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Download Nervous System III, part 2
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Nervous System III, part 2 Chapter 12 Special senses • Sensory receptors within complex sensory organs • Found in the head • • • • Smell in olfactory organs Taste in taste buds Hearing and equilibrium in ears Sight in eyes Smell • Chemoreception • Olfactory bulb • Olfactory epithelium • 3 cm2 An individual neuron contains a single type of odorant receptor Combine signals for diversity Nerve fibers within the olfactory bulb Cilia Olfactory Columnar receptor cells epithelial cells • http://www.youtube.com/watch?v=H_WFlTtP ZmE Olfactory stimulation • Receptors undergo sensory adaptation rapidly • Sense of smell drops by 50% within one second after stimulation Taste (gustation) • Chemoreceptors on taste buds • Sweet, sour, salty, bitter, umami • Each sensation triggered by the presence of different ions (e.g., H+ sour, Na+ salty) Taste receptors • One taste bud = 50-150 taste cells Tasting • Substance must be dissolved in saliva • Molecules interact with receptor on epithelial taste cell • Each cell is only responsive to one type taste sensation Hearing • Perception of energy carried by sound waves (pressure) • http://www.youtube.com/watch?v=0jyxhozq8 9g&list=PLBFFFFF039E4A8B05 Hearing loss • Conductive- external, middle ear; reconstruction of bones in middle ear • Central- rare, damage to neural pathway • Sensorineural- inner ear, death of hair cells Cochlear implants Equilibrium • • • • Dynamic- movement through space Static- head position Inner ear Vestibular apparatus- endolymph Equilibrium • Semicircular canal system – Rotational acceleration – Movement of endolymph, hair cells transduce (a) Head in still position (b) Head rotating Equilibrium • Semicircular canal system – Linear acceleration – Movement of otoliths, hair cells transduce – Some otoliths horizontal, some vertical Vision • Light translated to a mental image • Light enters eye, lens focuses light on retina • Retina photoreceptors transduce light into electrical signal • Electrical signals through neural pathways to brain Optics of the eye Focal point must hit the back of the eye (retina) Pupilchanges amount of light that enters Lens- bends light to focus on retina 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 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Light waves Image Retina Object Cornea 24 • Light energy changes to electrical energy • Occurs at retina • Hits visual receptors behind retina Visual Receptors • Rods • Long, thin projections • Contain light sensitive pigment called rhodopsin • Hundreds of times more sensitive to light than cones • Provide vision in dim light • Produce colorless vision • Produce outlines of objects • Cones • Short, blunt projections • Contain light sensitive pigments called erythrolabe, chlorolabe, and cyanolabe • Provide vision in bright light • Produce sharp images • Produce color vision • Fovea centralis contains just cones 26 Photoreceptors under layer of transparent neurons • Fovea- nothing to impede light Stereoscopic Vision • Provides perception of distance and depth • Results from formation of two slightly different retinal images Light waves Left eye Right eye In the brain • Nerves cross in brain • Binocular zone, constructs 3D representation
