Retina, Biology

RETINA -

  • It is inverted. Innermost, sensitive layer. The part of ratina which is attached to choroid is pars optica.
  • The part of retina attached to cilliary body is ora-serreta.
  • In retina 2 parts are clear -   (A) Pigmented layer          (B) Neuro-sensory layer.
  • Pigmented layer is of hexagonal or rectangular cells.
  • Fusein pigment present adopted to absorb light rays.
  • From these cells microvilli are given out to engulf extra pigment granules.
  • Inside it, a layer of rods and cones is present.
  • Rods are 1150 lakh and cones are 65 lakh.
  • Rods are mone long, meant to judge abject in dim light in it rodopsin (retinine + opsine or skotoprine) present for it vitamin A (ratinol) is necessary i.e. in defficiency of vit A. night blindness (nyctalopia) is caused.
  • Rhodopsin is known as visual purple.
1967_visual purple.png

  • Cones are meant to judge objects in sharp light due to visual violet iodopsin. & to distinguish colours.
  • In cones erythrolab (red), chlorolab (green) & cynolab (blue) are present.
  • Most domestic animals lack colour vision.
  • They see objects in shades of grey (Monochromic vision)
  • In squirrel, hen rods are absent. In rat, shrew & bat cones are absent.
  • Layer of rods and cones is attached to two layers of bipolar neurons where light impulses are converted in to nerve impulses so it is a Bio chemical process.
  • Neurons are attached to ganglions layer from where optic nerve fibres originate to form optic nerves.

689_retine.png

Posted Date: 10/3/2012 4:18:32 AM | Location : United States







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