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Special Terms involvedSpecial Terms involved
stimuli: changes in internal and
external environments to
living organismssensory system: system perceives
stimuli so organisms
can respond to
changes correctlyirritability: ability to respond to
stimuli
receptors: organs used to detect stimuli, specific, consists one or many sensory cells which they will send impulses to brain through nerve fibres
effectors: part of body that reacts to
a stimulus or produces
responses
stimulus
receptor central
nervous system
effector
response
SkinSkin at least five kinds of nerve
endings exist in dermis for
detecting touch, pressure,
temperature, pain and hair
movements
receptors in skin present all over
the body but are distributed
unevenly
largest organ in human body
touch or pain
receptor
pressure receptor
sweat gland
pain receptor
dermis
epidermis
hair
touch receptor
blood capillaries
To Investigate the To Investigate the Touch Discrimination Touch Discrimination
of Different Regions of of Different Regions of the Skinthe Skin
In which part of the body tested in this
experiment is the recorded distance the
shortest?Ans: Usually, the answer is finger tips.
your hand
dividers
hand of the
blindfolded student
What can you tell about the ability of the skin to discriminate touch points with reference to the recorded distance?Ans: The shorter the recorded distance, the more sen
sitive the part is.
your hand
dividers
hand of the
blindfolded student
TongueTongue tongue detects taste by taste buds taste buds present in the grooves on the
tongue’s surface and contain receptors sensitive to chemicals in solution form only
four kinds of taste buds present on tongue for detecting sweet, salt, bitter and sour
sweet
salty
sour
bitter
Taste buds
NoseNose on the upper roof of nasal cavity,
chemical receptors, olfactory cells,
responsible for detecting sense of
smell are situated
receptors can detect smell in
solution only as the lining of nasal
cavity is covered with mucous
layer
Relationship between Relationship between Smell and TasteSmell and Taste
taste and smell act to detect the presence of harmful substances, to stimulate appetite and to initiate the secretion of digestive enzyme
flavour depends on both taste and smell
smell affects flavour as odours pass through nose to nasal cavity
Location of the EyeLocation of the Eye
rectus muscles
optic nerve
oblique muscle
orbittear gland
muscle attachment to skull
eyeballoblique muscle
eyelid
iris
pupil
eyelash
Location of the EyeLocation of the Eye responsible for detecting light
eyeball is a spherical structure
which is protected in a bony
socket in the skull called orbit
eyeball attached to orbit by six
muscles
rotation of eye is brought about by
contraction of the muscles
Structure around the EyeStructure around the Eye blinking helps to keep the surface of ey
eball moist and clean by distributing tears produced by tear glands over the eyeball
tears contain sodium chloride, hydrogencarbonate and lysozyme which is used to kill bacteria
rate of tear flow and blinking will increase when foreign substance reaches eye surface
excess tear can drain away into
nasal cavity through duct in the
corner of the eye
eyelashes also help to stop dirt
and sweat from running into
eyes
Structures Structures and and
Functions of Functions of EyeEye
eye musclesclera
choroidretinayellow spot
blind spotoptic
nervevitreous hu
mour
ciliary muscle
iris
aqueous humour
lens cornea
conjunctiva
pupil
suspensory ligaments
wall of eyeball is made up of three layers: sclera, choroid and retina
Sclera The outer layer of wall white, tough and opaque
coat to protect eyeball keeps shape of eye and
provides anchorage for eye muscles
Cornea a transparent layer continue from scl
era allows light to pass through light is refracted into
interior of eye as it is curved protected by a transparent
layer called conjunctiva
Choroid middle layer of eyeball deeply pigmented to
absorb light and prevent internal reflection of light
contains lots of blood vessels to supply eye with food and oxygen and removes waste
Lens
within ring form by ciliary body
transparent biconvex in shape
compose of living cells
Lens
Suspensory ligaments and ciliary body
suspensory ligaments are used to hold lens in position. They are run from free edge of ciliary body
ciliary body contains ciliary muscles which can change thickness of lens by alternate contraction and relaxation during focusing
ciliary muscle
suspensory ligaments
Iris continuous with choroid lies just over ciliary body coloured part of eye as it is pigmented
Pupil hole in the centre of iris size of it is controlled
by radial muscles and circular muscles of iris
Aqueous and Vitreous Humour watery fluid filled the
anterior chamber in front of the lens inside the eyeball is aqueous humour
jelly-like substance filled the posterior chamber behind the lens is vitreous humour
aqueous humour
vitreous humour
they help in refracting light and
maintaining shape of eyeball
aqueous humour also helps cornea and lens to obtain food and oxygen from blood vessels in choroid layer by diffusion
Retina the innermost layer in eye
contains many light-sensitive cells, rods and cones, and nerve fibres
cones are sensitive to light of high intensity and responsible for colour vision. There are three types of cones which sensitive to blue, red and green
yellow spot is the part in the centre of retina which possesses cones only and it lies on the optical axis of eye
rods are sensitive to light of low
intensity and abundant in the
periphery of retina
densely packed with cones
no rod is presentgives the most di
stinct image and the greatest colour discrimination
Yellow Spot
Optic Nerve
optic nerve is a nerve which contains nerve fibres from rods and cones
it leaves the eyeball at the blind spot no sensitive cells at blind spot but only ner
ve fibres no nerve impulse can be generated when li
ght falls on the blind spot although image is formed on it, so it is incapable of detecting images
the point where the nerve fibres leave the eye-ball
no photo-receptors
cannot detect any image
Blind spot
blind spot optic nerve
Experiment to detect Experiment to detect the Presence of the Presence of
Blind SpotBlind Spot
What happens to the dot as you move the
book towards yourself ?Ans: While you are moving the book, the dot will su
ddenly disappear from your sight and then reappear again.
How would you explain this ?Ans: Before the dot disappears, the image falls on the
retina and detected by sensitive cells. However, when it falls on the blind spot, no nerve impulse can be generated and so no message received by the brain.
To illustrate the To illustrate the formation of an formation of an
Inverted Image on the Inverted Image on the Retina using a Retina using a
CardboardCardboard
What can you tell about the image ?
Ans: The image is smaller than the object but the shape remains the same and it is laterally inverted.
hand lens
window frame
cardboard
image
Does the light beam bend after passing through the attached lens ?Ans: Yes.
water with sodium fluores
cein
convex lens
plasticine
front view of the lens of the projector
convex lensprojector
Does the light beam meet at a point ? (This point is the focus of the lens)Ans: Yes.
water with sodium fluores
cein
convex lens
plasticine
front view of the lens of the projector
convex lensprojector
What is the shape of the image ?
Ans: The image is inverted and smaller than the object.
water with sodium fluores
cein
convex lens
plasticine
front view of the lens of the projector
convex lensprojector
What do the water and the back of the flask represent ?Ans: The water represents vitreous humour while
the back of flask represents retina.
water with sodium fluores
cein
convex lens
plasticine
front view of the lens of the projector
convex lensprojector
Change of Pupil SizeChange of Pupil Size pupil is the hole in iris which allows
light to pass through
pupil limits amount of light entering
the eye
two kinds of iris muscle control size of
pupil:
- circular iris muscle: makes pupil
constrict as they contract
- radial iris muscle:
pupil dilates as they
contract
change of size of pupil is
a reflex action and
automaticUnder Bright Light
circular muscles contract
radial muscles relax
pupil size decrease
reduce amount of light pass through
Under Dim Lightradial muscles
contract
circular muscles relax
pupil size increases
increase amount of light pass through
AccommodationAccommodation thick
lens thin lens
shorter focal
lengthlonger focal length
accommodation is the ability of the eye to adjust thickness of lens for viewing near and distant objects
helped by the action of ciliary muscles
ciliary muscles contract
Focusing Near Focusing Near ObjectsObjects
ring of ciliary body moves inwards and becomes s
maller in diameter
tension of suspensory ligaments reduces
lens becomes thicker
and more
curved
more light rays bend
and image of near
objects formed on
retina
lens becomes more convex
tension of suspensory ligament decreas
es
circular ciliary muscle contracts decrease in circumfer
ence
ciliary muscles relax
Focusing Distant Focusing Distant ObjectsObjects
ring of ciliary body moves outwards and becomes
wider in diameter
tension of suspensory ligaments increases
lens becomes thinner
and more
flattened
image of distant
objects formed on
retina
lens becomes less convex
tension of suspensory ligament increase
s
circular ciliary muscle relaxes increase in circumferen
ce
To demonstrate the To demonstrate the Need of Need of
AccommodationAccommodation
How is the distance between the lens and the projector related to the thickness of the lens?
Ans: The thicker the lens, the shorter is the distance between the lens and the projector.
water with sodium fluorescein
thinner convex lens
front view of the lens of the projector
convex lensprojector
Common Eye Common Eye Defects -- Defects --
Short SightShort Sight it occurs when light of distant object
focused in front of retina
may be due to eyeball too long or lens
becomes too curved
only near object can be seen clearly
corrected by wearing concave lenses
which diverge light from distant object
before reaching the eye to ensure its
image fall on retina sharply
Common Eye Common Eye Defects -- Long Defects -- Long
SightSight it occurs when light from near objects
focused behind the retina
may due to eyeball too short or lens
becomes too thin
only distant object can be seen clearly
corrected by wearing convex lenses
which converge light from near object
before reaching the eye
Common Eye Defects Common Eye Defects -- Colour Blindne -- Colour Blindne
ssss cone cells are responsible for colour vision there are three kinds of cone cells responsi
ble for detecting red, green and blue lights relative number of cones presents and bein
g stimulated determined the colour perceived
colour blindness is a hereditary defect and cannot be corrected by wearing glasses
Ans: 8
Ans: A line
Ans: Nothing
Ans: 5
Can You See?Can You See?
Function of Function of Mammalian EarMammalian Ear
enable mammal to hear so that
they can escape from danger
detect changes in position during
movement
Structure and FunctionStructure and Functions of Different Parts of s of Different Parts of
EarEar ear is divided into three parts:
outer ear, middle ear and inner
earOuter Ear
outer ear includes pinna and an auditory canal
outer ear
middle ear
inner ear
pinna a flap of cartilage covered with skin serve to collect sound
waves and detect direction of the sound
in some mammals, pinnae are movable so they can detect sound source efficiently as they can move their pinnae to the direction of sound source
pinna
auditory
canal lined with hairs and wax-secreting cells to prevent entry of dust or small insects
a membrane present at the end of auditory canal and it is called eardrum (typanum)
eardrum serve as a device to convert sound waves into vibrations as when sound waves strike it, they are translated into mechanical waves
eardrum
auditory canal
Middle Ear
air-filled cavity behind eardrum
contains three small bones, ear ossicles: outer hammer(malleus), middle anvil(incus) and inner stirrup(stapes)
eardrum
three ossicles link eardrum with oval window on the other side of the middle ear
oval window
round window
oval window leads to inner ear
vibrations from eardrum are transmitted by ear ossicles to the membrane covering oval window
round window is another opening in the middle ear which allows the exit of pressure caused by ear ossicles pressing on oval window
middle ear is connected to pharynx by a passage called Eustachian tube to equalize pressure on both sides of eardrum
ear ossicles also amplify vibrations before reaching oval window
Inner Ear
bony cavity in skull and filled with fluid called perilymph
inside this bony cavity is a group of membrane-bound structures which contain endolymph and receptors including cochlea and three semicircular canals
cochlea
structure that senses sound
coiled tube like a snail’s shell
divided into three canals which the middle one is bound by two membranescochlea
many sensory hair cells present on the
bottom membranes
endolymph is enclosed in the middle canal while canals on either side of middle canal contain perilymph
semicircular canalthree semicircular canals are involved in
detecting movement of head
both cochlea and semicircular canals have nerve fibres running to brain
these nerve fibres form auditory nerve
semicircular canals
Equalizing Pressure Equalizing Pressure on both Sides of the on both Sides of the
EardrumEardrum eardrum separate outer ear from the
middle ear
important to keep pressure in middle
ear as the same as atmospheric
pressure in order to have normal
hearing
Eustachian tube is used to equalize
pressure on both sides of eardrum and
it connects middle ear to pharynx
atmospheric
pressurepressure inside middle
ear
eardrum bulges inwards
(you feel pain)
When you are landing…
eardrum returns to normal position
Solution: Yawning or
SwallowingDuring swallowing, Eustachian tube is
opened to let more air from mouth enter
middle ear to equalize pressure on both
sides of eardrum
atmospheric pressure
pressure inside middle
ear
eardrum bulges
outwards
(you feel pain)
When you are travelling up a
hill...
eardrum returns to normal position
Solution: Yawning or
SwallowingDuring swallowing, Eustachian tube is
opened to let air in middle ear to pass
out through the Eustachian tube
To Locate an To Locate an Object by Object by
SoundSound
Did you have to move your head in order to locate the sound source ?Ans: The answer is supposed to be yes as sound wa
ves travel in air in all directions.
bell
Can you still locate the bell if one of your ears is stuffed with cotton wool?Ans: The answer is supposed to be no.
bell
Detecting Movement of Detecting Movement of HeadHead semicircular canals in inner ear detect
movement of the head
three fluid-filled semicircular canals
are situated at an angle of 90o to each
other
each canal is sensitive to movement
in different plane
at the base of each canal is a swollen part called ampulla which contains sensory cells with protruding hairs embedded in a gelatinous structure
Semi-circular canals are filled with endolymph Gelatinous mass (cupula) is found inside each ampulla
When the head
move, the
semi-circular
canals will
move in the
same direction
However, the
endolymph in
the canals will
move in
opposite
direction due to
inertia
The
endolymph
displaces the
gelatinous
mass inside
the ampulla
The sensory
hair cells
under the
gelatinous
mass is
stimulated
Nerve impulses
are generated
and transmitted
along the
auditory nerve
Movement of
endolymph
Sensory hair cells
Sensory nerve
ampulla
Endolymph presses against the gelatinous structure and
displaces it
Direction of head movement
In addition to information from
inner ear, the eye and pressure
receptors in feet and stretch
receptors in tendons also provide
messages to brain, informing it
about the position of your body
~~ ENDEND
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