Touch and Pain Somatosensation Touch o Touch receptors may be Simple bare neuron pain receptors Modified dendrite Merkel Disks Elaborated nerve ending Ruffini and Meissners o Stimulation opens sodium channels to trigger an action potential o Distortion due to size and density of Receptive fields Sensors o Mechanoreceptors activated by physical force Stretching of skin opens channels to activate them When activated they send AP s up the axon toward spinal cord o Sensory neuron body is located in the DRG o Afferent fibers go toward the CNS o Shallow layers Meissner s corpuscle and Merkel disks Fine detail movement exploring a objects shape o Deep layers Pacinian corpuscle detects high frequency vibrations and Ruffini endings Stretch perception of the shape of a grasped object Receptive Fields o Receptive fields a group of sensory neurons that converge on the same neuron in the spinal cord o The more closely packed the more sensitive the area is to touch Women have better detail touch than men o Merkel disks receptors that respond to light touch gentle stroking o Men and women have same amount of Merkel disks but women have smaller fingers causing Merkel disks compacted in a smaller area Touch receptors to brain o Info from touch receptors in the head enters the CNS through cranial nerves o Info from receptors below the head enters the spinal cord and travels through the 31 spinal nerves o Each spinal nerve has a sensory and motor component and connects to an area of the body Dermatomes o Dermatome skin area connected to a single sensory spinal nerve they overlap o Sensory info travel in distinct pathways Ex Touch pathway is distinct from pain pathways Somatosensory Cortex o Various areas of the somatosensory thalamus send impulses to different areas of the somatosensory cortex located in the parietal lobe o Damage to the somatosensory cortex can result in the impairment of o Rats investigate with their nose and mouth more than anything else o Each whisker has a large field cortical representation called Whisker body perceptions Whiskers rats Barrels Pain o Pain sensation begins with bare nerve endings receptors o Capsaicin chemical found in hot pepper stimulates pain receptors o Axons carrying pain info have little or no myelin impulses travel slowly But the brain processes pain info rapidly o Mild pain triggers release of glutamate in the spinal cord o Strong pain triggers release of glutamate and Substance P Substance P results in increased intensity of pain Pain receptors o Mechanical pinching and cutting o Thermal hot and cold o Polymodal all mechanical and thermal plus chemicals release when o Basis of inflammation nociceptors respond AND release chemical injured stimuli Pain and touch are not the same o From medulla to cerebral cortex touch and pain represented on contralateral side o Spinal cord for touch travels Ipsilateral side o Spinal cord for pain travels on contralateral side o Pain sensitive cells in spinal cord relay info to several areas of the Pain Pathways brain Pain control Somatosensory cortex responds to painful stimuli memories of pain and pain warning signals Central nuclei of the thalamus amygdala hippocampus prefrontal cortex and cingulate cortex are associated with emotional associations o Opioid mechanisms are sensitive to Opioid drugs o Activating opiate receptors blocks the release of substance P in the spinal cord and in the periaqueductal gray area of the midbrain Opiates bind to receptors in periaqueductal gray area o Capsaicin dumps substance P which can damage the actual pan receptor Releases substance p faster than neurons resynthesiszing it leaving the cells less able to send pain messages o Canabanoids also block certain kinds of pain Mainly in periphery of body Gate Theory o Spinal cord areas that receive messages from pain also receive input from touch receptors and axons descending from the brain These other areas that provide input can close the gates and decrease pain perception Non pain stimuli around it can modify intensity of the pain When you have an injury you decrease pain by rubbing skin o Pain signals reach conscious awareness in the thalamus and cortex o Descending pathways can keep the CNS from receiving pain signals they close gate to pain o The CNS activates neurons that release endorphins This blocks release of Substance P Keeps pain signals from getting in o Descending brainstem fiber excitatory opiate neuron inhibitory nociceptors excitatory Placebo o Placebo drug or other procedure with no pharmacological effect o Decreases pain perception by decreasing the brains emotional response to pain perception not the sensation itself o Decreases response in cingulate cortex but no in somatosensory cortex Pain sensitivity o Mechanisms of the body to increase sensitivity to pain include Damaged tissue releases histamine nerve growth factor and other chemicals that incase the responses of pain receptors Non steroidal anti inflammatory drugs ibuprofen decrease chemicals that pester pain receptors o Certain receptors become potentiated after an intense barrage of painful stimuli leading to increased stimuli Chronic pain Emotional pain o Resembles physical pain Increased activity in cingulate cortex when someone felt left out People taking acetaminophen reported less incidences of hurt feelings social pain Itch o Itch is not pain o The release of histamines by the skin producing itching sensations Activates distinct pathway in spinal cord to the brain Impulses travel slowly o Pain and itch have an inhibitory relationship Opiates increase itch while antihistamines decrease itch o Poorly understood maybe social communication o The Laughing is not normal laughter in that it doesn t predict laughter Tickling Temperature and Thirst Temperature regulation is one of the body s biological priorities o Uses two thirds of our energy o Basal metabolism energy used to maintain a constant body temperature while at rest o Homeostasis refers to temperature regulation and other biological processes that keep certain body variables within a fixed range o Temperature regulation is vital to normal functioning Affects behavior Set Point o Set point refers to a single value that they body works to maintain Ex levels of water oxygen glucose calcium protein fat o Negative feedback processes that reduce discrepancies from the set point behavior proceeds until relieves disturbance o Allostasis the adaptive way in which the body changes its set point in response
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