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Psychology Notes

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Western University
Psychology 2036A/B
Yves Bureau

Psychology NotesApril 3 The significance of pain Although not enjoyable the experience of pain serves important functions1 Produces withdrawal that prevents further injury 2 Serves as a basis of learning to avoid injurious objectssituations 3 Sets limits on activity and enforces inactivity andor rest Pain perception When contact with injurious stimuli occurs signals of tissue damage follow a particular route Nociceptors of the afferent sensory neurons of the PNS respond to the stimuli and they generate impulses that travel to the CNS Nociceptors are the afferent nerve endings that respond to pain stimuli Nociceptors exist as free nerve endings which means they are not encapsulated by any other tissue and they are freely exposed to the environment Nociceptors or fibre types AHas thinly myelinated axons that carry thermal or mechanical nociception and is associated with sharp or pricking pain They transmit impulses quickly 5 to 30 ms These fibres send messages through the thalamus and to the cerebral cortex CIs a polymodal nociceptor that can be activated by high intensity mechanical chemical and heat 45C It is slow conducting because it is not myelinated 05 to 2 ms and the pain is dull or aching These fibres send pain messages to the brain stem A and AAre fibres normally involved in proprioception Fibres that are encapsulated are not free to the environment but pressure can be put on them and this is responsible for proprioception When tissue is damaged there is release of a lot of chemicals Characteristics of sensory receptors in the skin Merkels disk receptor is stimulated by steady indentation to produce a pressure sensation and its adaptation is slow Meissners corpuscle receptor is stimulated by low frequency vibration to produce a gentle fluttering sensation and its adaptation is rapid Ruffinis corpuscle is stimulated by rapid indentation to produce a stretch sensation and its adaptation is slow Pacinian corpuscle is stimulated by vibration to produce a vibration sensation and its adaptation is rapid Hair receptor is stimulated by hair deflection to produce a brushing sensation and its adaptation is rapid or slow Theories of pain Gate control theoryStates that a neural mechanism in the dorsal horns of the spinal cord acts like a gate that can increase or decrease the flow of nerve impulses from peripheral fibres to the CNS thereby influencing the sensation of pain This theory states that this gatelike mechanism controls pain stimulation to the brain it is affected by nerve fibres activity and it is openedclosed through central control trigger activity in the spinal cord and brain The dorsal horn receives sensory information and the ventral horn sends out motor information A projection neuron carries pain to the brain C fibres activate it by inhibiting an inhibitory interneuron which is responsible for inhibiting the projection neuron This means that the projection neuron is activated which opens the gate and produces pain A and A fibres activate the inhibitory interneuron which means there is less activity of the projection neuron which means the gate is closed and there is less pain The gate theory says that pain sensations can be modified en route to the brain and they can be influenced by psychological factors The brain can control the amount of pain an individual experiences by transmitting messages down the spinal cord to block the transmission of pain signals The experience of pain is influenced by past experience attention and other cognitive activities through the central control trigger Involvement in other activities relaxation or positive experiences can lessen the pain experience by causing the gate to close Neuromatrix theoryThis is an extension of the gate control theory with a greater emphasis on the brains role in pain perception There is a neuromatrix or network of neurons that generates patterns called neurosignature patterns The origins of these patterns may be innate phantom limb pain or sensory and the patterns are responsible for producing a multidimensional experience of pain Pain perception is affected by sensory input activity of the nervous system and past experiences and expectations
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