form 2 chapter 1.1
TRANSCRIPT
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Form 2 ScienceChapter 1: The World Through Our Senses
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Sensory Organs, Stimuli and Senses
Response to stimuli
Sense Sensory Organ Stimuli Detected
Touch Touch, pressure, pain, heat, cold
Taste Taste (chemicals in food)
Smell Smell (Chemicals in air)
Sight Light
Hearing Sound
Sense of Touch - Skin
Pressure receptor Pain receptor Cold receptor
Touch receptor Heat receptor Sweat glands
(f)
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Receptor Function
Sensitive to touch. Many are found in hairless areas such as lips
and fingertips.
Sensitive to pain. They lie in the epidermis, close to the surface
to detect the slightest pain.
Sensitive to heat.
Sensitive to cold. Together with heat receptors, they enable us
to know how hot or cold an object is.
Sensitive to heavy pressure. Found deep within the skin
especially at the soles of the feet. Together with the touch
receptors, they enable us to identify the texture and weight of an
object.
Sensitivity of the
skin depends on:
The larger the concentration of
receptors, the more sensitive the skin isThe thicker the epidermis, the
deeper the receptors lie in the skin,
thus the less sensitive the skin is
Parts of body which is more sensitive Parts of body which is less sensitive
Elbows Back of body Lips Knees Fingertips
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Form 2 ScienceChapter 1: The World Through Our Senses
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Sense of Touch - Nose
Smell Receptor Nasal cavity Brain
Adaptation of the nose to detect smell
The smell receptors are
always covered with
mucus.Smells must dissolve in the
mucus before they can be
detected.
Smell receptors are located at
the roof of the nasal cavity.
This position allows thereceptors to have the maximum
exposure to the air current.
Sense of Touch - Tongue
How tastes are detected:
As we chew the food, chemicals in the food
dissolve in the saliva.
The dissolved chemicals stimulate the taste
receptors in the taste buds to produce
nerve impulses that are sent along nerves
to the brain.
The brain interprets the impulses andidentifies the taste of the food.
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Sense of Touch - Ear
Part Structure Function
Outerear
Pinna Shaped like a funnel.
Made of cartilage and
skin.
Ear /
auditory
canal
A 2.5cm long, narrow
tube lined with hair
Middleear
Eardrum A thin, stretched
membrane at the end ofthe ear canal.
Ossicles 3 small bones that
connect the eardrum
and oval window.
Oval
window
A thin, small membrane
at the end of the
ossicles.
Eustachiantube
A narrow tube thatconnects the middle ear
to the back of the throat.
Innerear
Cochlea A coiled tube filled with
fluid and lined with hair-
like sensory throat.
Auditory
nerve
Nerve fibres that
connect the ear to the
brain.
Semi-
circular
canals
3 semi-circular tubes
situated at right angles
to each other. Contain
fluid and sensory cells.
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Form 2 ScienceChapter 1: The World Through Our Senses
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Mechanism of hearing:
Sound reaches the ear Sounds is heard
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Sense of Touch - Eyes
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Parts Structure Function
Sclera White, tough outer layer.
Fibrous and opaque.
Choroid Black, middle layer. Rich with
blood vessels.
Retina Innermost layer.
Contains photoreceptors known
as cones and rods.
Cornea Curved transparent layer of the
sclera in front of the eye.
Conjunctiva Thin transparent layer in front of
the cornea.
Iris Coloured front part of the eye
that is continuous with the
choroid.
Consist of muscles.
Pupil The hole in the centre of the
iris.
Lens Transparent, biconvex andelastic disc.
Ciliary body Muscles attached to the lens.
Suspensory
ligaments
Strong fibres that connects the
lens to the ciliary body.
Aqueous Humour Watery, transparent liquid
between the cornea and lens.
Vitreous humour Thick, transparent jelly-like
substance inside the eyeball
Yellow spot (fovea) The most sensitive spot on the
retina.
Located directly opposite the
pupil.
Blind spot The spot where the optic nerveleaves the eye.
Has no photoreceptor at all.
Optic nerve Consists of nerves that connect
the retina to the brain.
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Mechanism of sight:
Light rays from object Object is seen