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Humans face constant changes in surroundings. These changes are called stimuli.
Examples of stimuli include light, sound and chemical substances.
Humans use their sensory organs to detect stimuli.
Humans have five sensory organs: eyes, ears, nose, skin and tongue
Eye
Eye
The sensory organs of vision
Stimulus - Light
There are 2 photoreseptors: -
Rod cells are sensitive to different light intensities including faint light but are not sensitive to the colours of light.
Cone cells are sensitive to light colors in bright conditions. There are three different types of cone cells, where each is sensitive to red light, green light and blue light.
How do we see?
How do we see?
ear
ear
Sensory organ for hearing
Stimulus - Sound (Vibration)
Structure of ear
Mechanism of Hearing
Mechanism of Hearing
nose
nose
Sensory organ for smell
Stimulus - Chemical Substances (present in the air)
Sensory cells for smell are tiny and covered with a layer of mucus.
Chemical substances in the air will dissolve in this layer of mucus and stimulate the cells to produce nerve impulses.
The nerve impulses are then sent to the brain to be interpreted to determine the type of smell.
tongue
tongue
Sensory organ for taste
Stimulus - Chemical Substances (food and drink)
Taste receptors can detect five types of basic tastes which are sweet, salty, sour, bitter and umami.
skin
skin
Sensory organ for touch
Stimulus - Touch, pain, heat, cold and pressure
Sensitivity of the Skin on Different Parts of the Body towards Stimuli
Sensitivity of the Skin on Different Parts of the Body towards Stimuli
The sensitivity of skin towards stimuli depends on:-
the number of receptors
the thickness of the skin epidermis.
Areas that are very sensitive to touch - tip of finger, tongue, nose and lips.
Areas that are less sensitive to touch - elbow, the sole of the foot and the back of the body.
Different Areas of the Tongue are More Sensitive to Specific Taste
Different Areas of the Tongue are More Sensitive to Specific Taste
Areas of the tongue are sensitive to all five tastes.
However, different areas of the tongue have different sensitivities towards specific taste.
Combination of the Sense of Taste and the Sense of Smell
Combination of the Sense of Taste and the Sense of Smell
chemical substances in food which dissolve in saliva and stimulate the taste buds, chemical substances in food also evaporate to form vapour which enters the nasal cavity and stimulates the smell sensory cells.
The combination of sense of taste and sense of smell causes food to taste better.
limitation of Senses, Defect in Sensory Organs
limitation of Senses, Defect in Sensory Organs
An optical illusion occurs when an object is viewed differently from the actual situation.
Blind spots are images that appear on blind spots.
Short-sightedness - image in front of retina, thick lens, long ball
how to fix → concave lens
Long-sightedness - images behind the retina, thin lenses, short balls
how to fix → convex lens
Astigmatism - cornea or uneven lens
how to fix → cylinder lenses
Human hearing limit → 20 Hz - 20 000 Hz.
Defects of Hearing - infection, injury, age and long exposure to loud sounds.
how to fix → hearing aids, implants & surgery.
exercise
exercise
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