Chapter 15 Neural Integration I: Sensory Pathways and the Somatic Nervous System

1. Chapter 15 Neural Integration I: Sensory Pathways and the Somatic Nervous System

2. 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

3. Simple vs. Complex Receptors Simple receptors • dendrites of sensory neurons • Branching tips of dendrites = free nerve endings • Not protected by accessory structures • Little specificity (i.e.: free nerve endings respond to stimulus caused by chemicals, pressure, temperature or trauma) Complex receptors • Found in sense organs • Example: eye’s visual receptors • Protected by accessory cells and CT • Specific (i.e.: receptors cells in eye are protected by accessory structures and CT, usually only stimulus reaches these cells is light)

4. Tonic vs. Phasic Receptors Tonic • Always active • A.k.aslow-adapting receptors: little change in receptor activity over time • Indicates background level of stimulation Phasic • Normally inactive • Provide info about intensity and rate of change of stimulus • A.k.a. fast-adapting receptors: respond strongly at first, activity declines

5. 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 Receptivefield 1 Receptivefield 2 Receptive field: area monitored by single receptor Larger field=harder to localize stimulus

6. 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

7. 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

8. 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

9. 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)

10. Types of Tactile Receptors • Phasic • Respond rapidly • Best at detecting initial contact and subsequent movement • Tonic; small receptive fields • Extremely sensitive • Found in stratum basale • Tonic; small receptive fields • Located between epidermal cells • Sensitive to touch/pressure

11. Types of Tactile Receptors • Phasic • Deep pressure • Provides somatic and visceral sensory info • Aka: Meissner’s • Phasic • Locations: eyelids, lips, fingertips, nipples, external genitalia • Fine touch/pressure or low frequency vibrations • Tonic • Located in dermis • pressure

12. 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