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  • 1.
    Blomberg, Clas
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical Biological Physics.
    Fluctuations for good and bad: The role of noise in living systems2006In: Physics of Life Reviews, ISSN 1571-0645, Vol. 3, no 3, p. 133-161Article, review/survey (Refereed)
    Abstract [en]

    The intention is to provide a broad overview of the role of noise and basic methods to describe noise effects in biological systems. It starts from a brief discussion of the statistical mechanical basis, and Brownian motion which is generalised to calculations of randomly induced transitions over energy barriers, and stochastic resonance. The description of discrete step processes provides another approach, which also is a basis of a stochastic description of chemical reactions. Macromolecular structure changes are considered as triggered by the background fluctuations. A strong emphasis is put on "fluctuation-dissipation" relations, relations between the irregular fluctuations and the dissipative spreading of energy towards a most probable distribution. We also take up some applications to non-linear systems, noise effects together with oscillations and signal transmission as well as models on unidirectional motion of various kinds with Brownian ratchets and active transport as examples.

  • 2. Blomberg, Clas
    Physics of Life2007Book (Other academic)
    Abstract [en]

    The purpose of the book is to give a survey of the physics that is relevant for biological applications, and also to discuss what kind of biology needs physics. The book gives a broad account of basic physics, relevant for the applications and various applications from properties of proteins to processes in the cell to wider themes such as the brain, the origin of life and evolution. It also considers general questions of common interest such as reductionism, determinism and randomness, where the physics view often is misunderstood. The subtle balance between order and disorder is a repeated theme appearing in many contexts. There are descriptive parts which shall be sufficient for the comprehension of general ideas, and more detailed, formalistic parts for those who want to go deeper, and see the ideas expressed in terms of mathematical formulas. - Describes how physics is needed for understanding basic principles of biology - Discusses the delicate balance between order and disorder in living systems - Explores how physics play a role high biological functions, such as learning and thinking. © 2007 Elsevier B.V. All rights reserved.

  • 3.
    Blomberg, Clas
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical Biological Physics.
    Physics of Life: the physicist's road to biology2007Book (Refereed)
    Abstract [en]

    The purpose of the book is to give a survey of the physics that is relevant for biological applications, and also to discuss what kind of biology needs physics. The book gives a broad account of basic physics, relevant for the applications and various applications from properties of proteins to processes in the cell to wider themes such as the brain, the origin of life and evolution. It also considers general questions of common interest such as reductionism, determinism and randomness, where the physics view often is misunderstood. The subtle balance between order and disorder is a repeated theme appearing in many contexts. There are descriptive parts which shall be sufficient for the comprehension of general ideas, and more detailed, formalistic parts for those who want to go deeper, and see the ideas expressed in terms of mathematical formulas. - Describes how physics is needed for understanding basic principles of biology - Discusses the delicate balance between order and disorder in living systems - Explores how physics play a role high biological functions, such as learning and thinking.

  • 4. Zeberg, Hugo
    et al.
    Blomberg, Clas
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical Biological Physics.
    Arhem, Peter
    Ion Channel Density Regulates Switches between Regular and Fast Spiking in Soma but Not in Axons2010In: PloS Computational Biology, ISSN 1553-734X, E-ISSN 1553-7358, Vol. 6, no 4, p. e1000753-Article in journal (Refereed)
    Abstract [en]

    The threshold firing frequency of a neuron is a characterizing feature of its dynamical behaviour, in turn determining its role in the oscillatory activity of the brain. Two main types of dynamics have been identified in brain neurons. Type 1 dynamics (regular spiking) shows a continuous relationship between frequency and stimulation current (f-I-stim) and, thus, an arbitrarily low frequency at threshold current; Type 2 (fast spiking) shows a discontinuous f-I-stim relationship and a minimum threshold frequency. In a previous study of a hippocampal neuron model, we demonstrated that its dynamics could be of both Type 1 and Type 2, depending on ion channel density. In the present study we analyse the effect of varying channel density on threshold firing frequency on two well-studied axon membranes, namely the frog myelinated axon and the squid giant axon. Moreover, we analyse the hippocampal neuron model in more detail. The models are all based on voltage-clamp studies, thus comprising experimentally measurable parameters. The choice of analysing effects of channel density modifications is due to their physiological and pharmacological relevance. We show, using bifurcation analysis, that both axon models display exclusively Type 2 dynamics, independently of ion channel density. Nevertheless, both models have a region in the channel-density plane characterized by an N-shaped steady-state current-voltage relationship (a prerequisite for Type 1 dynamics and associated with this type of dynamics in the hippocampal model). In summary, our results suggest that the hippocampal soma and the two axon membranes represent two distinct kinds of membranes; membranes with a channel-density dependent switching between Type 1 and 2 dynamics, and membranes with a channel-density independent dynamics. The difference between the two membrane types suggests functional differences, compatible with a more flexible role of the soma membrane than that of the axon membrane.

  • 5.
    Zeberg, Hugo
    et al.
    Karolinska Inst, Nobel Inst Neurophysiol, Dept Neurosci, Stockholm, Sweden..
    Blomberg, Clas
    KTH, School of Engineering Sciences (SCI), Physics.
    Arhem, Peter
    Karolinska Inst, Nobel Inst Neurophysiol, Dept Neurosci, Stockholm, Sweden..
    Reptitive Firing In Neurons - Analysing The Interaction Between Channel Density And Kinetics In Membrane Models2009In: Biophysical Journal, ISSN 0006-3495, E-ISSN 1542-0086, Vol. 96, no 3, p. 480A-480AArticle in journal (Other academic)
  • 6. Århem, P.
    et al.
    Klement, G.
    Blomberg, Clas
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical Biological Physics.
    Channel density regulation of firing patterns in a cortical neuron model2006In: Biophysical Journal, ISSN 0006-3495, E-ISSN 1542-0086, Vol. 90, no 12, p. 4392-4404Article in journal (Refereed)
    Abstract [en]

    Modifying the density and distribution of ion channels in a neuron (by natural up- and downregulation or by pharmacological intervention or by spontaneous mutations) changes its activity pattern. In this investigation we analyzed how the impulse patterns are regulated by the density of voltage-gated channels in a neuron model based on voltage-clamp measurements of hippocampal interneurons. At least three distinct oscillatory patterns, associated with three distinct regions in the Na-K channel density plane, were found. A stability analysis showed that the different regions are characterized by saddle-node, double-orbit, and Hopf-bifurcation threshold dynamics, respectively. Single, strongly graded action potentials occur in an area outside the oscillatory regions, but less graded action potentials occur together with repetitive. ring over a considerable range of channel densities. The relationship found here between channel densities and oscillatory behavior may partly explain the difference between the principal spiking patterns previously described for crab axons (class 1 and 2) and cortical neurons ( regular. ring and fast spiking).

  • 7. Århem, Peter
    et al.
    Blomberg, Clas
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical Biological Physics.
    Ion channel density and threshold dynamics of repetitive firing in a cortical neuron model2007In: Biosystems (Amsterdam. Print), ISSN 0303-2647, E-ISSN 1872-8324, Vol. 89, no 1-3, p. 117-125Article in journal (Refereed)
    Abstract [en]

    Modifying the density and distribution of ion channels in a neuron (by natural up- and down-regulation, by pharmacological intervention or by spontaneous mutations) changes its activity pattern. In the present investigation, we analyze how the impulse patterns are regulated by the density of voltage-gated channels in a model neuron, based on voltage clamp measurements of hippocampal interneurons. At least three distinct oscillatory patterns, associated with three distinct regions in the Na-K channel density plane, were found. A stability analysis showed that the different regions are characterized by saddle-node, double-orbit, and Hopf bifurcation threshold dynamics, respectively. Single strongly graded action potentials occur in an area outside the oscillatory regions, but less graded action potentials occur together with repetitive firing over a considerable range of channel densities. The presently found relationship between channel densities and oscillatory behavior may be relevance for understanding principal spiking patterns of cortical neurons (regular firing and fast spiking). It may also be of relevance for understanding the action of pharmacological compounds on brain oscillatory activity.

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