Lecture 4: Spinothalmic System (Anteriolateral System) Flashcards
Describe the fiber type alpha delta and type of sensation it carries.
small myelinated fiber with moderate conduction speed carrying cooling, 1st pain and crude touch sensations
Describe the fiber type C fibers and the type of sensation it carries
very small unmyelinated fibers that convey warming and second pain sensation.
Describe the sensory receptors associated with the anteriolateral system.
no specialized receptor organs, just free endings that contain a variety of receptors that are uniquely sensitive to substances, action that damage tissue and temperature.
Name 5 different receptors related to free endings of the anteriolateral system.
high threshold mechanoreceptors (pinching, cutting, stretching); thermal nociceptors (responsive to extreme temps); chemical nociceptors (responsive to chemicals given off by damaged tissue); any combination of the above 3 and “silent receptors that become awakened after tissue inflammation or injury (amplify pain response)
What causes a receptor to be sensitive to certain stimuli versus others?
there a variety of receptors that are sensitive to various “painful” things; depending on the channels a free nerve ending has, determines what stimulus it will respond to
Name the general name for channels located on free fibers that sense pain.
TRP receptor/ channel; temperature sensitive channels have a temperature range
True or false, a given free nerve ending has only one type of TRP channel.
False, some fibers may have mixes of TRP channels i.e. cold/cold fibers may also respond to very hot stimuli
Pain and temperature are carried by what two types of fibers?
C (70%) and delta fibers (30%)
What is the path of pain/temp fibers before they synapse
branches of pain and temp fibers enter and then ascend/descend 2 levels then synapse
Where do pain and temp fibers tracts cross the midline.
fibers cross the midline after synapsing ipsilaterally via the anterior white commissure
Cutting the Anteriolateral System (spinothalamic system) will produce what deficiencies?
Loss of all CONTRA pain and temp sensation two levels below and down
How are ALS fibers organized as they ascend and what type of cell axon is included in these tracts?
the axons are of the second cell in the chain and as the tract ascend, fibers are pushed more laterally (inferior fibers are most lateral
How are C and delta fibers arranged as the ALS tract ascends?
delta information runs contra laterally and runs in the lateral portion of the tract, C fibers run contralaterally and run in the anterior part of the ALS (some C fiber information stays ipsilateral)
What types of fibers are the exception to the ALS organization?
some visceral pain fibers don’t run in ALS and run instead in the Fasiciulus gracilis (cell bodies lie close the central canal)
Describe referred pain
visceral pain fibers may converge on the same dorsal horn cells getting pain info fro skin, because we rarely get pain from organs, the brain perceives that organ pain is coming form the skin
How does rubbing an injured spot chain the pain sensation.
by rubbing and activating AB fibers, you activate inteneurons that turn of the pain pathway
How do C fibers interact with interneurons normally to increase pain?
C fibers activate spinothalmic cells and indirectly inhibit interneurons (normally active) to increase pain
Why do we scratch an itch?
the sensation of itch activates spinothalamic c fiber nerves but not potential; scratching activates C pain fibers on the same interneurons to bring them to threshold. this signaling will inhibit the sponthalamic cells (itching brings interneurons to threshold and turns off itch pathway
Define hyperalgesia
increased sensitivity to pain
Define allodynia
pain due to stimuli that does usually cause pain
What is the root cause that can bring about hyperalgesia and allodynia?
an injury can shift the pain threshold causing allodynia and hyperalgesia
Name 5 mechanisms or hyperalgesia and allodynia.
1) substances released by damaged tissue alters the way the receptors respond (threshold, intensity) which may be permanent 2) injury could lead to accumulation of sodium channels leading to ectopic discharge 3) injury can up regulate receptors 4) excitatory neurons can become hyper excitable 5) interneurons that normally inhibit pain can change/die 6) loss of innervation of pain cells can cause non-pain fibers to sprout
What are the two pathways that tracts that ascend to the brain carrying pain fibers.
neospinothalamic pathway and the pale/archi spinothalmic pathway
Describe the neospinothalamic pathway
mostly delta fibers (first pain and small receptive field) it carries information from the contralateral side to the the VPL nucleus up tot eh somatosensory cortex
Describe the palow/archispinothalamic pathway
(emotional/ autonomic) mostly C fibers that carry information bilaterally to the brain to the thalamus and brainstem with output to the anterior cingulate and insular cortex
How are the paelo and neo pathways related?
they process the information via different systems and can work independently after receiving information from the spinal cord
How does emotion affect pain?
Pain can be modulated by strong emotion or by blocking opioid receptors (stops the placebo affect)
Where are descending pain modulated?
in the periaquadutal grey (midbrain) receives input from higher brain centers (amaygdala, hypothalamus, anterior cingulate cortex)
Where do descending pain modulation
dorsolateral funciculus
How are opioids related to pain relief?
the body has endogenous opiates that are produced by modulating interneurons that have been found to inhibit transmitter release by pain fibers
What are other ways of modulating pain via neurotransmitters?
there are a variety of receptors pre and post synaptic that modulate the signal based on the neurotransmitters from descending pathways (can amplify or reduce the descending signal)
What is the zone of Lissauer?
???? c and delta fibers that lie in contralateral DRG of the cervical region
