PSYC 211 - Chapter 7


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CHAPTER 7 – AUDITION, THE BODY SENSES AND THE CHEMICAL SENSES Audition Audition is generally regarded as the second most important sense behind vision. This section will describe the nature of the stimulus, the sensory receptors, the brain mechanisms devoted to audition and details in the physiology of auditory perception. The Stimulus The vibration of an object causes molecules of air to condense and pull apart, generating a sound wave moving away from the source at 700 miles per hour. Our ears will perceive sounds if our receptor cells are stimulated by vibrations between 30 and 20 000 times per second. Sounds can vary in their pitch, loudness and timbre. o Pitch: It is determined by the frequency of vibration in hertz (Hz) o Loudness: It is a function of intensity of the degree to which the condensations and rarefactions of air differ from each other. o Timbre: It provides information about the nature of the particular sound (eg. Oboe vs. train whistle). A mixture of different frequencies of vibration contributes to the timbre. The ear is an analytical organ . When two different frequencies of sound waves are mixed, we perceive both the original tones. Anatomy of the Ear and Mechanical Transduction of Sound Outer Ear: Sound is first funneled via the pinna through the ear canal to the tympanic membrane (eardrum) which vibrates. Middle Ear: It consists of a hollow region behind the eardrum. It contains bones called ossicles which act as a relay of vibration from the eardrum. There are 3 different bones: Malleus (hammer), incus (anvil) and stapes (stirrup) 1
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Inner Ear: The incus and stapes transmit vibrations to the cochlea , a structure that contains receptors. The stapes presses against a membrane behind the oval window , an opening that surrounds the cochlea. The Cochlea o It is a snail-shaped structure consisting of two and three quarters turns of a gradually tapering cylinder. o The cochlea is filled with fluid. The sound from the air must be transferred into this liquid medium. o It is divided into 3 segments: the scala vestibule , the scala media , and the scala tympani. The receptive organ (Organ of Corti) consists of the basilar membrane, the hair cells and the tectorial membrane. o Hair cells : They are the auditory receptor cells that are anchored via Deiters’s cells to the basilar membrane . Sound waves cause the cilia of the hair cells to bend through the bending of the basilar membrane to produce receptor potentials. o Deiter’s cells : A supporting cell found in the organ of Corti; sustains the auditory hair cells. o Basilar membrane: A membrane in the cochlea of the inner ear; contains the organ of Corti o Tectorial membrane: A membrane located above the basilar membrane; serves as a shelf against which the cilia of the auditory hair cells move A membrane covered opening called the round window allows the fluid inside the cochlea to move back and forth. If the cochlea were in a closed system, no vibrations would be transmitted through the
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