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Transcript
The Auditory & Vestibular Systems Psychology 355 Introduction Sensory Systems A. Sense of hearing, audition 1. Detect sound 2. Perceive and interpret nuances B. Sense of balance, vestibular system 1. Head and body location 2. Head and body movements Psychology 355 2 The Nature of Sound Sound A. B. C. D. E. F. Audible variations in air pressure Sound frequency: Number of cycles per second expressed in units called Hertz (Hz) Cycle: Distance between successive compressed patches Range: 20 Hz to 20,000 Hz Pitch: High and Low Intensity: Difference in pressure between compressed and rarefied patches of air Psychology 355 3 The Nature of Sound Psychology 355 4 The Nature of Sound Psychology 355 5 The Structure of the Auditory System Psychology 355 6 The Structure of the Auditory System I. Auditory pathway stages A. Sound waves B. Tympanic membrane C. Ossicles D. Oval window E. Cochlea fluid F. Sensory neuron response II. Brain stem nuclei output A. Thalamus to MGN to A1 Psychology 355 7 The Middle Ear Components of the Middle Ear Psychology 355 8 The Middle Ear I. Sound Force Amplification by the Ossicles A. Pressure: Force by surface area B. Greater pressure at oval window than tympanic membrane, moves fluids II. The Attenuation Reflex A. Response where onset of loud sound causes tensor tympani and stapedius muscle contraction B. Function: Adapt ear to loud sounds, understand speech better Psychology 355 9 The Inner Ear Anatomy of the Cochlea Psychology 355 10 The Inner Ear Anatomy of the Cochlea Psychology 355 11 The Inner Ear Physiology of the Cochlea Pressure at oval window, pushes perilymph into scala vestibuli, round window membrane bulges out Psychology 355 12 The Inner Ear The Organ of Corti Psychology 355 13 The Inner Ear Cilia Psychology 355 14 The Inner Ear Cilia Psychology 355 15 The Inner Ear Psychology 355 16 The Inner Ear Transduction by Hair Cells Sound: Basilar membrane upward reticular lamina up stereocilia bends outward Psychology 355 17 The Inner Ear Psychology 355 18 The Inner Ear I. The Innervation of Hair Cells A. One spiral ganglion fiber: One inner hair cell, numerous outer hair cells II. Amplification by Outer Hair Cells A. Function: Sound transduction B. Motor proteins: Change length of outer hair cells C. Prestin: Required for outer hair cell movements Psychology 355 19 The Inner Ear The Basilar Membrane Structural properties: Wider at apex, stiffness decreases from base to apex Psychology 355 20 The Inner Ear Psychology 355 21 Central Auditory Processes Auditory Pathway A. More synapses at nuclei than visual pathway, more alternative pathways B. Anatomy 1. Dorsal cochlear nucleus, ventral cochlear nucleus, superior olive, inferior colliculus, MGN, lateral lemniscus, auditory nerve fiber 2. Primary pathway: Ventral cochlear nucleus to superior olive to inferior colliculus to MGN to auditory cortex Psychology 355 22 Auditory Pathway Psychology 355 23 Auditory Pathway Psychology 355 24 Central Auditory Processes Response Properties of Neurons in Auditory Pathway A. Characteristic frequency Frequency at which neuron is most responsive B. Response More complex and diverse on ascending auditory pathway in brain stem Psychology 355 25 Encoding Sound Intensity and Frequency I. Encoding Information About Sound Intensity A. Firing rates of neurons B. Number of active neurons II. Stimulus Frequency, Tonotopy, Phase Locking A. Frequency sensitivity: Basilar membrane B. Frequency: Highest at base, lowest at cochlea apex C. Tonotopy: Systematic organization of characteristic frequency within auditory structure Psychology 355 26 Encoding Sound Intensity and Frequency Phase Locking Consistent firing of cell at same sound wave phase Psychology 355 27 Mechanisms of Sound Localization I. Techniques for Sound Localization A. Horizontal: Left-right, Vertical: Up-down II. Localization of Sound in Horizontal Plane A. Interaural time delay: Time taken for sound to reach from ear to ear B. Interaural intensity difference: Sound at high frequency from one side of ear C. Duplex theory of sound localization: 1. Interaural time delay: 20-2000 Hz 2. Interaural intensity difference: 200020000 Hz Psychology 355 28 Mechanisms of Sound Localization The Sensitivity of Binaural Neurons to Sound Location Monaural: Sound in one ear Binaural: Sound at both ears Superior olive: Cochlear nuclei input to superior olive, greatest response to specific interaural delay Psychology 355 29 Mechanisms of Sound Localization I. Delay Lines and Neuronal Sensitivity to Interaural Delay A. Sound from left side, activity in left cochlear nucleus, sent to superior olive B. Sound reaches right ear, activity in right cochlear nucleus, first impulse far C. Impulses reach olivary neuron at the same time summation action potential II. Localization of Sound in Vertical Plane A. Sweeping curves of outer ear Psychology 355 30 Mechanisms of Sound Localization A given binaural neuron indicates the amount of phase disparity between inputs from the left and right ear. Psychology 355 31 Auditory Cortex I. Acoustic Radiation A. Axons leaving MGN project to auditory cortex via internal capsule in an array B. Structure of A1 and secondary auditory areas: Similar to corresponding visual cortex areas II. Neuronal Response Properties A. Frequency tuning: Similar characteristic frequency B. Isofrequency bands: Similar characteristic frequency, diversity among cells Psychology 355 32 Auditory Cortex Principles in Study of Auditory Cortex Tonotopy, columnar organization of cells with similar binaural interaction Psychology 355 33 The Vestibular System I. Importance of Vestibular System A. Balance, equilibrium, posture, head, body, eye movement II. The Vestibular Labyrinth Lateral line Organs Small pits or tubes Function Sense vibration or pressure changes Psychology 355 34 The Vestibular System Head Rotation Head Angle Linear Acceleration Psychology 355 35 The Vestibular System The Otolith Organs Psychology 355 36 The Vestibular System The Otolith Organs Psychology 355 37 The Vestibular System I. The Semicircular Canals A. Function: Detect head movements II. Structure A. Crista: Sheet of cells where hair cells of semicircular canals clustered B. Ampulla: Bulge along canal, contains crista C. Cilia: Project into gelatinous cupula D. Kinocili oriented in same direction so all excited or inhibited together E. Semicircular canals: Filled with endolymph Psychology 355 38 The Vestibular System Psychology 355 39 The Vestibular System I. Push-Pull Activation of Semicircular Canals A. Three semicircular canals on one side 1. Helps sense all possible head-rotation angles B. Canal: Each paired with another on opposite side of head C. Push-pull arrangement of vestibular axons: Rotation causes excitation on one side, inhibition on the other Psychology 355 40 The Vestibular System I. The Vestibulo-Ocular Reflex (VOR) A. Function: Line of sight fixed on visual target B. Mechanism: Senses rotations of head, commands compensatory movement of eyes in opposite direction C. Connections from semicircular canals, to vestibular nucleus, to cranial nerve nuclei excite extraocular muscles Psychology 355 41 The Vestibular System Vestibular Pathology A. Drugs (e.g., antibiotics) can damage vestibular system B. Effects: 1. Trouble fixating on visual targets 2. Walking and standing difficult Psychology 355 42 Concluding Remarks Hearing and Balance A. Nearly identical sensory receptors (hair cells) B. Movement detectors: Periodic waves, rotational, and linear force C. Auditory system: Senses external environment D. Vestibular system: Senses movements of itself Psychology 355 43 Concluding Remarks Hearing and Balance A. Auditory Parallels Visual System 1. Tonotopy (auditory) and Retinotopy (visual) preserved from sensory cells to cortex code B. Convergence of inputs from lower levels Neurons at higher levels have more complex responses Psychology 355 44 End of Presentation Psychology 355