Special Terms involved stimuli: changes in internal and external environments to living organisms sensory system: system perceives stimuli so organisms can respond to changes correctly irritability: 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

Skin  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 Touch Discrimination of Different Regions of the 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 sensitive the part is. your hand dividers hand of the blindfolded student

Tongue  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

Nose  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 Smell 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 Eye rectus muscles optic nerve oblique muscle orbit tear gland muscle attachment to skull eyeball oblique muscle eyelid iris pupil eyelash

Location 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 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 Functions of Eye eye muscle sclera choroid retina yellow spot blind spot optic nerve vitreous humour 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 sclera  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 present  gives the most distinct 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 nerve 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

Experiment to detect the Presence of Blind Spot

What happens to the dot as you move the book towards yourself ? Ans: While you are moving the book, the dot will suddenly 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 formation of an Inverted Image on the Retina using a Cardboard

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 fluorescein convex lens plasticine front view of the lens of the projector convex lens projector

Does the light beam meet at a point ? (This point is the focus of the lens) Ans: Yes. water with sodium fluorescein convex lens plasticine front view of the lens of the projector convex lens projector

What is the shape of the image ? Ans: The image is inverted and smaller than the object. water with sodium fluorescein convex lens plasticine front view of the lens of the projector convex lens projector

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 fluorescein convex lens plasticine front view of the lens of the projector convex lens projector

Change 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 automatic Under Bright Light circular muscles contract radial muscles relax pupil size decrease reduce amount of light pass through

Under Dim Light radial muscles contract circular muscles relax pupil size increases increase amount of light pass through

Accommodation  thick lens  thin lens shorter focal length longer 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 Objects ring of ciliary body moves inwards and becomes smaller 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 decreases circular ciliary muscle contracts  decrease in circumference

ciliary muscles relax Focusing Distant Objects 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 increases circular ciliary muscle relaxes  increase in circumference

To demonstrate the Need of Accommodation

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 lens projector

Common Eye Defects -- Short 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 Defects -- Long Sight  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 -- Colour Blindness  cone cells are responsible for colour vision  there are three kinds of cone cells responsible 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?

Function of Mammalian Ear  enable mammal to hear so that they can escape from danger  detect changes in position during movement

Structure and Functions of Different Parts of Ear  ear is divided into three parts: outer ear, middle ear and inner ear Outer 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

Ê cochlea  structure that senses sound  coiled tube like a snail’s shell  divided into three canals which the middle one is bound by two membranes cochlea

 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

Ë semicircular canal  three 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 on both Sides of the Eardrum  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 pressure pressure inside middle ear  eardrum bulges inwards (you feel pain) When you are landing…

eardrum returns to normal position Solution: Yawning or Swallowing During 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 Swallowing During swallowing, Eustachian tube is opened to let air in middle ear to pass out through the Eustachian tube

To Locate an Object by Sound

Did you have to move your head in order to locate the sound source ? Ans: The answer is supposed to be yes as sound waves 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 Head  semicircular canals in inner ear detect movement of the head  three fluid-filled semicircular canals are situated at an angle of 90 o 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

âSemi-circular canals are filled with endolymph âGelatinous 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

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