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Auditory system and hearing Animal Body Function VIII Master Degree - Veterinary Medicine Summary 1 Introduction to the hearing 2 Sound waves 3 Components of the ear outer middle inner – cochlea and Organ of Corti 4 Transduction of auditory stimulus...

Auditory system and hearing Animal Body Function VIII Master Degree - Veterinary Medicine Summary 1 Introduction to the hearing 2 Sound waves 3 Components of the ear outer middle inner – cochlea and Organ of Corti 4 Transduction of auditory stimulus 5 Central pathways for hearing 6 Deafness 7 Differences in animal species for teaching purposes only  for teaching purposes only Introduction Sound is a constant in the environment (indoor and outdoor) Auditory system function: detect and analyze sound There are only a few animals that are not able to hear (deaf) or has limited auditory capacities Naked Mole Rat has a limited capacity to hear - Armadillos' hearing is absent only perceive sounds between 0.5 and 4 kHz https://wildlifeinformer.com/animals-that-are- deaf/  for teaching purposes only Introduction Many of the adaptations to the environment depend on an accurate sense of hearing In veterinary medicine, congenital ear defects and otitis can occur sound bat - https://askabiologist.asu.edu/sites/default/files/resources/articles/bats/silver_haired.mp3 https://askabiologist.asu.edu/echolocation https://www.americanscientist.org/article/the-acoustic- world-of-harbor-porpoises  for teaching purposes only The top “listeners” Age UK Hearing Aids, 2016  for teaching purposes only Hearing and sound waves Sounds are mechanical, pressure waves (sound waves) that move through a medium, as the air; created by a vibrating object Sound waves: longitudinal vibrations of molecules in the external environment with alternating phases of compression (increases in pressure) and rarefaction (decreases in pressure) https://www.acs.psu.edu/drussell/Demos/waves/wavemotion.html. these alternating changes in pressure produce the sensation of sound after they strike the tympanic membrane transduction to the brain  for teaching purposes only Hearing and sound waves Speed of sound? sound waves travel in the air (at sea level and 20ºC) about 343 m/s  for teaching purposes only Hearing and sound waves A sound wave can be characterized by: 1. frequency 2. period 3. amplitude 4. wavelenght  for teaching purposes only Hearing and sound waves Loudness of a sound is associated with the amplitude of the sound wave (dimension of a wave from peak to rough) decibel (dB) scale energy of the sound relative to the energy of a standard reference sound (0 dB)  for teaching purposes only Hearing and sound waves normal conversation: 60 dB loudest tolerable sound: 120 dB maximum dog barking is 110 dB 140 dB when you are talking during the classes! https://hearinghealthfoundation.org  for teaching purposes only Hearing and sound waves Pitch of a sound is related with the frequency of the sound wave frequency is the number of pressure oscillation cycles per unit of time - Hertz (Hz) 1 Hz = 1 cycles/second  for teaching purposes only Hearing and sound waves https://www.youtube.com/watch?v=wEL87lznGrg - The Pitch and Loudness of Sound, and a Comparison of Audible Frequency Ranges – Knowledge platform  for teaching purposes only Hearing and sound waves Fr equency? 3Hz W hich sound is the loudest? And with a higher pitch? Klein, 2020  for teaching purposes only The components of the ear Outer Middle Inner ear Klein, 2020  for teaching purposes only Outer ear The outer (external) ear: composed of the pinna and the ear canal channels sound waves to the ear canal and to the tympanic membrane (aka eardrum) the eardrum is a membrane between the outer and the middle ear ear canal of dogs are deeper than humans → more efficient funnel to carry sound to eardrum MSD Veterinary Manual, 2023  for teaching purposes only Outer ear The outer ear: composed of the pinna and the ear canal same animals are able to rotate/move the pinna to scan the environment and better collect sounds pinna movements are relevant for sound localization – importance of 2 ears! Pinna movements in bats. Valentine, 2002 natural shape of the pinna can act to selectively filter out or accentuate certain sound frequencies Pinna movements in cats. Populin, 1998  for teaching purposes only Middle ear oval (cochlear) window tympanic membrane Reece, 2015 Klein, 2020 Middle ear: air-filled cavity in the temporal bone Ossicles – malleus, incus, stapes are important in directing sound waves to the inner ear The 3 ossicles are connected to eact other – and foot plate of the stapes fits and is connected to the oval window transfer vibration (energy) from eardrum/tympanum to the oval window avoiding loss of energy as the sound wave is transferred from the air-filled to the fluid-filled (perilymph) environment of the inner ear with muscles attached to malleus and stapes: contract to ↓ the transfer of vibration (protective attenuation against loud sounds)  for teaching purposes only Middle ear oval (cochlear) window tympanic membrane Reece, 2015 Klein, 2020 Middle ear Malleus and incus: constitute a fuctional bent lever longer arm of the malleus attaching to the tympanic membrane and the shorter arm of the incus attaching to the stapes The design of the ossicles and the relative size difference between tympanic membrane and stapes has 2 purposes: 1. magnifies the vibratory pressure of the tympanic membrane transmitted to the stapes – crucial in the sound waves passage from air to fluid (perilymph) 2. but decreases the amplitude of sound waves at the vestibular window: protects the sensory cells of Organ of Corti  for teaching purposes only Middle ear oval (cochlear) window tympanic membrane Reece, 2015 Klein, 2020 Auditory tube connection to the nasopharinx main function: equalize the pressure in the tympanic cavity with the pressure in the external auditory canal  for teaching purposes only La Dame à la licorne - L'Ouïe, at Musée national du Moyen Âge (Cluny), Paris The Lady and the Unicorn – The hearing A very famous series of tapestries from the 1500s Anyone likes Harry potter movies? this tapestry is there. Where? Cover the Gryffindor common room in Harry Potter movies  for teaching purposes only Inner ear vestibular system: detects acceleration and static tilt of the head auditory system: detects and analyze sound  for teaching purposes only Inner ear and auditory system Bony labyrinth Series of tunnels within the petrous temporal bone Perilymph is the fluid contained within the bony labyrinth, surrounding and protecting the membranous labyrinth Membranous labyrinth is inside the bony labyrinth with endolymph that in the cochlear duct its fluid waves stimulate the auditory receptor cells Membranous tunnel within the bony labyrinth is common to vestibular and auditory parts The auditory portion of this inner ear complex is called the cochlea  for teaching purposes only Inner ear and auditory system Cochlea The cochlear portion of the labyrinth is coiled Two membranes: basilar and Reissner’s (vestibular) gives rise to Three scalae or chambers with perylymph: ↑ the vestibular duct or scala vestibuli (dorsally) sodium concentration the tympanic duct or scala tympani (ventrally) with endolymph: ↑ potassium, to maintain the cochlear duct or scala media, formed by endolympathic potential of +80mV the membranous portion of the labyrinth Reece, 2015  for teaching purposes only Inner ear and auditory system Reece, 2015 basilar membrane is the floor of the scala media atop this membrane lies the sensory organ for hearing - organ of Corti Organ of Corti occupies the full extent of the basilar membrane, from base to apex Klein, 2020  for teaching purposes only Inner ear and auditory system openstax, 2024 Organ of Corti: Its structural components include: sensory cells (mechanoreceptors – heavily innervated inner hair cells and outer hair cells with stereocilia (“hair”) tips embedded in the tectorial membrane) supporting cells tectorial membrane: gelatinous structure of glycoproteins embedding stereocilia’ tips Bechara Kachar, 2022  for teaching purposes only Inner ear: organ of Corti Reece, 2015 otosurgeryatlas.stanford.edu Organ of Corti: the key structure involved in the transduction of sound waves into action potentials Hair cell receptors synapse on sensory neurons that converge on cochlear part of the cranial nerve VIII Sound → bending of the hair cell cilia → alters the frequency of action potentials on the VIII fibers  for teaching purposes only Transduction of auditory stimulus Transduction sound waves or pressure waves in the air reach the ear the ear transduces this mechanical stimulus (pressure wave) into a nerve impulse Klein, 2020 (electrical signal) that the brain perceives as sound  for teaching purposes only Transduction of auditory stimulus 1. Sound waves are funneled and collected by the outer ear, creating vibrations of the tympanic membrane 2. These vibrations are transmitted through the middle ear by the ossicles and result in subsequent vibrations of the cochlear oval window 3. Sound energy is transferred in inner ear: through the perilymph of the scala vestibuli and through the endolymph of the scala media to the basilar membrane 4. Pressure waves cause the basilar membrane to move, Klein, 2020 resulting in pressure wave formation in the endolymph  for teaching purposes only Transduction of auditory stimulus 5. the movement of basilar membrane up and down causes its displacement and hair cells in the organ of Corti 5 are distorted, sending a signal through CN VIII 6. Remaining pressure waves are transferred to the scala 6 tympani and exit the inner ear via the round window  for teaching purposes only Transduction of auditory stimulus No sound: basilar membrane at rest Sound → movement of the traveling wave causes portions of the flexible basilar membrane to move up and down hair cell cilia is sheared back and forth against the anchored tectorial membrane changes the release of transmitter from the hair cells onto the VIII nerve neurons alters the firing rate of these neurons Overall: organ of Corti has transduced the sound wave energy into neural activity Klein, 2020  for teaching purposes only Transduction of auditory stimulus In more detail! Sound stimulus → leads to displacement of the basilar membrane upward stereocilia is displaced against the tectorial membrane, bending all the stereocilia laterally (i.e., toward the taller stereocilia) opening ion channels in the tip of the stereocilia due to increased tension on the tip of stereocilia (mechanically-gated channels) K+ influx along electrical gradient Reece, 2015 depolarization of the hair cells…  for teaching purposes only Transduction of auditory stimulus …depolarization of the hair cells opening of voltage-gated Ca2+ channels at the base of the cell influx of Ca2+ release of a neurotransmitter into the synaptic cleft between sensory hair cells and terminal ends of the cochlear nerve A receptor potential stimulates terminal ends of the cochlear nerve and an action potential will be present if the threshold is reached → the signal is transmitted to the chochlear nerve Reece, 2015  for teaching purposes only Transduction of auditory stimulus The transduction is the same regarding the type of sound? Klein, 2020  for teaching purposes only Transduction of auditory stimulus Sound intensity modulates the transduction magnitude The longer the sound wave amplitude (i.e. the louder the sound), a longer area of the basilar membrane is displaced more hair cells are sheared against the tectorial membrane affects the activity of a larger number of VIII nerve neurons This is one way that sound intensity (volume) is coded by the nervous system because of the unique characteristics of the basilar membrane Klein, 2020  for teaching purposes only Transduction of auditory stimulus The resonant properties of the basilar membrane is important for deciphering the sound These properties (in the basilar wider and membrane) are not uniform along its more lenght: flexible narrower and stiffer in the base towards its apex (near oval window) Reece, 2015  for teaching purposes only Transduction of auditory stimulus The resonant properties of the basilar membrane is important for deciphering the sound Klein, 2020 intermediate tones distort the with lower frequency sounds, displaced by high- basilar membrane from the the region of displacement is frequency sounds base to an intermediate region closer to the apex  for teaching purposes only Transduction of auditory stimulus The resonant properties of the basilar membrane is important for deciphering the sound  for teaching purposes only Transduction of auditory stimulus otosurgeryatlas.stanford.edu from 4.09; https://www.youtube.com/watch?v=PeTriGTENoc  for teaching purposes only Transduction of auditory stimulus https://otosurgeryatlas.stanford.edu/otologic-surgery-atlas/surgical-anatomy-of-the-ear/auditory-system/#  for teaching purposes only Transduction of auditory stimulus High-frequency sounds most affect hair cells and their associated VIII nerve neurons near the base (near oval window) As frequency ↓, the activated hair cells and neurons are progressively closer to the apex (pressure waves move farther, displacing the organ farther from the oval window) Tonotopic organization: orderly relationship between the frequency of a sound wave and the region of the cochlea activated by that frequency nervous system begins to decipher the frequency of a sound through the location of the hair cells and neurons most affected by that sound (its frequency) Central pathways for hearing for teaching purposes only 1. Action potentials from the cochlea travel along the cochlear portion (cochlear nerve) of the VIII to the cochlear nuclei in the medulla oblongata 2. The peripheral tonotopic localization is retained in the cochlear nuclei a) base of cochlea represented dorsally b) apex represented ventrally 3. Fibers from ventral cochlear nucleus form the trapezoid body 4. From there, neural activity is synaptically relayed to the superior olivary complex (a group of nuclei spanning the pontomedullary border region) 5. then is transmitted to the inferior (caudal) colliculus of the midbrain colliculus as an auditory reflex center 6. from there, goes to the medial geniculate nucleus of the thalamus, where is processed 7. finally the stimuli arrives at the auditory cortex of the temporal lobe Reece, 2015; Klein, 2020  Central pathways for hearing for teaching purposes only Klein, 2020 Principal components of the auditory pathway from hair cell to cerebral cortex in the temporal lobe  Central pathways for hearing for teaching purposes only Klein, 2020 The primary auditory cortex is represented primarily by the middle ectosylvian gyrus of temporal lobe Each cochlea is mapped bilaterally in the auditory cortex The auditory cortex is necessary for decoding and feature extraction of complex auditory information The association cortical areas surrounding the primary auditory cortex integrate various sensory stimuli → critical to understanding the surrounding environment Auditory reflex for teaching purposes only Middle ear reflex (acoustic stapedius reflex) protects the sensory cells by reflexively contracting the tensor tympani and stapedius muscles in response to loud sounds 1) The tensor tympani muscle, innervated by the trigeminal nerve, is attached to the muscular process of the malleus reflexively contracts in response to loud sound, limiting the movement of the malleus and the tympanic membrane reduces the force and amplitude of sound applied to the organ of Corti 2) A similar role is also played by the stapedius muscle, innervated by the facial nerve and attached to the muscular process of the stapes Contraction of this muscle pulls the stapes caudally, limiting its movement middle ear reflex – bilateral – loud sound in one ear triggers the reflex in the other Reece, 2015  for teaching purposes only Deafness Hearing requires two ears? animals can hear with only one ear So why 2 ears are important? spatial localization of the sound: requires two ears as the auditory system must detect the difference in time of arrival or intensity of sound impinging on the two ears conduction loss of sound transmission in the deafness outer or middle ear; inflammatory lesions or neoplasias can be causes Clinical deafness nerve or malfunction of the cochlear hair sensorineural cells or VIII nerve fibers; acquired deafness (e.g. inflammatory or ototoxic drugs) or congenital defects  for teaching purposes only Deafness conduction loss of sound transmission in the deafness outer or middle ear; inflammatory lesions or neoplasias can be causes Clinical deafness nerve or malfunction of the cochlear hair sensorineural cells or VIII nerve fibers; acquired deafness (e.g. inflammatory or ototoxic drugs) or congenital defects  for teaching purposes only Differences in animal species Among animal species: the number of coils or turns in the cochlea positively correlates with the size of the frequency range for hearing exceptions in some with specialized cochleas (e.g., horseshoe bat, kangaroo rat) Birds with a non-coiled cochlea – basilar papilla; Köppl (2022)  for teaching purposes only Hearing in aquatic animals Detection of airborne sound ≠ aquatic sound airborne sound: collected by the outer ear (pinna) → ear canal → vibration of the tympanic membrane → ossicles → cochlea → endolymph into motion → mechanical stimulation of hair cells → nerve impulses in the eighth cranial nerve to the brainstem and auditory cortex (50 msec) Aquatic sound - gather information, sense surrounding, locate food, protection and communication - mechanical and acoustical properties of water resemble those of the tissues of the bodies more so than air - sound travels farther than light in water and can be used at night, or in murky waters - underwater sound is 5x faster than airborne sound - sound provides a 3D “view” of the aquatic environment Blue whale moans - https://dosits.org/galleries/audio-gallery/marine-mammals/baleen-whales/blue- whale/?vimeography_gallery=9&vimeography_video=226913421 Dolphin - https://dosits.org/galleries/audio-gallery/marine-mammals/toothed-whales/common- dolphin/?vimeography_gallery=21&vimeography_video=227017593 Erathquake underwater sound - https://dosits.org/galleries/audio-gallery/other-natural-sounds/earthquake/  for teaching purposes only Hearing in aquatic animals: cetaceans and sirenians Relevant particularities: Among cetacean, toothed whales and porpoises (Odontoceti) can derive information about their environment by listening to echoes of sounds that they have produced (echolocation) Cetaceans and sireninans with no pinna and no functional ear canal or not attached to tympanic membrane Some cetaceans (odontocetes like orc and dolphins) with sound conduction to the middle and inner ears through specialized fat channels in the lower jaw middle and inner ears of cetaceans encased in bones outside the skull - keep the two ears acoustically isolated from each other Inner ear similar to terrestrial mammals, with some different features associated to a more complex auditory processing o More auditory ganglion cells tri-lobed jaw fats (orange), melon (green), ear bones (blue), and o Larger auditory nerve soft tissues (transparent) of dolphin. Obtained from dosits.org from o longer, thicker and stiffer basilar membrane (more tuned for higher frequency hearing) Univ of Rhode Island, that was provided byDarlene Ketten (Woods Hole Oceanographic Institution and Harvard Medical School)  for teaching purposes only Hearing in aquatic animals: fishes auditory system: primary sound detection system Sensory sound inner ear detection in fishes detect: vibration; water flow/ mechanosensory motion; low-frequency sounds over lateral line short distances (1-2 body lenghts)  for teaching purposes only Hearing in aquatic animals: fishes Thank you for your attention! Image generated by AI  References Klein, B. G. (2020). Cunningham's textbook of veterinary physiology, 6th edition. Elsevier Health Sciences. Reece, W. O., Erickson, H. H., Goff, J. P., & Uemura, E. E. (Eds.). (2015). Dukes' physiology of domestic animals. 13th edition, John Wiley & Sons. Clark, M.A et Douglas, M. & Choi, J. (2024. Hearing and Vestibular Sensation. OpenStax, Biology 2e, consulted in https://openstax.org/books/biology-2e/pages/36-4-hearing-and-vestibular-sensation Britannica, Encyclopaedia (2023). Hearing. Encyclopedia Britannica. https://www.britannica.com/science/hearing-sense Zola, Andrew (2023). Sound wave https://www.techtarget.com/whatis/definition/sound-wave Moriello, Karen (2022). Ear Structure and Function in Dogs. MSD Veterinary Manual, https://www.msdvetmanual.com/dog-owners/ear- disorders-of-dogs/otitis-media-and-interna-in-dogs Woodward, Michelle (2022). Otitis Media and Interna in Animals. MSD Veterinary Manual, https://www.msdvetmanual.com/ear- disorders/otitis-media-and-interna/otitis-media-and-interna-in-animals Valentine, D. E., Sinha, S. R., & Moss, C. F. (2002). Orienting responses and vocalizations produced by microstimulation in the superior colliculus of the echolocating bat, Eptesicus fuscus. Journal of Comparative Physiology A, 188, 89-108. Populin, L. C., & Yin, T. C. (1998). Pinna movements of the cat during sound localization. Journal of Neuroscience, 18 (11), 4233-4243. Bruss, David (2022). Neuroanatomy, Ear. Website consulted at https://www.statpearls.com/ArticleLibrary/viewarticle/864 Kachar, B (2022). High-Fidelity Stereocilia. Intramural Research Program, National Institutes of Health. Website consulted at https://irp.nih.gov/our-research/research-in-action/high-fidelity-stereocilia Rhode Island University & Inner Space Center. (2022). Discovery of Sound in the Sea. Website consulted in https://dosits.org/ Rako-Gospić, N., & Picciulin, M. (2019). Underwater noise: Sources and effects on marine life. In World Seas: an environmental evaluation (pp. 367-389). Academic Press. Popper, A. N. (2020) Aquatic Bioacoustics, Hearing and Sound Detection by Fishes, https://www.ahukini.net/. Wahlberg, M., Linnenschmidt, M., Madsen, P. T., Wisniewska, D. M., & Miller, L. A. (2015). The acoustic world of harbor porpoises. American Scientist, 103(1), 36-53. Quinn, S. (2021). Bass Senses: Hearing & Lateral Line. In Fisherman. Consulted in https://www.in-fisherman.com/editorial/bass-senses- hearing-lateral-line/379421 Evans, H. E., & De Lahunta, A. (2012). Miller's anatomy of the dog-E-Book. Elsevier health sciences. Köppl, C. (2022). Avian hearing. In Sturkie's avian physiology (pp. 159-177). Academic Press.