MGSLG. (2020). Module 3 Unit 1 study guide

Structure and functions of the parts of the human eye

Terminology & definitions

Biological term

Description

Accommodation

The ability to change the focal length of the object by changing the convex shape of the lens to assist with focussing on a near or distant object.

 

Astigmatism

 

Uneven the curvature of the lens or cornea resulting in distorted images

Effectors

Are muscles or gland that respond to the message from the nervous system (brain and spinal cord)

 

Hypermetropia

Long-sightedness caused by a lens that cannot become rounded enough to refract light, so the image falls behind the retina.

 

Myopia

Short-sightedness caused by a cornea that is too rounded, so the image falls short of the retina.

 

Neuron

One nerve cel.l

 

Photoreceptors

Specialized receptors to receive the stimulus of light and convert it to an impulse.  Photoreceptors in the retina of the eye are called rod and cone cells.

 

Receptors

Are located in the sense organs.  They convert a stimulus into an impulse.

 

Refraction

To bend light – refraction takes place when light passes through a lens that is bent by a convex [ () ] shape or a concave [ )( ] shape

 

Stereoscopic vision

Also known as binocular vision - to see with two eyes, where each eye will produce a slightly different image of the same object and allows us to judge distance, depth and size of an object.

 

The human body responds to a variety of stimuli, such as light, sound, touch, temperature, pressure, pain and chemicals (like taste and smell).

The eye (sight) and the ear (hearing and balance) are part of the peripheral nervous system.

Functioning of the eye – path of light:

  • Light rays pass from an object to the eye, through the transparent convex cornea, aqueous humour, the biconvex lens and vitreous humour
  • As the light rays pass through the curved surfaces of the cornea and the lens, light is refracted (bent)
  • The lens refracts the light rays and forms an inverted (upside-down) image on the retina, bringing the image into focus by making fine adjustments
  • The rod and cone cells (photoreceptors) are stimulated by the light rays and convert the stimulus into impulses
  • These impulses are transmitted along the optic nerve across the optic chiasma (cross-over) so that impulses enter the lower visual centres on opposite sides of the mid-brain at the occipital lobes
  • The upright images are interpreted for size, shape and colour of the object that was seen.



Last modified: Friday, 19 March 2021, 6:57 AM