chapter 1 f2
TRANSCRIPT
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CHAPTER 1CHAPTER 1
THE WORLD THROUGH OURS
SENSES
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SENSORY ORGANS & THEIRSENSORY ORGANS & THEIR
FUNCTIONSFUNCTIONS
Sensory organs are organs that allow organisms to
detect changes in their surroundings
Any change that is picked up by a sensory organ is
called stimulusThe five sense, sensory organs and stimuli are:
SENSORY ORGAN STIMULI SENSE
Eye Light Sight
Ear Sound Hearing
Nose Chemical vapour smell
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Skin Touch Touch
Tongue Chemicalsubstances
Taste
PATHWAY FROM STIMULUS TO REPONSE
When there is any change in environment that is
dangerous, an organism can detect the danger and react
to save itself
The reaction of an organism to a stimulus is known as
a response
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The pathway from stimulus to response can be
summarised as:a) Stimulus is detected by the receptors in sensory
organ
b) The sensory organ sends a message through the
nerves to the brain. This message is in the formof electrical signals called impulses
c) When the brain receives the messages, it
interpret the message and decide on the proper
response to stimulus through the effectors
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SENSE OF TOUCHSENSE OF TOUCH
The skin is the sensory of touchThe skin can detect pain, pressure, touch and changes
in temperature (hot or cold)
It has two layers, the dermis and epidermis
a) Dermis (inner layer)
Consists of a layer of thick connective tissues
Rich with blood capillaries
Has receptors to detect pain, touch, pressure, coldand hot
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Other structures: sweat glands, fatty layer and
muscle fibres
b) Epidermis (outer layer)
It has a thin layer
Composed of a layer of tough cells
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TYPE OF RECEPTOR FUNCTION
Pain receptor Sensitive to pain
Heat receptor Sensitive to hot objects
Pressure receptor Sensitive to heavy
pressureCold receptor Sensitive to cold objects
Touch receptor Sensitive to slight
pressure
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SENSITIVITY OF SKINSENSITIVITY OF SKIN
The skin has different degrees of sensitivity at
different parts of the body
The degree of sensitivity depends on:
a) Thickness of the epidermis
Thinner part of the skin is more sensitive towards
stimulus
b) Number of receptors
The part of the skin that has more receptors ismore sensitive towards stimulus
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APPLICATIONS OF THE SENSITIVITYAPPLICATIONS OF THE SENSITIVITY
OF SKINOF SKIN
A patient is normally given an injection on the forearm
or hip which have thicker epidermis. So the patient will
feel less pain when injected
The blind people use their fingertips to identify letters
and read Braille. This is because the fingertips have thin
epidermis and have many receptors that are sensitive to
touch
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SENSE OF SMELLSENSE OF SMELL
Nasal cavity
Nostril
Olfactory bulb
Smell
receptor
Smell receptors or sensory cells are found on
the top of the nasal cavity
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PATHWAY OF SMELL DETECTION
Chemical substances enter thenasal cavity
Chemical substances dissolve inmucus and stimulate smell
receptors
Impulses sent to the brainthrough the nerves
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Brain interprets the impulses
Smell identified
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The sensitivity of the nose is affected by:
a) The strength of the smell- A stronger smell will be detected by the nose
easily compared to a weaker smell
b) The presence of mucus in the nose- A lot of mucus will reduce the sensitivity of
the nose
- This is because very little of the chemical
vapour stimulate the smell receptors- Example: when a person has a flu
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SENSE OF TASTESENSE OF TASTE
The tongue is the sensory organ for taste
It can detect sweet, salty, sour and bitter tastes
The surface of the tongue has many taste buds
Each taste bud has many taste receptors fordetecting the flavour of a chemical substances
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Taste bud
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PATHWAY OF TASTE DETECTION
Chemicals in the food dissolve in thesaliva and stimulate the taste buds
Impulses sent to brain through thenerves
Brain interprets the taste and thentaste is identified
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The sense of taste is influenced by the
sense of smell because as we chew our food,chemicals from the food also move into the
nasal cavity and stimulate the smell receptors