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Lecture 9

Lecture 9 - Somatosensory Pathways

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Michelle French

PSL300H1F Lecture 9, Sept 30 so terminate in own nucleus z but functionally Somatosensory pathways part of same system 1) dorsal columns - medial lemniscus: fast, solely mechanoreceptive, small r.f.s, most Collateral branches of branches of afferents recent and most detailed organized somatopically 2) spinothalamic tract: many modalities, wide Axons originate from bottom of spinal cord in dynamic range neurons; pain- and medial location next to midline temperature-specific neurons Axons from top most cervical segments are 3) spinoreticulothalamic pathway: slowest, most lateral mixed modalities; pain-related neurons largest Rmbr from lower leg and body, some rec field, stop in reticular formation before going proprioceptive afferents (deep) in lateral white to thalamus, oldest matter st Dorsal columns 1 synapse in pathway at medulla within dorsal Organize fields on body so not mixed up column nuclei Somatotopic organization, maintained all the Post synaptic neuron has axon that crosses way thru tract, body representations keep midline and courses thru brain stem in medial separate lemniscus tract (ribbon like tract or computer segregation of cutaneous (superficial) and cable) very close to midline, somatotopic order, proprioceptive (deep) afferents terminates in specific nuclei within contralateral separation of slowly and rapidly adapting (opposite side) thalamus (if starts in left side afferents in dif bundles then terminate in right thalamus in ventral so everything strictly isolated so info not mixed caudal nucleus, so at back of ventral group; up specific nuclei of media lemniscus) Motor region along anterior bank of central sulcus Somatosensroy cortex aligned along posterior bank of CS Band of white matter on dorsal surface of spinal cord, axons coursing up to brain Collateral branches of primary afferents entering the dorsal horn, others branch into the dorsal columns and go up dorsal columns to the medulla junction (w spinal cord) where synapse to dorsal column nuclei, nuclei for all afferents from leg, arm, head region (ex. trigenital,cranial nerves all constitute dorsal colun nuclei) segregate dif parts of body Nuc z conctains proprioceptive affents of lower body and legs, travel up lateral part of white matter since not enough room in dorsal column Cytoarchatechtonic zones of cortex, layering of 3b cutaneous zone on posterior bank (down neurons changing Ex. Area of motor neurons much thicker inside) of central sulcus than area 3 Complete map of body but upside down Numbers indicate dif functional zones 3a along anterior border at bottom of central 3= primary somatosensory cortex, target of sulcus, mapping w same pattern as cutaneous inputs but representing muscles and deep tissue neurons from ventral caudal thalamus in Foot represented medially saginal plane of posterior end of thalamus; ventral tier of nuclei Rest of body hangs upside down so head and All mechanoreceptor input, somatotopic pharynx and inside of mouth represented mapping within each zone: laterally over at later fissure 3a gets proprioceptive signals, which are all Should say lateral fissure not later sulcus Mapping body doesnt produce picture of body, at one zone in the ventral caudal nucleus, distorted representation; Ex. Finger zone bigger anterior portion 3b mechano receptor info, cutaneous input than leg zone even though surface area of (bulk of ventral caudal nucleus) fingers much smaller Represents populations of afferents, where Primary somatosensory cortex first cortical area more in info comes from fingers are very rich source of afferents,
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