LectNeuro II Web 10

LectNeuro II Web 10 - Sensory systems Natural selection...

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Sensory systems • Natural selection immense variety of sensory receptors • Concentrated on body surfaces and toward head end of bilaterally symmetric animals • probably all produce receptor potentials in response to natural stimuli • convergent evolution • generally, “highly evolved” animals excel more in CNS development and versatility than in receptor capabilities
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Receptor properties studied predominantly by two methods Neurophysiology: Neurophysiology: information about mechanisms of function Behavioral studies: Behavioral studies: information about receptor capabilities and adequate stimulus
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Sharks and electroreceptors
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Ampullae of Lorenzini 1. Mechanoreceptors 2. Thermoreceptors 3. Hydrostatic pressure 4. Salinity detectors 5. Electric fields 1 μV/m or 1 flashlight cell every 1500 km (ca. 800 mi) Pore connecting to a bladder-like structure with sensory receptors at its base.
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flatfish agar cover agar cover; fish frozen, cut pieces Insulating plastic film electrodes fish and electrode Sharks and electroreceptors Ampullae of Lorenzini
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Interpreting Function depends on Studies of Electrophysiology and Behavior
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Mechanical Stimuli Mechanoreceptors: least specific of sensory receptors • free nerve endings sensitive to almost any movement (almost any nerve or muscle cell can be a potential mechanoreceptor, but with high threshold) true mechanoreceptors: more sensitive due to properties of membrane and coupling to environment
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Hair Cell Receptors Secondary receptors • Mechanoreceptors in fish •Hear ing
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Text Fig. 6.19 neuromast Fishes, aquatic amphibians convergent evolution
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Text Fig. 6.17 vertebrate hair cell
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Text Fig. 6.18
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Text Fig. 6.18
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Text Fig. 6.18
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Hair cell receptors stereocilia kinocilium efferent afferent
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neuromasts = lateral line organs
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Hearing • Noteworthy adaptation of hair cells • Phonoreception overlaps vibration sense at about 50 Hz • Many animals can hear; few communicate with sound (primarily birds, mammals) • Sound can be heard from any direction; good warning source basilar membrane (lagena) first elongates in crocodilians well developed cochlea of birds, mammals
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endolymph perilymph pinna Mammalian ear inner ear external ear canal e u s t a c h i an tu b
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LectNeuro II Web 10 - Sensory systems Natural selection...

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