SCIENCE - FORM 2 | |
The World Through Our Senses| |
SENSORY ORGANS AND THEIR FUNCTIONS
1. Sensory organs are used to detect every changes in the environment. (a) Sensory organs are possessed by human and all animals.
(b) Sensory organs allow the body to respond to the stimuli surroundings. Stimuli from the surroundings. Stimuli are changes that happen in the environment. (c) Sensory organs have receptors that receive the stimuli and then, send them as impulses to the brain to be analysed. The brain will then, give a response through the related effectors. Examples of effectors are muscles and glands.
2. The sensory organs found in humans are the skin, eyes, nose, ears and tongue.
3. Table 1.1 shows the stimuli for the sensory organs found in our body.
We have five sensory organs, i.e. eye, ear, nose, tongue and skin that are sensitive to different stimuli.
The Skin and the Sense of Touch
1. The skin is the outermost layer of the human body which covers and protects the human body.
2. The skin is a sensory organs which is sensitive to touch.
3. The human skin sonsists of two layers:
(a) The epidermis layer which consists of dead cells and acts as a protector. (b) The dermis layer consists of living cells, blood vessels, nerves and sweat glands. The dermis also has receptors which are sensitive to head, cold, contact (touch) and pressure.
4. Receptors are the ends of the nerves which are very sensitive to stimuli.
5. Each receptor is connected to a nerve. When stimulated, it sends a nerve signal known as an impluse to the brain to be interpreted.
6. Pain receptors are the closest to the skin surface. This is followed by touch receptors, heat receptors and cold receptors. Pressure receptors lie deep down in the adipose tissue beneath the dermis layer.
7. Different parts of the skin have different levels and sensitivity. The skin sensitivity depends on: (a) The depth of receptors in the skin. The palms of our hands, the lips and the neck are more sensitve than the soles of our feet. (b) How close together the receptors are. The parts of the skin which have receptors close to one another are more sensitive.
1. The arrangement of the apparatus is set up as shown in Figure.
2. Your partner is blindfolded using the piece of black cloth.
3. One or two toothpicks are used to prick the parts of the body as listed in the table below.
4. Your partner has to guess whether one or two tootpicks were used.
1. Skin on the different parts of the body have different degrees of sensitivity to touch.
2. The skin on the fingertips, lips, area behind the ear and neck are sensitive to touch.
3. The skin on the palm of the hand, knee, sole of the foot and elbow are not so sensitive to touch.
4. The other parts of the body that are very sensitive to touch are the eyelids and armpits.
Different parts of the body have different degrees of sensitivity to the stimulus of touch.
The Nose and the Sense of Smell
1. The nose is a sensory organ which is sensitive to smell.
2. The cavity of the nose is lined by 2 types of cells:
(a) Glandular cells which secrete slime ( muscus ).
(b) Cells of the smell receptors.
3. The cells of the smell receptors are found on the upper part of the nasal cavity, which are connected to the nerve endings that in turn convey smell impulses to the brain.
4. Chemical substances, inhaled through the nose, dissolve in the mucus and stimulate the sensory cells of smell. Then, impulses are sent to the brain through the nerves to be interpreted.
5. When we have flu, the thick layer of mucus in the nose hinders these sensory cells from being stimulated and we are then, unable to smell as usual.
6. Hair and mucus in the nasal cavity function to filter dust from the air so that only clean air can enter the lungs.
7. The sensivity of smell of animals such as cats, rats and dogs is greater than that of humans, which...