Quiz 3 - LO

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Dec 6, 2023

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Lecture 16: By the end of the class, you should be able to: 1. List the layers of the retina and the type of cell or cell process found in each layer. NGIIOOP NF Layer -> axons of retinal ganglion slides Ganglion Layer -> Inner plexiform layer -> Inner nuclear layer -> Outer plexiform layer-> Outer nuclear layer -> Photoreceptor layer-> 2. Describe the distribution and wavelength sensitivity of rods and cones across the retina, and explain why we have a blindspot. Centre of the Fovea, densely packed cones no rods, SMALL CONES As you move away from the fovea on both sides, you see more rods, less cones and less densely packed, cones are big. Rods are more sensitive to short wavelengths compared to cones, Deal with low level light TF more blue and green light. Cones are more sensitive to large wave lengths (RED). Bc it deals with colour vision. The blind spot is the optic disk, where there are no rods or cones TF no cells to see. The optic disk is on the nasal side of the fovea, the right side.

3. Describe photoactivation and transduction in the photoreceptors. Transduction  process which light is transformed to electrical signals, happens in photoreceptors In the dark: ROD PHOTORECEPTOR Transduction happens by cyclic GMP constantly keeping sodium coming into the photoreceptor and potassium leaving the receptor, The cell depolarizes (- 40mV) and releases glutamate to bind to bipolar cell receptors off the synaptic terminal of the photoreceptor. In the Light: ROD PHOTORECEPTOR Transduction happens by light entering the eye, rhodopsin breaking apart as photoactivation goes on, therefore straightening out the retinal and disconnecting from opsin. This makes the NA+ (sodium) channel stop, ultimately deactivating cGMP. Potassium is still leaving the receptor, therefore, the receptor hyperpolarizes to -70mV, as calcium channels close. The glutamate concentration is reduced, therefore less NTs released from the synaptic terminal of the photo receptor. Photoactivation  the bleaching (Breaking) of the photopigment which is on the outer segments of the photoreceptors Okay, so imagine that rhodopsin, which helps us see in low light, is like a sleepy friend. When it's dark, rhodopsin is chilling and relaxed. But then, when you turn on the light, it's like waking up your sleepy friend suddenly! When light hits your eyes, it tells the rhodopsin, "Hey, time to wake up and get active!" This light breaks rhodopsin apart, and it's like a big alarm clock for your eyes. Rhodopsin splits into two parts: retinal and opsin. It's as if they were holding hands, and when the light comes, they let go. This splitting makes a signal that tells your brain, "Hey, there's light here! Time to start seeing things clearly." So, the rhodopsin helps your eyes adjust from darkness to light quickly, so you can see what's around you

4. Define scotopic and photopic vision; describe the process of dark adaptation; discuss the contribution of rods and cones to this process. Scotopic  rod mediated in dim light (rods saturate in bright light) Phototopic  cone mediated in bright light. These two work together creating duplex vision Dark adaptation: increase in sensitivity with time in the dark as we switch from photopic to scotopic. Cones quickly adapt but have poor sensitivity in dim light, and rods slowly adapt but have good sensitivity in dim light. Sure! Imagine your eyes are like superheroes that can adapt to different lighting situations. Dark adaptation is how your eyes get used to seeing better when it's dark. When you go from a bright place to a dark one, like coming inside from a sunny day to a dimly lit room, your eyes need time to adjust. At first, it's hard to see because your superheroes aren't ready yet. It's like they're saying, "Wait, it's too dark here! We need time to power up!" Rods are the first to start getting ready. They're super sensitive to low light, so they quickly start becoming more active to help you see in the dark. It's like they put on their night vision goggles! Cones take a bit longer to get ready because they prefer bright light. But if you stay in the dark for a while, cones also start to adapt. They might not be as good in the dark as rods, but they try their best to help you see colors and details even in low light. So, dark adaptation is like your eye superheroes adjusting to the dark. Rods get ready quickly for night vision, and cones take a bit longer but still work hard to help you see colors and details in the dark!

5. List the 3 types of bipolar cell, and describe how their graded potentials change with light levels. Diffusion bipolar cells- bipolar retinal cell whose purpose is to spread out to get input from many cones -40mv  Depolarized in retinal ganglion cells by increase of photon caught by photoreceptors  This increases their rate of neurotransmitter release  Connects to rods or cones in peripheral retina  With up to 50 photoreceptors per bipolar cell (convergence) ON midget bipolar cells- bipolar cell that depolarizes in response to increased light cones capture -40mV  Depolarized in retinal ganglion cells by increase of photon caught by photoreceptors  Depolarization happens with more light in ON cells  This increases their rate of neurotransmitter release  Connects to cones in fovea  Each bipolar cell gets info from 1 cone OFF midget bipolar cells- bipolar cell that hyperpolarizes in response to increased light captured by cones below -70mV  Depolarizes in retinal ganglion cells with decrease in photon caught by photoreceptors  Depolarization happens less light in OFF cells  This decreases their rate of neurotransmitter release  Connects to cones in fovea  Each cell gets info from 1 cone

6. Describe the anatomy of midget, parasol, and bistratified retinal ganglion cells. Describe a 4th type of cell that is sensitive to light. P  Small bod and dendrites, thin axons, 70%, midget, syn with midget bipols M  Large bod and dendrites, thick axon, 10%, parasol, syn with diffuse bipols K  small or large cell bod and dendrites, 10% of RG, bistratified, synapse with diffuse or midget biopols Intrinsically sensitive RG Cells  stimulated by blue light, reduces melatonin 7. Define receptive field, and discuss how receptive-field-centre size across the retina affects acuity and sensitivity. RF  the part of the retina or the part of the visual field to which a neuron responds ganglion cell rf size determined by # of photoreceptors connected to that cell - Good acuity with small receptive field - Good sensitivity with large receptive field - Convergence of rods onto RG cells makes good sensitivity - Lack of convergence of cones onto RG cells makes good acuity Lecture 17: 1. Describe the luminance (ON/OFF), spatial and temporal responses of midget, parasol, and bistratified retinal ganglion cells. On the Board Lateral Inhibition: Horizontal cells. It helps your eyes make things pop and stand out! - Antagonistic neural interaction between adjacent regions of the retina (horizontal cells), suppresses the firing. - This enhances contrast between light and dark regions, sharpening the perception of edges and contours. The relationship between spatial opponency and lateral inhibition improves your ability to detect boundaries and differences in luminance. -

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