NSCI 110 1st Edition Lecture 23 Outline of Last Lecture I. Ganglion cells have concentric, surround-sound, antagonistic receptive fieldsa. Results in distinct action potential ratesb. Receptive fields are larger for cortical cellsi. Simple feature detection cellsii. Complex feature detection cellsiii. Hypercomplex feature detection cellsII. Color is encoded through opponent processinga. Single opponentb. Double opponentOutline of Current Lecture I. Sound waves consist of compressed air and rarefied air particlesa. Frequency is the number of cycles per second (pitch)b. Amplitude is the height of the wave (loudness)II. Threshold is the minimum frequency at which a sound can be heard 50% of the timea. Amount of energy needed to hear very low frequency sounds is highIII. Basic anatomy of the human eara. Outer, middle, inner earb. The cochlea has three different chambers, including the Organ of Cortii. Basilar membrane moves in response to sound vibrations and causes hair cells to move and relay action potentials to the cortexCurrent Lecture- Both visual and auditory systems transduce stimuli into perceptions- The auditory system in designed to encode basic stimuli features and through parallel and serial pathways, a “sound” is perceived- Properties of sound waveso Air molecules are compressed (top portion of wave on graph) or rarefied (bottomportion of wave on graph) Larger the wave either direction, the greater the magnitude of compression or the oppositeo Frequencies correlate with pitch (# of cycles per second) Higher frequency produces a higher pitch soundo Louder sounds can have the same frequency (amplitude of the waves can differ)- Threshold is the minimum frequency at which we can hear something 50% of the timeThese notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.o Hertz # of cycles per second Our hearing range is from 20-20,000 Hertz Amount of energy required to hear at very low frequencies is high, then decreases (better at detecting a stimuli as auditory), then increases at very high frequencies- From 1,000-3,000 Hertz we are very sensitive to sounds (involving language usually)- Most music can reach up to about 5,000/6,000 Hertz As you age, threshold increases because the hair cells in the cochlea tend to die off- The ability to hear higher frequencies decreases- May differ depending on environment in which you are raised- Anatomy of the earo Outer/middle/inner ear divides into sectionso Pinna Catches sound waves and deflects them into the external ear canalo Auditory canalo Tympanic membraneo Ossicles Malleus Incus Stapes - Amount of energy per unit is the highest here because of condensationo Oval window Behind this structure is a fluid this is where energy is transferred from solid to liquid mattero Cochlea Looks like a snail shell Three different chambers- Energy from stapes causes fluid movement in the uppermost chamber Organ of Corti- Basiliar membrane (in between second and third chambers) moves up (compression) and down (refraction)o Compression pushes fluid out of the chamber and causes transduction- Fluid that is just above this membrane therefore moves- Tectorial membrane (rigid) sits just above the outer (3 rows of increasing height) and inner hair cellso Neurons form synapses with these hairs cells this is what is responsible for the transduction of these signalso To initiate transduction, the hair cells must move o The hair cells change the tension of the basilar membrane (changes our ability to hear certain frequencies)o Stereocilia project into the path of the fluid that moves in and out of the chamber Once in lower chamber, fluid flows out of cochlea into the round window- This round window is how energy is released- Ears “popping”- This path leads to the Eustachian tube - Transducing sound waves into neural impulseso High frequency sounds encoded at the end of the cochlea near the oval window Cochlea shows tonotopic organization starting tip (thinnest) engages highest frequencies- Tension of the basilar membrane changes down the cochlea Sound waves at medium frequencies cause peak bending of the basilar membrane at this point- Why do we lose hearing at older age?o Channel involving higher frequencies is narrower, so loss of hair cells has a biggerimpact smaller densities needed for encoding higher frequencies - For test: up to page 331 (section labeled anatomy of central nervous
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