Unformatted text preview: Audition Audition Questions to answer this lecture Questions to answer this lecture What is the nature of the stimulus that the brain perceives as sound? How does the nervous system transduce changes in air pressure into our impression of sounds? How does auditory system analyze sound waves? What pathway does info travel from the auditory receptors to the neural cortex How does the brain understand language and If a tree falls in the woods and no I f a tree falls in the woods and no one is around to hear it, does it make a sound? The Stimulus for Audition The Stimulus for Audition
Sound movement of air molecules from a source of vibration Sound waves energy generated by this displacement of molecules causes waves of changing air pressure Travel at a fixed speed of 1100 feet per second Physical Properties of Sound Waves Physical Properties of Sound Waves
Frequency (pitch) # of cycles a wave completes in a given amt of time cycles/sec (Hz) Amplitude (loudness) the intensity of sound, measured in dB Complexity (timbre) mixture of frequencies, can be simple or complex, difference in sound btw a violin and trumpet Anatomy of the auditory system Anatomy of the auditory system Outer Ear (The pinna) Sound arrives outer ear Catches sound waves Outer ear funnels in sound to eardrum Made of cartilage and flesh Eardrum Eardrum Vibrates when sound waves hit Miniature drum Tympanic Membrane Middle Ear Middle Ear Vibrating eardrum causes ossicles to vibrate 3 bones Malleus (hammer) attached to eardrum & incus Incus (anvil) connected to both bones Stapes (stirrup) attached to incus and to the oval window, membrane btw middle ear and inner ear. Amplify and convey Inner Ear Inner Ear
Cochlea contains the receptor cells Transduces sound vibrations into electrical signal Transmitted to brain Inner Ear Inner Ear Cochlea Cochlea Hollow compartments filled with lymphatic fluid Receptor cells and support cells sit w/in the organ of Corti. Inner hair cells auditory receptors in tectorial membrane Outer hair cells help to "tune" the cochlea and provide support Basilar Membrane Basilar Membrane Floats in fluid Bounces up and down Hair cells embedded on membrane have several stereocilia cilia sheared back and forth under the tectorial membrane. When stereocilia are pulled, the hair cell depolarizes. This signal is transmitted to the auditory nerve to the brainstem. Basilar Membrane Basilar Membrane
Spiralshaped organ in cochlea mechanically separates frequency components of sound. Floats in lymphatic fluid Dif frequencies max amplitude at dif locations on BM. High freq max response at base, closest to oval window. Low frequencies max response at apex (tip) Tonotopic organization Thinner/narrower at base of cochlea than at tip (apex) High frequencies vibrate at base low frequencies at the apex. Properties of the BM set up gradient, not properties of hair cells Basilar membrane Basilar membrane Hair Cells Hair Cells Transduce sound waves into neural activity 3500 inner hair cells (auditory receptors) Deflection of cilia opens mechanically gated ion channels (allow primarily K+ and Ca+2) to enter cell. Hair cell does not fire an axn potential: ions depolarize cell, opening vgated ca+2 channels; which trigger the release of NT (Glu) at end of cell. Glu bind to receptors and thus trigger action potentials in the auditory nerve 12,000 outer hair cells sharpen the resolving power of the cochlea by contracting or relaxing, and changing stiffness of tectorial membrane Pressure from the stirrup on oval window makes cochlear fluid move Waves travel thru cochlear fluid cause the basilar and tectorial membrane bend Bending membranes stimulate the cilia at the tips of the outer hair cells Generates graded potentials in inner hair cells, which act as auditory receptor cells Listen Closely!!! Listen Closely!!! Brief Summary of Events Inner hair cells synapse w/cells that form the auditory nerve (cochlear nerve) Auditory nerve forms part of 8th cranial nerve Continuing the Auditory Continuing the Auditory Pathway governs hearing and balance Cochlear nerve axons enter brainstem at the level of the medulla, synapse in cochlear nucleus Cochlear nucleus sends connections to superior olive and trapezoid body Superior Olive Superior Olive Ventral cochlear nucleus cells project to nuclei in medulla called the superior olive. Where differences timing and loudness of the sound in each ear are compared Helps determine the direction the sound came from. Interaural Time differences Binaural Cues Binaural Cues
Interaural Time Difference (ITD) biological binaural cue is the splitsecond delay between the time when sound from a single source reaches the near ear and when it reaches the far ear. Interaural Amplitude (intensity) Difference (IAD) Sound amplitude and pressure differences between each ear Inferior Colliculus Inferior Colliculus Located below superior colliculi visual processing centers Relays ascending auditory system Integrates info before sending to the thalamus and cortex sound source localization from superior olivary complex & dorsal cochlear nucleus Part of auditory thalamus, represents thalamic relay btw inferior colliculus and auditory cortex. Several dif nuclei with dif neurons and fxn. Projects to the primary auditory cortex (Area 1) MGN may influence the direction and maintenance of attention. Medial Geniculate Nucleus Medial Geniculate Nucleus (MGN) Primary Auditory Cortex Primary Auditory Cortex Processing of auditory info. Located on the temporal lobe Tonotopic organization Multiple auditory areas (like visual cortex). Involved in tasks such as identifying and segregating auditory "objects" and identifying location of a sound in space. Performs basics of hearing; pitch, volume. Auditory (Vestibular) Pathway Auditory (Vestibular) Pathway
Hair cells → spiral ganglion. → cochlear nerve → vestibulocholear nerve → medulla oblongata (superior olive) → inferior colliculus (midbrain) → thalamus → auditory cortex Purpose is to keep tabs on position/motion of head in space. detect rotation, shake or nod your head (angular acceleration). detect motion along a line elevator drops, lean body (linear acceleration) 3 semicircular canals detect angular acceleration in 3 mvnt dimensions, each canal detects motion in a single plane Lateralization Lateralization Anatomical asymmetry is correlated to fxnal assymmetry; left temporal cortex analyzes language related sounds right temporal cortex analyzes music related sounds 30% of lefthanders have unique pattern
bilateral representation of speech opposite to right handers Aphasia Aphasia
Impairment of language affect production or compreh. of speech & ability to read or write. May affect single or multiple aspects of language Ex: ability to name obj./read Due to: Brain injury, tumors, stroke, infections Men and women equally affected. ~1 mil. US persons currently have aphasia Wernicke’s Area Wernicke’s Area Region of the brain important in language development. Located on the temporal lobe on the left side of the brain and is responsible for the comprehension of speech Language development or usage can be seriously impaired by damage to this area. Wernicke’s Aphasia Wernicke’s Aphasia Damage temporal lobe Long sentences no meaning Difficulty w/ comprehension often unaware of mistakes.
"You know that smoodle pinkered and that I want to get him round and take care of him like you want before," meaning "The dog needs a walk." Broca’s Area Broca’s Area Region of brain w/functions linked to speech production. Broca’s patients lost the ability to speak after injury to the posterior inferior frontal gyrus Studies of chronic aphasia have implicated an essential role of Broca’s area in various speech and language functions. Broca's area Broca's area . Damage frontal lobe . Short phrases produced w/great effort Ex: "Walk dog" Comprehension fine Aware of difficulties, easily frustrated by speaking problems. Language and Music Language and Music Language and music are universal to humans Oral language follows similar basic structural rules People in all cultures create and enjoy music Both based on sound Audition in Non human species Audition in Non human species Plays a huge role in communication Birdsong attracting mates, demarcating territories, announcing location, or presence
Varies in diversity and complexity Areas of brain specializing for production and comprehension/ lateralization (left hemisphere) Echolocation Like sonar to identify what is in the surrounding environment Map objects in environment In summary… In summary… What is the nature of the stimulus that the brain perceives as sound? Energy in sound waves How does the NS transduce changes in air pressure into our impression of sounds? Pathway from outer to inner ear, from sound waves to action potentials Basilar membrane and tonotopic organization How does auditory system analyze sound waves? What pathway does info travel from auditory receptors to neural cortex Hair cells to cochlear nerve to 8th cranial nerve, MGN, auditory cortex How does the brain understand language and music Next class… Next class… Somatosensory System ...
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- Spring '10
- hair cells, auditory receptors, Basilar Membrane Basilar Membrane, Basilar Membrane Basilar