12th Zoology

Photochemistry of Retinal visual Pigments

Photochemistry of Retinal visual Pigments

Rhodopsin or Visual Purple is a puplish red photosensitive pigment
present in the outer segment of the rods (120 million rods). It is made up of protein portion, an opsin (scotopsin) combined with an aldehyde of vitamin
A called Retinene 1, which is referred to as a retino. On exposure to light,
rhodopsin is bleached, ie., broken down to retinene and opsin, but is
resynthesised in the dark. Some of the retinene recombines with scotopsin to
form rhodopsin while some are reduced to vitamin A. The rods are extremely
sensitive to light and are responsible for vision in dim light. This is called
SCOTOPIC VISION. (Retinal visual Pigments)

Cones also contain visual pigments made up of retinene, combined
with a protein opsin (photopsin). Three pigments each responding to
different wavelength are found in man. There are three primary colors namely
red, green and blue. Color vision is a function of bright light vision and cones
are responsible for color perceptions. (Retinal visual Pigments)

In bright light maximum perception of colors is at the fovea region of the retina where rods are absent and only cones are present. In dim light when the rods in the extra foveal retina function, colors are not perceived and the various colors appear as shades of grey. Cones function in bright light and the system has more acuity and can perceive colors (PHOTOPIC VISION).

Photochemical basis of retinal function is a basis of conversion of
light energy into nerve impulses. It is this process that excites the nerve fibres
and sets up nerve impulses.

The impulses generated in the receptor neurons in response to
generator potentials in the cones are interpreted by the brain as the
appropriate intermediate colour. The interpretation or perception of colour
pictures seen by our eyes is a complex function of the brain. It is located in
the occipital lobe of the cerebral cortex. (Retinal visual Pigments)

The visual pathway – Retinal visual Pigments

The axons of ganglion cells pass through the eyeball at the posterior
end and form the optic nerve which enters the cranial cavity. Therefore this
region of the retina lacks receptors and is unable to perceive images which
fall on it. This region is called optic disc and when charting the field of vision
it is referred to as the blind spot. (Retinal visual Pigments)

Related Topics in Zoology:

Bio Zoology All Important Topics

  1. Human Physiology Introduction

  2. Nutrition

  3. Carbohydrates Poly hydroxyaldehydes (or) ketones

  4. Proteins (Polypeptides)

  5. Lipids

  6. Vitamins – Functions Of Vitamins

  7. Deficiency of Vitamin

  8. Minerals – Water – Role of water

  9. Balanced diet

  10. Obesity

  11. Digestive System

  12. Dental Caries (Tooth decay)

  13. Root Canal Treatment

  14. Peptic ulcer

  15. Hernia and Types

  16. Appendicitis (Appendix)

  17. Gall Stones

  18. Hepatitis

  19. Fractures – Types of fractures

  20. Mechanism of fracture

  21. Dislocation of joints

  22. Arthiritis

  23. Rickets and Osteomalacia – Orthopedics

  24. Muscles

  25. Mechanism of muscle contraction

  26. Types of muscle contraction

  27. Myasthenia Gravis

  28. Respiration – Process of pulmonary respiration

  29. Mechanism of Breathing

  30. Regulation of Respiration

  31. Pneumonia Tuberculosis Symptoms Treatment

  32. Bronchitis – Acute bronchitis, Chronic Bronchitis Causes

  33. Circulatory System – Functioning of Human heart

  34. Cardiac Cycle

  35. Coronary blood vessel and its significance

  36. Myocardial infarction

  37. Angina pectoris

  38. Angiogram – Angioplasty

  39. Atherosclerosis

  40. Heart block Echo cardiography Heart Valves

  41. Rheumatic Heart Disease (RHD), ICCU – (Intensive Coronary Care Unit)

  42. Blood Pressure

  43. Heart transplantation

  44. Pulse rate

  45. Cardio Pulmonary Resuscitation (CPR)

  46. Blood – Composition of plasma – Blood cells

  47. Clotting of Blood or Haemostasis

  48. Thrombosis

  49. Nervous system Co-ordination systems

  50. The Brain – Fore Brain, Midbrain, Hindbrain

  51. Memory

  52. Sleep – Types of sleep

  53. Stroke – Brain haemorrhage

  54. Alzheimer – Meningitis (Brain fever)

  55. Conditioned reflex

  56. Electroencephalography EEG

  57. Right and Left brain concept

  58. Spinal cord functioning

  59. Chemical co-ordination – Functions of Endocrine glands

  60. Hypothalamus

  61. Pituitary gland – hormone

  62. Hormones of Neurohypophysis – vasopressin

  63. Thyroid gland

  64. Parathyroid Gland

  65. Pancreas

  66. Adrenal gland

  67. Gonads

  68. Receptor Organs – Eye

  69. Photochemistry of Retinal visual Pigments

  70. Errors of refraction

  71. Optometry – Retinopathy

  72. Cataract – Lens Replacement – Glaucoma – Nyctalopia

  73. Eye Infections and Eye Care

  74. Ear

  75. Mechanism of hearing

  76. Defects of the ear

  77. Hearing Aid – Noise pollution

  78. Skin and functions of skin

  79. Melanin functions

  80. Effects of solar radiation / UV radiation – Skin grafting

  81. Dermatitis

  82. Tongue – Mechanism of Stimulation

  83. Excretion Ureotelism Nephron

  84. Mechanism of urine formation

  85. Renal Failure, Dialysis, Kidney Machines

  86. Kidney stone – Kidney transplantation

  87. Diabetes mellitus

  88. Functioning of male reproductive system

  89. Functioning of female reproductive system

  90. Ovulation and fate of the ovum – Menstrual cycle

  91. Fertilization

  92. Birth control

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