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Copyright © 2007 Wolters Kluwer Health | Lippincott Williams & Wilkins Neuroscience: Exploring the Brain, 3e Chapter 11: The Auditory and Vestibular Systems.

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Presentation on theme: "Copyright © 2007 Wolters Kluwer Health | Lippincott Williams & Wilkins Neuroscience: Exploring the Brain, 3e Chapter 11: The Auditory and Vestibular Systems."— Presentation transcript:

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2 Copyright © 2007 Wolters Kluwer Health | Lippincott Williams & Wilkins Neuroscience: Exploring the Brain, 3e Chapter 11: The Auditory and Vestibular Systems

3 Copyright © 2007 Wolters Kluwer Health | Lippincott Williams & Wilkins Introduction Sensory Systems –Sense of hearing, audition Detect & localize sound Perceive and discriminate –Sense of balance, vestibular system Head and body location Head and body movements

4 Copyright © 2007 Wolters Kluwer Health | Lippincott Williams & Wilkins The Nature of Sound Sound –Audible variations in air pressure –Sound frequency: Number of cycles per second expressed in units called hertz (Hz) –Cycle: Distance between successive compressed patches

5 Copyright © 2007 Wolters Kluwer Health | Lippincott Williams & Wilkins The Nature of Sound Sound –Range: 20 Hz to 20,000 Hz –Pitch: High pitch = high frequency; low frequency = low pitch –Intensity: High intensity louder than low intensity

6 Copyright © 2007 Wolters Kluwer Health | Lippincott Williams & Wilkins The Structure of the Auditory System Auditory System

7 Copyright © 2007 Wolters Kluwer Health | Lippincott Williams & Wilkins The Structure of the Auditory System Auditory pathway stages –Sound waves –Tympanic membrane –Ossicles –Oval window –Cochlear fluid –Sensory receptor and neuron response

8 Copyright © 2007 Wolters Kluwer Health | Lippincott Williams & Wilkins Sound Force Amplification by the Ossicles –Pressure: Force per surface area e.g. dynes/cm –Greater pressure at oval window than tympanic membrane, moves fluids The Attenuation Reflex –Response where onset of loud sound causes tensor tympani and stapedius muscle contraction –Function: Adapt ear to loud sounds, understand speech better The Middle Ear 2

9 Copyright © 2007 Wolters Kluwer Health | Lippincott Williams & Wilkins The Inner Ear Anatomy of the Cochlea Perilymph: Fluid in scala vestibuli and scala tympani Endolymph: Fluid in scala media Endocochlear potential: Endolymph electric potential 80 mV more positive than perilymph

10 Copyright © 2007 Wolters Kluwer Health | Lippincott Williams & Wilkins Physiology of the Cochlea –Pressure at oval window, pushes perilymph into scala vestibuli, round window membrane bulges out The Response of Basilar Membrane to Sound –Structural properties: Wider at apex, stiffness decreases from base to apex Research: Georg von Békésy –Endolymph movement bends basilar membrane near base, wave moves towards apex The Inner Ear

11 Copyright © 2007 Wolters Kluwer Health | Lippincott Williams & Wilkins Travelling wave in the Basilar Membrane The Inner Ear

12 Copyright © 2007 Wolters Kluwer Health | Lippincott Williams & Wilkins The Organ of Corti and Associated Structures The Inner Ear

13 Copyright © 2007 Wolters Kluwer Health | Lippincott Williams & Wilkins Transduction by Hair Cells –Research: A.J. Hudspeth. –Sound: Basilar membrane upward, reticular lamina up and stereocilia bends outward (towards largest) The Inner Ear

14 Copyright © 2007 Wolters Kluwer Health | Lippincott Williams & Wilkins The Innervation of Hair Cells –One spiral ganglion fiber: One inner hair cell, numerous outer hair cells Amplification by Outer Hair Cells –Function: Sound transduction –Motor proteins: Change length of outer hair cells –Prestin: Required for outer hair cell movements The Inner Ear

15 Copyright © 2007 Wolters Kluwer Health | Lippincott Williams & Wilkins Central Auditory Processes Auditory Pathway

16 Copyright © 2007 Wolters Kluwer Health | Lippincott Williams & Wilkins Response Properties of Neurons in Auditory Pathway –Characteristic frequency: Frequency at which neuron is most responsive - from cochlea to cortex –Response Properties more complex and diverse beyond the brain stem –Binaural neurons are present in the superior olive Central Auditory Processes

17 Copyright © 2007 Wolters Kluwer Health | Lippincott Williams & Wilkins Encoding Sound Intensity and Frequency Encoding Information About Sound Intensity –Firing rates of neurons –Number of active neurons

18 Copyright © 2007 Wolters Kluwer Health | Lippincott Williams & Wilkins Encoding Sound Intensity and Frequency Stimulus Frequency –Tonotopic maps on the basilar membrane, spiral ganglion & cochlear nucleus

19 Copyright © 2007 Wolters Kluwer Health | Lippincott Williams & Wilkins Phase Locking –Low frequencies: phase-locking on every cycle or some fraction of cycles –High frequencies: not fixed Encoding Sound Intensity and Frequency

20 Copyright © 2007 Wolters Kluwer Health | Lippincott Williams & Wilkins Techniques for Sound Localization –Horizontal: Left-right, Vertical: Up-down Localization of Sound in Horizontal Plane –Interaural time delay: Time taken for sound to reach from ear to ear –Interaural intensity difference: Sound at high frequency from one side of ear –Duplex theory of sound localization: Interaural time delay: 20-2000 Hz Interaural intensity difference: 2000-20000 Hz Mechanisms of Sound Localization

21 Copyright © 2007 Wolters Kluwer Health | Lippincott Williams & Wilkins Interaural time delay and interaural intensity difference Mechanisms of Sound Localization

22 Copyright © 2007 Wolters Kluwer Health | Lippincott Williams & Wilkins The Sensitivity of Binaural Neurons to Sound Location Mechanisms of Sound Localization

23 Copyright © 2007 Wolters Kluwer Health | Lippincott Williams & Wilkins Mechanisms of Sound Localization Delay Lines and Neuronal Sensitivity to Interaural Delay –Sound from left side, activity in left cochlear nucleus, sent to superior olive –Sound reaches right ear later; delayed activity in right cochlear nucleus. –Impulses reach olivary neuron at the same time  summation  action potential

24 Copyright © 2007 Wolters Kluwer Health | Lippincott Williams & Wilkins Barn Owl : Space Map in Inf. Colliculus This is a computational map!

25 Frog calls (Hyla regilla) Encounter call Advertisement call

26 Model of short-pass duration selectivity Leary et al (2008) Excitation is delayed and inhibition increases in duration with longer-duration stimuli.

27 Intracellular recordings from a short-pass duration-selective neuron Made in the auditory midbrain of a frog

28 Frog calls (Hyla regilla) Encounter call Advertisement call

29 Recordings from neurons selective for short and long intervals Neuron A – selective for short intervals Neuron B – selective for long intervals

30 Models of long-interval selectivity Edwards et al (2008) Model A – Each pulse produces an EPSP followed by an IPSP. IPSP and EPSP from following pulse overlap at fast rates (short intervals). Model B – There is depression of excitation at fast pulse repetition rates.

31 Human speech also has periodic AM flatounet.net

32 Copyright © 2007 Wolters Kluwer Health | Lippincott Williams & Wilkins Primary Auditory Cortex –Axons leaving MGN project to auditory cortex via internal capsule in an array –Structure of A1 and secondary auditory areas: Similar to corresponding visual cortex areas Auditory Cortex

33 Copyright © 2007 Wolters Kluwer Health | Lippincott Williams & Wilkins Target distance and relative velocity

34 Copyright © 2007 Wolters Kluwer Health | Lippincott Williams & Wilkins

35 Principles of Auditory Cortex –Tonotopy, columnar organization of cells with similar binaural interaction –Unilateral lesion in auditory cortex: No deficit in understanding speech. But, Localization deficit. –Lesion in striate cortex: Complete blindness in one visual hemifield –Different frequency band information: Parallel processing e.g. frequency-specific localization deficit assoc. with small lesion. Neuronal Response Properties –Frequency tuning: Similar characteristic frequency –Isofrequency bands: Similar characteristic frequency, diversity among cells –Multiple computational maps- Bat auditory cortex. Auditory Cortex

36 Copyright © 2007 Wolters Kluwer Health | Lippincott Williams & Wilkins Importance of Vestibular System –Balance, equilibrium, posture, head, body, eye movement Vestibular Labyrinth –Otolith organs - gravity and tilt –Semicircular canals - head rotation –Use hair cells, like auditory system, to detect changes The Vestibular System

37 Copyright © 2007 Wolters Kluwer Health | Lippincott Williams & Wilkins The Otolith Organs: Detect changes in head angle, linear acceleration –Macular hair cells responding to tilt The Vestibular System

38 Copyright © 2007 Wolters Kluwer Health | Lippincott Williams & Wilkins The Vestibular System The Semicircular Canal Structure

39 Copyright © 2007 Wolters Kluwer Health | Lippincott Williams & Wilkins Push-Pull Activation of Semicircular Canals –Three semicircular canals on one side Helps sense all possible head-rotation angles –Each paired with another on opposite side of head –Push-pull arrangement of vestibular axons: The Vestibular System

40 Copyright © 2007 Wolters Kluwer Health | Lippincott Williams & Wilkins Central Vestibular Pathways The Vestibular System

41 Copyright © 2007 Wolters Kluwer Health | Lippincott Williams & Wilkins The Vestibulo-Ocular Reflex (VOR) –Function: Line of sight fixed on visual target –Mechanism: Senses rotations of head, commands compensatory movement of eyes in opposite direction –Connections from semicircular canals, to vestibular nucleus, to cranial nerve nuclei  excite extraocular muscles The Vestibular System

42 Copyright © 2007 Wolters Kluwer Health | Lippincott Williams & Wilkins The Vestibulo-Ocular Reflex (VOR) The Vestibular System

43 Copyright © 2007 Wolters Kluwer Health | Lippincott Williams & Wilkins Concluding Remarks Hearing and Balance –Nearly identical sensory receptors (hair cells) –Movement detectors: Periodic waves, rotational, and linear force –Auditory system: Senses external environment –Vestibular system: Senses movements of itself

44 Copyright © 2007 Wolters Kluwer Health | Lippincott Williams & Wilkins Concluding Remarks Hearing and Balance (Cont’d) –Auditory Parallels Visual System Tonotopy (auditory) and Retinotopy (visual) preserved from sensory cells to cortex code –Convergence of inputs from lower levels  Neurons at higher levels have more complex responses

45 Copyright © 2007 Wolters Kluwer Health | Lippincott Williams & Wilkins End of Presentation

46 Copyright © 2007 Wolters Kluwer Health | Lippincott Williams & Wilkins Components of the Middle Ear The Middle Ear

47 Copyright © 2007 Wolters Kluwer Health | Lippincott Williams & Wilkins Mechanisms of Sound Localization Localization of Sound in Vertical Plane –Vertical sound localization based on reflections from the pinna


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