Neuro Chapt 14
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- Sensory/discriminative system
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Processes information about pain and causes withdrawal from stimulus.
Mediated through afferent nerve fibers, spinal cord, brain stem & higher pain centers. - Motivational/affective system
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determines conditioned or learned approach and avoidance behavoirs.
Mediated through the interaction of the reticular formation, limbic system and brain stem. - Cognitive/evaluative system
- Cultural influences may block, modulate or enhance the perception of pain.
- Somatogenic pain
- Physical cause
- Psychogenic pain
- No known physical cause, however not imaginary and just as distressing
- A protective mechanism that alerts the individual to a condition that is immediately harmful.
- Acute pain
- How is acute pain relieved?
- After chemical mediators that stimulate the nociceptors are removed.
- What are some characteristics of chronic pain?
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-Persistent
-continuous or intermittent
-may develop insidiously or suddenly
-lasting at least 6 months
-cause may not be known
-does not respond to usual therapy
-painful areas not easily differentiated
-complete relief is usually not possible - What are some characteristics of acute pain?
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-sudden
-painful areas differentiated
-Self-limited or readily corrected - A point at which a stimulus is perceived as pain.
- Pain Threshold
- A phenomenon in which intense pain in one area may increase the pain threshold in another area
- Perceptual dominance
- The duration of time or the intensity of pain an individual will indure before outwardly responding to it.
- Pain tolerance
- What factors decrease pain tolerance?
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-repeated exposure
-fatigue
-anger
-boredom
-apprehension
-sleep deprivation - What factors increase pain tolerence?
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-alcohol consumption
-medication
-hypnosis
-warmth
-distracting activities
-strong belief's or faith - What physiological signs would you assess in a infant who is in pain?
- -increased HR, BP, RR, decreased O2 sat, sweating, pallor or flushing.
- What other infant expressions would signal an experience of pain?
- Crying, lowered brows, vertical bulge and furrows in forehead, tighten closed eyes, chin quiver
- True or False.... Children usually have higher pain thresholds than adults.
- FALSE, they usually have lower thresholds. Children are also as adults are, highly individual in responses to pain.
- What changes in pain threshold and pain tolerance would you expect in the elderly?
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-Increased pain threshold: caused by neuropathies and changes in skin,
-Decrease in pain tolerance - What are nociceptors and what is the function?
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-They are pain receptors, part of the afferent pathway.
-carry signals to the spinal cord which transmits signal to brain. - What portions in the CNS are responsible for interpetation of pain?
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-Limbic System
-reticular tracts
-thalamus
-hypothalamus
-medulla
-cortex - What is the role of the limbic and reticular formation in interpretaion of pain?
- Alerting, arousal and motivational behaviors.
- What is the role of the medulla and hypothalamus in interpretation of pain?
- Activation of "fight or flight", the release of corticosteroids and cardiovascular responses.
- Nociceptors respond to...
- chemical, mechanical and thermal stimuli
- How do Unimodal nociceptor respond and where are they found?
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-respond to one type of sensory modality (Mechanosensitive)
-found in skin, mucous membranes and some walls lining cavities - How do Polymodal nociceptors respond and where are they found?
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-respond to more than one sensory modality (mechanosensitive, thermosensitive and chemosensitive)
-found in deep tissues and skin.
"Majority of nociceptors" - Are nociceptors evenly distributed in the body?
- No, Maldistribution affects the relative sensitivity to pain at different areas in the body.
- Polymodal nociceptor responsible to transmitting diffuse burning or aching sensations
- C-fibers
- Why is transmission though C-fibers relatively slow?
- Because they are small and unmyelinated
- Carries well-localized, sharp pain sensations.
- Larger myelinated A& fibers.
- Important in initiating rapid reactions to stimuli.
- A& fibers
- What and where does the Neospinothalamic Tract carry?
- Acute pain impulse to the brain
- What and where does the Paleospainothalmic tract carry?
- dull and burning pain impulse to the brain.
- What is the efferent pathway responsible for?
- inhibition of afferent pain signals.
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What is the periaqueductal?
(PAG) - Gray matter suffounding the cerebral aqueduct
- Explain the efferent pathway.
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-Efferent neurons located in the PAG form synapses with structures in the medulla the inhibit pain.
-from the medulla the impulse is transmitted through the spinal cord to the dorsal hour to impair or block transmission of nociceptive impulses. - Where do secondary neurons transmit information?
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-From the substantia getainosa and laminae to the ventral and lateral horn
-Crossing, in the same or adjacent spinal segments to the other side of the cord. - Specificity theory of pain
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Include 4 major cutaneous sensations:
touch, warmth, cold, and pain
-direct relationship between the stumulus and perception of pain.
-fails to accout for adaptation - Intensity theory of pain
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Pain results from excessive stimulation of sensory receptors or a pathologic condition that promotes summation of impulses by nonnoxious stimuli.
-does not account for intense stimulation at some sites that is not painful - Pattern theory of pain
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-perception of pain results from stimulus intensity.
-nonspecific receptors transmit patterns of nerve impulses from the skin to the spinal cord.
-does not account for adaptation. - Gate control theory of pain
- Cells in the substantia gelatinosa function as a gate, regulating transmission of impulses to the CNS
- Where are neuromodulators found?
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In pathways that mediate information about painful stimuli
-Periphery, ascending & descending spinal tract, the cortex & GI tract - What do the release of prostaglandins do to nociceptors?
- Cause depolariziation of adgacent nociceptors.
- What contributes to pain inhibition in the medulla and pons.
- Norepinephrine and 5-hydroxytryptamine
- What contributes to inhibition of pain in both the afferent and efferent fibers of the spinal cord?
- Substance P and other neurotransmitters.
- They inhibit transmission of pain impulses in the spinal cord to the brain.
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Endorphins (endogenous morphines)
-Beta-Lipotropin (beta, alpha and gamma)
-Enkephalin
-Dynorphin - Located in hypothalamus and responsible for general sensations and well-being.
- Beta-Lipotropin
- Found in neurons of the spinal cord, it is a weaker analgesic that the others, but more potent and longer lasting than morphine.
- Enkephalin
- A powerful endorphin, originates in the neual lobe of the pituitary.
- Dynorphin. 50 times more powerful than beta-Lipotropin
- Where do all endorphins act?
- They act by attaching to opiate receptors on the plasma membrane of the afferent neuron, inhibiting the release of excitatory neurotransmitters.
- What factors increase levels of circulating endorphin and other neurotransmitters?
- Stress, exessive physical exertion, acupuncture, & intercourse.
- What does an increase of endorphins do to the pain threshold?
- Raises the pain threshold.
- List 3 classifications of Acute pain
- Somatic, Visceral and Referred pain
- List some charateristics of somatic pain
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-Superficial (from skin or closed surface)
-sharp and well localized OR
-dull, aching and poorly localized
-Accompanied with Nausea and Vomiting - Define Visceral pain
- Pain in internal organs, the abdomen, or the skeleton
- List some characteristics of viceral pain
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-poorly localized (due to lesser # of mechanoreceptors)
-associated with N & V, hypotension, restlessness and in some cases shock
-often radiates - Define Referred pain
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-pain is present in an area removed or distant from it's point of origin.
-Area of referred pain is supplied be the same spinal segment as the actual pain - List some physiologic Responses to pain
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-Increased HR, RR, BP
-Pallor or flushing
-Diaphoresis
-Dilated pupils
-Elevated blood sugar
-decreased gastric secretion and motility
-Decreased blood flow to viscera & skin
-Occasional nausea - Which type of pain is more difficult to control? Chronic or Acute
- Chronic
- What 4 changes in the nerve terminals, afferent fibers and CNS may contribe to chronic pain?
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-changes in sensitivity of neurons (lower threshold)
-spontaneous impulses from regenerating peripheral nerves
-reoragnization of nociceptive neuron after peripheral nerve injury
-Loss of pain inhibition in the spinal cord. - Increase in the exitability of medullary and spinal neurons arising from persistent stimulation from injured peripheral nerves.
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-Central Sensitiation
-Cause spinal cord neuron to be more sesitive to all of its inputs. - Pain caused be a lesion or dysfunction in the CNS (brain or spinal cord)
- Central pain
- What are some cause of central pain?
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-infarction
-hemorrhage
-abscess
-degeneration
-tumors
-tramatic injury - Name 2 characteristic of central pain.
- Irritating and constant (causes considerable suffering)
- Result of trama or disease of the peripheral nerves.
- Neuropathic pain
- What is the pathophysiologic process of neuropathic pain?
- Injured nerves become hyperexcitable and generate ectorpic discharges with spontaneous firing of some neurons with low thresholds for mechanical, chemical or thermal stimuli
- What are some physiologic responses to chronic pain?
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-If intermittent, then the same respones as acute
-If persisant, physiologic adaptation, normal vital signs even though pain is not relieved. - The most chronic pain condition is?
- Low back pain
- A painful condition from an infection or disease that damages a peripheral nerve
- Neuralgias
- A 2 types of neuralgias that caused severe burning pain that is triggered by normally nonnoxious stimuli
- Causalgia and Reflex sympathetic dystrophies
- How does causalgia present?
- -severe, diffuse and persisent pain occurs in the extremity supplied by the injured nerve
- Reflex sympathetic dystrophies are associated with?
- Vasospasm and vasomotor changes. If muscle wasting occurs amputation my be needed.
- A condition where pain is cause by stimuli that normally does not cause pain
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Hyperesthesias
-increased sensitivity and decreased pain threshold - What causes myofascial pain syndromes?
- myositis, fivrositis, myofibrositis, myalgia and muscle strain.
- What is myofascial pain the result of?
- Muscle spasm, tenderness, & stiffness
- What is hemiagnosia?
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-Inability to identify source of pain on one side (affected side)
-painful stimuli produes discomfort, anxiety and distress but no attempt to withdraw from.
-associated with stroke pt. - Pain that a person feels in an amputated limb after the stump is completely healed.
- Phantom limb pain
- Small hypersensitive regions in muscle or connective tissue that when stimulated cause pain in specific area
- Trigger points
- 3 major catagories of pain syndromes that result in chronic pain in cancer patients.
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-pain from advancing disease
-pain associated with treatment
-pain from coexisting unrelated disease - Deafferentation pain is...
- a loss of sensory input from a portion of the body.
- Describe deafferentation pain
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-constant, dull, viselike ache with paroxysms of burning or electric shock-like sensations.
-poorly controlled by peripheral & epidural analgesia - Is chronic postoperative pain is possible surgical interventions for cancer?
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Yes. Small percentage with
Thoracotomy
radical mastectomy
radical neck dissection
surgical amputation