Sense Organs

1. Sense Organs

2. Chemoreceptors • Taste and smell sensory receptors • Most primitive sense, all animals have it • Important in finding food, locating a mate and detecting chemicals • Location varies by animal • Jacobsen’s organ - snakes

3. Taste • 4 primary types of taste • Sweet, sour, salty, bitter, • umami? Cheeses, broth, seafood, Asian foods • Microvilli of taste cell has receptor proteins for food molecules

4. Smell • 10 – 20 million olfactory cells!! (modified neurons) • Declines with age • Located on roof of nasal cavity • Olfactory bulb (extension of brain) has direct connection with limbic system (emotions and memory) • Smell and taste work together in cerebral cortex • Sometime molecules from smell travel to mouth and you taste it

5. Vision • Photoreceptors – sensitive to light • Some animals have “eye spots”, some have image forming eyes • Insects have color vision, shorter spectrum but includes ultraviolet light • Some fish, all reptiles, most birds • monkeys, apes and humans only mammals • Stereoscopic vision (binocular – in front) • Panoramic vision – eyes on side, prey

6. Human Eye

7. Human eye • 3 layers • Sclera – clear outer layer • Cornea – refracts light rays • Conjunctive – moistens • Pupil – light enters • Choroid – middle, includes blood vessels • iris – color of eye, regulates light entrance • Ciliary muscle – holds lens in place • Retina – inner layer, metallic • Rods –sensitive to light, black and white, night vision • Cones – color vision • Fovea centralis – acute vision

8. Eye • Lens • Refracts and focuses light, can be replaced • Aqueous humor • Water solution, anterior of eye, behind lens • Glaucoma – pressure builds up • Vitreous humor • Gel material in posterior of eye • Stabilizes the shape of eye, support retina • Optic nerve – sends info to brain • Blind spot – optic nerve exits the retina, no rods or cones

9. Disorders of eye • Presbyopia – old-sightedness • lens loses its ability to accommodate near objects • Nearsighted (myopia) • Elongated eyeball, image in focus in front of retina • Farsighted (hyperopia) • Shortened eyeball, image focused behind the retina • Astigmatism • Cornea or lens is uneven, image is fuzzy • Cataract – aging, exposure to sun, lens is milky and cannot transmit light rays

10. Hearing and balance – The Ear • Mechanoreceptors • sensitive to pressure, sound waves and gravity • Outer ear – pinna flap, auditory canal • Middle ear – tympanic membrane (ear drum) • Ossicles – stapes (stirrup), incus (anvil), malleus (hammer) • Eustachian tube – equalization of pressure • Inner ear – contains fluid • Semicircular canals, vestibule – equilibrium • Cochlea - hearing

11. Sound • Auditory canal tympanic membrane malleus incus stapes oval window  endolymph in cochlea  hair cells of cochlea  synapse with nerve fibers of auditory nerve basilar membrane “organ of corti” nerve impulse travels to brain stem  auditory area of cerebral cortex = sound!!

12. Sense of Balance • Semicircular canals – mechanoreceptors • Rotational equilibrium – head rotation • Gravitational equilibrium – straight line movement

13. Sensory receptors in animals • Lateral line – fish – • Detects water currents and pressure waves • Collection of hair cells with cilia • Statocysts – gravitational equilibrium • Cnidarians, molluscs, crustaceans • Give information only about the head