Biology XI : 21 Neural control & coordination(4 Eyes and Mechanism

Eyes and Mechanism of Vision Anatomy of Eyes Location: Orbits (Sockets in the skull) Walls of the eye ball are composed of 3 layers: Rods and cones contain photopigments (light sensitive proteins). Cones facilitate daylight (photopic) vision and colour vision. In the human body, cones are of three types and each type possesses its own photopigments that respond to green, red and blue light. Rods facilitate twilight (scotopic) vision. Contains purplish-red pigment called rhodopsin (contains derivative of vitamin A) The region where the optic nerves leave the eye and the retinal blood vessels enter is called the blind spot since no photoreceptor cells are present here. Lateral to the blind spot, the macula lutea (a yellowish pigmented spot) is present, with a central pit called fovea. Fovea: Thinned-out portion of the retina where only cones are present. Visual resolution is the greatest here. Aqueous chamber: Present between the cornea and the lens. Contains fluid aqueous humour. Vitreous chamber: Present between the lens and the retina. Contains fluid vitreous humour. Mechanism of Vision Photopigments in the eye consist of opsin (a protein) and retinal (an aldehyde of vitamin A).