Olfactory sensation takes place through nose when olfactory receptors respond to different type of smell. A person experience olfactory sensation when smell reaches his brain through a narrow canal in the nasal passage.
We can observe that olfactory sensitivity differ for different individuals. A strong smell from chemical compounds may cause sensation in one individual but the same small may not cause any sensation in another individual A person gets habituated to a particular smell when there is continuous experience of it.
There are five types of sensations which are as follows:
(i) Visual Sensation (ii) Auditory Sensation (iii) Olfactory Sensation (iv) Gustatory Sensation (v) Touch Sensation (skin)
(i) Visual Sensation : It is the most important sensation among all the sensations. The process of visual sensation includes – composition of the eye, its internal organs, the nerves that go towards the brain and the brain. The presence of light is inevitable to experience the visual sensation. The white part of the eye is called sclera which is made of white fibres. It is not transparent and protects the inner hart of the eye. The
black part of the eye is called pupil through which light enters the eye and reaches the retina. The grey or blue area in the sclera is known as iris and also the ciliary muscles of the eye. Because of it, the colour of the eye can be seen. The ciliary muscles are not inter connected neither they touch each other. The space between ciliary muscles is known as pupil. The pupil is not an organ. It is a 1/8 inch hole in the centre of the
iris.
One can experience visual sensation (can see things) when the rays of light from the external object enter the eye through the pupil. These rays reach the retina by passing through the transparent vitreous humor in the space within the eye which is the area for visual sensation. The intensity of light that reaches the retina depends on the contraction and expansion of the ciliary muscles. The ciliary muscles are very sensitive to the intensity of light rays. They get expanded when the light increases and the size of the pupil becomes small. The size of the pupil increases when the light decreases. Retina and ciliary muscles are important to experience the visual sensation of near and far objects.
(ii) Auditory Sensation : Adequate auditory sense organ is essential for an individual in order to be connected with the outer world. A sharp and active auditory sensation is must to understand the direction of sound, its distance and ability to differentiate between sound waves. Normally, an individual can hear and distinguish sound waves from 20 to 20,000. Hz i.c. CPS (cycle per second). But we can not hear sound waves with more than 20,000 Hz or less than 20 Hz, The auditory sensation is divided in to three parts:
(a) Outer ear : It includes the ear lobe, auditory canal and the ear drum.
(b) Middle ear : This part includes three inter connected bones like hammer, anvil and stirrup. It has Eustachian tube whose second part opens in the throat.
(c) Inner ear : The inner ear has three main parts which are
(1) Middle ear
(2) Cochlea and
(3) Semicircular canals.
From the environment, sound waves enter into the external auditory canal and in middle ear then stimulates the ear drum. The ear drum vibrates with the sound waves and activates the three bones.
The vibration of these three bones transmits the concentrated energy to cochlea and sets the fluid inside the cochlea into a wave motion. The fluid waves make the basilar membrane to move bending the auditory receptors. The sensation of hearing takes place when the neural impulses reach the auditory area in the brain through the auditory nerve.
(iii) Olfactory Sensation : We experience olfactory sensation through nose. When molecules of chemical compounds dissolved in the air reach the olfactory receptors in the nose. Smell receptors (hair like structures) are found in a narrow canal of the nasal passage. They are connected with the base of the brain through olfactory nerves. Each such cell responds to different type of smell. This is how olfactory sensation takes place. We can observe that olfactory sensitivity differ for different individuals. A strong smell from chemical compounds may cause sensation in one individual but the same smell may not cause any sensation in another individual. Continuous experience of a particular smell makes a person habituated to it. As a result, the intensity of this sensory experience decreases.
(iv) Gustatory Sensation : We experience taste sensation through tongue when chemical substances from the external environment having physical stimuli of taste come in contact with the tongue. Apart from taste sensation, tongue also helps in the development of speech. Tongue is a muscular organ attached to the end of jaws. The taste buds spread over the entire surface of the tongue arouse the experience of taste. They are also known as taste receptors. Every taste bud is connected with the ends of taste receptors. When a substance is put over the tongue, it melts in saliva and stimulates the taste buds. Its neural stimulation reaches the brain and arouses the experience of taste.
(v) Touch Sensation (skin) : Owing to the layer of skin on the entire human body, we experience touch sensation. Mainly there are four types of touch sensation which includes - warmth, cold, touch pressure and pain. According to different studies and experiments performed in psychological laboratories, we experience touch sensation due to excitation of sensory receptors spread all over the skin. When the skin of the face is stimulated, it sends message to the brain. This is how we experience touch sensation. Similarly, sensation from shoulder to waist is sent through excited skin receptors via spinal cord to the brain which is the centre point of the touch sensation. Hence we experience touch sensation. As our skin stimulus activates more than one type of receptors, we experience different types of touch sensation at one time. For example When a drop of rain water falls on the body, we experience both sensation of coolness and touch simultaneously.