1. Using a labelled diagram, describe the anatomy of the
EYE
Special senses respond to stimuli involved in vision, taste, smell, hearing and balance. The
organs that receive these stimuli are the eye, nose and ear.
Sight - The eye:
The eye has been studied for decades and it consists of the fo...
1. Using a labelled diagram, describe the anatomy of the
EYE
Special senses respond to stimuli involved in vision, taste, smell, hearing and balance. The
organs that receive these stimuli are the eye, nose and ear.
Sight - The eye:
The eye has been studied for decades and it consists of the following external structures:
The extrinsic eye muscles aim the eyes for following movement and for convergence.
The lacrimal apparatus consists of a series of ducts and glands that produce tears.
The eyelids protect the eyes and eye lashes have ciliary and tarsal glands that are responsible
for lubricating the eye.
The conjunctiva is a mucous membrane that covers the anterior eyeball and lines the eyelids
and produces lubricating mucus.
The eyeball has three layers:
- Sclera;
o Forms most of the outer layer that protects and is tough and fibrous.
o The anterior portion is the cornea which allows light and is transparent.
- Vascular layer;
o This layer provides nutrition to the internal eye structure.
o The posterior portion is the choroid which prevents light from scattering in the eye
and is pigmented.
, o Anterior modifications include the ciliary body and the iris.
- Sensory layer.
o Consists of two-layered retina which is a pigmented epithelium and the inner most
coat that contains the photoreceptors.
o Rods are dim light receptors and cones are receptors that provide for colour vision
and high visual acuity.
o The fovea contrails, on which acute focusing occurs, contains only cones.
The optic disc is the point where the optic nerve leaves the back of the eyeball.
The optic disc results in the blind spot of our vision since no photoreceptors exist there.
The lens is also the major light-bending structure of the eye which is known as a refractory
function.
The convexity of the lens is increased by contraction of the ciliary body for close focus.
Anterior to the lens is the aqueous humor, which provides nutrients to the avascular lens and
cornea, and posterior to the lens is the vitreous humor.
Errors of refraction include:
- Myopia;
- Hyperopia;
- Astigmentation.
The pathway of light through the eye is as follows:
Cor o A uq se u Tg hh ro o A uq se Le o V ui tsr e Ret i
ne o h ru m p u p i l o h ru m ns rh u m o na
aThe pathway of nerve impulses from the retina of the eye:
The overlap of visual fields and inputs from both eyes to each optic cortex provides for depth
perception. Eye reflexes also include:
Any sound that enters the acoustic meatus causes the eardrum to vibrate. The external
structures are only involved in the transmission of sound.
The structure of the middle ear includes:
Ossicles;
Pharyngotympanic tube.
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