Detection of Environment

•Eye•Ear•Skin

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

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 eyeball 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 and Structures and Functions of EyeFunctions of Eye

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

Retinathe 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 ne

rve fibres no nerve impulse can be generated when

light 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

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

Focusing near object

Light from near object

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

Focusing far away object

Light from far away object

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 Defects -- Short Common Eye Defects -- Short SightSight 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

Short sight

Light from distant object

Correction of short sight

Light from distant object

Diverging lens

( Concave lens )

Common Eye Defects -- Long Common Eye 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

Long sight

Light from near object

Correction of long sight

Light from near object

Converging lens

( Convex lens )

Common Eye Defects -- Colour BliCommon Eye Defects -- Colour Blindnessndness cone cells are responsible for colour vis

ion there are three kinds of cone cells resp

onsible for detecting red, green and blue lights

relative number of cones presents and being 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 ski

n 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

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

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

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