleshy part on the outside of the head, called the pinna, plus the canal that leads to the ear drum. 3) The middle ear starts at the eardrum, which is formally known as the tympanic membrane. This is connected to the inner ear by a series of minuscule bones, the malleus, the incus, and the stapes, which are known collectively as the ossicles. 4) The ossicles act by focusing the energy collected on the large tympanic membrane onto the small oval window, which results in amplification. The middle ear also contains two tiny muscles called the tensor tympani and the stapedius, which act like a gain (or “volume”) control. 5) n the operation of this muscular volume control, the muscles, when contracted, prevent the ossicles from moving as much as they normally would, thereby reducing the amount of energy transmitted to the inner ear and, in essence, “turning down the volume.” This system is activated within milliseconds when a loud sound is encountered, either in the environment or originating within the body. In the case of vocalization, the system activates itself just before you start to speak, which is the reason you do not experience your own voice as deafeningly loud. 6) The auditory portion of the inner ear is the cochlea, which is just 4 mm in diameter and resembles a snail. It is made up of three canals running along its length—the tympanic canal, the vestibular canal, and the middle canal—and is filled with fluid. 7) When the ossicles push on the oval window, vibrations are transmitted to the fluid filling the cochlea, which in turn causes the basilar membrane to vibrate. This membrane is five times wider at its apex than at its base. On top of the membrane is the organ of Corti, which contains a framework of supporting cells plus the main sensory cells: the inner hair cells 1 (humans have about 3500 of these) and the outer hair cells (humans have about 12,000 of these). 8) From the tops of the hair cells protrude tiny stiff hairs called stereocilia that contact the tectorial membrane, which lies over the organ of Corti. 9) The basilar membrane “encodes” the frequency of the stimulus as a function of its shape. When the ossicles transmit vibrations to the oval window, this energy is transmitted to the fluid filling the inner ear and causes the basilar membrane to begin vibrating as well. Which portion of the basilar membrane shows the greatest amplitude depends on the frequency of the sound (a process resembling “sympathetic vibration”). Because the basilar membrane is wedge shaped, it encodes frequency along its length. High frequencies preferentially affect the narrow end of the basilar membrane (the base), whereas low frequencies have the greatest affect where the membrane is widest (the apex). 10)Movement of the basilar membrane, induced by vibrations in the cochlear fluid, causes the stereocilia of the hair cells to bend. Very small movements of the stereocilia produce rapid changes in the ion channels of the stereocilia. These changes appear to be the result of the action of tip links, which are mechanical tethers between adjacent stereocilia. 11)When the stereocilium sways over, the tip link pulls open its ion channel(s), causing an extremely rapid depolarization. When the stereocilium sways back upright, the ion channel snaps shut again. The whole process takes a fraction of a millisecond. The depolarization leads to an influx of Ca2+ ions at the base of the hair cell, resulting in the release of transmitter—most likely glutamate. Auditory System Pathways Run from the Brainstem to the Cortex Study questions: 12)After leaving the cochlea, auditory information is “sharpened” in the medial geniculate nucleus and auditory cortex by neurons that are excited by certain frequencies but inhibited by neighboring frequencies. 13)The superior olivary complex is the first level that receives input from both ears. This is important for binaural interaction (that is, stereo), which allows for the spatial localization of sound sources. 14)Tonotopic organization is the term used to describe the maintenance of an orderly arrangement according to frequency within the auditory projections, as revealed by studies employing the uptake of 2-deoxyglucose to reveal brain areas selectively activated by exposure to particular frequencies. Studies of human subjects using PET and fMRI show that pure tones chiefly activate the primary auditory cortex, but that speech activates other cortical regions as well, and that the same regions are activated when subjects try to lip-read. Pitch Information Is Encoded in Two Complementary Ways Study questions: 15)The frequencies to which humans are sensitive range from about 20 Hz to as much as 20,000 Hz. Up to 2000 Hz, we can discriminate differences of as little as 2 Hz between tones, although this minimal discriminable frequency difference is larger above 2000 Hz. 16)One theory of pitch perception is called the place coding. “Place” refers to the location on the basilar membrane that is particularly affected by the sound. Each part of this structure 2 responds preferentially to a particular frequency. In this schema, if the brain knows the place on the basilar membrane where a sound has its greatest effect, it also knows the sound’s frequency. 17)An alternative theory of pitch perception, called the temporal coding, argues that the frequency of a sound is directly encoded in the pattern of action potentials. Contemporary views of pitch perception incorporate both theories: Temporal coding is especially effective for lower frequencies, whereas place coding is especially effective at higher frequencies. Brainstem Auditory Systems Are Specialized for Localizing Sounds Study questions: 18)Binaural processing of sounds may occur at various brainstem locations, including the superior olivary complex and also at the level of the inferior colliculus; bipolar neurons are thought to perform these comparisons. Hearing Loss Is a Major Disorder of the Nervous System • There are three main causes of hearing loss and deafness • Treatments for deafness focus on replacing missing stimulation Study questions: 23)What are the three major forms of deafness? a) Conduction deafness involves problems with the outer or middle ear that prevent transmission of vibratory stimuli to the inner ear. b) Sensorineural deafness involves disorders of the cochlea or eighth cranial nerve that interfere with the transduction and transmissionof auditory information to the brain. c) Central deafness involves disorders of the auditory systems of the brain, with highly variable symptoms. 24)Hearing may be at least partially restored in individuals who are profoundly deaf through the use of cochlear implants, which, in the case of sensorineural deafness, bypass the damaged cochlea to stimulate the auditory nerve directly. Although present implants are limited to a range of about 32 different frequencies, such devices have been shown to aid in the development of language skills. Such stimulation dramatically increases the metabolic activity of the auditory cortex, indicating that it is activating the cortex, and outcomes are especially good for patients who are young. Vestibular Perception The Receptor Mechanisms for the Vestibular System Are in the Inner Ear Study questions: 25)The vestibular system detects the force of gravity on the body and the acceleration of the head in three dimensions. This system consists of three s
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