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Chapter 15 Neural Integration I: Sensory Pathways and the Somatic Nervous System © 2012 Pearson Education, Inc. Sensory Receptors Detect info about external/internal environment • 3 classifications of sensory receptors: • Interoceptors: monitor internal environment • Exteroceptors: monitor external environment • Proprioceptors: monitor position of muscles/joints • Stimulus translated to AP CNS = transduction © 2012 Pearson Education, Inc. Simple vs. Complex Receptors Simple receptors Complex receptors • dendrites of sensory neurons • Found in sense organs • Branching tips of dendrites = free nerve endings • Example: eye’s visual receptors • Not protected by accessory structures • Protected by accessory cells and CT • Little specificity (i.e.: free nerve endings respond to stimulus caused by chemicals, pressure, temperature or trauma) • Specific (i.e.: receptors cells in eye are protected by accessory structures and CT, usually only stimulus reaches these cells is light) © 2012 Pearson Education, Inc. Tonic vs. Phasic Receptors Tonic Phasic • Always active • Normally inactive • A.k.a slow-adapting receptors: little change in receptor activity over time • Provide info about intensity and rate of change of stimulus • Indicates background level of stimulation • A.k.a. fast-adapting receptors: respond strongly at first, activity declines © 2012 Pearson Education, Inc. • Receptor specificity: receptors sensitive to specific stimuli • Examples: • Touch receptors sensitive to pressure, not chemical stimuli • Taste receptors sensitive to chemicals, not pressure stimuli • Sensation: arriving information from receptors via AP • Perception: conscious awareness of sensation Receptive field 1 Receptive field: area monitored by single receptor Larger field=harder to localize stimulus © 2012 Pearson Education, Inc. Receptive field 2 Interpretation of Sensory Information • Sensory neurons relay info from receptor to specific cortex areas • Link between receptor and cortical neuron = labeled line • Axons of labeled line carry info about 1 type of stimulus (modality) • Sensory coding = translation of complex sensory info into meaningful patterns of AP • CNS interprets modality based on labeled line • Cannot tell difference between true/false sensation • i.e.: rub eyes = mechanical stimulus causes visual of flashes of lights; any activity along optic nerve travels to visual cortex = visual perception © 2012 Pearson Education, Inc. Nociceptors • Tonic • Locations: • superficial portions of skin • Joint capsules • Periosteum • Walls of BVs • Detects: pain • Myelinated Type A fibers: fast or prickling pain (i.e.: injection or deep cut) • Type C fibers: slow or burning/aching pain © 2012 Pearson Education, Inc. Thermoreceptors • Phasic • Free nerve endings in dermis, skeletal muscles, liver and hypothalamus • More cold than warm • Carried along same pathway as pain sensations • Info sent to • Thalamus • reticular formation of midbrain • Primary sensory cortex © 2012 Pearson Education, Inc. Mechanoreceptors • Stimulus caused by distortion of plasma membranes • Three classes: • Tactile (touch, pressure, vibration) • Baroreceptors (pressure changes in BVs) • Proprioceptors (position of joints/skeletal muscles) © 2012 Pearson Education, Inc. Types of Tactile Receptors •Phasic •Respond rapidly •Best at detecting initial contact and subsequent movement •Tonic; small receptive fields •Located between epidermal cells •Sensitive to touch/pressure © 2012 Pearson Education, Inc. •Tonic; small receptive fields •Extremely sensitive •Found in stratum basale Types of Tactile Receptors •Aka: Meissner’s •Phasic •Locations: eyelids, lips, fingertips, nipples, external genitalia •Fine touch/pressure or low frequency vibrations •Tonic •Located in dermis •pressure © 2012 Pearson Education, Inc. •Phasic •Deep pressure •Provides somatic and visceral sensory info Chemoreceptors • Only respond to water or lipid soluble substances dissolved in body fluids • Info sent to brain stem (i.e. respiratory and cardiovascular centers), not cortex • Located in: • carotid and aortic bodies • monitor pH, CO2 and O2 levels © 2012 Pearson Education, Inc.