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Sense Organs: The Eye

  • Overview of Sense Organs

    • Sense organs are specialized structures that contain receptors to detect external stimuli and produce neural signals.
    • Key sense organs and their corresponding stimuli:
    • Eye: detects light
    • Nose: detects smell
    • Tongue: detects taste
    • Ear: detects movement and gravity
    • Skin: detects touch and temperature change

  • Receptors in the Eye

    • All receptors in the eye primarily detect light; some are also capable of detecting color.
    • The retina is the key structure within the eye containing light-sensitive receptors.
    • Types of receptors in the retina:
    • Rod cells: responsible for vision in low-light conditions
    • Cone cells: responsible for color vision and detail in brighter light

  • Signal Transmission

    • The retina sends nerve impulses to the brain via the optic nerve.

  • Optical Functions of the Eye

    • The eye functions by focusing light rays on the retina.
    • It achieves focus through:
    • Changing the shape of the lens to accommodate near and distant objects
    • Adjusting the shape of the iris and pupil to control light intensity entering the eye

  • Common Visual Defects

    • The eye may sometimes fail to focus light rays correctly on the retina, leading to visual defects:
    • Long-sightedness (hyperopia): difficulty focusing on nearby objects
    • Short-sightedness (myopia): difficulty focusing on distant objects
    • Corrective measures for visual defects include:
    • Long-sightedness: corrected with convex lenses
    • Short-sightedness: corrected with concave (diverging) lenses

  • Diagrams

    • Students should be able to draw and label diagrams illustrating the internal structure of the eye, including formations related to short-sightedness and long-sightedness as well as the causes and correction methods.

Questions

  1. The structure in the eye that changes light energy into electric signals is:

    • A) choroid layer
    • B) iris
    • C) lens
    • D) retina (Correct Answer)

  2. Which defect usually causes astigmatism?

    • A) an eyeball that is too long
    • B) the curvature of the cornea
    • C) the lens loses its elasticity
    • D) the retina is damaged

  3. The function of the iris is to:

    • A) control the amount of light going to the retina
    • B) determine the color of objects being looked at
    • C) focus light rays onto the retina
    • D) prevent dust and bacteria from damaging the eye

  4. The refraction (bending) of light rays to focus an image happens in:

    • A) conjunctiva and cornea
    • B) cornea and lens
    • C) lens and retina
    • D) retina and cornea