Mechanism sensory

Figure 3. Neurophysiological preparation of Trichoplusia ni. Head, thorax and gut are removed. Tungsten electrodes were placed into the hemocoel along side abdominal ganglion VIII (at Rl), the ventral nerve cord (at R2) and the abdominal wall (ground, Rj). Injections of alkaline-dissolved BTI -endotoxin, methamidophos and phospholipase-A2 were into the second pair of abdominal prolegs (Ch). Mechanical sensory stimulation with a glass probe was at the anal proleg (S). Activity in the ventral nerve cord was monitored through 24 h post-treatment (38-40) (see Figure 4).

Figure 4. Time dependency of nervous activity in the ventral nerve cord of Trichoplusia ni injected with 3.7 PPM alkaline-dissolved BTI 6-endotoxin (Sandoz), with 10 PPM methamidophos (MMP) and with 35 PPM phospholipase-A2 (P-A2). Mechanical sensory stimulation is given at arrow S. The control response was the same as the recording for P-A2. BTI and P-A2 were injected into T ni at their respective LDjq.

The vestibular system is named for its position within the vestibule of the temporal bone of the skuU. It is located in the inner ear along with the auditory sense. The vestibular system has both central and peripheral components. This chapter deals with the mechanical sensory function of the peripheral end organ and its abdity to measure Hnear and angular inertial motion of the skuU over the frequency ranges encountered in normal activities. The transduction process used to convert the mechanical signals into neural ones is also described. 

Taste-active chemicals react with receptors on the surface of sensory cells in the papillae causing electrical depolarization, ie, drop in the voltage across the sensory cell membrane. The collection of biochemical events that are involved in this process is called transduction (15,16). Not all the chemical steps involved in transduction are known however, it is clear that different transduction mechanisms are involved in different taste quaUties different transduction mechanisms exist for the same chemical in different species (15). Thus the specificity of chemosensory processes, ie, taste and smell, to different chemicals is caused by differences in the sensory cell membrane, the transduction mechanisms, and the central nervous system (14). 

It-from-bit embodies the central notion that every it - that is, every aspect of reality electrons, protons, photons, fields of force, or even the what we call space-time itself - is in the deepest sense a derivative of experimentally deduced answers to yes/no questions that is, to bits. If we allow ourselves for a moment to go back to the roots of what it is that we by convention call reality, we see that it is something that is literally defined by a particular sequence of yes/no responses elicited from either a mechanical or (our own biological) sensory apparatus in other words, reality s origin is fundamentally information-theoretic. 

In the gastrointestinal tract, drugs or toxins, as well as mechanical stimulation, induce emesis by activation of sensory receptors on afferent neurons in the vagus and sympathetic nerves. Information is relayed to the vomiting centre via the nucleus tractus solitarius... 

Nociceptors are a specific subset of peripheral sensory organs, which respond to noxious stimuli. A8 mechan-oreceptors and C-polymodal nociceptors are the two main classes of cutaneous nociceptors. The sensory quality of pain evoked by activation of A8-fibres is... 

As early as 1848, it had been suggested that sensory receptors transduce only one sensation, independent of the manner of stimulation. Behavioral experiments tend to support this theory. In 1919, Renqvist proposed that the initial reaction of taste stimulation takes place on the surface of the taste-cell membrane. The taste surfaces were regarded as colloidal dispersions in which the protoplasmic, sensory particles and their components were suspended in the liquor or solution to be tested. The taste sensation would then be due to adsorption of the substances in the solution, and equal degrees of sensation would correspond to adsorption of equal amounts. Therefore, the rate of adsorption of taste stimulants would be proportional to the total substances adsorbed. The phenomenon of taste differences between isomers was partly explained by the assumption that the mechanism of taste involves a three-dimensional arrangement for example, a layer of fatty acid floating on water would have its carboxylic groups anchored in the water whereas the long, hydrocarbon ends would project upwards. 

The function of a sensory system is to select suitable modalities from the multitude presented by the environment, and translate them into corresponding modalities of sensory information that are then projected and processed into the various parts and finally submitted to the central processing-unit, the brain. A working hypothesis of the mechanism by which the taste system senses chemical compounds is that macromolecules that are... 

MeUi G, Keswani SC et al (2006) Spatially distinct and functionally independent mechanisms of axonal degeneration in a model of HIV-associated sensory neuropathy. Brain 129(Pt 5) 1330-1338 MendeU JR, Sahenk Z (2003) Clinical practice. Painful sensory neuropathy. N Engl J Med 348(13) 1243-1255... 

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