Is due to the touch corpuscles present in the epidermis of the human skin.
Is due to the taste buds in the papillae of the tongue. The tip of the tongue is the most sensitive to sweet taste, and the rear is sensitive to bitter taste. The middle part of the tongue is not sensitive at all i.e. can be used to place a bitter pill while ingesying it.
To see an object, its image must be formed on the retina. The convexity of the lens of the eye increases when the object is nearer and decreases when the object is far away to get the image on the retina in each case. The property of the lens by which it can adjust its convexity to form distinct image of the object at various distances is called accommodation. When the ciliary muscles do no work properly to bring about accommodation of the lens, the eye becomes defective.
The human retina contains two types of cells
1. Cone Cells - Meant for daylight vision, also responsible for colour vision
2. Rod Cells: Meant for nighttime or low intensity vision.
Since humans have many more cone cells as compared to rod cells, they are much better at seeing the objects in bright intensity as compared to others. Humans see with both the eyes together and both the eyes form separate images of an object. These two separate images are then fused in the brain to create an impression of depth. (Otherwise, the human retina is a 2-D structure and cannot give a perception of depth). This difference in images in the two eyes is referred to as binocular disparity.
When a person can see nearer objects distinctly but not the ones lying far away, he is said to be suffering from myopia. In this case, the convexity of the lens of his eye cannot be sufficiently decreased to form the image of the distant object on the retina. It is remedied by the use of concave glasses.
Refers to a person’s ability to see the distant objects clearly but not the near ones. It is remedied by the use of convex glasses.
A person suffering from it can see the vertical lines clearly but not the horizontal ones, or vice versa. It is remedied by the use of cylindrical glasses.
If a person cannot distinguish between different colours (especially between red and green), he is said to be suffering from this defect. It is a sex-linked disorder i.e. occurs due to recessive genes on the 23rd pair of chromosomes.
Owes to the presence of smell-perceiving cells present in the lining of nasal chambers.
Is due to the vibration of the ear membrane in the inner ear. Made possible by the incidence of sound waves on it.