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Q1.    Briefly describe the structure of the following:

 (b)     Eye

Answers (1)

Eye: We know that eyes are in spherical structures that consist of three layers. 

1. The outer layer is composed of sclera and cornea. 

  • The sclera is an opaque tissue that is usually known as white of the eye. It is composed of dense connective tissue. 
  • The cornea is a transparent anterior portion of the eye that lacks blood vessels and is nourished by lymph from the nearby area. It is slightly bulged forward and helps in focusing light rays with the help of the lens. 

2. The middle layer of eye is vascular in nature and contains choroid, ciliary body, and iris. 

  • Choroid lies next to the sclera and contains numerous blood vessels that provide nutrients and oxygen to the retina and other tissues. 
  • Ciliary body: The choroid layer is thin over the posterior region and gets thickened in the anterior portion to form ciliary body. It contains blood vessels, ciliary muscles, and ciliary processes. 
  • Iris: At the junction of sclera and cornea, the ciliary body continues forward to form a thin colored partition called iris. It is the visible coloured portion of eye. The eye contains a transparent, biconvex, and elastic structure just behind the iris. It is known as a lens. The lens is held in position by suspensory ligaments attached to the ciliary body. The lens divides the eyeball into two chambers — an anterior aqueous and posterior vitreous chamber. 

3. The innermost nervous coat of eye contains retina. The retina is the innermost layer. It contains three layers of cells — inner ganglion cells, middle bipolar cells, and outermost photoreceptor cells. The receptor cells present in the retina are of two types — rod cells and cone cells. 

  • Rod cells —The rods contain the rhodopsin pigment (visual purple) that is highly sensitive to dim light. It is responsible for twilight vision. 
  • Cone cells —The cones contain the iodopsin pigment (visual violet) and are highly sensitive to high-intensity light. They are responsible for daylight and colour visions. The innermost ganglionic cells give rise to optic nerve fibre that forms optic nerve in each eye and is connected with the brain. 
Posted by

Priyanka Kumari

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