Ch.13The Peripheral Nervous System

Ch.13The Peripheral Nervous System - Ch.13: The Peripheral...

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Ch.13: The Peripheral Nervous System (PNS) and Reflex Activity Shreya Buch Peripheral Nervous System (PNS) (fig.13.1) 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 Part 1- Sensory Receptors and Sensation Sensory Receptors Structures specialized to respond to stimuli Activation of sensory receptors results in depolarization that trigger impulses along the afferent PNS fibers coursing to the CNS The realization of these stimuli, sensation (awareness of stimulus) and perception (interpretation of the meaning of the stimulus), occur in the brain Sensory receptors are classified by: (1) By the type of stimulus they detect (2) By their body location ,and (3) By their structural complexity (1 ) Receptor Classification by Stimulus Type Mechanoreceptors – respond to touch, pressure, vibration, stretch, and itch-receptors generate impulse when they or surrounding tissue are deformed by a mechanical force Thermoreceptors – sensitive to changes in temperature Photoreceptors – respond to light energy (e.g., retina) Chemoreceptors – respond to chemicals in fluid (e.g., smell, taste, changes in blood chemistry) Nociceptors – sensitive to pain-causing stimuli-respond to potentially damaging stimuli that result in pain (e.g., extreme heat, extreme cold, excessive pressure) (2) Receptor Class by Location: a) 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 (vision, hearing, taste, equilibrium) b) Interoceptors Respond to stimuli arising within the body-also called
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visceroceptors Found in internal viscera and blood vessels Sensitive to chemical changes, stretch, and temperature changes, tissue stretch Their activity cause us to feel pain, discomfort, hunger, thirst c) Proprioceptors Respond to internal stimuli, like 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 (3 ) Receptor Classification by Structural Complexity (Table 13.1) 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, associated with special sense (vision, hearing, equilibrium, smell, taste) Simple Receptors: Unencapsulated Free dendritic nerve endings Respond chiefly to temperature and pain Also receptors for itch locted in the dermis Merkel (tactile) discs-in deeper layers of epidermis, for lighter touch Hair follicle receptors- free nerve endings wrap around hair follicles, are also light touch receptors that detect bending of
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Ch.13The Peripheral Nervous System - Ch.13: The Peripheral...

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