IPS Week 3 Summary PDF

3.1 unpacking transmission 5 steps of nociception 1. transduction 2. conduction 3. transmission 4. modulation 5. transmission definition transmission is the process of neural activation and an impulse or action potential that is generated. this stage begins at the synapse bw 1st (via Lissauer’s trac...

3.1 unpacking transmission 5 steps of nociception 1. transduction 2. conduction 3. transmission 4. modulation 5. transmission definition transmission is the process of neural activation and an impulse or action potential that is generated. this stage begins at the synapse bw 1st (via Lissauer’s tract) and 2nd order neurons at dorsal horn of sc and ends in brain perception follows AP s that ascend 2nd-order afferent pathways like the spinothalamic tract and carries information on pain, temp, and crude touch to terminal synapses in the brain, such as the thalamus. doesn’t end in thalamus continues via 3rd and 4th order neurons to other structures in the brain dorsal horn contains a network of interneurons & 2nd order neurons that are architecturally classified by REXED LAMINAE rexed laminae gray matter laminae that are associated w prim neuron types: A beta, A delta and C fibers interneurons are nerves that allow for communication bw sensory or motor nerves and the CNS neurons can also modulate sensory input- either facilitate or inhibit nocicepetion at the PNS or CNS 2nd order neurons project input into thalamus interneurons have a role sensory modulation & in descending inhibition rexed laminae part of post gray column or dh of sc fxnally: mediate synapses bw 1st order neurons (w interneurons) and 2nd order neurons (structures work as a intermediary processing center for sensory info) 1. lamina 1: 2nd order neurons on interneurons: marginal zone; synapse w A delta and C fibers- mediate info of pain, crude touch and temp 2. lamina 2: aka substantia gelatinosa- synapses w c fibersmediates sensory info on slow noxious stimulu from mechanical, thermal and chemical recpetors (perceived as secondary pain) 3. lamina 3: 4. lamina 4: receives presynaptic terminals from A beta neurons 5. lamina 5: receives presynaptic terminals from A delta 6. laminae 6: has presynaptic terminals from A alpha neurons neurons lamina 1 & 2: heavily involved in mediation of info associated w nociception lamina 3 & 4 form the nucleus proprioception lamina 5 and 6: form base of post gray column 2nd order neuron activation 2nd order neuron synapse on 3rd order neurons, then 3rd onto 4th neurons. these neurons are found in the sc and brain 2nd order neurons associated w nociception are nerves that direct info (noxious stimulus), from 1st order neurons in the DH , along the sc as part of the spinothalamic tract, up thru the brainstem and into the thalamus 2nd-order neurons follow pathways that project info on somatic nociception, both superficial and deep, both immediate and local info to visceral nociception, slow and nonspecific info from the viscera AND mediate emotional and autonomic responses to nocicepetion “SAVE” 3rd and 4th-order neurons then project nociceptive info from presynaptic terminals w 2nd order neurons to other structures w/in brain ex: primary somatosensory cortex this will then predicate the modulation of nociception & experience of pain. pre-synaptic terminal physiology once an AP reaches the pre-synaptic jxn bw 1st order and 2nd order and interneurons, the 1st order neurons release additional substances or neuropeptides that activate the synapses of either interneurons or 2nd-order neurons. primary neuropeptides released by A-delta 1st order neurons is glutamate, while the primary neuropeptide released by first-order C fibers at the synapse jxn is substance P anatomically occurs in rexed laminae most involved are rexed laminae 1 & 2 type of neurons that synapse on lamina I are stimulus specific: mechan chem, or temp, and can be mediated by A delta or C fibers. vs neurons that synapse on lamina II considered to be multireceptive or polymodal, and are mediated primarily by C fibers. once a nociceptive AP is generated at 2nd-order neuron, it will be transmitted to the brain via ascending afferent pathways like the spinothalamic tract (ST) From the ST to other structures of the brain via 3rd and 4th order neurons as part of transmission. summary 3.2 Transmission Systems & Pathways Introduction - Anterolateral System - Signals nociception thermal sensation & non-discriminatory touch - Spinothalamic tract is 1 part of this system - Other tracts are the spinoreticular & spinomesencephalic tract - Spinothalamic Tracts - A complex arrangement of ascending 2nd order neurons within anterolateral system - Carries both noxious & non-noxious info from A beta, A delta, C-Fibers from periphery to thalamus - Pathways - Anterior Pathway - Lateral Pathway - Neospinothalamic - Youngest in terms of biological evolution - Paleospinothalamic - In b/w Neo- & Archi- Archispinothalamic tract - Tract is older - Prior to medulla, many 2nd order neurons travel independently of spinal column - All carry information that terminate in thalamus Important Note - Spinoreticular & Spinomesencephalic tracts travel parallel to spinothalamic - Not traditionally considered to be a part of spinothalamic tract Take Aways - Anterolateral system is umbrella architectural categorization of sensory pathways that ascend sc to brain - Spinothalamic tracts made of 3 phylogenetically unique ascending 2nd order neurons - Neo, Paleo, Archispinothalanmic Tracts - Anterolateral system has established pathways through sc to brain 3.4 brain projections medulla and pons projections from the medulla and pons to the reticular formation 1. neospinothalamic (A delta)- few projections in medulla and pons 2. paleospinothalamic (C fibers) 3. archispinothalamic (C fibers) these two more in pons and medulla anatomically rf extends entire length of the brainstem (hind & midbrain) info delivered to the rf originates from C-fibers via branches of the paleo and archi tracts -neo: quicker fibers w heavier myelination -responsible for providing us our immediate experience of pain rf is our primary center for regulation of sensory arousal, and levels of consciousness such as being asleep or being awake direct output of stimulus sent to RF therefore, projections are responsible for alertness to pain info from RF sent to parafascicular, the central medial thalamus, the hypothalamus, the limbic system, as well as the primary somatosensory cortex ultimately reproduce out autonomic visceral and emotional response to pain c fibers: carry nociceptive info response for visceral pain periaqueductal gray PAG and tectum via spinoreticular tract & tectum via hind and mid brain spinomesencephalic and/or spinotectal tract (interchangeable) projections from mid-brain to PAG and tectum 1. neospinothalamic 2. paleo (c fibers) 3. archi (c fibers) primary contributors of projections to PAG and tectum tectum is main mediator for how we reactively behave to nociception PAG: alter sensory input before it’s experienced & mediate sympathies responses to sensation projections responsible for inhibition, facilitation of input and autonomic responses to nociception PAG and tectum have diffuse 3rd order synaptic connections include: modularity rf, parafascicular, centromedian thalamus, hypothalamus, limbic system and primary somatosensory cortex - will mediate additional inputs outside of just our autonomic response to nociception - will include emotional and visceral response thalamus and primary somatosensory cortex projections from 1. neo (a delta)- primarily come from thalamus and PSC 2. paleo (c fibers) 3. archi ( c fibers) 95% of fibers being delivered to thalamus from ST come from neo and ant pathways v small contributions of archi and paleo tracts terminate at VPI and even more at VPL of thalamus VPI= ventral post inf aspect of thalamus VPL= ventral pst lat aspect of thalamus nociceptive and discriminatory info from the neo tract coming from A-delta and C-fibers are then sent to the sensory cortex via 3rd order neurons and the same can be said for the paleo and archi tract. - info sent to somatosensory cortex via 3rd order neurons summary 3.5 Visceral Nociception Visceral Nociception - slow & non specific pain 1. 2. afferent sensory n from viscera broadly distributed across DRG & spine overlapping/bilateral distribution of afferent n (not segmentally oriented) - unlike acute somatic noxious stim & neurons (segmental) 3. decreased ratio of afferent fibers to cell bodies - less info but more interpretation cross talk b/w visceral & somatic neurons! -ascending info goes through paleo & archispinothalmaic tracts referred pain - MSK urinary tract hyperpathia nociplastic pain: central sensitization chronic manifestation of pain female reproductive organs biliary tract liver gallbladder bile ducts Summary unlike somatic nociception, visceral nociception = slow & non specific distribution of visceral pain is patterned & associated w/ generalized overlapping & bilateral distribution of afferent n referee visceral pain & referred MSK pain = 2 distinct pathophysiological processes