Lecture 7 (Chapter 8) Pain Sensation PDF

PA I N OUTLINE 1. General principles of sensation and sensory systems 2. The sense of touch 3. The sense of pain GENERAL PRINCIPLES O F S E N S AT I O N A N D S E N S O RY S Y S T E M S  S E N S O RY RECEPTION Sensory receptors: specialized receptors that are sensiti...

PA I N OUTLINE 1. General principles of sensation and sensory systems 2. The sense of touch 3. The sense of pain GENERAL PRINCIPLES O F S E N S AT I O N A N D S E N S O RY S Y S T E M S  S E N S O RY RECEPTION Sensory receptors: specialized receptors that are sensitize to some form of energy Activated by an external stimulus Sensory receptors are responsible for converting that energy to the electrochemical language of neurons  C L A SS I F I C AT I O N O F S E N S O RY SYSTEMS Mechanical Visual Chemical Smell: odorous substances Touch: contact with body surface Seeing: visible radiant energy Taste: substances in contact with Pain: tissue damage tongue Hearing: sound vibrations Electrical Common chemical: CO2, pH, osmotic pressure Vestibular: head Electroreception: differences in Vomeronasal: pheromones movement/orientation density of electrical currents Joint: position Thermal Magnetic Muscle: tension Cold: decrease in skin temperature Magnetoreception: orientation to earth’s magnetic field Warmth: increase in skin temperature S E N S O RY S Y S T E M S H AV E R A N G E S O F RESPONSIVENESS D I F F E R E N T I AT I N G B E T W E E N STIMULI Labeled lines: particular neurons are labeled for distinctive sensory experiences We can discriminate between different sensations because they are communicated by different neurons SIGNAL TRANSDUCTION  STIMULUS CODING S T I M U LU S I N T E N S I T Y S T I M U L U S L O C AT I O N A more intense stimulus will Spatial properties of a stimulus are generate more action potentials represented by labeled lines that convey spatial information  A D A P TAT I O N : progressive loss of response when stimulus is maintained 1. Tonic receptors: display little or no adaptation 2. Phasic receptors: display adaptation  Sensory input can be suppressed by different means: Accessory structures can limit input: close your SUPPRESSION eyes! Top-down (hierarchical) neural control can filter or suppress input  LEVELS OF S E N S O RY PROCESSING RECEPTIVE FIELDS RECEPTIVE FIELDS TOUC  F I B E R S T H AT LINK RECEPTORS TO THE NERVOUS SYSTEM SIGNAL TRANSDUCTION Dorsal column system First order: synapse in ipsilateral dorsal column nuclei (gracile and cuneate) Second order: synapse in contralateral thalamus Third order: synapse in the contralateral somatosensory cortex PA I N COMPONENTS O F PA I N SIGNAL TRANSDUCTION TRP CHANNELS TRPV1: capsaicin receptor TRPM3: high temps TRPM8: cold temps PEOPLE WITHOUT PA I N Congenital analgesia: SNC9 loss-of-function mutation Na+V1.7  A N T E R O L AT E RAL SYSTEM: First order: synapse in the ipsilateral dorsal horn of the spinal cord Second order: synapse in the contralateral thalamus Third order: synapse in the contralateral somatosensory cortex  D E S C E N D I N G PA I N M O D U L AT I O N First order: synapse in the periaqueductal gray Second order: synapse in the raphe nucleus Serotonin release Third order: synapse in the spinal cord grey matter Opioid release  ITCH Itch fibers = also free nerve endings C-fibers Terminate in the pons Sensitive to: 1. Histamine 2. Chloroquine-like substance E M O T I O N A L PA I N A N D P H Y S I C A L PA I N PRACTICE QUESTIONS What is signal transduction? Discuss the different ways that information about a stimulus can be transduced? Describe how touch or pain stimuli are sensed and perceived by the brain? Include the neurons that transport this information from the receptor to the brain, and each place those neurons synapse. What does “labeled lines” mean? Why might our brains be organized in this way? Compare and contrast: Meissner corpuscles, Ruffini endings, Pacinian corpuscles, Merkel discs, free nerve endings