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Chapter 8

Chapter 8: Organization of the Sensory Systems.docx

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Zachariah Campbell

Chapter 8 Organization of the Sensory System Sensory Receptors - Specialized cells that transduce, convert, sensory energy into neural activity - Receptors are Energy Filters o Sensory receptors designed to respond only to a narrow band of energy w/in each modality’s energy spectrum o Differences of sensory range for each species & individual - Receptors Transduce Energy o Vision: light energy  chemical energy  In photoreceptors of retina  Chemical energy  action potentials o Auditory: Air-pressure waves  # of forms of mechanical energy  Mechanical energy activates auditory receptors  action potentials o Somatosensory System: Mechanical energy activates mechanoreceptors (cells sensitive to touch/pain)  Somatosensory receptors  action potential o Taste & Olfaction: various chemical molecules carried by the air or contained in food fit themselves into receptors of various shapes to activate action potentials. o For pain sensation, tissue damage releases a chemical that acts like a neurotransmitter to activate pain fibers and thus produce action potentials. Chapter 8 - Receptive Fields Locate Sensory Events o Receptive Fields: Specific part of world to which it responds  Every receptor organ & cell has o Locate sensory events in space – receptive fields of adjacent sensory receptors may overlap – relatively different responses to events help in localizing sensations - Receptors Identify Change & Constancy o Sensory receptors differ in sensitivity, adapt slowly/rapidly or react to only specific type of energy o Rapidly Adapting Receptors: Detect whether something is there  Easy activation  Stop responding quickly  Ex. Rod sensitive to visible light of any wavelength, lower response thresholds o Slowly Adapting Receptors: Adapt more slowly to stimulation  Ex. Cones sensitive to color & position - Receptors Dinstinguish Self from Others Chapter 8 o Exteroceptive: Receptors that respond to external stimuli o Interoceptive: Receptors that respond to our own activity  Vestibular organs, muscles & joints  Help interpret meaning of external stimuli o Optic Flow: When we run, visual stimuli stream by us o Auditory Flow: When we move past sound source – there are changes in intensity of the sound that take place b/c of our changing locations - Receptor Density Determines Sensitivity o Two-Point Sensitivity: Ability to recognize presence of two pencil points close together o Fovea  Cones: Packed into fovea  Rods: Packed in peripheral Neural Relays - All receptors connected to cortex through sequence of 3 or 4 intervening neurons - Info can be modified at diff stages in relay, allow sensory system to mediate diff responses - Hierarchy of motor responses in brain - Relays Determine Hierarchy of Motor Responses o Some in spinal cord o Some in brain stem o Some in neocortex o Pain pathway (PAG) periaqueductal gray matter  Pain relays in neocortex localize pain, identify kind of pain, external cause, & potential remedies - Message Modification Takes Place at Relays Chapter 8 o Gating: Inhibition of sensory info can be produced by descending signals form cortex, through the periaqueductal gray matter to lower sensory relays  Brain can gate transmission of pain stimulus from SC to brain o Inhibition gates many sense when we are occupied - Relays Allow Sensory Interactions o McGurke Effect: If someone behind you is saying “ba” but another person in front of you is mouthing the word “da” – you hear articulated sound of “da” – this viewed lip movement modify the auditory perception Central Organization of Sensory Systems - Sensory Information is Coded o After transduction all sensory info encoded by AP that travel along peripheral-system nerves until they enter the brain or SC & tracts w/in CNS o Every bundle carries same kind of signal o Presence of a stimulu
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