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Physics 1251 The Science and Technology of Musical Sound Unit 2 Session 12 MWF The Human Ear Physics 1251 Unit 2 Session 12 The Human Ear Foolscap Quiz: A student guitarist plays a chord on his electric guitar. When he mutes the strings he notices that his acoustic guitar on the rack beside the amplifier is also ringing. What is the name of the relevant effect and what is happening? Resonance. The strings of the acoustic guitar were tuned to some frequency that he played. The strings picked up the energy from the vibrations of the air that were “in resonance.” Physics 1251 Unit 2 Session 12 The Human Ear Ludwig van Beethoven (1770-1827) 9 th Symphony (Choral) Composed when he was profoundly deaf. Physics 1251 1′ Lecture: Unit 2 Session 12 The Human Ear The human ear is a highly sensitive sound receptor in which • pressure fluctuations in the outer ear are transformed • into vibrations of small bones (the ossicles) in the middle ear • that are ultimately communicated to the cochlea located in the inner ear, • where the vibrations are further transformed by stereocilia (hair cells) • into neural impulses distributed by frequency. Physics 1251 Unit 2 Session 12 The Human Ear Anatomy of Ear Middle Ear Outer Ear Inner Ear Physics 1251 Unit 2 Session 12 The Human Ear Anatomy of the Ear • 80/20Outer Ear: 1. Pinna – (the feather) matches ear canal to outside world. 2. Meatus – ( the passageway) conducts sound into head. 3. Tympanium – (the drum) transforms pressure fluctuations into displacement. Physics 1251 Unit 2 Session 12 The Human Ear Outer Ear • Pinna ——→ • Meatus ———→ ←— Tympanium Physics 1251 Unit 2 Session 12 The Human Ear Anatomy of Ear Middle Ear Physics 1251 Unit 2 Session 12 The Human Ear Anatomy of the Ear • 80/20Middle Ear: The Ossicles (little bones) 1. Malleus ― (the hammer) moved by Tympanium. 2. Incus ― (the anvil) supported by ligaments that protect against loud percussion. 3. Stapes ― (the stirrup) force multiplied by 1.3 because of lever action. Physics 1251 Unit 2 Session 12 The Human Ear Tympanic Membrane (Ear Drum) micrograph (view from inside) ←————— Tympamium ←——— Malleus and ligaments Physics 1251 Unit 2 Session 12 The Human Ear The Ossicles Malleus ——→ ←—— Incus ←—— Stapes Physics 1251 Unit 2 Session 12 The Human Ear Ossicles (Micrographs) Malleus Incus Malleus Incus Tympanium Stapes Stapes Physics 1251 Unit 2 Session 12 The Human Ear Anatomy of Ear Inner Ear Physics 1251 Unit 2 Session 12 The Human Ear Anatomy of the Ear • 80/20Inner Ear: Cochlea – (the Snail) converts displacement into neural impulses. Auditory Nerve – neural impulses to brain Semicircular canals – detect motion and orientation Physics 1251 Unit 2 Session 12 The Human Ear Anatomy of Inner Ear ←—— Semicircular Canals Oval Window Round Window ←—— Cochlea Physics 1251 Unit 2 Session 12 The Human Ear Cochlea (micrograph) “The Snail” • • o~ oval window r~ round window 2 mm Physics 1251 Unit 2 Session 12 The Human Ear Structure of Cochlea 1. Spiral cone 2. Divided by Basilar Membrane 3. In on top half 4. Out on bottom 5. “Sloshing “ Physics 1251 Unit 2 Session 12 The Human Ear Anatomy of Cochlea Micrograph Section Basilar ——————→ Membrane © Kansas State School of Medicine Physics 1251 Unit 2 Session 12 The Human Ear Microstructure of Cochlea Basilar ——————→ ↑ Membrane Organ of ↑ Auditory Nerve → → Corti Physics 1251 Unit 2 Session 12 The Human Ear Stereocilia (Hair Cells) Physics 1251 Unit 2 Session 12 The Human Ear Outer Hair Cell in Cross Section Physics 1251 Unit 2 Session 12 The Human Ear Inner Hair Cells Synapse ⇘ Afferent Efferent Physics 1251 Unit 2 Session 12 The Human Ear Organ of Corti and Basilar Membrane Vibration ←——— Outer Hair Cells ←————— Inner Hair Cells Physics 1251 Unit 2 Session 12 The Human Ear Detail of Hair Cell Stereocilia Physics 1251 Unit 2 Session 12 The Human Ear Action of Hair Cell Vibration )))) Neurotransmitter released Nerve Hair Cell Depolarizes Hair Cell Physics 1251 Unit 2 Session 12 The Human Ear Function of Stereocilia Stimulation in HC Causes neurotransmitter to stimulate neuron in Auditory Nerve Physics 1251 Unit 2 Session 12 The Human Ear Frequency Response of Hair Cells Physics 1251 Unit 2 Session 12 The Human Ear Frequency Discrimination in Cochlea • 20 Hz to 20 kHz (typical in Humans) • Resonances in Basilar membrane and in HC cause spatial separation by frequency. • Differential movement of membranes stimulate HC. • Minimum stimulation required for response. Inhibition of neighbors causes non-linear response. Physics 1251 Unit 2 Session 12 The Human Ear Neuronal Decoding of Sound (Schematic) Low Frequency High Frequency Frequency response localized in Cochlea Physics 1251 Unit 2 Session 12 The Human Ear Neuronal Response to Sound • • Frequency → Where? The location where in the Cochlea the stereocilia are stimulated. Intensity → How many? The number of HC that are stimulated by the sound determines the perceived loudness. Physics 1251 Unit 2 Session 12 The Human Ear 80/20Repeated acoustic trauma can cause permanent and profound hearing loss or deafness. If you have experienced temporary hearing loss due to loud sounds you have had a warning. Stereocilia do regenerate daily. Physics 1251 Unit 2 Session 12 The Human Ear Hearing Loss due to Over Stimulation causes Excitotoxicity Too much Ca2+ poisons the neuron. Physics 1251 Unit 2 Session 12 The Human Ear Extreme Acoustic Trauma Guinea Pig Stereocilia damage (120 dB sound) Control, not exposed After Exposure Physics 1251 Unit 2 Session 12 The Human Ear How do you protect yourself? Ear Plugs Wear Them! Physics 1251 Unit 2 Session 12 The Human Ear How does Anatomy affect perception? • • • • Frequency response Loudness perception Phase insensitivity Deafness • Disruption of “acoustic chain.” • Nerve death. • Remedies • Restore chain or increase amplitude Physics 1251 Unit 2 Session 12 The Human Ear Summary: Anatomy : Outer, Middle and Inner Ear. Function: Outer – converts pressure fluctuations to displacement. Middle – amplifies displacement, protects against loud noise. Inner – converts displacement to neural impulses, sorted by frequency. Physics 1251 Unit 2 Session 12 The Human Ear • Physiology determines function. • No phase detection mechanism. • Large “non-linear” range of 12 orders of magnitude in intensity • Three (3) orders of magnitude in frequency (20 Hz to 20 kHz). • Trauma (due to loud sounds) is a cause of deafness.