Sensory cortex

An inevitable consequence of ageing is an elevation of brain iron in specific brain regions, e.g. in the putamen, motor cortex, pre-frontal cortex, sensory cortex and thalamus, localized within H- and L-ferritin and neuromelanin with no apparent adverse effect. However, ill-placed excessive amounts of iron in specific brain cellular constituents, such as mitochondria or in specific regions brain, e.g. in the substantia nigra and lateral globus pallidus, will lead to neurodegenerative diseases (Friedreich s ataxia and Parkinson s disease (PD), respectively). We discuss here a few of the examples of the involvement of iron in neurodegenerative diseases. From more on iron metabolism see Crichton, 2001. 

Pavlovian (cue Giutamate, NMDA Mediai prefrontai cortex, sensory cortex, anterior cinguiate, dorsai thaiamus, iaterai amyg-daia, centrai nucieus of amyg-daia May account for common clinical observa- Treatment with NMDA receptor antago-... 

The areas of the brain that retained the greatest concentrations of the label after intravenous Injection of [ H]BZ Into cats (16) were motor cortex, sensory cortex, caudate nucleus, lateral geniculate, and medial geniculate Smaller concentrations were retained In thalamus, hippocampus, hypothalamus, medulla oblongata, colliculi, cerebellar cortex, the pyramids of the medulla, cerebral white matter, and cerebellar white matter ... 

Auditory cortex Sensory cortex Medial geniculate body Ventral thalamic nucleus... 

The main components of brain limbic system are amygdala, orbitofrontal cortex, sensory cortex, and thalamus. This part of brain is involved in the emotional processing and learning (Bechara et al. 2000 Rolls 2000). In what follows, the primary components of the brain limbic system are briefly described and then a mathematical model of brain limbic system is introduced. Finally, the mathematical model is integrated with a PID and a semiactive inversion algorithm to develop a... 

A mathematical relationship between the components of brain limbic system was proposed by Moren and Balkenius (2000) from the descriptive physical model of the limbic system that provides a qualitative sense of the overall functioning of the system. Figure 2 shows the structure of the Moren-Balkenius computational BEL model. As depicted in the figure, the BEL model has four components of the so-called limbic system of the brain amygdala, orbitofrontal cortex, sensory cortex and thalamus. Of them, amygdala and orbitofrontal cortex perform an important function in emotional processing (Moren and Balkenius 2000). 

Opioid actions at a number of other supraspinal sites (thalamic levels, the amygdala and the sensory cortex) are likely to be of relevance to analgesia. 

The slow (deep sleep) -waves probably originate in the eortex beeause they survive separation from, or lesions of, the thalamus. However, the rhythm and appearanee of spindles in earlier phases of the sleep eyele do depend on links with the thalamus (see Steriade 1999). Unlike stimulation of the specific sensory relay nuclei in the thalamus, which only affects neurons in the appropriate sensory areas of the cortex, the nonspecific nuclei can produce responses throughout the cortex and may not only control, but also generate, cortical activity. Certainly, in vitro studies show that neurons of the non-specific reticular thalamic nucleus (NspRTN) can fire spontaneously at about 8-12 Hz (equivalent to EEG a-rhythm) or lower, and that low-frequency stimulation of this area can induce sleep. 

Figure 22.5 Pathways involved in cortico-thalamic synchrony and EEG arousal. The ascending reticular activating system (ARAS) extends from the cephalic medulla through the pons and midbrain to the thalamus (see Moruzzi and Mayoun 1949). It is activated by impulses in collaterals of the spinothalamic sensory pathway running to specific thalamic nuclei (SpThNc) and in turn activates much of the cortex, partly through the non-specific thalamic nuclei (NspThNc), which also receive inputs from SpThNc and also via the nucleus basalis (NcB). Its stimulation is followed by EEG arousal. It is probable that reciprocal links between cortical areas and the thalamus, particularly NspThN, lead to slow-wave (8 Hz) cortical EEG synchrony and, in the absence of appropriate sensory input and ARAS activity, a sleep state...

Motion sickness is caused by stimulation of the vestibular system. This area contains many histaminic (Hj) and muscarinic cholinergic receptors. The higher brain (i.e., cerebral cortex) is affected by sensory input such as sights, smells, or emotions that can lead to vomiting. This area is involved in anticipatory nausea and vomiting associated with chemotherapy. 

Named for the bones of the cranium under which they lie, the lobes are conspicuously defined by prominent sulci of the cortex, which have a relatively constant position in human brains. Each lobe is specialized for different activities (see Figure 6.3). Located in the anterior portions of the hemispheres, the frontal lobes are responsible for voluntary motor activity, speaking ability, and higher intellectual activities. The parietal lobes, which are posterior to the frontal lobes, process and integrate sensory information. The occipital lobes, located in the posterior-most aspects of the cerebrum, process visual information, and the temporal lobes, located laterally, process auditory information. 

These ascending sensory pathways cross from one side of the CNS to the other so that sensory input from the left side of the body is transmitted to the somatosensory cortex of the right cerebral hemisphere and visa versa. Therefore, damage to this region of cortex in a given hemisphere results in... 

Saper, C.B., Iversen, S., and Frackowiak, R., Integration of sensory and motor function the association areas of the cerebral cortex and the cognitive capabilities of the brain, in Principles of Neuroscience, 4th ed., Kandel, E.R., Schwartz, J.H., and Jessell, T.M., Eds., McGraw-Hill, New York, 2000, chap. 19. 

As discussed, the first-order neuron is the afferent neuron that transmits impulses from a peripheral receptor toward the CNS. Its cell body is located in the dorsal root ganglion. This neuron synapses with the second-order neuron whose cell body is located in the dorsal horn of the spinal cord or in the medulla of the brainstem. The second-order neuron travels upward and synapses with the third-order neuron, whose cell body is located in the thalamus. Limited processing of sensory information takes place in the thalamus. Finally, the third-order neuron travels upward and terminates in the somatosensory cortex where more complex, cortical processing begins. 

All ascending tracts cross to the opposite side of the CNS. For example, sensory input entering the left side of the spinal cord ultimately terminates on the right side of the cerebral cortex. These tracts may cross — at the level of entry into the spinal cord a few segments above the level of entry or within the medulla of the brainstem. The locations of specific ascending tracts are illustrated in Figure 7.2 and a summary of their functions is found in Table 7.1. 

The cell bodies of third-order sensory neurons are located in the thalamus. These neurons transmit the pain signal to the somatosensory cortex. The function of this region of the brain is to localize and perceive the intensity of the painful stimulus. Further transmission of the signal to the association areas of the cerebral cortex is important for the perception and meaningfulness of the painful stimulus. 

Groenewegen, H. 8r Uylings, H. (2000). The prefrontal cortex and the integration of sensory, limbic and autonomic information. Prog. Brain Res. 126, 3-28. 

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