Class8_and9_Audition_Olfaction

Class8_and9_Audition_Olfaction - Outline Audition and...

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1 Audition and Olfaction Outline • Physics of Sound • Structure of the Ear – Middle ear – Inner ear • Sound Processing – Frequencies – Localization • Vestibular System Sound • Hearing involves the detection of sound waves • Usually detect sound waves traveling through air – Can also detect sound waves in liquids (swimming/diving) and solids Components of Sound Hertz ( Hz ) – cycles per second of sound wave, perceived as pitch High frequency Low frequency Frequency: Number of pulses per second Components of Sound Amplitude or intensity – perceived as loudness Pure tone – a tone with a single frequency – number of cycles – of vibration Most sounds in the real world are not pure tones, they consist of multiple frequencies
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2 Outline • Physics of Sound • Structure of the Ear – Middle ear – Inner ear • Sound Processing – Frequencies – Localization • Vestibular System Figure 9.1 External and Internal Structures of the Human Ear (Part 1) Middle Ear The middle ear concentrates sound energies. Stapedial reflex: muscles contract and reduce sound’s effect Inner Ear Inner ear structures convert sound into neural activity. Mammals have a fluid-filled cochlea , a spiral structure with a base and an apex . The base is nearest the oval-window membrane. Figure 9.2 Basilar Membrane Movement for Sounds of Different Frequencies
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3 Basilar Membrane Sound waves cause the basilar membrane to vibrate. Different parts respond to different frequencies: • High frequency – activates narrow base of basilar membrane • Low frequency - activates wider apex Inner Ear Components The organ of Corti contains hair cells that bend when the basilar membrane vibrates When hair cells detect a vibration, they stimulate the vestibulocochlear nerve which sends a signal to the brain Progression of Sound Sound wave outer ear middle ear (can be dampened) basilar membrane vibration hair cells detect vibration vestibulocochlear nerve Outline • Physics of Sound • Structure of the Ear – Middle ear – Inner ear • Sound Processing – Frequencies – Localization • Vestibular System Figure 9.6 Auditory Pathways of the Human Brain What You Need to Know Auditory (vestibulocochlear) nerve brainstem thalamus auditory cortex
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4 Thalamus and Auditory Cortex Neurons within the brain are organized tonotopically. They are arranged in a map according to the frequencies they respond to. PET and fMRI show main activation is in the primary auditory cortex (in the temporal lobe). Figure 9.7 Mapping Auditory Frequencies in the Cat Inferior Colliculus (Part 2) Encoding Frequencies • Minimal discriminable frequency difference – the ability to detect a change in frequency • Hearing tests Place theory • Place theory: frequency is determined by the place on the basilar membrane where excitation is greatest Figure 9.2 Basilar Membrane Movement for Sounds of Different Frequencies Temporal (Volley) Theory • Temporal (volley) theory: the frequency of
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Class8_and9_Audition_Olfaction - Outline Audition and...

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