eye Flashcards
How we see objects
Light rays from the object enter the eye and are refracted by the cornea, and the aqueous humour onto the lens.
The lens causes further refraction and the rays are brought to a focus on the retina.
The photoreceptors of the retina are stimulated by the light rays. This causes nerve impulses to be produced at the photoreceptors and be transmitted to the brain via the optic nerve.
The brain processes and interprets the nerve impulses, allowing us to see the object.
stimulus (change in light intensity) → photoreceptors in retina are stimulated → sensory neurone in optic nerve transmits impulses to the brain → relay neurone in brain → motor neurone transmits impulses from brain to iris → effector (iris)
near objects
When focusing on a near object, the ciliary muscles in the eyes contract to relax their pull on the suspensory ligaments.
The suspensory ligaments slacken, relaxing their pull on the lens.
The lens, being elastic, becomes thicker and more convex, decreasing its focal length.
The light rays from the near object are sharply focused on the fovea of the retina.
pupil reflex in response to bright light
In bright light, the circular muscles of the iris contract, and the radial muscles of the iris relax → the pupil constricts to reduce the amount of light entering the eye.
pupil reflex in response to dim light
In dim light, the radial muscles of the iris contract, and the circular muscles of the iris relax → the pupil dilates to allow more light to enter the eye.
why the amount of light needs to be controlled
The amount of light entering our eyes needs to be tightly controlled so that there should be sufficient light for us to see, yet not too much so that the photoreceptors of the retina will not be damaged.
the principal functions of component parts of the eye in producing a focused image of distant objects on the retina
When focusing on a distant object, the ciliary muscles in the eyes relax, pulling on the suspensory ligaments.
The suspensory ligaments become taut, pulling on the edge of the lens.
The lens becomes thinner and less convex, increasing its focal length.
The light rays from the distant object are sharply focused on the fovea of the retina.
