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ch 11 definitions

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Simon Fraser University
PSYC 365
David Cox

Chapter 11: Pain Afferent (sensory) - Nerve cells that conduct impulses form a sense organ to central nervous site, or from lower to higher level sin spinal cord and brain neurons Nociceptors - Afferent nerve endings that respond to pain stimuli A-delta fibres - Afferent peripheral fibres thats associated with transmitting sharp, distinct pain - Small myelinated fibres that transmit impulses very quickly C-fibres - Afferent peripheral fibres thats associated with transmitting diffuse, dull or aching pain - Transmit impulses slowly because not myelinated - Mostly determine motivational and affective elements of pain, which send pain messages to brain stem and lower portions of forebrain - Comprise 60% of all sensory afferents, involved when pain is diffuse, dull or aching Substantia gelatinosa - First two layers where sensory input is thought to be modulated - Sensory aspects of pain strongly influenced by activity in A-delta fibres which send messages through thalamus on their way to cerebral cortex Gate control theory - Suggests neural mechanism in dorsal horns of spinal cord acts like a gate that can increase or decrease flow of nerve impulses from peripheral fibres to central nervous system thereby influencing sensation of pain - Pain not sensation thats transmitted directly from peripheral nerve endings to brain, rather sensations are modified as they are conducted to brain by way of spinal cord, also influenced by downward pathways from brain that interpret experience - Gate-like mechanism that is able to control flow of pain stimulation to brain - Information enters dorsal horns by way of primary afferent neurons; information passes through substantia gelatinosa, where information is modulated by stimulation from periphery as well as by feedback from fibres descending from brain affects activity of transmission cells causing them to either conduct (excitatory influence) or not (inhibitory influence) pain sensations to brain - Small A and C fibres open gate, large A-beta fibres tend to close gate - Gate may be closed by activity in spinal cord and by messages descending from brain Central control trigger - In gate control theory of pain, specialized system of large-diameter, rapidly conducting fibres that activate selective cognitive processes that then influence, by way of descending fibres, the opening and closing of gate - Experience of pain is influenced by past experience, attention, and other cognitive activities through the central control trigger - Affective reactions (ex. Anxiety, focus, fear) can exacerbate experience by affective central control and opening gate - Intense involvement in relaxation, positive experiences can mute pain experience and cause gate to close Phantom limb pain - Experience of pain in an absent body part - Common to those who have undergone amputation, limb very vivid to amputee, can tell you precise position of phantom, - Phantom limb behaves very much like normal limb, moves in perfect coordination with other limbs, can experience many sensations ; 80%feel Neuromatrix theory - Extension to gate control theory, which greater emphasis placed on brains role in pain perception; genetically determined neuromatrix or network of brain neurons distributed throughout many areas of brain, widespread network of neurons that generates patterns, processes information that flows through it and produces pattern felt as a whole body Neurosignature patterns - Neuromatrix-generated patterns - Patterns may be generated from sensory input, or innately produced (phantom limb) - Responsible for producing a multidimensional experience of pain Periaqueductal grey area - Area of the midbrain thats involved in pain reception Acute pain -
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