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Questions and Answers
What is the primary function of the G protein transducin in the phototransduction cascade?
What is the primary function of the G protein transducin in the phototransduction cascade?
- To activate rhodopsin upon light stimulation
- To hydrolyze cGMP into GMP
- To open sodium channels in the outer segment membrane
- To activate a phosphodiesterase enzyme (correct)
What is the role of cGMP in the phototransduction process?
What is the role of cGMP in the phototransduction process?
- cGMP is responsible for the dark current in photoreceptors
- cGMP is converted to 5'GMP upon light stimulation
- cGMP activates the G protein transducin
- cGMP keeps sodium channels open in the dark (correct)
What is the primary function of the Na/K ATPase pump in the phototransduction process?
What is the primary function of the Na/K ATPase pump in the phototransduction process?
- To pump sodium out of the inner segment and potassium into the inner segment (correct)
- To maintain the dark current in the photoreceptor cell
- To activate the G protein transducin upon light stimulation
- To convert cGMP into 5'GMP
What is the primary structural component of the rhodopsin molecule?
What is the primary structural component of the rhodopsin molecule?
What is the initial event that triggers the phototransduction cascade?
What is the initial event that triggers the phototransduction cascade?
How does the closure of sodium channels in the outer segment membrane affect the photoreceptor cell's electrical state?
How does the closure of sodium channels in the outer segment membrane affect the photoreceptor cell's electrical state?
What triggers phototransduction in photoreceptors?
What triggers phototransduction in photoreceptors?
What is responsible for the light-induced changes in the electrical activity of photoreceptors?
What is responsible for the light-induced changes in the electrical activity of photoreceptors?
What maintains a slight negative electrical charge in photoreceptors in the dark?
What maintains a slight negative electrical charge in photoreceptors in the dark?
What carries the message from activated ganglion cells to the brain?
What carries the message from activated ganglion cells to the brain?
Which process involves the conversion of cyclic GMP to GMP?
Which process involves the conversion of cyclic GMP to GMP?
What initiates an electrical current flow through the retina in phototransduction?
What initiates an electrical current flow through the retina in phototransduction?
Which of the following is the key event during the phototransduction process that leads to the hyperpolarization of the photoreceptor cell membrane?
Which of the following is the key event during the phototransduction process that leads to the hyperpolarization of the photoreceptor cell membrane?
What is the role of the enzyme RPE65 in the visual cycle?
What is the role of the enzyme RPE65 in the visual cycle?
How does the binding of light to rhodopsin in the photoreceptor cell lead to the activation of the G protein transducin?
How does the binding of light to rhodopsin in the photoreceptor cell lead to the activation of the G protein transducin?
What is the role of cGMP in the phototransduction process?
What is the role of cGMP in the phototransduction process?
What is the primary function of the enzyme LRAT (Lecithin retinol acyltransferase) in the visual cycle?
What is the primary function of the enzyme LRAT (Lecithin retinol acyltransferase) in the visual cycle?
How does the structure of rhodopsin contribute to its role in phototransduction?
How does the structure of rhodopsin contribute to its role in phototransduction?
What is the purpose of the rapid decrease in cGMP levels during phototransduction?
What is the purpose of the rapid decrease in cGMP levels during phototransduction?
How do horizontal cells contribute to the center-surround organization of receptive fields in the retina?
How do horizontal cells contribute to the center-surround organization of receptive fields in the retina?
What is the role of the enzyme 11-cis retinol dehydrogenase (11cRDH) in the visual cycle?
What is the role of the enzyme 11-cis retinol dehydrogenase (11cRDH) in the visual cycle?
What is the primary function of the RPE cells in the metabolism of vitamin A?
What is the primary function of the RPE cells in the metabolism of vitamin A?
How do RPE cells contribute to the formation of the interphotoreceptor matrix (IPM)?
How do RPE cells contribute to the formation of the interphotoreceptor matrix (IPM)?
What is the primary role of the phagocytosis of photoreceptor outer segment discs by RPE cells?
What is the primary role of the phagocytosis of photoreceptor outer segment discs by RPE cells?
What is the primary consequence of the accumulation of the substance A2E in the lipofuscin of RPE cells?
What is the primary consequence of the accumulation of the substance A2E in the lipofuscin of RPE cells?
What is the primary purpose of the rapid shedding and phagocytosis of photoreceptor outer segment discs by RPE cells?
What is the primary purpose of the rapid shedding and phagocytosis of photoreceptor outer segment discs by RPE cells?
Which of the following is the primary role of glucose transporters located on the apical and basal membranes of the retinal pigment epithelium (RPE) and the endothelium of retinal capillaries?
Which of the following is the primary role of glucose transporters located on the apical and basal membranes of the retinal pigment epithelium (RPE) and the endothelium of retinal capillaries?
Which ion movement is primarily responsible for maintaining the slight negative electrical charge in photoreceptors in the dark?
Which ion movement is primarily responsible for maintaining the slight negative electrical charge in photoreceptors in the dark?
What is the primary function of the enzyme lecithin retinol acyltransferase (LRAT) in the visual cycle?
What is the primary function of the enzyme lecithin retinol acyltransferase (LRAT) in the visual cycle?
Which process is responsible for the phagocytosis and degradation of photoreceptor outer segment discs in the retinal pigment epithelium (RPE)?
Which process is responsible for the phagocytosis and degradation of photoreceptor outer segment discs in the retinal pigment epithelium (RPE)?
What is the primary role of anaerobic glycolysis in the retinal metabolism?
What is the primary role of anaerobic glycolysis in the retinal metabolism?
What is the specific carrier protein involved in the transport of all-trans retinol from photoreceptors to the RPE?
What is the specific carrier protein involved in the transport of all-trans retinol from photoreceptors to the RPE?
Which enzyme in the visual cycle is responsible for the conversion of all-trans retinol to 11-cis retinol?
Which enzyme in the visual cycle is responsible for the conversion of all-trans retinol to 11-cis retinol?
In the phagocytosis of photoreceptor discs, which protein plays a crucial role in the oxidation of all-trans retinol back to 11-cis retinal?
In the phagocytosis of photoreceptor discs, which protein plays a crucial role in the oxidation of all-trans retinol back to 11-cis retinal?
What is the primary function of CRALBP in the metabolism of vitamin A within the eye?
What is the primary function of CRALBP in the metabolism of vitamin A within the eye?
Which protein is involved in the spatial summation and modulation of photoreceptor cells' responses through inhibitory feedback?
Which protein is involved in the spatial summation and modulation of photoreceptor cells' responses through inhibitory feedback?
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Study Notes
Phototransduction
- Light absorption in photoreceptors triggers transformation of 11-cis retinal to all-trans retinal, which is moved into the cytoplasm and reduced to all-trans retinol
- All-trans retinol is transported to the RPE by specific carrier proteins within the interphotoreceptor matrix (IPM)
- RPE contains enzymes that convert all-trans retinol to 11-cis retinol, which is then oxidized back to 11-cis retinal and transported back to photoreceptors for incorporation into disc outer segments
Cycling of cGMP
- cGMP keeps Na+ channels open in the outer segment, allowing depolarization
- Light stimulation triggers a cascade that leads to a decrease in cGMP concentration, closing Na+ channels and hyperpolarizing the cell membrane
- When cGMP levels are restored, ion channels open, and the cell becomes depolarized again, releasing glutamate
Information Processing
- Photoreceptors maintain a slight negative electrical charge of about -40 mV in the dark due to active transport of cations such as sodium and calcium
- Light stimulation triggers a series of biochemical changes, leading to hyperpolarization of the cell membrane and a decrease in glutamate release
- Retinal neurons are designed as ON and OFF cells, responding differently to light conditions
- Receptive fields are arranged in a center-surround pattern, with light activation in the center and antagonistic response in the surround
Retinal Cells
- Bipolar cells have center-surround receptive fields and respond with graded potentials
- Ganglion cells have center-surround receptive fields and respond with action potentials
- Horizontal cells receive input from many photoreceptors, contribute to spatial summation, and impact surround responses of bipolar cells
- Amacrine cells have center-surround receptive fields and respond with action potentials, with AII amacrine cells playing a key role in the rod pathway
RPE Cells
- RPE cells phagocytose fragments from the continual shedding of photoreceptor outer segment discs
- RPE cells metabolize and store vitamin A, contributing to the biochemical process in the rod disc renewal system
- RPE cells contribute to the formation of the interphotoreceptor matrix (IPM) between the RPE layer and photoreceptors
Retinal Metabolism
- Glucose is the primary source of energy for retinal tissue, entering the tissue via facilitated diffusion
- Glucose metabolism switches from glycolysis to oxidative metabolism in retinal tissue
- High oxygen utilization in photoreceptors requires high blood flow in the choriocapillaris
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