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Sensory Mechanisms Sensory receptors and the brain Sensation Perception • Action potentials transmitted by sensory receptors to the brain • Sensory receptors ▫ Specialized neurons/epithelial cells ▫ Extero- and interoreceptors ▫ Convert energy to changes in membrane potentials and transmit to brain ▫ Four functions: transduction, amplification, transmission, and integration • Interpretation of the stimuli by the brain • Ex. colors, taste, sound, smell 1. Follow the movement of the rotating pink dot with your eyes. 2. Stare at the cross in the center. 3. Concentrate on the cross at the center for a long period of time. Is the blue side in the front or back of the cube? Types of sensory receptors Mechanoreceptors Physical deformation Stretch receptors in muscles and hair cells Pain receptors Excess heat, pressure, presence of chemicals, prostaglandins Naked dendrites called nociceptors Chemoreceptors Presence and concentrations of chemicals in the environment Osmoreceptors in brain, gustatory and olfactory receptors, pheromone receptors in moth antennae Thermoreceptors Heat or cold Skin receptors and interoreceptors in the hypothalamus EM receptors EM energy photoreceptors: infrared in snakes, electroreceptors in eels, rods and cones in humans Vision and photoreceptors * All have pigment molecules that absorb light Eye cup of planarians Compound eyes of insects, crustaceans, polychaetes Ommatidia are sensitive to movement! Single lens eyes of jellyfish, polychaetes, spiders, mollusks Single lens eyes of vertebrates Sclera Choroid Retina with rods and cones Ciliary body Fovea (center of visual field, most cones) Suspensory ligament Cornea Iris Optic nerve Pupil Aqueous humor Lens Vitreous humor Optic disk (blind spot) Structure of the human eye Central artery and vein of the retina Hearing and equilibrium in invertebrates Ciliated receptor cells Statolith Cilia Sensory nerve fibers Statocysts in invertebrates Tympanic membrane 1 mm Hearing and equilibrium in mammals 1 Overview of ear structure 2 The middle ear and inner ear Incus Middle ear Inner ear Outer ear Stapes Skull bones Semicircular canals Malleus Auditory nerve, to brain Pinna Tympanic membrane Hair cells Cochlea Eustachian tube Auditory canal Tectorial membrane Tympanic membrane Oval window Eustachian tube Round window Cochlear duct Bone Vestibular canal Auditory nerve Basilar membrane Axons of sensory neurons 4 The organ of Corti To auditory nerve Tympanic canal 3 The cochlea Organ of Corti Chemoreceptors and taste Taste buds in mammals Sensilla in insects Chemoreceptors and smell Brain Action potentials Odorant Olfactory bulb Nasal cavity Bone Epithelial cell Odorant receptors Plasma membrane Odorant Chemoreceptor Cilia Mucus