Define adaptation - Answer Reduction of sensory responsiveness when stimulation is unchanging. It prevents us from having to respond continuously to unimportant information
Explain the adaptation process for the visual pathway - Answer Low levels of Ca++ activate recoverin which activates rh...
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NROS 418 Exam 3 questions with correct answers
Define adaptation - Answer Reduction of sensory responsiveness when stimulation is unchanging. It prevents us from having to respond continuously to unimportant information
Explain the adaptation process for the visual pathway - Answer Low levels of Ca++ activate recoverin which activates rhodopsin kinase, phosphorylates rhodopsin, arrestin binds and shuts off pathway
Explain the adaptation process for the auditory pathway - Answer (prolonged stimulus) Stereocilia are bent, tip links are stretched, channel opens. There is an interface plaque on the tall stereocilia which is where the tip link attaches. On the internal side is a myosin motor that is associated with that plaque. Under normal circumstances, the tip link is trying to pull down where the myosin motor is trying to pull up. When you open the channels that allow in K+ and Ca++, the Ca++ comes in, binds to calmodulin which is associated with the neck of the myosin which causes it to decrease its upward movement so it is coming down the actin filaments. As the motor travels down, the stretch on the tip link decreases so the channels open decreases. Decrease responsiveness of that hair cell to that degree of
bending
What is a receptive field? - Answer The region of sensory space whose stimulation results in a change in firing rate of the neuron
Primary receptor pick up information from spatial domain in organ where stimulation occurs, second/third order neuron receive summation of multiple stimuli from prior neurons, higher order are most complex as they get the most summation of stimuli
Why does the organization of the eye guarantee that we have a blind spot? Why can't we normally detect the blind spot? - Answer The axons of retinal ganglion cells converge at the optic disc and extend through the retina as the optic nerve. This area has no photoreceptors. The disc lies nasal to the fovea of each eye, so light coming from a single point never falls on both blind spots simultaneously, so we are unaware of them.
What is different about the fovea and the rest of the retina? Why is visual acuity best when images fall on the fovea? - Answer It has a high density of photoreceptors
The proximal neurons of the retina are shifted aside so light has direct access to the
photoreceptors, reducing blur from light scattering. Also, the PRC in the fovea have very small receptive fields.
What are the main differences in the functions of rods and cones? Why can't you see color in the dark? - Answer Rods have more membranous disks thus more photopigments so they have high sensitivity in dim light and night
Cones have less disks thus less photopigments so they have lower light sensitivity but they respond to different wavelengths of light to detect color. At night they are not able to respond to light so the color cannot be detected.
Describe the connections that result in the on-center off surround receptive field of a retinal ganglion cell. - Answer Center cone cell connected to an on-center bipolar cell with mGluR6 receptors that are inhibited by glutamate. When light hyperpolarizes the PRC, it causes the bipolar cell to be depolarized, releasing glutamate onto the on-center ganglion cell causing its excitation
Describe the connections that results in the off-center on-surround receptive field of a retinal ganglion cell. - Answer Center cone cell connected to an off-center bipolar cell with AMPA receptors, glutamate excites off-center bipolar, so with light the PRC is hyperpolarized and doesn't release glutamate to excite the bipolar cell, inhibiting the release of glutamate onto the off-center ganglion cell causing its
inhibition What do we mean by the term "lateral inhibition?" What is the functional effect of such inhibition on the selectivity of a response to a stimulus? - Answer Lateral inhibition suppresses excitation of surrounding neurons to sharpen the central focus and preserve spatial clarity of the original stimulus. It helps to sharpen stimulus selectivity and increase the specificity of the signal
Photoreceptors are depolarized at rest, thus releasing glutamate tonically. Why is this useful? - Answer There are many ions flowing into the cell so the random opening or closing of channels will not affect the membrane potential of the cell (thus not depolarizing bipolar or ganglion cells); only the closing of a large number
of channels, through absorption of a photon, will affect it and signal that light is in the visual field. Hence, the system is noiseless.
Are the retinal ganglion cell receptive fields all the same size? What would be the advantages of a large receptive field be? - Answer The size of the receptive field varies according to its eccentricity (position relative to the fovea) and the position of neurons along the visual pathway
Large receptive field allow for detecting changes over a wide area
Describe the organization of the LGN. Consider its layers, the distribution of parvocellular and magnocellular neurons (and what the difference between them is) and the visual field represented in each LGN. Describe the receptive field of LGN neurons. - Answer Layers 1,4,6 receive input from contralateral eye and 2,3,5 ipsilateral Layers 1 and 2 receive info through magnocellular pathway: Larger cells so info from a large number of bipolar cells can converge onto single magno ell. Fast-
conducting cells process course outlines, motion, and other "where" properties of visual stimulus
Layers 3-6 receive information through parvocellular pathway: Small, slow-
conducting cells. Process info about color, shape, contrast, size, detail, clarity, and other "what" properties of visual stimulus
Left visual field project to right LGN and vice versa
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