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Pain - Coggle Diagram

- - - - hypothesis to explain these phenomena: gate theory of pain
        
        suggests that certain neurons of the dorsal horns, which project an axon up the spinothalamic tract, are:
        
        excited by both large-diameter sensory axons and unmyelinated pain axons
        
        and inhibited by an interneuron
        
        which is excited by the large sensory axon and inhibited by the pain axon
        
        pain axon alone maximally excites the projection neuron
        
        However, if the large mechanoreceptive axon fires concurrently, it activates the interneuron and suppresses nociceptive signals.
  - - - One is a zone of neurons in the midbrain called the periventricular and periaqueductal gray matter (PAG).
        
        Electrical stimulation of the PAG can cause a profound analgesia that has sometimes been exploited clinically.
        
        normally receives input from several brain structures, many of them appropriate for transmitting signals related to emotional status.
        
        send descending axons into various midline regions of the medulla, particularly to the raphe nuclei (which use the neurotransmitter serotonin).
        
        These medullary neurons in turn project axons down to the dorsal horns of the spinal cord
        
        they can effectively depress the activity of nociceptive neurons.
  - - - At the cellular level, exert multiple effects
        
        suppressing the release of glutamate from presynaptic terminals
        
        inhibiting neurons by hyperpolarizing their postsynaptic membranes
    - - effect prevened by specific blocker of opioid receptors, naloxone
- - - - strong mechanical stimulation, extremes in temperature, oxygen deprivation, and exposure to certain chemicals, etc.
        
        Hyperalgesia
        
        sensitivity of tissue that has already been damaged or inflamed
        
        can be primary or secondary
        
        inflammatory chemicals modulate the excitability of nociceptors
        
        e.g.
        
        1 more item...
  - - - majority: polymodal nociceptors
        
        respond to mechanical, thermal, and chemical stimuli
        
        but also many show selectivity in their responses
        
        mechanical nociceptors, showing selective responses to strong pressure
        
        thermal nociceptors, showing selective responses to burning heat or extreme cold
        
        chemical nociceptors, showing selective responses to histamine and other chemicals.
      - bring information to the CNS at different rates
        
        fast, sharp, first pain
        
        caused by the activation of Aδ fibers
        
        duller, longer lasting second pain
        
        caused by the activation of C fibers
- - - - branch immediately, travel a short distance up and down the spinal cord in a region called the zone of Lissauer
        
        then synapse on cells in the outer part of the dorsal horn in a region known as the substantia gelatinosa
      - nociceptor axons from the viscera enter the spinal cord by the same route as the cutaneous nociceptors
        
        Within the spinal cord, there is substantial mixing of information from these two sources of input
        
        referred pain
  - - - axons of the second-order neurons immediately decussate and ascend through the spinothalamic tract along the ventral surface of the spinal cord
        
        spinothalamic fibers project up the spinal cord and through the medulla, pons, and midbrain without synapsing, until they reach the thalamus
        
        some come to lie alongside the medial lemniscus in the VP nucleus, but the two groups of axons remain distinct from each other.
        
        Other spinothalamic axons end in the small intralaminar nuclei of the thalamus
    - - from the face and head
        
        small-diameter fibers in the trigeminal nerve synapse on second-order sensory neurons
        
        in the spinal trigeminal nucleus of the brain stem
        
        axons of these cells cross and ascend to the thalamus in the trigeminal lemniscus.