Somatosensory system

About: Somatosensory system is a research topic. Over the lifetime, 6371 publications have been published within this topic receiving 316900 citations.

Molecular profiling reveals synaptic release machinery in Merkel cells.

Abstract: Merkel cell-neurite complexes are somatosensory receptors that initiate the perception of gentle touch. The role of epidermal Merkel cells within these complexes is disputed. To ask whether Merkel cells are genetically programmed to be excitable cells that may participate in touch reception, we purified Merkel cells from touch domes and used DNA microarrays to compare gene expression in Merkel cells and other epidermal cells. We identified 362 Merkel-cell-enriched transcripts, including neuronal transcription factors, presynaptic molecules, and ion-channel subunits. Antibody staining of skin sections showed that Merkel cells are immunoreactive for presynaptic proteins, including piccolo, Rab3C, vesicular glutamate transporter 2, and cholecystokinin 26-33. These data indicate that Merkel cells are poised to release glutamate and neuropeptides. Finally, by using Ca2+ imaging, we discovered that Merkel cells have L- and P/Q-type voltage-gated Ca2+ channels, which have been shown to trigger vesicle release at synapses. These results demonstrate that Merkel cells are excitable cells and suggest that they release neurotransmitters to shape touch sensitivity.

Short-latency somatosensory evoked potentials.

Abstract: • Short-latency components of the somatosensory evoked potential (SEP) were studied in 20 subjects who had median nerve stimulation using knee, forehead, and ear reference recordings. Six potentials were identified (P10, P12, P14, N19, P20, P23). Potential P10 seems to originate in the brachial plexus, P12 most likely is generated in dorsal column nuclei and medial lemniscus, P14 is probably thalamic in origin but is frequently bilobed and may have a second generator source, and N19 may originate in sensory radiation or cortex. The origin of P20 is unclear, and P23 appears to be generated in the contralateral somatosensory cortex. Clinically, we recommend using right, left, and bilateral median nerve stimulation at 4 Hz. Intensity of stimulus should produce at least a small thumb twitch. It was only with knee reference recording that all early potentials were seen.

Functional role of unmyelinated tactile afferents in human hairy skin: sympathetic response and perceptual localization

Abstract: In addition to A-beta fibres the human hairy skin has unmyelinated (C) fibres responsive to light touch. Previous functional magnetic resonance imaging (fMRI) studies in a subject with a neuronopathy who specifically lacks A-beta afferents indicated that tactile C afferents (CT) activate insular cortex, whereas no response was seen in somatosensory areas 1 and 2. Psychophysical tests suggested that CT afferents give rise to an inconsistent perception of weak and pleasant touch. By examining two neuronopathy subjects as well as control subjects we have now demonstrated that CT stimulation can elicit a sympathetic skin response. Further, the neuronopathy subjects' ability to localize stimuli which activate CT afferents was very poor but above chance level. The findings support the interpretation that the CT system is well suited to underpin affective rather than discriminative functions of tactile sensations.

Behavioral Organization of Reticular Formation: Studies in the Unrestrained Cat. I. Cells Related to Axial, Limb, Eye, and Other Movements

Abstract: Veterans Administration Medical Center, Sepulveda 91343, and Department of Psychiatry, School of Medicine, University of California, Los Angeles, California 90024 SUMMARY AND CONCLUSIONS 1. We have recorded single-unit activity in medial reticular formation (RF) units in unrestrained, behaving cats. A total of 306 cells have been analyzed. Neuronal activity was observed during a variety of natural, spontaneously occurring behaviors, during rapid eye movement (REM) and non-REM sleep states, after sensory stimulation, and during elicited reflexes. 2. Most RF units discharged maximally in conjunction with a specific movement or group of movements. The companion paper (41) deals with cells related to movements of the facial musculature, while the present paper deals with all other cell types. 3. The most common RF cell types discharged during specific movements of the axial skeleton. Cells related to limb, respiratory, pharyngeal and laryngeal, jaw, and tongue movements were also observed. Reticular eye movement-related cells, previously investigated by others, were also seen in our unrestrained cats. A small percentage of cells were maximally activated by applied auditory, visual, vestibular, somatosensory, or proprioceptive stimuli. 4. Cells related to axial movement, which as a group constituted 38.2% of all RF cells, could be subdivided into cells related to neck extension, neck dorsiflexion, and ipsilateral or contralateral movement of the spine. 5. Cells related to active ipsilateral movement, constituting 19.3% of all medial RF cells, were the single most common cell type in the RF. Thirty-four percent of these cells did not respond to passive head movement, while 48% responded to passive head movement to the contralateral side and 18% to passive movement to the ipsilateral side. Neck proprioceptors contribute to the passive movement response in certain of these cells. 6. Cells related to limb movement constituted 6.9% of the cells encountered. Most were related to movement of the proximal portion of one limb. Cells related to movement of the distal portion of the limb were quite rare, constituting only 1.0% of RF cells. 7. While most RF cells were active only in relation to a single, directionally specific movement, we found a cluster of pontine RF cells, which discharged in relation to several limb and neck movements. 8. Cells related to several movements, eye movement, vestibular stimulation, and cells without spontaneous activity in sleep or waking were localized to restricted portions of the medial RF fields. Cells related to axial, proximal limb movements or somatic stimulation were intermingled throughout the entire region explored. 9. The unrestrained preparation allows the direct observation of the behavioral correlates of increased RF unit discharge. Most RF cells discharge in relation to a specific movement or group of movements of the axial musculature. Each movement-defined cell type has a different pattern of sleep, sensory and reflex activity, and anatomical localization. Anatomical intermingling of certain cell types may facilitate the synthesis of complex movement sequences from simpler elements commanded by individual RF cells.

Touch and tactile neuropathic pain sensitivity are set by corticospinal projections

Abstract: Current models of somatosensory perception emphasize transmission from primary sensory neurons to the spinal cord and on to the brain1-4 Mental influence on perception is largely assumed to occur locally within the brain Here we investigate whether sensory inflow through the spinal cord undergoes direct top-down control by the cortex Although the corticospinal tract (CST) is traditionally viewed as a primary motor pathway5, a subset of corticospinal neurons (CSNs) originating in the primary and secondary somatosensory cortex directly innervate the spinal dorsal horn via CST axons Either reduction in somatosensory CSN activity or transection of the CST in mice selectively impairs behavioural responses to light touch without altering responses to noxious stimuli Moreover, such CSN manipulation greatly attenuates tactile allodynia in a model of peripheral neuropathic pain Tactile stimulation activates somatosensory CSNs, and their corticospinal projections facilitate light-touch-evoked activity of cholecystokinin interneurons in the deep dorsal horn This touch-driven feed-forward spinal-cortical-spinal sensitization loop is important for the recruitment of spinal nociceptive neurons under tactile allodynia These results reveal direct cortical modulation of normal and pathological tactile sensory processing in the spinal cord and open up opportunities for new treatments for neuropathic pain