Mechanism of Photoreception
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Questions and Answers

What is the primary reason the rod cells release neurotransmitter in complete darkness?

  • The Na$^+$ pump is continuously pumping out Na$^+. (correct)
  • Light hits the retina, stimulating cones.
  • The Na$^+$ channels are closed.
  • Rhodopsin is inactive.

    • What occurs in rod cells when light hits the retina?

  • Hyperpolarisation reduces neurotransmitter release. (correct)
  • Trans-retinal activates rhodopsin to open Na$^+$ channels.
  • Bipolar cells are inhibited, preventing action potentials.
  • Na$^+$ channels open to allow depolarisation.

    • During dark adaptation, what happens to rhodopsin as the eyes adjust to darkness?

  • It continuously produces trans-retinal.
  • All rods adapt in less than 10 minutes.
  • It becomes less sensitive to light.
  • Cis-retinal accumulates, increasing sensitivity. (correct)

    • How does the content of neurotransmitter release from rod cells change in response to light?

    <p>It decreases in bright light due to hyperpolarisation.</p> Signup and view all the answers

    Which process explains the changing permeability of the rod cell membrane during dark adaptation?

    <p>Rhodopsin transforms to close Na$^+$ channels.</p> Signup and view all the answers

    What is the effect of the bipolar neuron when it receives decreased neurotransmitter from the rod in dim light?

    <p>It becomes depolarised and generates an action potential.</p> Signup and view all the answers

    What is the consequence of neurotransmitter release at the synapse between the rod cell and bipolar cell in complete darkness?

    <p>It hyperpolarises the bipolar cell preventing action potential.</p> Signup and view all the answers

    What happens to the Na$^+$ channels in rods when they are bleached during light exposure?

    <p>They close, reducing Na$^+$ permeability.</p> Signup and view all the answers

    What is the role of retinal in the composition of rhodopsin?

    <p>It acts as a photosensitive compound that undergoes a change in light.</p> Signup and view all the answers

    What occurs to rhodopsin when it is exposed to bright light?

    <p>It undergoes a process known as bleaching.</p> Signup and view all the answers

    What is the isomerization process of retinal when light is involved?

    <p>Cis-retinal converts to trans-retinal.</p> Signup and view all the answers

    How long does it take for trans-retinal to be converted back to cis-retinal?

    <p>A few minutes.</p> Signup and view all the answers

    What happens to rods in bright light conditions?

    <p>They become saturated and unresponsive.</p> Signup and view all the answers

    Which statement correctly describes the relationship between opsin and retinal in rhodopsin?

    <p>Retinal forms a strong covalent bond with opsin.</p> Signup and view all the answers

    What is the result of the bleaching process in rhodopsin?

    <p>Rhodopsin loses its ability to respond to light stimuli.</p> Signup and view all the answers

    Which structural change occurs in rhodopsin upon absorbing a photon of light?

    <p>Retinal undergoes a conformational change.</p> Signup and view all the answers

    Study Notes

    Mechanism of Photoreception

    • Rods contain the pigment rhodopsin
    • Rhodopsin is formed by the combination of:
      • A light-absorbing carotenoid molecule called retinal (retine)
      • A protein called opsin
    • Retinal exists in two isomeric forms:
      • cis form (in dark)
      • trans form (in light)
    • When a rod cell is exposed to light, light causes the retinal molecule to change from its cis form into a trans form
    • This change puts strain on the molecule and the bond between retinal and opsin is broken
    • This causes the rod cell to bleach
    • enzymes convert trans-retinal to the original cis-retinal in the dark
    • This process takes a few minutes
    • In dim light, rhodopsin is bleached
    • In bright light, rhodopsin is bleached, and rods lose their photosensitivity

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    Description

    Explore the fascinating process of photoreception in rod cells, focusing on the role of rhodopsin and its components, retinal and opsin. Understand how light affects the isomerization of retinal and the biochemical changes that follow in response to light exposure. This quiz will test your knowledge on the intricacies of visual processes in dim and bright light.

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