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19 Cards in this Set
- Front
- Back
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somatosensory
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afferent info taken from joints, tendons, and the surface of the body
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the NS receives a lot of info from sensory and/or afferent systems
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- this info is processed within the CNS
- CNS integrates info and interacts with both incoming and stored info to create an outgoing signal - a single fiber from the distal limbs has an avg. of 350-450 synaptic ends |
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within the somatosensory system exists 4 different routes from hte periphery to the cerebral cortex
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all 4 follow the same basic layout
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basic layout
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info is collected in a variety of places (from specific nerve endinds)
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primary afferent fibers
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have NCBs in a ganglion (usually dorsal root or spinal [for body] or cranial [for head])
- central processes always travel to the SC or BS and synapse there |
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2nd order neurons
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are activates (assuming the primary is excitatory) in the bs
- cross the midline and ascend to reach the VP thalamus, target for most sensory pathways; part of the lateral thalamic nucleus - synapses in the VP thalamus, most sensory pathways will relay here |
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thalamic neurons send their axons
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through the PLIC (partly made of axons of thalamic neuron cells going to the cerebral cortex)
- in SS systems the axons will synapse in S1 (post-central gyrus and paracentral lobule) |
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variance in 4 pathway
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types of axons
- as they approach their 1st synapse, different axons seperate in order to activate different 2nd order populations - however 3rd route of the pathwy is simlar for all most of the time SS experience does not occur until the corticol neurons are activated - perception occurs during cortical neuron activation, not peripheral neuron activation |
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DCML
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provides specific names for the 3 orders of neurons in the basic pathway
primary: generally almost always large caliber, heavly myelinated fibers - carries T and P signals - most low-threshold mechanoreceptors are also carried by this patthway -primary fibers participate in peripheral nerve plexi as primary fibers travel centrally they project/synapse on the ng/nc -2nd order NCB are found in the ng/nc - 2nd order axons travel across the midline - ascend on the ipsilateral side, then cross the midline at the mdulla and ascend the rest of the way on the contral lateral side - tract of 2nd order neurons = medial lemniscus 2nd order axons project to the VPL 3rd order axons project ot S1 via PLIC the DC-ML is a prototype for somatotopic repres of the CNS - info is carried from 1 place to another in an precise manner - bodys surface and deep strucutres are precisely mapped within a projection pathway (based on where the tracts or NCBs are located) the number of receptors in the skin determine the limits of discriminatory touch of that part of the body |
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somatotopy
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medial lemniscus
- after crossing midline, axons from the ng and nc join this bundle - upper part of the body --> ascends in the poster (in the pons, medial) part of the bundle - lower part of the body --> ascends in the anterior (in the pons, lateral) part of the bundle - as they ascend lower body fibers move more laterally and upper body fibers move more medially in the VPL thalamus - LB fibers = synapse laterally - UB fibers = syna med cerebral cortex - leg and foot = medial surface of the hemispheres (posterior paracentral lobule) - arm = lateral surface (post-central gyrus) |
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cortical representations
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homunculus showing how much of the cerebral cortex is devoted to each portion of the body
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deficits
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anything happening in the CNS has potential to damage this system
- spinal injuries, stroke in the cerebral hemisphere Damage is revealed in deficits by: discriminatory touch (esp time-modulated/time-coded) - touch is difficult to destroy (b/c other systems provide touch too) - time-coded =ability to do graphesthesia Vibratory sense - test w/ tuning fork - gold std. for testing fcnalitiy of DCML sterogonisis - abiltity to preceive an object by sense of touch postition sense - tested in toes and fingers |
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ALS
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more complex
afferents --> P and T -test with pinprick inputs comes from pain (high-threshold) receptors Adelta and C fibers - enter through the dorsolateral sulcus enter the SC and synapse on the same side (w/in 2-3 segments of where they entered) - usually in laminae I, II, V 2nd order neurons are located in the SC NOT the BS immed. send their axons across the midline at the anterior white commissure to the the ALS tract actually conisits of 3 tracts with different targets spinothalamic tract: VPL --> S1, some go to other thalamic nuclei (CM --> projects tp large areas of the cerebral cortex but not to SS) spinomesencephalic: PAG in the midbrain spinoreticular: reticular formations in the medulla and pons |
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ALS differences from DC-ML
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local
- the primary neuron only projects 2-3 segments around where it enters the SC crossing point - the 2nd order neurons cross the midline through the ant. white commisssure in the SC - the axon turns and ascends as 1 of 3 tracts of the ALS mult. targets self regulation - has features that allows it to decrease synaptic activity in resonse to large amounts of stim interneuons - are almost always found here - located in the dorsal horn b/w the 1st and 2nd order neurons |
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spinoreticular tract of ALS
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2nd order neurons ascend and send off several branches:
to the reticular formation in the medulla and pons - ALS pathway is often activated by strong, intense stimuli - these branches activate cells in the central part of the reticular formation -- project upwards and comminucate with cells in several thalmic ncu -- acts to aorunse the cortex |
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spinomesencephalic tract of ALS
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to the midbrain PAG
- some also go to the deep layer of the tectum (spinotectum fibers - act to direct the eyes towards the souce of the painful stim) part of pain-modulating system -have descending projections that arise in the PAG and activate bs raphe nuclei (use 5-HT) -axons descend in the spinal cord and comm woth the interneurons at the 1st level of synaptic relay |
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als deficit
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pin prick sensitivity is used alsmost exclusivley to test ALS
temp sensiblilt and sensation can be tested |
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trigeminal sensory pathway
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enters at the pons, carries info to 3 trigmeinal nuclei
- mesencephalic - cheif sensory --> located at the same level as incoming fibers - spinal trigeminal --> extends all the way down the upper spinal cord |
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trigeminal pathway
Pain, touch, temp ALS homolog |
fibers are similar to ALS (Adelta and C fibers)
CB in the trigeminal ganglion Central projections enter the CNS at the pons - fibers of the CNS run downward forming the spinal tract of CN V - travel down to the upper level of the SC - as they descend, they send off fibers to the upper areas of the spinal nucleusof CN V (most go to the bottom 1/3) primary axons synapse in the spinal nucleus of V - 2nd order axons cross midline to contralateral side and form the VTTT (carry T and P up to the thalamus, ascends next to the ML) 2nd order neurons synapse in the VPM (this is the nucleus for sensory afferents to the face) 3rd order axons still travel through the PLIC to the primary SS cortex - the face area is the lower 3rd of the postcentral gyrus |
