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Neuroscience: Exploring the Brain, 3e

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Presentation on theme: "Neuroscience: Exploring the Brain, 3e"— Presentation transcript:

1 Neuroscience: Exploring the Brain, 3e
Chapter 11: The Auditory and Vestibular Systems

2 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

3 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

4 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

5 The Structure of the Auditory System

6 The Structure of the Auditory System
Auditory pathway stages Sound waves Tympanic membrane Ossicles Oval window Cochlear fluid Sensory receptor and neuron response

7 The Middle Ear 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 2

8 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

9 The Inner Ear 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

10 The Inner Ear Travelling wave in the Basilar Membrane

11 The Inner Ear The Organ of Corti and Associated Structures

12 The Inner Ear Transduction by Hair Cells Research: A.J. Hudspeth.
Sound: Basilar membrane upward, reticular lamina up and stereocilia bends outward (towards largest)

13 The Inner Ear 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

14 Central Auditory Processes
Auditory Pathway

15 Central Auditory Processes
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

16 Encoding Sound Intensity and Frequency
Encoding Information About Sound Intensity Firing rates of neurons Number of active neurons

17 Encoding Sound Intensity and Frequency
Stimulus Frequency Tonotopic maps on the basilar membrane, spiral ganglion & cochlear nucleus

18 Encoding Sound Intensity and Frequency
Phase Locking Low frequencies: phase-locking on every cycle or some fraction of cycles High frequencies: not fixed

19 Mechanisms of Sound Localization
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: Hz Interaural intensity difference: Hz

20 Mechanisms of Sound Localization
Interaural time delay and interaural intensity difference

21 Mechanisms of Sound Localization
The Sensitivity of Binaural Neurons to Sound Location

22 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

23 Barn Owl : Space Map in Inf. Colliculus
This is a computational map!

24 Frog calls (Hyla regilla)
Advertisement call Encounter call

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

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

27 Frog calls (Hyla regilla)
Advertisement call Encounter call

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

29 Models of long-interval selectivity
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. Edwards et al (2008)

30 Human speech also has periodic AM

31 Auditory Cortex 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

32 Target distance and relative velocity


34 Auditory Cortex 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.

35 The Vestibular System 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

36 The Vestibular System The Otolith Organs: Detect changes in head angle, linear acceleration Macular hair cells responding to tilt

37 The Vestibular System The Semicircular Canal Structure

38 The Vestibular System 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:

39 The Vestibular System Central Vestibular Pathways

40 The Vestibular System 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

41 The Vestibular System The Vestibulo-Ocular Reflex (VOR)

42 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

43 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

44 End of Presentation

45 The Middle Ear Components of the Middle Ear

46 Mechanisms of Sound Localization
Localization of Sound in Vertical Plane Vertical sound localization based on reflections from the pinna

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