The Peripheral Nervous System and Reflexes

The Peripheral Nervous System and Reflexes - The Peripheral...

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Unformatted text preview: The Peripheral Nervous System (PNS) P A R T A Peripheral Nervous System (PNS) ¡ PNS – all 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 PNS in the Nervous System Figure 13.1 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 Type ¡ Mechanoreceptors – respond to touch, pressure, vibration, stretch, and itch ¡ Thermoreceptors – sensitive to changes in temperature ¡ Photoreceptors – respond to light energy (e.g., retina) ¡ Chemoreceptors – respond to chemicals (e.g., smell, taste, changes in blood chemistry) ¡ Nociceptors – sensitive to pain-causing 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 ¡ Include 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 one’s movements ¡ 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 Receptor Classification by Structural Complexity Simple Receptors: Unencapsulated ¡ Free dendritic nerve endings l Respond chiefly to temperature and pain ¡ Merkel (tactile) discs ¡ Hair follicle receptors Simple Receptors: Encapsulated ¡ Meissner’s corpuscles (tactile corpuscles) ¡ Pacinian corpuscles (lamellated corpuscles) ¡ Muscle spindles , Golgi tendon organs, and Ruffini’s corpuscles ¡ Joint kinesthetic receptors Unencapsulated Receptors Table 13.1.1 Simple Receptors:Encapsulated Table 13.1.2 From Sensation to Perception ¡ Sensation is the awareness of changes in the internal and external environment ¡ Perception is the conscious interpretation of those stimuli Organization of the Somatosensory System ¡ Input comes from exteroceptors, proprioceptors, and interoceptors ¡ The three main levels of neural integration in the somatosensory system...
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This note was uploaded on 01/06/2012 for the course BIOL 2401 taught by Professor Elainefanin during the Fall '11 term at Collins.

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The Peripheral Nervous System and Reflexes - The Peripheral...

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