Vision 1. What does perception depend on (think law of specific nerve energies)? Describe the general path that stimulus energy takes through our brain, leading to conscious perception.Perception depends on what type of receptors are stimulated (law of specific nerve energies-in which neurons are active, impulses in certain neurons indicate light, wheras impulses in others indicate sound.), how many/how much they are stimulated, in what pattern they are stimulated, and what neurons those sensory neurons project to- brain can be tricked. Path: receptors on sensory neurons (retinal photoreceptors) nerve to the CNS (optic nerve) Thalamus( lateral geniculate nucleus) primary cortex (primary visual cortex 1 (V1) also called striate cortex) association cortex (secondary visual cortex (V2-V8)2. How does light enter the eye? Describe the path it takes through the cell layers of the retina and the path of signal transduction.Photons of light enter through the pupil; it is focused by cornea and lens to the retina at the back of the eye***Path through retina: messages go from receptors at the back of the eye to bipolar cells (center of eye) those cells send messages to ganglion cells the ganglion cell’s axons send messages back to brain. Amacrine cells also help out and they refine the input to ganglion cells, enabling them to respond specifically to shapes, movements, or other visual features. ** photoreceptorshorizontal cellsbipolar cellsamacrine cells ganglion cellsPath of signal transduction: in absence of lights, photoreceptor cells spontaneously fire; absoribing light reduces the amount that they fire; photoreceptor cells have inhibitory synapses with bipolar cells; Decreasing inhibition by reducing the spontaneous firing rate of photoreceptors increases the firing of the bipolar cell(s) with which the photoreceptor cells synapse; The bipolar cells have excitatory synapses with ganglion cells, and so they pass the message along3.How are rods and cones similar and different? On what point of the retina are cones mostdensely packed? With which types of cells do photoreceptors synapse? Do they excite or inhibit those cells (review slide 17 of the notes)?Rods: respond well to faint light, overstimulated by bright light, abundant in periphery, necessary for black and white vision. Cones: need bright light to respond but provide more detailed info, abundant in center, fovea, which is a depression in the retina where light hits unimpeded by other cells, essential for color visionPhotoreceptors synapse with bipolar cells and they inhibit, yet bipolar cells excite synapseswith ganglion cells4. On what is our perception of color based? What happens when the same photo pigment is produce in two different types of cones?Color is not a property of light- its our perception based on the wavelength with which photons hit photoreceptors. Our perception of individual colors is based on the relative rates of responding of three different subtypes of cones that respond to certain ranges of wavelengths (trichromatic theory/ Young-Helmholtz theory). We perceive the shortest visible wavelengths as violet (44-700)Color vision deficiency occurs when the same photo pigment or no code for all three types of cones are produce in two different types of cones1. Describe the path of the optic nerve – what and where do fibers cross, and to what two areas do they project? The axons of what type of cells make up the optic nerve, and what is the result of the optic nerve passing through the retina blind spot?Axons of ganglion cells combine to form the optic nerve, which carries info form the eye to the brainWhere the axons accumulate and leave the eye as the optic nerve interrupts the layer of receptor cells of the retina, creating a blind spot (not typicallynoticed because our brain fills in gaps in a predictable environment) the optic nerves from the two eyes meet at the optic chiasm= half of the axons from each eye cross to the opposite side of the brain and the other half stay on same sideNasal side- contralateralTemporal sides- IpsilateralEnd result= all information from right side of each eye is processed by the left brain hemisphere, and that from the left side of each eye is processed by the right hemisphere.Projections are both contralateral and ipsilateral 2. What type of ganglion cells that project to the lateral geniculate thalamus are important for distinguishing detail and which are more important for perceiving motion? How else do these cell types differ?Receives input from three types of ganglion cells via the optic nerve:– Parvocellular : small receptive fields, good at discerning detail, color, and answering “what”– Magnocellular : large receptive fields, good at discerning motion, depth, and answering “where”– Koniocellular : diverse group with multiple functionsPoint- information segregation and processing in the visual system occurs prior to itreaching the cortex.3. What is V1 necessary for? What is it not necessary for? V1/ striate cortex- is in occipital cortex and most visual information from the lateral geniculate nucleus of the thalamus’s goes here. People who damage this report no conscious vision, no visual imagery, and no visual images in their dreams. This is necessary for conscious perception those who are blind may respond to some aspects of visual info, such as blindsight because downstream connections are functioningBlindsight= the ability to respond in limited ways to visual information without perceiving it consciously AuditionDescribe the path that sound takes through the ear – at which point(s) does the sound travel as waves of air and where is it converted to waves through fluid? At what points would damage cause conductive versus nerve deafness?Receptors on sensory neurons nerve to the CNS thalamus primary cortex (A1) association cortexAir filled in middle ear and fluid filled in cochleaSound waves are focused by pinna and directed into auditory canal hit tympanic membrane hits ossicles (malleus, incus, stapes)/middle ear hits oval windown displaces fluid in cochlea and basilar membrane moves axons of the hair cells carry info to the brain as the auditory nerve Conductive deafness can be temporary, occurs in the middle ear and can be correct with surgery or hearing aid; sound isn’t conducted properly to the receptor cells, can be caused by disease, infection, or
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