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The Special Senses Life Science FLSS All images used are taken from copyright-free sources e.g. Wikicommons Media or produced by UWS staff. Special senses • • • • • Sight Hearing Taste Smell Touch Information about external environment brain response as necessary • • • Senses interpret different forms of energy Brain receives info from senses Info/energy converted to electricity in a form brain can interpret Sensory neurones Specialised structures at dendrites which respond to: • Light • Pressure • Chemicals Cell bodies often close to spinal cord Sight Iris Eyelashes Eyebrow Upper eyelid (palpebra) Lacrimal caruncle Medial commissure Lateral commissure Palpebral fissure Pupil Conjuctiva (over sclera) Lower eyelid (palpebra) Sneakydaycrawler (2007) http://commons.wikimedia.org/wiki/File:Hazel_eye_(1).jpg Tear production a. tear gland / lacrimal gland, b. superior lacrimal punctum, c. superior lacrimal canal, d. tear sac / lacrimal sac, e. inferior lacrimal punctum, f. inferior lacrimal canal, g. nasolacrimal canal Erin_Silversmith (2006) http://commons.wikimedia.org/wiki/File:Tear_system.svg Holly Fischer (2013) Http://commons.wikimedia.org/wiki/File:Three_Main_Layers_of_the_Eye.png?uselang=en-gb Retina • Image is focussed onto this inner lining • Retina has neurones which are sensitive to light • Light causes changes in photosensitive pigments • Changes are converted to nerve impulses • Impulses transmitted to brain via the optic nerves Retinal Cells Two types of photoreceptors: • Rods – Dim light – Black and white • Cones – Bright light – Distinguish colour (red/green/blue) OpenStax College (2013) http://commons.wikimedia.org/wiki/File:1414_Rods_and_Cones.jpg?uselang=en-gb Rods and cones OpenStax College (2013) http://commons.wikimedia.org/wiki/File:1414_Rods_and_Cones.jpg?uselang=en-gb Pupil constriction/dilation PUPIL Bright Light • Pupil constricts • Circular muscles of iris contracts • PARASYMPATHETIC CONTROL Dim Light • Pupil dilates • Radial muscles of iris contract • SYMPATHETIC CONTROL UWS Staff (2015) Hearing Hearing • • • • • Ears Sound = sound waves / vibrations of air Tympanic membrane (eardrum) vibrates Ossicles vibrate Via oval window, causes fluid in cochlear duct to vibrate • Hair cells stimulated • Nerve impulses initiated in cochlear part of vestibulocochlear nerve brain BruceBlaus. (2013) http://commons.wikimedia.org/wiki/File:Bl ausen_0328_EarAnatomy.png BruceBlaus. (2013) http://commons.wikimedia.org/wiki/File:Blausen_0330_EarAnatomy_MiddleEar.png BruceBlaus. (2013) http://commons.wikimedia .org/wiki/File:Blausen_03 29_EarAnatomy_Internal Ear.png Balance • 3 semicircular canals (one in each plane of space) • Fluid-filled • Movement of head movement of fluid stimulation of hair cells send impulses via vestibular part of vestibulocochlear nerve brain Sense of balance involves brain integrating messages from: • Eyes • Inner ear • Proprioreceptors in muscles and joints Taste • • • • • • 10,000 taste buds in your mouth Chemoreceptors Sweet, sour, bitter, salt (and umami) Sweet and salty are least sensitive Bitter ones are most sensitive Some researchers doubt the simplicity of this model BITTER Rainer Zenz (2007) http://commons.wikimedia.org/wiki/Tongue SALTY SOUR SWEET Taste bud Sunshineconnelly (2007) http://commons.wikimedia.org/wiki/File:Anatomy_and_physiology_of_animals_Taste_buds_on_the_tongue.jpg?uselang=en-gb Smell • Also detected by chemoreceptors, in nasal cavity – activated by volatile chemicals in the air • Smell contributes to the fine perception of taste BruceBlaus. (2013) http://upload.wikimedia.org/wikipedia/commons/2/2e/Blausen_0872_UpperRespiratorySystem.png Olfactory bulb 1: Olfactory bulb 2: Mitral cells 3: Bone 4: Nasal epithelium 5: Glomerulus 6: Olfactory receptor cells Chabacano (2007) https://commons.wikimedia.org/wiki/File:Olfactory_system.svg Touch receptors • Different receptors for hot, cold, pain, pressure and light touch • Unevenly distributed on skin and mucous membranes • Meissner’s corpuscles – detect light touch • Pacinian corpuscles – detect pressure • Free nerve endings – itch/tickle/temp/pain (slowly and rapidly adapting) US-Gov (2005) https://commons.wikimedia.org/wiki/File:Skin.png