SENSORY ORGANS-BIOLOGY- TNPSC,TET,RRB,SSC SCIENCE (GK) STUDY MATERIAL

SENSORY ORGANS

  1. SCLEROTIC LAYER
    The transparent bulging, circular part of
    sclerotic layer which lies in the front is called
    cornea.
    Cornea is covered by the thin conjunctiva.
  2. CHOROID LAYER
    Choroid layer starts from iris which is next to
    cornea. It controls the amount of light
    entering intothe eye.
    The circular aperture of iris is called pupil.
    Next is lens (proteinous). It is biconvex in nature.
    Space between lens and cornea is filled with a transparent watery fluid called Aqueous Humour.
    The space behind the lens is filled with Vitreous Humour.
  3. RETINA
    Image of the object is formed on retina.
    Rod cells: Sensitive to dim light
    Cone cells: Color sensitive for 3 primary colors (Red, Blud and Green)
    Yellow spot (Macula Lutea): On retina, finest image is formed here.
    Blind spot: No image formation takes place here as the optic nerves innervate the eyeball here. Also the rods and cones are absent here.
    Color of eye is the color of the iris.
    Cornea is donated in eye donation
    Eyes glow in animals due to tapetum.
    DEFECTS OF EYE
    Myopia: Cannot see distant objects, image formed before retina, concave lens is used.
    Hypermetropia: Cannot see near objects, image formed behind retina, convex lens is used.
    Astigmatism: Curvature of cornea becomes irregular and image is not clear. Cylindrical lens is used.
    Cataract: Due to defective protein metabolism the lens becomes opaque.
    Gloucoma: Due to defect in aqueous humour.
    Xerophthalmia: It is due to deficiency of Vitamin A.
    Presbiopia: In this, power of accommodation of lens decreases due to age factor and defected metabolism. Can be removed by bifocal lens.
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EAR
MIDDLE EAR
It encloses 3 ear ossicles.
Middle ear is connected to the pharynx by Eustachian tube.
INTERNAL EAR
Various parts are there which perform 2 acts: Maintenance of balance and hearing.
Succulus and cochlea parts are associated with hearing. It is filled with a flud, perilymph.
In the internal ear are 3 semi-circular canals and utriculus which are filled with a fluid, endolymph. They perform the balancing act.

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