HUMAN EAR GSS 106 The Human Ear 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. Audible Range The human ear is an amazing sound sensing device. It can sense an enormous range of intensities. A loud sound is about a million million (10 12 ) times greater than that of the weakest sounds. The complete audible range is 20-20,000 Hz. You should be able to calculate the corresponding wavelength Anatomy of the human ear Outer ear, middle ear, inner ear Outer ear: Pinna - external part, Auditory canal Middle ear: Eardrum - hard membrane, Ossicles Inner ear: Oval window, Cochlea, Auditory nerve 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. The Human Ear Ludwig van Beethoven ( ) 9 th Symphony Composed when he was profoundly deaf. Anatomy of Ear Outer Ear Middle Ear Inner Ear The Human Ear Anatomy of the Ear Middle 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. The Human Ear Tympanic Membrane (Ear Drum) micrograph ( view from inside) Tympamium Malleus and ligaments Physics 1251Unit 2 Session 12 The Human Ear The Ossicles Malleus Incus Stapes Ossicles (Micrographs) Malleus Incus Stapes MalleusIncus Stapes Tympanium Anatomy of the Ear Inner Ear: Cochlea (the Snail) converts displacement into neural impulses. Auditory Nerve neural impulses to brain Semicircular canals detect motion and orientation Anatomy of Inner Ear Semicircular Canals Cochlea Oval Window Round Window C ochlea (micrograph) The Sn ail o~ oval window r~ round window 2 mm Structure of Cochlea 1. Spiral cone 2. Divided by Basilar Membrane 3. In on top half 4. Out on bottom 5. Sloshing Anatomy of Cochlea Micrograph Section Basilar Membrane Kansas State School of Medicine Microstructure of Cochlea Basilar Membrane Organ of Corti Auditory Nerve Stereocilia (Hair Cells) Outer Hair Cell in Cross Section Inner Hair Cells Afferent Efferent Efferent Synapse Detail of Hair Cell Stereocilia Vibration )))) Action of Hair Cell Hair Cell Depolarizes Neurotransmitter released Hair Cell Nerve Function of Stereocilia Stimulation in HC Causes neuro- transmitter to stimulate neuron in Auditory Nerve Frequency Response of Hair Cells Repeated 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. Hearing Loss due to Over Stimulation causes Excitotoxicity Too much Ca 2+ poisons the neuron. The Human Ear Extreme Acoustic Trauma Control, not exposed After Exposure Guinea Pig Stereocilia damage (120 dB sound) How do you protect yourself? Ear Plugs Wear Them! How does Anatomy affect perception? Frequency response Loudness perception Phase insensitivity Deafness Disruption of acoustic chain. Nerve death. Remedies Restore chain or increase amplitude 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. 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. The Human Voice A useful model for the human voice is a system that resonates for and filters sound waves. The source of the sound waves is vibration of the vocal folds that reside in the larynx. Those sound waves are filtered by changing the shape of the vocal tract comprising the larynx, the pharynx above it, the mouth and the nasal cavity DBHM Diaphragm action pushes air from the lungs through the vocal folds, producing a periodic train of air pulses. This pulse train is shaped by the resonances of the vocal tract. The basic resonances, called vocal formants, can be changed by the action of the articulators to produce distinguishable voice sounds, like the vowel sounds.