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Sensation of light

Sensation of light. 39. Retina. rod. cone. Bipolar cell. Horizontal cell. amacrine cell. ganglion cell. 5 cell types, 50 various cells. 40. Chemical and light signals. neuron photoreceptor. NEUROTRANSMITTER. LIGHT. G protein –coupled receptor ( rodopsin ).

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Sensation of light

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  1. Sensation of light

  2. 39. Retina rod cone Bipolar cell Horizontal cell amacrine cell ganglion cell 5 cell types, 50 various cells

  3. 40. Chemical and light signals neuron photoreceptor NEUROTRANSMITTER LIGHT G protein –coupled receptor (rodopsin) G protein –coupled receptor Effector enzyme Effector enzyme opszin retinál G protein (transducin) G protein Secondary messenger (increase of amount) Secondary messenger (decrease of amount) Ion channel (open or close) Ion channel (close)

  4. 41. Phototransduction dark light cGMP-gated Na+- channel Na+: K+: OUTWARD Na+: INWARD K+: OUTWARD Dark current K+- channel K+ K+ Na+ Na+ depolarized state hyperpolarization - 40 mV -40 - -70 mV Na+/K+ pump light impulse

  5. 42. Phototransduction retinal binding site Space between discs George Wald Nobel Prise, 1967 disc membrane opsin cytosol retinal cytoplasmic tail cis-retinal Light absorption curved cytoplazmic tail rhodopsin= opsin + retinal retinal: isomerization (G-protein-coupled metabotropic receptor) trans-retinal opsin: structural change non-curved cytoplazmic tail

  6. 43. K+ K+ Na+ Na+ Na+ Na+ K+ Na+ R GDP Dark current - depolarization cGMP-gated ion channel cGMP phosphodiesterase rod rhodopsin cGMP T I + K+ transducin Na+ + I + I guanilyl cyclase GTP cGMP Transducin: G-protein rodopsin: G-protein-coupled metabotropic receptor glutamate neurotransmitter (analogous release)

  7. 44. Na+ Na+ Na+ Na+ K+ K+ K+ Na+ R GDP GDP GTP GTP Phototransduction - hyperpolarization cGMP-gated ion channel cGMP phosphodiesterase rhodopsin cGMP T T I + GMP I + K+ + I transducin LIGHT Na+ I + I + + I • 1 photon activates 500 transducin molecules, which in turn close several • hundred ionchannel, and protects the entrance of 106 Na+ • - Approximately 10% of the incoming light reaches the retina glutamate neurotransmitter

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