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BIOB32H3 (79)


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University of Toronto Scarborough
Biological Sciences
Kenneth Welch

Peripheral Nervous System PNS Peripheral Nervous System PNS PNSall neural structures outside the brain and spinal cord Includes sensory receptors peripheral nerves associated ganglia and motor endings Provides links to and from the external environment Sensory Receptors Structures specialized to respond to stimuli Activation of sensory receptors results in depolarizations that trigger impulses to the CNS The realization of these stimuli sensation and perception occur in the brain Receptor Classification by Stimulus Mechanoreceptorsrespond to touch pressure vibration stretch and itch Thermoreceptorssensitive to changes in temperature Photoreceptorsrespond to light energy eg retina Chemoreceptorsrespond to chemicals eg smell taste changes in blood chemistry Nociceptorssensitive to paincausing stimuli Receptor Class by Location Exteroceptors Respond to stimuli arising outside the body Found near the body surface Sensitive to touch pressure pain and temperature Includes the special sense organs Receptor Class by Location Interoceptors Respond to stimuli arising within the body Found in internal viscera and blood vessels Sensitive to chemical changes stretch and temperature changes Receptor Class by Location Proprioceptors Respond to degree of stretch of the organs they occupy Found in skeletal muscles tendons joints ligaments and connective tissue coverings of bones and muscles Constantly advise the brain of ones movements Receptor Classification by Structure Receptors are structurally classified as either simple or complex Most receptors are simple and include encapsulated and unencapsulated varieties Complex receptors are special sense organs Simple Receptors Unencapsulated Free dendritic nerve endings Merkel discs Root hair plexuses Simple Receptors Encapsulated Meissners corpuscles and Krauses end bulbs Pacinian corpuscles Muscle spindles Golgi tendon organs and Ruffinis corpuscles Joint kinesthetic receptors Structure of a Nerve Nervecordlike organ of the PNS consisting of peripheral axons enclosed by connective tissue
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