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Chapter 13 NOTES.docx

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Emily Agard

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Chapter 13 NOTES - The Peripheral Nervous System provides links from the world outside our bodies - Includes all neural structures, outside the brain and their associated ganglia and efferent motor endings Sensory Receptors and Sensation Sensory Receptors - Sensory receptors are specialized to respond to changes in their environment (stimuli) - Sensation is awareness of the stimuli and perception is the interpretation of the meaning of the stimulus - Classified in three ways: (1) by the type of stimulus they detect; (2) by their body location; and (3) by their structural complexity Classification by Stimulus Type - Mechanoreceptors respond to mechanical force (touch, pressure) - Thermoreceptors  respond to temperature changes - Photoreceptors  retina in the eye; respond to light - Chemoreceptors  respond to chemicals in solution - Nociceptors  respond to potentially damaging stimuli that result in pain Classification by Location - Exteroceptors  sensitive to stimuli arising outside the body - Interoceptors  respond to stimuli inside the body - Proprioceptors  respond to stimuli inside the body but their location is much more restricted; occur in skeletal muscles, tendons, joints and ligaments in connective tissue coverings of bones and muscles. Monitor stretching. Classification by Receptor Structure - General senses monitor most of the types of general sensory information - Special senses (vision, hearing, smell, taste and equilibrium) are housed by complex sense organs - The general senses are in charge of sensation (pressure, touch, stretch and vibration), temperature monitoring and pain - Nonencapsulated (free) nerve endings are resent nearly everywhere in the body. They are nonmyelinated, small-diameter group C fibres and their distal endings usually have knob like swelling. Mostly respond to temp change and painful stimuli. Responding to cold located in superficial dermis and to heat are deeper in the dermis. - Free nerve endings also mediate itch (thin layer in dermis) - Some other free nerve endings include: Tactile (merkel) cells: they lie in the deepest layer of the epidermis and function as light touch receptors. Hair follicle receptors: wrap around the hair follicle and detect bending of hairs - Encapsulated nerve endings consist of one or more fiber terminals of sensory neurons enclosed in a connective tissue capsule. They include: Tactile corpuscles  receptors for discriminative touch and are located in the beneath the epidermis in the dermal papillae Lamellar corpuscles  scattered deep in the dermis and respond the pressure when it is first applied Bulbous corpuscles  respond to deep and continuous pressure and are found deep in dermis, hypodermis and joint capsules Muscle spindles  detect muscle stretch and initiate a reflex that consists the stretch; located in skeletal muscles Tendon organs  located in the tendons and initiates a reflex that causes the contracting muscle to relax Joint kinesthetic receptors  they monitor stretch in the articular capsules that enclose synovial joints Sensory Integration: From Sensation to Perception General Organization of the Somatosensory System - It is the part of the sensory nervous system serving the body and limbs that receives inputs from Exteroceptors, proprioceptors and interoceptors. - Three main levels of neural integration operate in the somatosensory system: (1) Receptor Level, (2) Circuit Level and (3) Perceptual Level - (1) Receptor Level  sensory reception and transmission to CNS. This will only occur if the stimulus matches the receptor, the stimulus must be applied to the receptors receptor field and the stimulus energy must be converted into the energy of a graded potential, a process called transduction Two types of graded potentials: generator potential is when the receptor region is part of a sensory neuron and a receptor potential which is when the receptor is in a separate cell. Adaptation is a change in sensitivity in the presence of a constant stimulus (walking into bright room after being in the dark). Phasic receptors are fast adapting (lamellar and tactile corpuscles). Tonic receptors provide a sustained response with little to no adaptation. - (2) Circuit Level  processing in ascending pathways (deliver impulses to the appropriate region of the cerebral cortex for localization and perception of the stimulus) - (3) Perceptual Level  processing in cortical sensory centers Transmission Lines: Nerves and Their Structure and Repair Nerves and Associated Ganglia - A nerve is a cordlike organ that is part of the PNS - Axon is surrounded by endoneurium, a delicate layer of loose connective tissue - The perineurium, coarser connective tissue, binds groups of fibers into bundles called fascicles - The epineurium, a tough fibrous sheath, encloses all the fascicles to form the nerve - Mixed nerves conta
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