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NATS 1860 Note 15

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York University
Natural Science
NATS 1860
Keith Schneider

NATS 1860 Note 15 Mechanical Receptors and Hearing - Exam information - Review of visual cortical areas - Sound and pressure - The auditory system and frequency map - Hair cells (auditory receptors) - Artificial hearing: cochlear implants - Sound localization - Echolocation (bats and humans) Exam Information - It will be 60 minutes long. - It is closed book: no notes, no computers, no calculators, no cell phones, etc. - There are 30 multiple choice questions and about 6 from each week – 3 from each lecture including the two from today - There will be 5 options on each answer - The only valid excuse for missing the exam is the valid medical notes o Missing the exam or cheating results in a zero on the exam. - Use the lecture and the previous lecture reviews to know exactly is necessary o Use what is reviewed as to what is most important Orientation Selective V1 Neuron - LOOK AT FIGURE 6.8 - LOOK AT HOW RECEPTIVE FIELDS COMBINE TO PROCUDE THE VISUAL FIELD IN THE PRIMARY VISUAL CORTEX o This is usually three P cells that provide this Motion Selective V1 Neurons - There is excitation and inhibition from Retinal M Cells - Excitation before inhibition: respond to motion - Inhibition before excitation – no response o If there is motion that hits the excitatory first, then there is a response. If the opposite direction hits the inhibitory first, there is no direction. Dorsal and Ventral Visual Streams - The Dorsal is on the front and the ventral at the bottom o Remember that there are two hemispheres o The Dorsal pathway receives its information from motion cells and is involved in vision fraction  People with damage to this can tell you what it is, but can’t grab it  They can’t control their movements o The Ventral pathway gets its orientation from vision pathways, and it involves in object recognition of tools, faces, houses, trees, etc.  Damage to this area is when people can’t recognize them, but can grab them. Ventral Pathway - It starts with V1 then moves to higher form vision areas o In V1 you have line an curve recognition o Then you have those lines join together to make angles o Those angles then form shapes o And those shapes make faces and objects. Hearing and Mechanical receptors - They’re specialized neurons that are specialized for detecting changes in pressure. - They’re present in skin (somatosensory receptors) o All nerve cells have this characteristic (they’re sensitive to pressure) - Hearing is a pressure sense – there are specialized cells that respond to changes in pressure - Key Point: deformation of the receptor membrane in a cell that is sensitive to pressure opens ion channels, which depolarizes the neuron and causes it to send spikes to the brain o This occurs with all cells in our bodies o Even though the cells in our retina are specialized for picking up photoreceptors and ganglion cells for generating spikes, when deforming those cells end up opening ion channels, depolarizing, and then sending spikes to the brain  This is why when people get hit in the head they see stars because it triggers action potentials to the brain. - Auditory hair cells: specialized to respond to pressure waves in fluid. o They’re receptors specifically to fluid. Physics of Pure Tones - The simplest way to produce a pure tone is to take a tuning fork or any vibrating objects, and if you hit a tuning fork against a hard edge, the prongs will vibrate back and forth, thus compressing the air in front of them in one direction, and then rarify it in one of them o What we hear is the alternate vibrations of higher density air, and lower density vibrations o This produces a smooth wavy curve. - The speed of sound at sea level is about 340m/s Sound - Compress and expand air by vibrations. - Vibrations cause alternate impressions and expansions (rarifications) of air as something vibrates - There is no sound in a vacuum (outer space) o The sound of our brains end up as waves in water as well. - Figure 7.3 of our books shows how over a period of time the air pressure relative to the average over time o When listening to a pure tone, it has two characteristics:  Amplitude (loudness)  The smaller the amplitude the softer, the larger the louder.  Time: the amount before the sound repeats itself  This is called the period, which is just equal to the time per vibration.  Frequency is equal to 1/period. o Usually we talk about the frequency of sound. o They are measured in Hertz (Hz) and it is equal to cycles per second. o Example; healthy auditory humans can hear from about 20 Hz up to 20,000 Hz o When bats use echolocation, they can hear up to 100,000+ Hz.  Therefore, humans do not have the widest range of hearing in the animal kingdom The Ear - Study Figure 7.5 o It shows the outer part of the ear, outer ear canal (cue tip) o If you puncture the eardrum you will have hearing loss.  The eardrum vibrates if a sound is coming into our ear (it’s all filled with ear) those sound waves hit the eardrum and cause it to vibrate. o Behind the ear drums are small bones ossicles  They transmit the vibrations from the ear drum to the fluid filled chamber that involves stimulating nerve cells when we hear to the cochlea  The cochlea is all curled up in order to prevent sound coming back to the other ear. - Consider Figure 7.6 o Conceptually, you can unroll the cochlea – it’s not unrolled in our brain, but it functions as a long tube.  The small bones are before the basilar membrane that runs down the middle of the cochlea (it’s the medium blue membrane of the cochlea)  This is where all of our auditory receptors sit. Cochlea and Frequency - How does the physical and mechanical properties of the basilar membrane allow for the frequency of sound be analyzed o Figure on Page 176 shows the outer ear canal’s little bones transmitting vibrations to the fluid filled cochlea  Cochlea is filled with fluid, causing the basilar membrane to go up and down. o Parenthetically, your ears pop when you go flying because your bones go to the back of your mouth that equalize air pressures (important for
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