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1.
This paper is concerned with conduction of the nervous impulse in a myelinated axon and the effect of demyelination on conduction
characteristics. A model of nerve conduction called the “gunpowder fuse” model is presented which accurately predicts conduction
velocities in both myelinated and unmyelinated nerves. The effect on conduction velocity in this model by reducing myelin
thickness is examined by utilizing basic data and building and equivalent circuit. The result is a curve relating reduced
conduction velocity to reduced myelin thickness. A similar analysis and resultant curve is derived from a saltatory conduction
model.
Supported in part by National Multiple Sclerosis Society Research Grant No. 516 and Air Force Grant AFOSR 669-67. 相似文献
2.
A. M. Semenov 《Microbial ecology》1991,22(1):239-247
Three groups of physiological processes in microorganisms are considered the physiological basis of oligotrophy: the greater
substrate affinity of the oligotrophs' transport systems, efficient or “economical” metabolism, and existence of a “master
reaction” or “rate-determining steps” controlling the rate of metabolism. Heterotrophic microorganisms are divided into three
unequal groups according to “reaction norma.” Two groups representing the extremes are small groups with the “narrow” reaction
norma, regarding the concentrations and structure of the assimilated organic compounds and variability limits of the physiological
characteristics mentioned above. The third, intermediate group includes the majority of microorganisms with the “wide” reaction
norma. 相似文献
3.
Revin VV Yudanov MA Revina ES Maksimov GV Gruniushkin IP 《Biochemistry. Biokhimii?a》2006,71(10):1096-1100
Rhythmic excitation of a rabbit myelin nerve increased diacylglycerol (DAG) content from 1.53 to 2.17 microg/mg lipids. Inhibition of phosphoinositide-specific phospholipase C decreased DAG content. This suggests involvement of this enzyme in processes accompanying rhythmic excitation. The increase in membrane potential of the nerve fiber (K+-depolarization) was accompanied by increase in DAG and phosphatidylinositol monophosphate and decrease in phosphatidylinositol triphosphate and phosphatidylinositol diphosphate content. Treatment of the nerve with DAG or a protein kinase C activator increased (45)Ca influx by 40%, whereas treatment with an inhibitor of this enzyme, polymyxin, inhibited this parameter by 34%. The role of phosphoinositides and protein kinase C in the regulation of Ca2+ transport during rhythmic excitation of the myelin nerve is discussed. 相似文献
4.
We studied monosynaptic reflex discharges (MRD) recorded from the ventral roots (VR) of rats subjected to systemic administration
with thyroliberin, thyroxin, or 4-aminopyridine (4-AP). Under such conditions, in some of the experiments the MRD amplitude
reached values sufficient to excite non-active VR fibers. In these cases, immediately after the MRD peak had been reached,
abnormally increased responses (AIR) developed, whose amplitude was 2–2.5 times higher than the amplitude of highly facilitated
MRD. Proofs are presented that AIR reflect excitation of “neighboring” VR fibers, which were not involved in the reflex response,
and MRD plays the role of a “stimulus” exciting these fibers. Therefore, we demonstrate the possibility of transmission of
excitation from “active” to “silent” fibers within a nerve trunk under conditions of the development of “superreflexia”. This
state can be considered a model of excitation spreading via a non-synaptic pathway under conditions of hyperexcitability of
the CNS structures, in seizure states in particular.
neirofiziologiya/Neurophysiology, Vol. 32, No. 2, pp. 120–127, March–April, 2000. 相似文献
5.
Axon excitation increases the number of acetylcholine receptors (ACR) of the Schwann cell (SC) depending on the frequency of rhythmic excitation (RE) and on intercellular concentrations of K+, Ca2+, and acetylcholine. During RE, activity of axonal acetylcholine esterase is decreased, thus providing for high intercellular acetylcholine concentration. Increased intercellular concentration of acetylcholine activates phosphoinositide-specific phospholipase C (PIPLC) of the myelin nerve fiber. During RE, K+ depolarization and acetylcholine exocytosis can activate Ca2+ entry via Ca2+ channels, thus inducing SC ACR phosphorylation mediated by PIPLC stimulation. 相似文献
6.
Shuzhen Yang Rui Zhang Changchao Hu Jie Xie Jingquan Zhao 《Photosynthesis research》2009,99(2):99-106
Light state transition is a physiological function of oxygenic organisms to balance the excitation of photosystem II (PSII)
and photosystem I (PSI), hence a prerequisite of oxygen-evolving photosynthesis. For cyanobacteria, phycobilisome (PBS) movement
during light state transition has long been expected, but never observed. Here the dynamic behavior of PBS movement during
state transition in cyanobacterium Synechocystis PCC6803 is experimentally detected via time-dependent fluorescence fluctuation. Under continuous excitation of PBSs in the
intact cells, time-dependent fluorescence fluctuations resemble “damped oscillation” mode, which indicates dynamic searching
of a PBS in an “overcorrection” manner for the “balance” position where PSII and PSI are excited equally. Based on the parallel
model, it is suggested that the “damped oscillation” fluorescence fluctuation is originated from a collective movement of
all the PBSs to find the “balance” position. Based on the continuous fluorescence fluctuation during light state transition
and also variety of solar spectra, it may be deduced that light state transition of oxygen-evolution organisms is a natural
behavior that occurs daily rather than an artificial phenomenon at extreme light conditions in laboratory. 相似文献
7.
It was shown that understanding the mechanism of rhythmic excitation in cells and tissues requires the combination of physiological and biophysical approaches. Systemic studies of changes in the physicochemical characteristics of the object were carried out by a protocol that takes into account the mode of rhythmic excitation and the functional sate of the object being studied. The validity of the approach was proved in studies of rhythmic excitation in somatic nonmyelinic and myelinic nerves, and in model systems. The approach can be used in studies of many physiological processes. 相似文献
8.
G. K. H. Zupanc M. M. Zupanc 《Journal of comparative physiology. A, Neuroethology, sensory, neural, and behavioral physiology》2008,194(2):119-134
Theodore H. Bullock (1905–2005) was a pioneer of integrative and comparative neurobiology and one of the founders of neuroethology.
His work—distinguished by the tremendous number of different research themes and animal taxa studied—provided the basis for
a comprehensive analysis of brain evolution. Among his major achievements are: one of the first physiological analyses of
rhythmic central pattern generators; the first simultaneous recording from both the presynaptic and postsynaptic region of
a chemical synapse; the demonstration of intercellular communication through graded potentials; and the discovery of two novel
sensory organs formed by infrared receptors in pit vipers and electroreceptors in electric fish. He was also one of the first
who applied computational tools to the analysis of complex neural signals and to perform a comparative analysis of cognitive
events. His two-volume treatise “Structure and function in the nervous system of invertebrates” (with G. Adrian Horridge)
remains the most comprehensive, authoritative review of this topic ever written. In addition to his research merits, his legacy
is particularly based on his cosmopolitan way of thinking and acting, his large, worldwide school of students, and his committed
advocacy for comparative and systems-oriented neurobiology. 相似文献
9.
E. J. Murphy 《Bulletin of mathematical biology》1958,20(4):305-307
Ferroelectric polarization currents have characteristics which may be of use in the study of the nerve impulse either directly
or indirectly through the suggestion of parallel experiments in the two domains. For example, the “all or none” aspect of
the excitation of the nerve impulse can be considered to correspond in some sense to the coercive force required for the reversal
of a ferroelectric polarization. The refractory period then corresponds to the lack of a relaxation process in ferroelectric
polarization; for a second application of voltage in a given direction does not produce a ferroelectric current; it is necessary
that the polarization be reversed by a reversal of voltage. The “heat block” in nerve conduction may correspond to a ferroelectric
Curie point at about 40°C. Velocities of propagation of ferroelectric polarization are of the order of magnitude of the velocities
of sound and therefore in a range suitable for the interpretation of the observed velocities of nerve impulses. These and
other parallels between ferroelectric behavior and the characteristics of the nerve impulse suggest that there may be a useful
degree of similarity between the molecular processes responsible for the nerve impulse and those responsible for ferroelectric
polarization. *** DIRECT SUPPORT *** A01E2080 00002 相似文献
10.
The mechanism of activation of Na, K-ATPase in nerve fibres during rhythmic excitation was studied. 3H-ouabain binding to the nerve was found to be dependent on the frequency of rhythmic excitation. During rhythmic excitation 3H-ouabain binding was increased in all nerves tested. The maximum of 3H-ouabain binding in squid and crab nerves was observed at 10 impulses/s, and in frog nerve at 100 impulses/s. The level of bound glycoside decreased during high-frequency excitation. Rhythmic excitation did not change Na, K-ATPase affinity to ouabain, but it appeared to increase the concentration of ouabain sensitive sites in the nerve membrane. The enhancement of 3H-ouabain binding to nerve during rhythmic excitation is interpreted as arising from transformation of "inactive" forms of the enzyme to "active" ones. 相似文献
11.
Gale Young 《Bulletin of mathematical biology》1941,3(1):5-12
It is shown that the current “two-factor” theory of nerve excitation can account for sustained inhibition or enhancement by
a sequence of stimulus pulses, and for the decrease in the reinforcement period with each successive pulse of the train. 相似文献
12.
V. G. Zalesski 《Plasma Physics Reports》2011,37(13):1196-1201
Electron emission influence from gas-discharge plasma on plasma emitter energy parameters is considered. It is shown, that
electron emission from plasma is accompanied by energy contribution redistribution in the gas-discharge from plasma emitter
supplies sources—the gas-discharge power supply and the accelerating voltage power supply. Some modes of electron emission
as a result can be realized: “a probe measurements mode,” “a transitive mode,” and “a full switching mode.” 相似文献
13.
Anatol Rapoport 《Bulletin of mathematical biology》1952,14(1):35-44
The spread of excitation in a “random net” is investigated. It is shown that if the thresholds of individual neurons in the
net are equal to unity, a positive steady state of excitation will be reached equal to γ, which previously had been computed
as the weak connectivity of the net. If, however, the individual thresholds are greater than unity, either no positive steady
state exists, or two such states depending on the magnitude of the axone density. In the latter case the smaller of the two
steady states is unstable and hence resembles an “ignition point” of the net. If the initial stimulation (assumed instantaneous)
exceeds the “ignition point,” the excitation of the net eventually assumes the greater steady state.
Possible connections between this model and the phenomenon of the “preset” response are discussed. 相似文献
14.
Source-sink landscape theory and its ecological significance 总被引:2,自引:0,他引:2
Exploring the relationships between landscape pattern and ecological processes is the key topic of landscape ecology, for
which, a large number of indices as well as landscape pattern analysis model were developed. However, one problem faced by
landscape ecologists is that it is hard to link the landscape indices with a specific ecological process. Linking landscape
pattern and ecological processes has become a challenge for landscape ecologists. “Source” and “sink” are common concepts
used in air pollution research, by which the movement direction and pattern of different pollutants in air can be clearly
identified. In fact, for any ecological process, the research can be considered as a balance between the source and the sink
in space. Thus, the concepts of “source” and “sink” could be implemented to the research of landscape pattern and ecological
processes. In this paper, a theory of sourcesink landscape was proposed, which include: (1) In the research of landscape pattern
and ecological process, all landscape types can be divided into two groups, “source” landscape and “sink” landscape. “Source”
landscape contributes positively to the ecological process, while “sink” landscape is unhelpful to the ecological process.
(2) Both landscapes are recognized with regard to the specific ecological process. “Source” landscape in a target ecological
process may change into a “sink” landscape as in another ecological process. Therefore, the ecological process should be determined
before “source” or “sink” landscape were defined. (3) The key point to distinguish “source” landscape from “sink” landscape
is to quantify the effect of landscape on ecological process. The positive effect is made by “source” landscape, and the negative
effect by “sink” landscape. (4) For the same ecological process, the contribution of “source” landscapes may vary, and it
is the same to the “sink” landscapes. It is required to determine the weight of each landscape type on ecological processes.
(5) The sourcesink principle can be applied to non-point source pollution control, biologic diversity protection, urban heat
island effect mitigation, etc. However, the landscape evaluation models need to be calibrated respectively, because different
ecological processes correspond with different source-sink landscapes and evaluation models for the different study areas.
This theory is helpful to further study landscape pattern and ecological process, and offers a basis for new landscape index
design.
__________
Translated from Acta Ecologica Sinica, 2006, 26(5): 1444–1449 [译自: 生态学报] 相似文献
15.
Otto E. Rössler 《Bulletin of mathematical biology》1972,34(3):343-353
For a certain class of physical machines, termed “structure-determined,” the problem of self-reproduction can be reduced to
the problem of serial message reproduction. Serial message reproduction however presupposes a sort of “open system” constraint.
This leads to the principle of pseudo, or exogenously standardized, respectively, self-reproduction. It seems to be consistent
with both chemical and biological self-reproduction. It thus may reflect a general principle of biological design.
The proposed principle is a physico chemical analog to Robert Rosen's abstract relational self-reproduction constraint. 相似文献
16.
Keith Johnson 《Journal of biological physics》2012,38(1):85-95
Water nanoclusters are shown from first-principles calculations to possess unique terahertz-frequency vibrational modes in
the 1–6 THz range, corresponding to O–O–O “bending,” “squashing,” and “twisting” “surface” distortions of the clusters. The
cluster molecular-orbital LUMOs are huge Rydberg-like “S,” “P,” “D,” and “F” orbitals that accept an extra electron via optical
excitation, ionization, or electron donation from interacting biomolecules. Dynamic Jahn–Teller coupling of these “hydrated-electron”
orbitals to the THz vibrations promotes such water clusters as vibronically active “structured water” essential to biomolecular
function such as protein folding. In biological microtubules, confined water-cluster THz vibrations may induce their “quantum
coherence” communicated by Jahn–Teller phonons via coupling of the THz electromagnetic field to the water clusters’ large
electric dipole moments. 相似文献
17.
Water represents the major component of most food systems. During thermal or high-pressure processing, physical and chemical
properties of water are changed. The p–T diagram represents an obvious presentation of isoproperty lines and their pressure
and temperature dependencies. In this work, 15 different properties of pure water are shown as isoproperty lines in the pressure–temperature
landscape. By using functional relationships from the “International Association for the Properties of Water and Steam” and
databases from the “National Institute of Standards and Technology,” highest accuracy is guaranteed. Applying the generated
graphs, a compact overview is given and a wide range of thermal and high-pressure processes can easily be compared. The different
pressure and temperature dependencies of all properties showed the complexity of medium conditions during thermal and high-pressure
processing. An extended understanding of pressure–temperature dependencies will improve process concepts as well as industrial
applications at high temperature and high isostatic pressure. 相似文献
18.
Luis Emilio Bruni 《Biosemiotics》2008,1(1):113-130
This article considers categorical perception (CP) as a crucial process involved in all sort of communication throughout the
biological hierarchy, i.e. in all of biosemiosis. Until now, there has been consideration of CP exclusively within the functional
cycle of perception–cognition–action and it has not been considered the possibility to extend this kind of phenomena to the
mere physiological level. To generalise the notion of CP in this sense, I have proposed to distinguish between categorical
perception (CP) and categorical sensing (CS) in order to extend the CP framework to all communication processes in living
systems, including intracellular, intercellular, metabolic, physiological, cognitive and ecological levels. The main idea
is to provide an account that considers the heterarchical embeddedness of many instances of CP and CS. This will take me to relate the hierarchical nature of categorical sensing and perception
with the equally hierarchical issues of the “binding problem”, “triadic causality”, the “emergent interpretant” and the increasing
semiotic freedom observed in biological and cognitive systems.
相似文献
Luis Emilio BruniEmail: |
19.
Maria Isabel Aldinhas Ferreira 《Biosemiotics》2012,5(2):269-289
In this paper architectural forms are presented as symbolic forms issued from the complex semiosis that characterises human cognition (Ferreira (2007, 2010)). Being semiotic objects, these symbolic forms are, consequently, context- dependent_they emerge and have meaning, i.e., they are assigned a functional and/or aesthetic value, in particular physical, social and cultural frameworks. As it happens with all semiotic objects, architectural forms, whatever their nature, are not static but highly interactive. In fact, they act as agents of specific semiotic processes, engaged in a permanent dialectic relationship with the environment they are embedded in. From this dialectics important physical, social, cultural and economic changes frequently arise, redefining this way the original framework for decades to come. As Pallasmaa (2009) points out: “Architecture is existentially rooted, and it expresses fundamental existential experiences, the complex condensation of how it feels to be human being in this world. Architecture grounds and frames existence and creates specific horizons of perception, understanding and identity.” Architecture happens in the context of particular landscapes both natural and man-made, individuating spaces, assigning them an identity, turning the frequently undifferentiated physical environment into “locus”, “place”, “site”, “ort”, definitely contributing to the definition of the mental map that individual minds are able to share collectively. The fundamental role played by architectural forms in the definition of “place” and identity and in the shaping or reshaping of a physical, social and cultural environment is analysed in this paper through a case study that observes the consequences of this dynamics in the development of the social and cultural tissue of a particular city. 相似文献
20.
V. A. Ilyukhina 《Journal of Evolutionary Biochemistry and Physiology》2010,46(3):321-333
The paper summarizes literature data and results of many-year Laboratory studies disclosing principles of the multiform spatial-time
organization of differing by rates of neurophysiologic brain processes as the universal “language” of its informational-controlling
functions. There are considered current concepts of electrogenesis and physiological significance of ratios of gradual changes
of biopotentials and impulse activity of neurons considered in studies of cerebral mechanisms of regulation of normal and
pathological states, and organization of human psychic activity. Put forward and argumented are concepts of the probability
principle of hierarchical organization of differing by rates of neurophysiologic processes brain zones, structures, and areas
in formation of the brain systems participating in provision of the higher psychic functions and states. It is proposed to
discuss the concept of the brain as the “swimming,” many-contour, neurodynamic informational-controlling suprasystem with
universal, hierarchically organized neurodynamic structures—”functional organs” by A.A. Ukhtomskii (1978), of which formation
provides large informational brain capacity and a wide specter of adaptive possibilities of the human organism. 相似文献