Biol 224 Theme 12

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  1. Glutamate
    • -carboxylate anions and salts of the non-essential AA glutamic acid
    • -most abundant excitatory neurotransmitter in the vertebrate nervous system
    • -key role in learning and memory
    • -stored in chemical vesicles in the chemical synapses
    • -nerve impulses stimulate release from pre-synaptic cell and bind to post synaptic glutamate receptors
  2. Glutamate Receptor
    • -sodium-calcium channel that makes the cell voltage dependent
    • -activation results in voltage dependent flow of Na+ and Ca2+ ions into the cell and K+ out of the cell
    • -Ca2+ flow through the receptor is thought to be critical to synaptic plasticity(cellular mechanism for learning and memory)
  3. Single Lens Eye
    • -found in vertebrates, squid, octopus, some snails and annelids 
    • -light is transmitted through the pupil to the retina located at the back of the eye
    • -light is captured by photorecepetors
  4. Photoreceptors
    • -specialized cells located in the retina
    • -have phototransduction capability (convert visible electromagnetic radiation into electrical signals)
    • -differ from other sensory receptor cells because their cell membrane potential is slightly depolarized when at rest
  5. Selera
    -strong outer white sheath around eye
  6. Cornea
    • -continuous with sclera but thin and clear 
    • -has two cavities (anterior, posterior)
  7. Anterior Cavity
    -holds aqueous humor
  8. Posterior Cavity
    • -holds thick vitreous humor
    • -maintains eye shape
  9. Iris
    -pigmented smooth muscle controlling size of pupil
  10. Photon
    -fundamental unit of electromagnetic radiation with the properties of both a particle and a wave
  11. Layers of the Eye
    • Deepest-rods and cones-up against the sclera 
    • Intermediate-Bipolar Cells-interneurons that synapse with photoreceptors and ganglion cells(transparent)
    • Shallowest(closest to front of eye)-Ganglion Cells-send axons out of eye into optic nerve(transparent)
  12. Amacrine Cells
    • -interneurons in the retina
    • -responsible for 70% of input to retinal ganglion cells
  13. Bipolar Cells and Ganglion
    • -both transparent cells
    • -responsible for other 30% of input to retinal ganglia and are regulated by amacrine cells
  14. Rods
    • -sensitive to low intensity light
    • -used mostly at night
    • -do not discriminate color
    • -vitamin A increases sensitivity to light at night
  15. Cones
    • -require more light for stimulation
    • -fewer cones than rods
    • -detect color(in humans)
    • -outer segment contains pigment
    • -inner segment contains nucleus and other organelles 
    • -synaptic terminal filled with neurotransmitter vesicles(no axons)
  16. Visual Pigments
    • -retinal and opsin
    • -compounds bound together 
    • -in humans cone pigments composed of retinal, plus 1 of 3 opsins
    • -each different type of opsin detects a different wavelength(red, green or blue)
    • -birds have 5 different opsins
  17. Retinal
    -chromophore vitamin A derivative that absorbs energy from light
  18. Opsin
    • -G protein coupled receptors that convert light into metabolic energy
    • -enable vision in low light 
    • -rhodopsin in rods
    • -photopsins in cones
    • -convert a photon of light into an electrochemical signal, which changes membrane permeability to ions
    • -plasma membrane protein
  19. Membrane Potential in Dark
    • -In the absence of light and under the influence of glutamate membrane potential is
    • in a slightly depolarized state (closer to zero than we would expect[normal value of -70mV])
    • -Na channel open, K closed
    • -results in continuous release of glutamate
    • -interpreted as absorbance of light
    • -get 11-cis-retinal
  20. Membrane Potential in Light
    • -In the presence of light and in the absence of glutamate membrane potential is in
    • a hyperpolarized state (farther from zero than we would expect)
    • -Na channel closed, K open
    • -glutamate release is stopped
    • -interpreted as visual image
    • -get all trans-retinal
  21. Rhodopsin
    • -seven transmembrane receptor covalently bound to retinal
    • -assosiated with three different G proteins known as transducins (Gtα, Gtβ, Gtγ)
    • -extremely sensitive to low light
    • -enable vision in low light
    • -responsible for first events in perception of light
  22. Light Effects on Sodium Channel
    • -all 11-cis-retinal are converted to all-trans-retinal
    • -activates G-transducin 
    • -G-Transducin then activates phosphodiesterase 
    • -phosphodiesterase convert cGMP into GMP which cause cGMP bound to Na channels(keeping them open) to dissociate 
    • -closes Na channels and results in hyperpolarization
  23. Dark Effects on Sodium Channel
    • -constant glutamate release stimulates the conversion of GTP to cGMP(with release of two Pi)
    • -cGMP binds to Na receptors which open and activate them, resulting in the membranes constant slightly depolarized state in darkness
  24. Light Absorption in Red Cones
    • -absorb 0 blue wavelengths
    • -can absorb up to 31% of green wavelengths
    • -up to 83% of yellow wavelengths
  25. Light Absorption in Green Cones
    • -absorb 0% of blue wavelengths
    • -67%of green wavelengths
    • -83% of yellow wavelengths
  26. Light Absorption in Blue Cones
    • -100% of blue wavelengths
    • -36% of green wavelengths
    • -0% of yellow wavelengths
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Biol 224 Theme 12
Theme 12
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