PSYC 210 Behavioral NeuroScience Hearing Notes 2 10 20 Inervation of Cochlea Vibrations of the basilar membrane wiggle the stereocilia The back and forth motion of the stereocilia opens and closes channels at their tips When the channels open positive ions enter and depolarize hair cells which releases neurotransmitter onto auditory nerve fibers Scala media contains a very high concentration of Kt K enters the hair cell when the channels at the tip of stereocilia open and the hair cells becomes depolarized K diffuses in the perilymph at the base of cells when tip channels are closed No need for Na K pump hair cells Volley Theory Basilar membrane vibration in response to 500 Hz tone Motion of sterocillia on hair cells Excitatory NT release AP in auditory nerve fiber In response to a 500 Hz there are 500 action potentials spaced 2 msec apart The volley theory proposes the number of action potential equals the frequency of the sound and interval b w them equal and period of the stimulus frequency Intensity Encoding Mechanism The threshold of auditory nerve fibers vary regularly w low threshold fibers on the pilar side of the inner hair cells and high threshold fiber on the other side The low thresholds fibers have high spontaneous activity rates while the high threshold fibers fewer have low spontaneous activity rates In a loud environment low threshold fibers saturate and use the reduced number of high threshold fibers To make it easier to hear use sunglasses for the ears Fingers on earplugs try it Cochlear Implants Auditory nerve fibers send message to brian folklore depolarization produced by neurotransmitters For deaf people the nerve can be depolarized by with electrical current from a cochlear implant Band frequency gets modulated it is a pitch band within what you hear What Role for Frequency Speech can be recognized using 4 bands of noise Can you recognize this sound generated with Ascending Auditory Pathway Auditory nerve projects to the cochlear nucleus on the side of the brain stem From the cochlear nucleus parallel pathways convey info inferior colliculus in the midbrain Sound Localization in Superior Olive Location of a sound must be computed by auditory system Two cues difference in the arrival time of the sound at each ear Intensity difference b w the two ears caused by the head Lateral superior olive computes intensity difference Descending Pathway Efferents Two pathways project from the SOC to the cochlea Medial system around MSO large myelinated fibers Lateral system around LSo thin unmyelinated fibers Tonotopic Map Info from several brainstem auditory structures is combined in the inferior colliculus Imaging studies have show that there is a good tonotopic map in the inferior colliculus The goal is to combine the correct frequencies Auditory Areas in Neocortex Primary auditory cortex is in the temporal lobe on the bank of the Sylvian fissure Wernicke s area involved in speech analysis Broca s area for speech production All component of speech identified and comb before the info reaches this level Werineke s gets fluent speech Broca s aphasia nonfluent speech comprehnsion good repetition poor Weirneke s aphasias fluent comprehension poor repetition poor