Physio Pain & Inflammation (8)

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  1. Generator Region
    • tip of a sensory receptor (specifically one that detects pressure [mechanoreceptor], temperature, or pain)
    • deformation of this tip region gives rise to a series of action potentials in the sensory nerve fiber which then conducts these action potentials to the CNS
  2. Generator Potential
    • a local, graded depolarization caused by deformation of a sensory receptor (or, say, a large change in temperature)
    • the deformed portion of its cell membrane becomes more permeable to positive ions (eg. Na+), leading to greater increased permeability → action potential
  3. Transduction
    taking one type of energy & converting it into another kind of energy
  4. Impulse Initiation (Coding) Region
    part of a nerve adjacent to its generator region where if the generator potential is large enough, it turns into an action potential

    generator potential must reach a certain threshold for an action potential to be generated

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  5. Local Excitatory Currents
    • out-flowing current that causes the cell membrane to generate action potentials at a frequency related to the magnitude of the local current
    • the link between the generator potential in the receptor & the excitation of the sensory nerve membrane
  6. What does a greater stimulus intensity result in?
    • more FREQUENT (not more intense) action potentials
    • sensory impulses from the skin are FREQUENCY coded/modulated
    • our perception of how intense a stimulus is depends on a sensory nerves firing frequency
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  7. Adaptation
    • when the generator potential & consequently the action potential frequency decline even though the stimulus intensity on a receptor is maintained
    • as a receptor adapts sensory input to the CNS is reduced & the sensation is perceived
    • as less intense
  8. Slow Adaptation
    the generator potential decays slowly, leading to a reduction in action potential frequency even though the stimulus has remained the same
  9. Rapid Adaptation
    the generator potential decays rapidly, leading to a profound decease in action potential frequency even though the stimulus intensity & duration remain the same
  10. Tonic Responses
    • responses in which there is no adaptation
    • responses are identical & equally separated in time
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  11. Phasic Responses
    • responses in which (slow or fast) adaptation occurs 
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  12. Why is the phenomenon of adaptation important?
    it prevents “sensory overload” & allows less important or unchanging environmental stimuli to be ignored
  13. Accommodation
    • a slowing down of the rate of action potential production even though the generator potential may show no change
    • occurs in the impulse generation region of a sensory nerve fiber (where generator potential is converted to an AP)
    • is a gradual increase in threshold caused by multiple nerve depolarizations that causes Na+ channels to be inactivated
    • it results in a decrease in action potential frequency or loss of sensory nerve action potentials altogether
  14. Compression
    • the first stage of encoding in which sensory neurons modify the environmental stimulus intensity into a coded intensity that's a logarithmic function of the actual stimuli
    • nerves have a much smaller range of firing frequencies than there is a range for stimuli intensities
    • & inherent limitations: can only fire at a maximum frequency
    • a100 fold variation in stimulus intensity is compressed into a 3-4 fold range in coded intensity after a receptor has processed the stimulus
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  15. Types of Pain
    • 1. Somatic Pain
    • 2. Visceral Pain
  16. Somatic Pain
    • 1. Superficial: body surface, skin
    • 2. Deep: muscles, joints, bones, connective tissue
  17. Visceral Pain
    • strong contractions in visceral smooth muscle (comes from internal organs)
    • a forcible deformation of hollow organs
    • can come from inadequate O2 delivery - ischemia
    • eg. muscle contractions from eating something that doesn't agree; exertional angina (ischemia) results in pain
  18. afferent neurons (sensory)
    carry nerve impulses from sense organs toward the central nervous system
  19. efferent neurons (motor)
    carry nerve impulses away from the central nervous system to effectors such as muscles or glands
  20. Nociceptors (pain receptors)
    • primary afferent neurons that transmit pain
    • in skin they're free (naked) nerve endings of myelinated & unmyelinated neurons
    • carry information primarily on 2 types of fibers: Aδ & C
    • : large, myelinated, fast transmission
    • C: small, unmyelinated, slow transmission (are often involved in chronic pain)
  21. What types of nociceptors respond to what stimuli?
    • 1. mechanical: respond to strong applied
    • pressure & sharp objects
    • 2. thermal: signal either burning heat (>45°C) or
    • extreme cold
    • 3. chemical: respond to K+, pH (acids), neuroactive
    • substances, or irritants
    • 4. polymodal: respond to combinations of the
    • above stimuli
  22. Why do nociceptors NOT normally fire, meaning we are unaware of their existence?
    b/c they have a higher threshold than other types of receptors
  23. How can pain (especially in the skin) be characterized?
    it's often biphasic w/ a sharp & localized initial pain (carried by Aδ fibers) followed by a more diffuse, delayed, & longer-lasting pain (carried by the slower conducting C fibers)
  24. Hyperalgesia
    • increased sensitivity to pain stimuli in tissues that were previously damaged or are undergoing inflammation
    • caused by chemical substances released locally from damaged tissue, blood cells, or nerve endings (eg. prostaglandins, serotonin, substance P, K+, H+, kinins, histamines, & leukotrienes)
  25. What are the 5 cardinal symptoms of inflammation?
    • redness, heat, swelling, pain, loss of function
    • 1. Rubor: redness caused by vasodilation & increased blood flow
    • 2. Calor: as vessels dilate, more warm core blood from inside can move to the periphery → increased temperature at the site
    • 3. Tumor: swelling caused by increased vascular (BV) permeability at the site of inflammation
    • 4. Dolor: pain from substance P released at the injury site by nerve endings
    • 5. Functio laesa: loss of function
  26. What is secreted from noiceptive nerve endings in the presence of tissue damage/inflammatory mediators?
    • substance P - is perceived as pain
    • triggered specifically by histamine & other inflammatory mediators
    • it increases capillary permeability, further contributes to inflammation, & activates mast cells
  27. Cognitive Sensations of Pain
    • interpretation of pain signals is under powerful control of the CNS
    • nociceptors may fire rapidly w/out eliciting sensations of pain in some situations, while in others sensation of pain may be crippling but the nociceptors are almost totally quiet
  28. Gate Control Hypothesis
    • a theory about how pain can be mitigated & go practically unnoticed
    • an afferent fiber synapses with a projection neuron & when a stimulus occurs, a pain signal is generated
    • however also synapsing w/ projection neurons are inhibitory neurons, that can modulate what the projection neuron goes on to signal
    • inhibitory neurons can decrease outputs of a projection neuron if induced to do so
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  29. Referred Pain
    • pain that originates from a visceral site is sensed as coming from a superficial site distant from the site of origin
    • can be explained by spinal sensory connections & their patterns of embryonic development
    • lots of times superficial/skin afferent neurons synapse in the same ganglia as afferent neurons that come in from the viscera
  30. Guarding
    • a protective reflex which produces muscle rigidity (often important diagnostically) & tends to protect the affected body part
    • it may compress blood vessels causing ischemic muscle pain which adds to the original discomfort
Card Set:
Physio Pain & Inflammation (8)
2014-01-23 02:38:51
MBS Physiology
Exam 1
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