Sensory and Perceptual Processes

• Overview of Sensory Processes
• Chemical Senses
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• Pain
• The Great Canadian Theory: Melzack & Wall's Gate Control Theory of Pain
• Hearing
• Psychophysics
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Components of Sensation/Perception

• External stimulus
• Receptors
• Transduction of the physical stimulus into neural activity
• Sensory neurons
• Transmit the information to the CNS
• CNS
• Reception and processing of the information

Components of pain

• Physical sensation
• skeletal NS, CNS (brainstem,thalamus, cortex)
• Physical reaction
• CNS (cortex, basal ganglia, cerebellum, brain stem), skeletal NS, ANS (particularly sympathetic)
• Cognition
• CNS (cortex, hippocampus)
• Affect
• limbic system, cortex, brain stem

Physical Sensation of Pain

• Receptors = Nociceptors 
• C and Adelta fibers
• Sensory neurons
• Spinothalamic neurons
• CNS processing
• Thalamic projections to somatosensory area
• Perceptual component
• Thalamic projections to limbic system & premotor cortex
• Affective component
• Thalamic projections to prefrontal cortex
• Cognitive component

Physical Reaction to Pain

• Spinal interneurons
• Connect afferent (sensory) with efferent (motor) systems - Pain reflex
• Spinal inhibitory interneurons and Midbrain (periaqueductal gray) downward projections
• Gate control
• Thalamic projections
• to basal ganglia and cerebellum
• Prefrontal and premotor effects

Modern Gate Control Theory

Measuring Pain

• Perception scales:
• Verbal 
• Numerical
• Visual
• McGill Pain Questionnaire
• Sensory
• Affective
• Evaluative

A Complete Assessment

• Sensory
• Physiological
• Behavioural
• Affective
• Cognitive
• Sociocultural

Killing Pain 

• Drugs
• Opiates: Opiate receptors in thalamus and PAG
• Antidepressants: Increase serotonin
• Accupuncture/Accupressure/Electrical Stimulation
• Stimulate large A fibers and "close the gate"
• Release endorphins (endogenous opiates)
• Surgery
• Cordotomy
• Cognitive and affective modulation of pain