PSYC 210Behavioral 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 periodof 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 electricalcurrent 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