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Sensory System
Published in Peter Kam, Ian Power, Michael J. Cousins, Philip J. Siddal, Principles of Physiology for the Anaesthetist, 2020
Peter Kam, Ian Power, Michael J. Cousins, Philip J. Siddal
The primary somatosensory cortex contains six horizontally arranged cellular layers numbered I to VI, with layer I at the cortical surface. Layer IV receives important projections from the ventrolateral posterior nucleus and the ventral posteromedial nucleus. From here, information is conveyed to layers I to III and ventrally to layers V and VII. Lesions that involve the primary somatosensory cortex result in the inability to localize precisely fine cutaneous stimuli on the body surface, inability to assess the degree of pressure on the skin and inability to identify objects by touch or texture (astereognosis).
Patty
Published in Walter J. Hendelman, Peter Humphreys, Christopher R. Skinner, The Integrated Nervous System, 2017
Walter J. Hendelman, Peter Humphreys, Christopher R. Skinner
We have already considered some of the components of the thalamus, the largest gray matter complex in the diencephalon, in previous chapters. The ventral posterolateral (VPL) and ventral posteromedial nuclei of the thalamus relay sensory information from the body and face, respectively, to the somatosensory areas of the cerebral cortex. Chapter 7 included a discussion of the ventral anterior and ventral lateral nuclei, both involved in the initiation and coordination of motor function. All of these thalamic nuclei, as well as others to be considered later, have ‘specific’ functions in that they are connected to discrete regions of the cerebral cortex.
ENTRIES A–Z
Published in Philip Winn, Dictionary of Biological Psychology, 2003
The dendrites of sensory neurons contact taste buds so that information can be sent to the CNS for processing. The action of molecules at receptor sites on the taste buds stimulates activity in these sensory neurons. Several nerves carry information away from the tongue to the CNS: the CHORDA TYMPANI (part of the FACIAL NERVE) carries information from the front of the tongue; the lingual branch of the GLOSSOPHARYNGEAL NERVE carries information from the back; and the VAGUS NERVE carries taste information from the palate and epiglottis. These nerves converge on the NUCLEUS OF THE SOLITARY TRACT from where information is relayed to the THALAMUS (especially the ventral posteromedial nucleus) directly and via the PARABRACHIAL NUCLEI. The thalamus, which is the major relay station for cortical input, sends axons to the primary GUSTATORY CORTEX located in the frontal insular and opercular cortices. This is the principal taste pathway, but fibres conducting gustatory information also reach the AMYGDALA and LATERAL HYPOTHALAMUS. Given that the amygdala is concerned with the ascription of motivational significance to stimuli (that is, deciding whether or not a stimulus is pleasant or aversive) and the lateral hypothalamus performs complex computations involving gustatory and visceral sensations, the representation of gustatory information in these places is not surprising. Perhaps the most curious aspect of the taste pathway however is that taste is not represented bilaterally in the cortex, unlike the other senses.
Emerging targets and uses of neuromodulation for pain
Published in Expert Review of Neurotherapeutics, 2019
Beatriz Costa, Isadora Ferreira, Alisson Trevizol, Aurore Thibaut, Felipe Fregni
The afferent fibers of the vagus nerve project to the spinal nucleus of the trigeminal nerve and the nucleus of the solitary tract (NST) [67]. The spinal nucleus of the trigeminal nerve receives sensitive fibers not only from the vagus nerve, but also from the trigeminal, facial, and glossopharyngeal nerves. The axons cross the midline in the brainstem and project, through the anterior trigeminothalamic tract, to the contralateral ventral posteromedial nucleus (VPM) of the thalamus. The NTS is at the center of the nuclei that form the gray matter of the medulla oblongata and receives information from multiple visceral organs, enteroceptive information and afferent signals from the spinal cord, the brainstem (area postrema, gray periaqueductal gray substance, and the parabrachial nucleus), brain (hypothalamus, thalamus and amygdala), and the cerebellum [67]. The NTS has projections to the locus coeruleus, raphe nuclei, amygdala, hippocampus, and the VPM. The locus coeruleus sends noradrenergic input to the raphe nuclei, the thalamus, the hippocampus, and the neocortex [58,67]. The raphe nuclei are mostly formed by serotonergic neurons, which project to the midline and intralaminar nuclei of the thalamus, the hippocampus, and the neocortex. Moreover, there are reciprocal connections between the LC and the raphe nuclei [58,67]. The VPM receives information from the amygdala, the postrema area, the hypothalamus, the reticular formation, the raphe nuclei, and the NST [58,67]. Most of the neurons located in the VPM are modulated through glutamatergic, cholinergic and GABAergic tonus, especially from the NST. The structures here described, especially the NST and its relation to the LC and the raphe nuclei, are part of the pain inhibitory system, which involves the inhibition of nociceptive transmission at the spinal cord [68]. This hypothesis is corroborated by studies that showed a decreased activity of second-order nociceptive neurons in the spinothalamic and spinoreticular tract of the spinal cord as well as in the trigeminal nuclear complex following the activation of afferent vagal fibers [58].