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Detection of Environmental Conditions in Mammals Irritability • The ability to respond to stimuli • The Stimuli Receptors Nerve effectors brain impulses (external then generate (muscles generates are or nerve sent internal) orto nerve impulses glands) theare brain impulses detected then after for being by receptorssuitable stimulated interpretation carrying produces suitable or senseresponses responses organs to the effectors Eye • Sense organ for receiving light • Protected by the skull Structures around the eye-ball • Tear glands: secrete tears which – wash away dust – contain lyzozyme which kills bacteria – moisten the eye surface • Eyelids – protect eye from damage • Eyelashes – protect the eye from large particles to enter it Internal structure of the eye-ball • Wall of eye-ball consists of 3 layers 1. Sclera • maintain the shape of the eye-ball • protects the inner structures • provides anchorage to eye muscles Internal structure of the eye-ball 2. Choroid • With many blood vessels and pigment • Pigment Blood vessels absorbs supplies extra light oxygen to and nutrients prevent reflection to the eyes, of light and inside to the remove which eyeball metabolic may wastes blur thefrom image them Internal structure of the eye-ball 3. Retina • Contains light sensitive cells (photoreceptors) and nerves • Rods for blackand-white vision • Cones for colour vision Internal structure of the eye-ball Yellow spot • densely packed with cones • no rod is present • gives the most distinct image and the greatest colour discrimination Internal structure of the eye-ball Blind spot • the point where the nerve fibres leave the eye-ball • no photo-receptors cannot detect any image Internal structure of the eye-ball Cornea • Continuous with sclera • Protected by conjunctiva • To allow light to enter • To refract light onto the retina Internal structure of the eye-ball Pupil • The opening which allows light to enter the eye-ball Iris • To control the size of the pupil Change in the pupil size • Iris is made of circular muscles and radial muscles –antagonistic pair Increase in the pupil size • At dim light : circular muscles relax; radial muscles contract • increase in size of pupil Decrease in the pupil size • At bright light : circular muscles contract; radial muscles relax • decrease in size of pupil Internal structure of the eye-ball Lens • Transparent, elastic, biconvex structure • To focus light rays on the retina by changing its convexity Internal structure of the eye-ball Suspensory ligaments • Hold the lens in position Ciliary body • Regulates the curvature of the lens by contraction and relaxation of the ciliary muscles Accommodation • The ability of the eye to focus objects at varying distances onto the retina • Light entering the eye is refracted successively at the cornea, the aqueous humour, the lens and the vitreous humour. • The image is formed on the retina and the retina sends signal along the optical nerve to the brain, causing the sensation of sight. • The image formed on the retina is inverted but is interpreted as erect. Focusing near object Light from near object Focusing on near objects Lens become Ciliary Tension muscles of suspensory more contract convex ligaments is decreased Decrease in circumference Focusing far away object Light from far away object Focusing on distant objects Ciliary Tension muscles of suspensory relax ligaments Lens become less convex is increased Increase in circumference Accommodation Object Near Distant Ciliary Muscle Shape Contract Thicker Relax Focal length Shortened Thinner Lengthened Near Point and Far Point • The average normal eye can focus objects easily from about 25 cm, i.e., the near point, to infinity, i.e. the far point. • This range of distance of clear vision varies from one person to another and decreases with age. Short sight Light from distant object • The eyeball is a bit too long. • The lens lacks the ability to accommodate for a distant object. Correction of short sight Light from distant object Diverging lens ( Concave lens ) Long sight Light from near object • The eyeball is a bit too short. • The lens lacks the ability to accommodate for a near object. Correction of long sight Light from near object Converging lens ( Convex lens ) Causes Defect Eye lens Eye ball Correction Short sight Too thick Too long Concave lens Long sight Too thin Too short Convex lens Eye defects • Short-sighted – Image of a distant object formed in front of the retina – Lens too thick – Eye-ball too long – Correction: wear concave lens Eye defects • Long-sighted – – – – Image of a near object formed behind the retina Lens too thin Eye-ball too short Correction: wear conves lens Eye defects • Colour blindness – Defect of one or more of the three types of cone cells – Unable to distinguish between colours – Inherited Class Practice 1. Which of the following statements about the lens is/are correct ? (1) The image formed on the retina is real. (2) The pupil is smaller in bright light than in dim light. (3) When the object distance changes, the eye focuses an object by chaning the focal length of the eye lens. Internal structure of the eye-ball Anterior chamber • Filled with aqueous humour – to refract light onto the retina – to maintain the shape of the eye-ball – to supply nutrients to the conjunctiva, conera and lens Internal structure of the eye-ball Posterior chamber • Filled with vitreous humour – to refract light onto the retina – to maintain the shape of the eye-ball Internal structure of the eye-ball Optic nerve • To transmit nerve impulses to the optic centre in the cerebral cortex of the brain for interpretation Basic Fact of EAR • Ears are used to detect SOUND in environment. • Ears help to detect movement & position. • Ear is divided into Outer Ear, Middle Ear & Inner Ear. Structure of EAR • Outer Ear: EAR PINNA, EAR CANAL & EAR DRUM. • Middle Ear: EAR BONES • Inner Ear: EUSTACHIAN TUBE & ADENOIDS. Outer Ear • It is the part which is visible and is made of folds of skin and cartilage. • It leads into the ear canal, which is about one inch long in adults and is closed at the inner end by the eardrum. • The eardrum is a thin, fibrous, circular membrane covered with a thin layer of skin. • It vibrates in response to changes in the air pressure that constitute sound. • The eardrum separates the outer ear from the middle ear. Middle Ear • It is a small cavity which conducts sound to the inner ear by means of three tiny, linked, movable bones called "ossicles." • These are the smallest bones in the human body and are named for their shape. • The hammer (malleus) joins the inside of the eardrum. • The incus joint with the hammer and to the stapes. • The base of the stapes fills the oval window which leads to the inner ear. Inner Ear • The inner ear is a very delicate series of structures deep within the bones of the skull. • It consists of a maze of winding passages, called the "labyrinth". • The front (see cochlea) is a tube resembling a snail's shell and is concerned with hearing. • The rear part is concerned with balance. Detection of SOUND 1. 2. 3. 4. 5. Sound waves (air vibrations) are collected by the OUTER EAR. Sound waves vibrate the EAR DRUM. Vibrations are amplified by the EAR BONES. Vibrations change the pressure of the FLUID of the INNER EAR. Vibrations are transmitted to signals to the brain via nerve impulses. Intensity Cues in Stereo • When the volume of two speakers are equal, we will hear the sound as come from the centre. Structure of the ear • Three regions: • Inner Outer ear Middle ear ear Process of hearing • Sound waves are collected by the ear pinna Process of hearing • Sound waves pass along the external auditory canal to the ear drum Process of hearing • Ear drum converts Sound waves makesound the earwaves druminto to vibrate mechanical vibrations Process of hearing • Ear bones transmit and amplify vibrations drum transmits vibration to the ear bones Process of hearing • Ear bones transmit vibration to the oval windows Process of hearing • Oval window causes the perilymph in the upper canal of the cochlea to vibrate Process of hearing • Perilymph transmits vibrations to the endolymph in the middle canal Process of hearing • The sensory hair cells send on theoff bottom nerve membrane of the middle canal are stimulated impulses Process of hearing • The auditory centre nerve transmits interpretsthe theimpulses nerve to the auditory impulses and produce centre of thethe sensation cerebralofcortex hearing Process of hearing • The Round vibrations windowofbulges perilymph outwards are transmitted into the to the round middle ear cavity window to release pressure Equalizing the pressure on both sides of the eardrum • The middle ear is air-filled – This The ear atmospheric causes drum thecannot ear pressure drum vibrate tomay curve properly become inwards and higher or or lower outwards causes pain than and thetemporarily air pressuredeaf in the middle ear Equalizing the pressure on both sides of the eardrum • The pressure on both sides of the ear drum can be equalized by the Eustachian tube • It Eustachian is openedtube onlyisduring connected swallowing to the pharynx or yawning Detection of movement by the ear • At Thethesemi-circular Above base the cochlea of eachcanals are canal three is areasemi-circular perpendicular swelling called canals to ampulla each other to detect head movement all planes – They are responsible for detecting headinmovement Detection of movement by the ear • Semi-circular Gelatinous mass canals (cupula) are filled is found withinside endolymph each ampulla Detection of movement by the ear • The Nerve When However, endolymph sensory the impulses head the move, endolymph displaces hair are generated cells theunder the semiin circular gelatinous the and canals gelatinous transmitted canals will mass will move move inside mass along isin the the in the same direction opposite ampulla stimulated auditory nerve direction due to inertia Detection of movement by the ear • Nerve impulses are generated and transmitted along the auditory nerve to • the cerebrum: aware of the direction of head movement • the cerebellum: leads to appropriate responses of the muscles to maintain body balance Nose - the olfactory organ • For detection of smell • By olfactory cells on the upper part of nasal cavity • Covered with mucus – to dissolve chemicals in air which stimulate the olfactory cells to produce nerve impulses to the cerebrum Tongue - the taste organ • Detected by taste buds on the upper surface of the tongue which are stimulated by chemicals dissolved in saliva • Different regions detect different tastes • Flavour of food is given by both the bitter sense of taste and sour odour of it salty sweet The skin • Contains many receptors for the sensation of touch, cold, hot, pain and pressure • The distribution of them are uneven throughout the skin