Special Sense Organs - eyes

Special sense organs

the human body is provided with numerous sense organs, that enable us to detct changes in own body as well as changes, in external environment .internal sense oran help to maintain homeostatisis of body .these organs are called special sens organs which is located in eyes ears, nose and tongue.

Eyes Organs of sight

there are 2 eyes situiated in the orbital cavity , as the rgans of sight eyes are supplied with the .the optic nerve from the brain each eye is a spherical hollow ball having a diameter of about 2.5 cm due to shape it is also know as eyeball.

Structure

each eye is composed of 3 concentic layers in its wall
1 the outer fibrous layer sclera.
2 the middle vascular.
3 the inner nervous tissue layer.
the outer fibrous layer is thick tough, which is composed of sclera and corea the main fuction of this layer are
protection.
2 proiding frim surface for the insertion of eye muscles.
3 mainatance of the shape of the eye ball.

Rod and cons are the photoreceptor which helps in vision in drak and light respectively .
sclera and cornea.
the sclera forms the outermost covering layer in the eyes.the cornea is anterior modified of the sclera function is to keep the shape of eye ball ,protective layers and entry of light ray.
Choroid
it forms the main part of a vascular layer ,that lines the sclera internally its function is to supplies blood and blood vessels.
ciliary body .
it is provided with smooth muscles and secretory cells and helps in lens movement eliminate defects of vision like myopia and hypermetropia.
iris
its in anterior extended part from the ciliary body lying between the cornea and the lens and helps on diaphgram of camera .
retina
it is respondible for the photoreceptor. it is extremely delicate and sensitive structure stimulated to light rays, it is thickest at the posterioir part and gradually thins out anteriorly finally ending at ciliary body.
Lens
it is biconvex made of transparent connective tissue and helps in reflection and refraction of light.
physiology of vision
when a light fall in an object it comes to eye ,through passing the lens and falls in retina during .this process stimulation occurs formin 4 diffent changes in the eye.
1 refraction of the light ray .
2 accomulation of the lens constriction of the pupils .
3 that movement of the eyeball.
4 constriction of the pupil.

different types of defects in the eye

myopia

a person who cannt see far object properly corrected by concave lens.

hypermertopia

a person who cannt see near object properly corrected by convex lens.

Astigmatism

uneven curvature of corena cornea a defect to vision cause light rays from the object are used at diffent points on the retina corrected by using glasses.

presbiopia

occurs in old age due to people suffer from farsightness due to loss of elascity of the lens .

Reference:

Agrawal, sarita. principle of biology. 2nd edition . kathmandu: Asmita book Publication, 2068 ,2069

Mehta, Krishna Ram. Principle of biology. 2nd edition. kathmandu: Asmita, 2068,2069.

Jorden, S.L. principle of biology. 2nd edition . Kathmandu: Asmita book Publication, 2068.2069.