Chapter 8
Sense Organs
Eye Abnormalities
- When there is a long distance between the cornea and lens or lens and retina or sometimes there is too powerful lens, the person suffers from myopia. In this particular situation, the image of a distant object falls in front of the retina. That is, when the object distance is 20 feet, light rays go into the eye almost parallel. In such type of condition, individual has to wear concave lens to adjust the light rays coming from distant object, so that image can fall on retina.
Sense of Smell
The superior nasal conches consist of chemoreceptor nerve cells which are situated in mucous membrane of roof of the nose. Both sides of nasal septum, the nerve fibers from the cell septum, and the nerve fires from the cell bodies enter through the cribriform plate of the ethmoidal bone to meet olfactory bulb. Number of nerve fibers which form the olfactory tract, from where it goes backwards to the olfactory area in the temporal lobe of the cerebral cortex in each hemisphere. Here impulses are interpreted, and Oduor is sensed.
Taste of Sensation
The facial nerve works for anterior two third of tongue and glossopharyngeal nerve works for posterior two-third of tongue. Axons of these nerves go to taste nuclei in medulla, then to thalamus and from here to taste area of cerebral cortex of brain.Ear
- Ear is the origin of hearing. The VIII cranial nerve carries sensation of hearing towards cerebral cortex of brain in the hearing area where interpretation occurs. Most part of ear is situated in the petrous part of the temporal bone except the pinna lying outside.
External Ear:
- Pinna or auricle is the outer part of ear which is a expanded part, projecting from the side of head. This part is made of fibroelastic cartilage which is covered with the skin. The size of the pinna is variable in different animals. The expanded outer edge is known as helix and the lower most part is known as lobule. It is composed of fibrous and adipose tissue, supplied with blood capillaries.
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