Second-order perception

A second theory of phantom pain suggests that second-order neurons in the dorsal horn of the spinal cord become hyperactive. Spontaneous firing of these neurons causes transmission of nerve impulses to the brain and the perception of pain. 

Since the reaction of intermediates is so fast, the concentration of the radical intermediate changes dramatically, yet the concentrations of the natural compounds in the skin with which the intermediate reacts (via second-order processes) do not change perceptibly. 

Olfactory perception translates abstract chemical features of odorants into meaningful neural information to elicit appropriate behavioral responses (Shepherd, 1994 Buck, 1996). Specialized bipolar olfactory sensory neurons (OSNs) are responsible for the initial events in odor recognition. These have ciliated dendrites exposed to the environment, and a single axon that extends into the brain and forms synapses with second order projection neurons (PNs) (Shepherd, 1994 Buck, 1996). In arthropods and mammals, the first olfactory synapse is organized into glomeruli, spherical structures in which afferent olfactory neuron axons synapse with projection neuron dendrites (Hildebrand and Shepherd, 1997). 

Fig. 7.32 The two textures (left field and right field) have the same first-order statistics (the same number of black dots), but they differ in second-order statistics. In the left field the dots fall at random, whereas in the right field there are at least 10 dot diameters between dots. [Reprinted by permission from B. Julesz, Experiments in the Visual Perception of Texture Sci. Am., 232, 34 (1975).]...

An example of a second-order reaction which can be optimized in respect to the MSTR is shown in Figure 4-83. The value for the optimum process temperature approximately amounts to 125 C. Hazardous secondary effects, which would become perceptible only above temperatures of 170°C, would be excluded inherently safely. 

The weak, but perceptible, gadohnium(III) irregularity in the ionic radii is difficult to explain via Eq. (3) since the virial theorem should make the average radius of the 4f shell smaller in Gd(III), and its slightly increased ionic radius cannot be explained that way unless the outer shells (5s and 5p) expand as a second-order effect of the 4f contraction. 

Descending neural pathways inhibit pain perception and efferent responses to pain. The cerebral cortex, hypothalamus, thalamus and brainstem centers (periaqueductal gray [PAG], nucleus rhaphe magnus [NRM] and locus coeruleus [LC]) send descending axons to the brainstem and spinal cord that modulate pain transmission in the dorsal horn. These axonal terminals either inhibit release of noxious neurotransmitters from primary afferents, or diminish the response of second-order neurons to the noxious input. Several neurotransmitters play critical roles in... 

Figure 3.4. (1) Peripheral noxious mediators activate nociceptor endings via a process termed transduction. (2) Noxious impulses are delivered to the spinal cord dorsal horn via the process of conduction in afferent fibers, (3) The process of transmission describes synaptic transfer of noxious impulses from primary afferents to second-order cells In dorsal horn, (4) Modulation describes inhibitory and facilitatory effects of spinal interneurons on noxious transmission, (5) Descending inhibition refers to descending brainstem, midbrain, and cortical inhibitor nerve endings which supress pain transmission, (6) Cortical perception Includes neocortical sites of pain localization and limbic centers responsible for emotional and suffering components of pain, (7) Supraspinal responses Include sympathetic, neuromuscular, and neuroendocrine responses to pain. From Sinatra RS, Pain pathways. In Sinatra RS,Vlscusl G,de Leon-Casasola 0, Ginsberg B,ed. Acute Pain Management. Cambridge University Press, 2009,...

Having resolved the molecular perception problem and achieved a unique representation of all atoms, bonds, and rings in the molecule, the second major step is the definition of the most useful measure for local similarity of atoms and atomic environment. For the purpose of COSMO/rag, we need to achieve the state that atoms are considered as most similar, if their partial molecular surfaces and surface polarities, i.e., polarization charge densities, are most similar. But since the latter is not known, at least for the new molecule under consideration, we have to ensure that the local geometries and the electronic effects of the surrounding atoms are most similar. Obviously, two similar atoms should at legist be identical with respect to their element and their hybridization. Turning this information into a unique real number, a similarity index of the lowest order (zeroth order) can be defined for each atom from the atom element numbers and... 

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