SPAU 3304 Exam 2 Notes
SPAU 3304 Exam 2 Notes SPAU 3304
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This 11 page Study Guide was uploaded by Kimberly Notetaker on Monday March 7, 2016. The Study Guide belongs to SPAU 3304 at University of Texas at Dallas taught by Dr. Garst in Spring 2016. Since its upload, it has received 115 views. For similar materials see Communication Sciences in Linguistics and Speech Pathology at University of Texas at Dallas.
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Date Created: 03/07/16
Location of energy changes: (OUTER) (MIDDLE) (INNER) Acoustic Energy Mechanical Energy Electrochemical Energy Sounds (physical) Conducted “Sensed” Interpreted OUTER EAR: o Pinna (acts as a resonator) » “Funneling” effect of pinna » Resonance 5000 – 6000 Hz range » If no pinna, would drop ~10dB o External auditory meatus » Portions: o Outer 1/3 cartilaginous with cilia and glands o Inner 2/3 bony, thin skin » 25 – 35mm long, 7mm diameter » “S”-shaped (develops with age) **The top of the TM does not line-up with bottom (Therefore, EAM longer on the bottom) o Embryology » Develop of Pinna begins about 6wks gestation » Adult-like shape at 20wks o Auditory and non-auditory roles » Non-Auditory Functions: o Keep ear canal clean (cilia clean dust, insects, etc.) o Skin lining, growth outward o Glands in skin secrete cerumen: 1) Water repellent 2) Protect from insects » Auditory Functions: o Acoustics and Resonance Resonance in a Tube: Sound quality changes with length of tube EAM 1 – 1.5 inches Resonance of closed tube = 4x length Result of resonance equals a gain in 2500 – 4000 Hz Enhances mid-frequencies (acts as a band- pass filter) o Resonances of the outer ear » Concha resonant frequency about 5,000 Hz » EAM resonant frequency about 2,500 – 4,000 Hz » Together produce a gain in acoustic pressure at around 2,500 to 5,000 Hz » Amplifying most important sounds for speech recognition o Functions of the Outer Ear: 1. Acts as a resonator 2. Protects the TM 3. Sound localization MIDDLE EAR: // (Acoustic Energy mechanical) Changes in Mode of Transmission: 1. Sound Waves 2. Eardrum Vibrates, ossicles set into motion 3. Ossicles move membrane at oval window o Tympanic membrane (Sections, attachment, vibration) o Cone shape (concaved) o 2 sections: Pars flaccida (outer region); more flaccid Pars tensa (little further in, more support/stronger) o More stability o More elasticity o Umbro: point of attachment with malleus o Cone of light Function of TM: Vibrates when sound enters ear canal Vibrates to all frequencies Lower frequencies as one unit Higher frequencies in different locations o Ossciular chain (bones, ligaments, muscles) Ligaments (bone-to-bone) and Muscles Malleus: 3 ligaments 1. Superior malleal ligament 2. Anterior malleal ligament 3. Lateral ligament Muscle: tensor typani (protective measure; more difficult to set into motion) o Incus: 2 ligaments 1. Superior incudal ligament 2. Posterior incudal ligament o Stapes: Muscle: Stapedius o Middle ear space (air filled) 1. Malleus 2. Ligaments 3. Incus 4. Ligament 5. Stapedius (the muscle attached to the Stapes) 6. Stapes 7. Eustachian Tube (ET goes to the nasopharynx, naturally closed (opens periodically)) a. Drainage of middle ear secretions b. Pressure equalization 8. Tensor Tympani (attachment to the Malleus bone; protective role) o Oval window (footplate of the stapes on the oval window) o Connects to fluid-filled cochlea o Membrane in-between o Eustachian tube o Auditory and non-auditory roles (including impedance mismatch definition and methods of regaining; surface area ratio and ossicular lever) o Non-auditory: (Eustachian Tube) Provides ventilation Pressure changes Drainage o Auditory: 1. SOUND TRANSMISSION » Acoustic to Mechanical Energy o Sound travels via the ossicles across the middle ear cavity 2. IMPEDANCE MISMATCH (how sound travels when there’s a change in mediums; change in impedance) » Impedance = resistance to sound transmission » Occurs with change in the medium (air, liquid) » Change in medium in auditory system: o Middle ear = air o Inner ear = fluid » Fluid (of the inner ear) is denser than air o Said to have “more impedance” or greater resistance » Ossicular chain serves to overcome impedance mismatch between air and fluid (in cochlea) Regains Intensity Lost in IM (via 2 methods) a. Surface Area Ratio Surface area of tympanic membrane compared to the oval window (higher pressure at the oval window) Tympanic membrane 17.3** (21 – 15x depending on source) times larger than the oval window P (pressure) = F (force) / A (area) Force from the TM is transferred to the stapes footplate, Increase in energy per unit of area Take home: greater sound pressure concentrated at the oval window due to the area ratio. b. Ossicular Lever (ossicles act as a lever) This lever action increases force of the system. Mechanical advantage o Malleus (1.3x longer than incus) and incus move as a unit o Force applied to the malleus is 1.3 times at the incus o Lever action even if bent 3. ACOUSTIC REFLEX » Muscles of middle ear in constant tension » With acoustic reflex they exert an increased pull » Sounds above 80 dB SL » Reduces about 10 – 30 dB » Greatest for low frequency sounds (below 1000 Hz) o Not helpful for high intensity, high freq. sounds » Reflex occurs within 10 – 150 msec for high intensity sounds. o Not true for one time sound (like a gun shot) INNER EAR o Anatomy of general location o Hole in the temporal bone of the skull o “Bony Labyrinth” describes channels and cavities o Vestibule (oval window connects to this), Cochlea, Semicircular Canals (make up the Vestibular System) o Fluid filled perilymph o Oval window (connection point between M/I ear) o Round window (opens up to the middle ear space) o Cochlea and vestibular system (Purpose, fluid content, main structures) 1. Cochlea: Hearing 2. Vestibular System: (set in temporal bone) » Balance/equilibrium and Proprioception (RondaRight on Ellen) » Ampulla (bulges) in semicircular canals, utricle, and saccule o Membranous labyrinth o Pouches: Utricle and Saccule (filling the space of The Vestibular) o Semicircular canals: superior, posterior, lateral o Fluid filled: endolymph o Cochlea (anatomy, regions, membranes, fluid makeup) » Shell shaped » Resembles a tube of decreasing diameter » Spiral canal is about 35mm long » Coils about 2.5 times » Helicotrema (up at the very top); if uncoiled, at very end/furthest away from the oval window » Modiolus – central space through which the nerve runs Reissner’s membrane Basilar membrane Spiral lamina, spiral ligament, stria vascularis, spiral ganglion Spiral Lamina or Spiral Limbus: point of attachment for Reissner + Basilar Membranes Spiral Ligament: connects Basilar membrane to bony outside Stria Vascularis: set of cells that line the lateral wall of the cell bodies (part of the PNS); sensory cells traveling down the auditory nerve Organ of Corti anatomy: OHC, IHC, supporting cells, tectorial membrane 1. Spiral limbus 2. Spiral lamina 3. Tectorial Membrane » Gelatinous, made mostly of water » Lies on top/parallel of basilar membrane » Supportive cells and hair cells between (basilar membrane and tectorial membrane) Basilar membrane moves up in traveling wave Tectorial Membrane is not set into wave as BM 1. Sensory Cells: transform mechanical motion to electrical impulses » Covered by protective membrane reticular lamina o Outer Hair Cells o Inner Hair Cells » Hair Cells: o IHC (1 row; n ~3,500); rounder, closer to the spiral lamina o OHC (3-5 rows; n ~12,000); taller, thinner shape » Upper surface of the hair cells with cilia (or stereocilia) » Cilia are longer, weigh more, on the Outer Hair Cells, closer to the Apex. » Also, embedded into the Tectorial Membrane vs. Cilia on top of Inner Hair Cells is NOT embedded; not making contact at rest. o Rods of Corti: separate row of IHC from OHC 2. Supportive Cells: not cells of hearing Hensen’s Cells Deiters Cells – below the OHC Cells of Claudius Process of hearing: 1. Macromechanics: fluid movement in inner ear A. TONAL TOPIC ORGANIZATION (where along the cochlea we’re going to have vibrations) » High frequency and low frequency sounds vibrate at different places along the basilar membrane Mass and Stiffness Gradient of Basilar Membrane Apex vs. Base Wider (5x as wide) Narrow Flaccid Stiffer Vibrates w/ lower frequencies Higher frequencies Greater mass Spiral lamina & Spiral ligament span larger at base B. TRAVELING WAVES » In and out motion of the stapes footplate becomes up and down motion of basilar membrane 1. Stapes footplate moves toward scala vestibule 2. Reissner’s membrane deflects downwards 3. Endolymph moves in scala media 4. Moves Basilar membrane downward (where it moves reliant on Tonal Topic Organization) 5. Perilymph in S. Tympani causes bulging of round window » Point of Basilar Membrane’s maximal displacement depends on the sound’s frequency. **The higher the frequency, the closer to the base. » Wave continues as the sound continues » Region of wave movement is called the ‘envelope of the traveling wave’ » BM wave grows » Maximal height of the traveling wave indicates the intensity 2. Micromechanics: hair cell activation in the Organ of Corti (rests on top of the Basilar Membrane) Mechanical into electrochemical energy (Organ of Corti); hair cell movement into nerve impulses the brain can interpret I. PASSIVE RESPONSE (when BM vibrates to sound) **Recall OHC cilia are embedded in the Tectorial Membrane; Inner Hair Cells are NOT Excitation of hair cells: Motion of basilar membrane Narrows space with the tectorial membrane OHC cilia shear (bending) by deflection with the tectorial membrane Eddies of the endolymph cause stereocilia of IHC to bend. Resting Membrane potential (no sound present) Endolymph about 100mV more positive than perilymph Inside of hair cells negatively charged compared to endolymph (and that of perilymph) Separated by the reticular lamina Endolymph: +50 to +80mV Inside Hair Cells: -80 to -100mV Depolarization process (Global) OHC cilia are embedded in tectorial membrane When basilar membrane moves causes cilia to bend sideways called shearing Ion channels open at the tips of the stereocilia Positively charged ions to flow from the endolymph into the hair cells. o That flow starts a nerve impulse… Change from negative value inside the hair cell and the cell becomes depolarized. **Basilar membrane moves UP – cilia deflect toward stria vascularis causes depolarization (cell becomes less negative) **Basilar membrane moves DOWN – cilia deflect toward modiolus causes hyperpolarization (restoring the charge) » Ca channels pump out calcium/Potassium pumps remove K ((cell becomes more negative)) II. ACTIVE RESPONSE // Active Mechanism of the Outer Hair Cells (How OHC affect Inner Hair Cells) Called an “Active” mechanism because of OHC expansion/contraction AKA Outer Hair Cell Motility (active mechanism) o When cilia shear toward the stria vascularis o The OHC shrink and become fatter as K + Ca enter the cell (very little space in between) o When cilia move toward modiolus OHC become taller and thinner As potassium and calcium leave the cell o OHC movement accentuates tectorial membrane movement OHC Motility Affects the IHC o Increased fluid movement may help deflect the IHC cilia. o Tectorial membrane can also be pulled downward enough to deflect IHC cilia. o Even with low intensity sounds ((gain from the active mechanism)) Active Mechanism (of the OHC) o Most important with low-intensity sounds o Without the active mechanism, would not detect low-intensity sounds o Increases movement of the basilar membrane o Increases the peak amplitude of the traveling wave (perceived louder) 2 Additional Potentials: 1) Cochlear Microphonic: electrochemical response of the cochlear hair cells to acoustic stimulation Review: o Calcium and Potassium enter cell when cilia hear toward stria vascularis Cell becomes less negative (depolarization) o Potassium leaves the cell when cilia shear towards modiolus. Returns to negative; more negative than at rest (hyperpolarization) Cells return to negative polarity o More negative than in silence Called Cochlear Microphonic » Fluctuation in cell polarity in response to sound » Alternating current 2) Summating Potential The hair cell is more positive during stimulation o Becomes less negatively charged The louder the sound the greater the effect ((voltage change)) Summating Potential = Change in voltage of the hair cells Hair cells that are more positive (less neg) when sound is present, release excitatory neurotransmitter, stimulating VIII nerve. Action potentials o Summating potential causes neurotransmitter release from the base of the hair cell o Neuron dendrites absorb neurotransmitter o Can create action potential o Nerve fibers are also tonotopically organized Intensity and Frequency Encoding o MORE INTENSE the sound… More neurotransmitter is released More often the neuron fires Larger number of neurons fire o HIGHER the FREQUENCY… Faster repeated firing of neurons Central Auditory System: o Afferent and efferent fibers 1) Afferent fibers (ascending); ~30,000 neurons 2) Efferent fibers (descending); ~500 neurons o AFFERENT PATHWAY: Type I and Type II neurons (1 order neurons; dendrites contact bottom hair cells) Type I Fibers: o 90 – 95% of 30,000 neurons o Bipolar neurons o Innervate IHC’s exclusively o ~20 Type 1 fibers connect to 1 IHC (many-to-one connection) o Myelinated axons Type II Fibers: (only connecting to OHC) o 5 – 15% of 30,000 o Pseudomonopolar neuron (know what this looks like) o Each fiber innervates ~10 OHC’s (one-to-many connection) o Not myelinated – slower o More complex branching o Major auditory relay nuclei o EFFERENT NEURONS: Type I and Type II » Originate in brain – signals to cochlea » ~500 efferent compared to 30,000 afferent 1) Type I: Contact Type I afferent neurons » Affect absorption of excitatory neurotransmitter 2) Type II: Connect to side of OHC » Can inhibit active mechanism Central Auditory Processing o Responsible for… Sound localization and lateralization Auditory discrimination Auditory pattern recognition Temporal aspects of audition Auditory performance with competing and degrading signals Sound Localization » One ear: to process frequency and intensity » Two ears: (binaural hearing); needed to locate hearing Localization: process of locating the source or direction of a sound in space o Aspects affecting localization: Time (temporal) cues Difference in arrival time at each ear Phase difference at each ear Intensity cues TEMPORAL CUES: I. Interaural TIME Difference (ITD) o Stimulus arrives later at the opposite ear from source o Time difference is processed by the auditory system II. Interaural PHASE Difference (IPD) o When a signal arrives it has a difference in phase at each ear » Phase difference is frequency dependent. o Only low-frequency sounds provide unambiguous cues o Phase difference is not meaningful for high-frequency sounds. INTENSITY CUE I. Interaural Level Difference (ILD) o Difference in intensity of signal between ears Head Shadow: sound blocked by head must diffract o Human head is a barrier to frequency > 1800 Hz o Head shadow only occurs for high frequency sounds » Give rise to an ILD (Interaural Level Difference) LOW frequencies: o Larger wavelength o No head shadow o Provide little information about localization due to intensity changes o Signal Amplitude = minimal change HIGH frequencies: o Signal Amplitude = bigger change Summary… ITD: applies to both low/high frequencies IPD: less meaningful with high frequency sounds ILD: head shadow with high frequency Guest speaker // CHILL (Children and Infant Listening Lab) » Early Hearing Detection and Intervention (EHDI) o Newborn hearing screening Established in ‘99 1-3-6 Methodology: Hearing screening by 1 month o Use objective tests (OAE, ABR) Evaluation (by 3 months) Early intervention (6 months) o Otoacoustic Emissions (OAE): measures an “echo” response from the OHC to the cochlea Elicited by a click stimuli Middle frequencies (can’t adjust intensity) o Auditory Brainstem Response: electrodes measure a neural response from brainstem and CN VIII Evoked potential of the auditory system (afferent)
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