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Grade 12: Sense Organs Receptors • Receptors detect a variety of different stimuli such as light, sound, touch, temperature, pressure, pain and chemicals (taste and smell). Receptor Types Chemoreceptors • respond to changes in chemical concentrations Pain receptors • respond to tissue damage Thermoreceptors • respond to changes in temperature Mechanoreceptors • respond to mechanical forces Photoreceptors • respond to light Photoreceptors • Rods for vision in dim light (120 million) – Found more towards periphery • Cones for color vision and visual acuity (6 million) – Only work in bright light – Three types: red, green, and blue • Overlap of three ranges gives us all the colors – Color blindness is sex-linked (males) The Eye The Eye - Protection • Protected by bony cavity in the skull = Orbit • Fat and connective tissue lies between eye ball and skull • Exposed part of the eye is protected by a thin membrane = conjunctiva • Eyelids • Eyelashes prevent foreign particles entering • Tears secreted by lachrymal glands keeping conjunctiva moist, anti-bacterial The Eye: Structure Function • Sclera – Protects inner structures – Maintains shape of eye • Cornea – Transparent, permits light to enter eye – Refracts lights rays as to focus them on retina • Choroid – Pigmentation prevents reflection of light within the eye • Suspensory ligaments – Holds lens in position • Ciliary muscles – Alters shape of lens to “accommodate” for near or far objects • Iris – Contains radial and circular muscles which control amount of light entering the eye (Pupillary Mechanism) The Eye: Structure Function • Retina – Light sensitive layer(has photoreceptor rod/cone cells) so is responsible for image formation – Rod Cells responsible for images in dim light – Cone Cells responsible for images in bright light and for colour vision • Lens – Transparent therefore refracts light focusing it on retina – Ability to change shape for near or distant vision (accomodation) • Aqueous Humour – Maintains shape of the cornea – Supplies lens and cornea with food and oxygen – Minor role in refraction • Vitreous Humour – Maintains shape of eyeball – Minor role in refraction Focusing On Retina • as light enters eye, it is refracted by • convex surface of cornea • convex surface of lens • image focused on retina is upside down and reversed from left to right Accommodation changing of lens shape to view objects less than 6m away (near vision) Accommodation changing of lens shape to view objects less than 6m away (near vision) Pupillary Mechanism Adjustment of pupil size under varying light conditions Pupillary Mechanism Also known as pupil reflex! • In dim light – Radial muscles of iris contract – Circular muscles relax – Pupil dilates – Amount of light entering eye increases • In bright light – Circular muscles of iris contract – Radial muscles relax – Pupil constricts – Amount of light entering eye reduces Diseases and Disorders of the Eye • Long-sightedness (Hypermetropia) – – – – Eyeball too rounded Inability for lens to become more convex (especially the elderly) Image of near object focuses beyond retina They can see more than 6m away • Short-sightedness (Myopia) – – – – Eyeball too long Inability of lens to become flat enough (less convex) Image of far objects focus in front of retina They can see less than 6m away • Astigmatism – Unequal cornea or lens – If degree of astigmatism is great enough to cause eyestrain, headaches, distortion of vision, perscription lenses will be needed for clear and comfortable vision. Diseases and Disorders of the Eye Diseases and Disorders of the Eye • Cataracts – The clear transparent lens of the eye becomes cloudy or opaque – Synthetic lens (intraocular implant) can be surgically implanted if necessary through using microscopic instruments • Glaucoma – – – – – Too much pressure in the eye Leads to permanent damage of the optic nerve Eventually leads to blindness (2nd leading cause) Early detection is important Treated with drops to reduce pressure or surgery • Colour blindness – Sex linked characteristic (affects mostly males) – Difficulty in seeing red-green colour – Complete colour-blindness individuals see everything in shades of grey Optical illusions Eyes are playing tricks on our brains • The Dutch artist M.C. Esher mixed realistic detail with strange perspectives that also provide optical illusion's. • Waterfall created in 1961. Julian Beever Julian Beever External Ear • Pinna (auricle) • collects sounds waves • auditory canal • aka ear canal • carries sound to tympanic membrane • eardrum • aka ear tympanic membrane • vibrates in response to sound waves Middle Ear • auditory ossicles • vibrate in response to tympanic membrane • malleus (hammer), incus (anvil), and stapes (stirrup) • aka hammer, anvil & stirrup • oval window • stapes (stirrup) vibrates against it to move fluids in inner ear Auditory Tube • eustachian tube • connects middle ear to throat • helps maintain equal pressure on both sides of tympanic membrane • usually closed by valve-like flaps in throat Inner Ear • System of labyrinths •Bony labyrinth • bony canal in temporal bone • filled with perilymph • made up of semi-circular canals, the vestibule (saccule and utricle) and the cochlea. • Membranous labyrinth • tube within bony labyrinth • filled with endolymph • contains the organ of corti Inner Ear Parts of Inner Ear • cochlea • functions in hearing • snail-shaped • Have hearing receptor cells (hair cells) that bend with different frequencies to generate a nerve impulse = Organ of Corti • semicircular canals • functions in equilibrium and balance • fluid-filled Hearing Process • Pinna trap and direct sound waves along auditory canal • Sound waves hit tympanic membrane causing it to vibrate • This causes ossicles to vibrate • Stirrup causes membrane on oval window to vibrate • Sends waves in perilymph of vestibular canal • Organ of Corti in the Cochlea is stimulated • Stimulus is turned into nerve impulse • Auditory Nerve sends signals to Cerebrum to be interpreted Balance and Equilibrium • Sudden changes in speed and direction causes endolymph in semicircular canals to move • These canals are in three different planes, fluid in at least one canal will move if ones speed or direction changes • Movement of flood stimulates receptors called cristae within the ampullae to move • Ampullae are found at the base of each semi circular canal • Cristae send impulses along vestibular nerve branch to cerebellum Balance and Equilibrium • • • • In the sacculus and utriculus When direction of head changes, gravitational pull stimulates different receptors called maculae to move Maculae send signal along vestibular branch of the auditory nerve to the cerebellum Cerebellum sends impulses to muscles to restore balance and equibilbrium Adaptations of the Ear • Pinna is large and projected out of head to capture sound waves • Cerumen (wax) and hairs in auditory canal trap small organisms preventing entry • Cerumen prevents drying out • Hammer is attached to tympanic membrane so it can vibrate along with the tympanic membrane • Stirrup is attached to oval window • Oval window also vibrates creating waves in the perilymph of the vestibular canal • Eustachian tube allows air to be released out of, or taken into, thus equalizing pressure between middle and outer ear (prevents tympanic membrane bursting. • Round window acts as a cushion absorbing the pressure coming from the waves • Cochlea contains the organ of corti which is the receptor picking up the stimulus of sound • Auditory nerve arising from the cochlea transmits sound to the cerebrum of the brain Diseases and Disorders of the Ear • Middle Ear Infection – Most common cause of earaches. – Caused by viruses and bacteria – Fluid build up results in increased pressure and inflammation – Treated using medication or grommets, which are tiny plastic buttons with a fine hole in the middle. These are inserted into eardrum allowing air to enter giving time for the eustachian tube to recover with all the fluid build up. • Deafness – Can be caused by: Fluid in the middle ear, damage to ear drum, hardened wax in the ear, hardening of ear tissue, age, injuries to parts of the ear, nerves or brain responsible for hearing. – Treatment depends on the cause, not all cases are treatable. Hearing aids make sound louder so that person can listen and communicate. Cochlear Implants can also be used to treat deafness. These don’t work by amplifying sounds but rather by stimulating the auditory nerve in side the cochlear as the organ of corti would normally do