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Lecture 9

lecture 9

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University of Toronto St. George
Doug Mac Kay

09 Somatosensory PathwaysSeptember 28 2007Somatosensory pathwaysdorsal columnsmedial lemniscusofast most accurate small receptive fieldsoonly mechanoreceptorsocomposed of branches of primary afferents traveling up dorsal column to dorsal root to medulla and synapse at dorsal column nucleithere are changes at the synapse and medial lemniscus crosses midline to opposite side to ventral caudal V in thalamusCmedial lemniscusribbonlike tract rather than round tractalso have mechanoreceptors from the head thconveyed by cranial nerves V nervetrigeminal nerveterminates in the principal nucleus of V sensory nucleus in medulla and joins with medial lemniscusspinothalamic tractomany modalities wide dynamic range neuronsomechano pain and temperaturespecific neuronsspinoreticulothalamic pathwayoslowest mixed modalitiesopainrelated neuronsoseveral synapsesafferents go to spinal cord to reticular formation in medulla and pons of the brainstem to the thalamuslots of convergence of inputs and processing from different modalitiesDorsal columnsSomatotopic organizationoAfferents that are going up the column maintain the origin of where they came from and end up in a separate region of the dorsal column nucleisegregation of cutaneous superficialat more dorsal part of dorsal column and proprioceptive deepat deep half of dorsal column afferentsoproprioceptive afferents from the leg from lumbar spinal cord are pushed out of the dorsal column to the side because there is not enough room in the medial region of the dorsal column to put all of the proprioceptive afferents togetherhave their own bundle and nucleus in dorsal column nucleiseparation of slowly and rapidly adapting afferents in own bundles in dorsal columnsV target for the medial lemniscus that carries mechanoreceptive C informationoPart of ventral tier of thalamic nucleiImportant for motor controlmotor cortex in area 4Sensory afferents projects up to primary somatosensory cortex area 3 found in posterior bank of central sulcusPrimary somatosensory cortexS1 or area 3 divided into 2 partsoarea 3areceives proprioceptive map of body somatotopic1
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