Journal Article•
Rapid pressure changes and surface displacements in the squid giant axon associated with production of action potentials.
01 Jan 1982-Journal of Physiological Sciences (PHYSIOLOGICAL SOCIETY OF JAPAN)-Vol. 32, Iss: 1, pp 69-81
TL;DR: In this article, it was shown that the squid giant axon swells when an action potential is generated, reaching its maximum swelling at the peak of the action potential, and that the undershoot of the membrane potential is associated with a marked shrinkage of the axon.
Abstract: By using both optical and mechano-electric detectors, we have shown that the squid giant axon swells when an action potential is generated. The maximum swelling is reached at the peak of the action potential. The undershoot of the membrane potential is associated with a marked shrinkage of the axon. We have also demonstrated these mechanical changes in axons from which a major portion of the axoplasm has been removed. We have examined the effects of changing the tonicity of the external medium and of applying several chemical reagents.
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Journal Article•
TL;DR: A model for mechanical displacements as arising from the driving of surface wave modes in which potential energy is stored in elastic properties of the neuronal membrane and cytoskeleton while kinetic energy is carried by the axoplasmic fluid is presented.
Abstract: Many diverse studies have shown that a mechanical displacement of the axonal membrane accompanies the electrical pulse defining the action potential (AP). We present a model for these mechanical displacements as arising from the driving of surface wave modes in which potential energy is stored in elastic properties of the neuronal membrane and cytoskeleton while kinetic energy is carried by the axoplasmic fluid. In our model, these surface waves are driven by the travelling wave of electrical depolarization characterizing the AP, altering compressive electrostatic forces across the membrane. This driving leads to co-propagating mechanical displacements, which we term Action Waves (AWs). Our model allows us to estimate the shape of the AW that accompanies any travelling wave of voltage, making predictions that are in agreement with results from several experimental systems. Our model can serve as a framework for understanding the physical origins and possible functional roles of these AWs.
103 citations
TL;DR: In this article, the authors provide a comprehensive overview of the underlying mechanics of both acoustic energy and neuronal membranes, defining the primary variables for a subsequent review of the field's proposed mechanisms supporting LIFU's neuromodulatory effects.
Abstract: Low intensity focused ultrasound (LIFU) has been gaining traction as a non-invasive neuromodulation technology due to its superior spatial specificity relative to transcranial electrical/magnetic stimulation. Despite a growing literature of LIFU-induced behavioral modifications, the mechanisms of action supporting LIFU's parameter-dependent excitatory and suppressive effects are not fully understood. This review provides a comprehensive introduction to the underlying mechanics of both acoustic energy and neuronal membranes, defining the primary variables for a subsequent review of the field's proposed mechanisms supporting LIFU's neuromodulatory effects. An exhaustive review of the empirical literature was also conducted and studies were grouped based on the sonication parameters used and behavioral effects observed, with the goal of linking empirical findings to the proposed theoretical mechanisms and evaluating which model best fits the existing data. A neuronal intramembrane cavitation excitation model, which accounts for differential effects as a function of cell-type, emerged as a possible explanation for the range of excitatory effects found in the literature. The suppressive and other findings need additional theoretical mechanisms and these theoretical mechanisms need to have established relationships to sonication parameters.
11 citations
TL;DR: In this paper , the authors introduce the concept of paths of abstraction, and use historical and contemporary examples to point to their role in guiding the development of relevance criteria which support modeling strategies in science.
Abstract: Abstract In philosophy of science, abstraction tends to be subsumed under representation, often being described as the omission of a target’s features when it is represented. This approach to abstraction sidesteps cognitive aspects of abstraction processes. However, cognitive aspects of abstraction are important in understanding the role of historically grounded epistemic criteria supporting modeling in science. Drawing on recent work on the relation between metaphor and abstraction, we introduce the concept of paths of abstraction, and use historical and contemporary examples to point to their role in guiding the development of relevance criteria which support modeling strategies in science.
5 citations
Posted Content•
22 Sep 2008
TL;DR: In this paper, a biological model of memory based on the mechanical oscillations of axons during action potential and on the changes in the extra cellular matrix composition when a mechanical strain is applied on it was presented.
Abstract: We expose first a biological model of memory based on one hand of the mechanical oscillations of axons during action potential and on the other hand on the changes in the extra cellular matrix composition when a mechanical strain is applied on it. Due to these changes, the stiffness of the extra cellular matrix along the most excited neurons will increase close to these neurons due to the growth of astrocytes around them and to the elastoplastic behavior of collagen. This will create preferential paths linked to a memory effect. In a second part, we expose a physical model based on random walk of the action potential on the array composed of dendrites and axons. This last model shows that repetition of the same event leads to long time memory of this event and that paradoxical sleep leads to the linking of different events put into memory.
1 citations
DOI•
TL;DR: A universal mathematical model is necessary in order to interpret all biophysical changes observed during the nerve impulse, and the key to achieving this task is to adapt the Hodgkin–Huxley model.
References
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TL;DR: Outer hair cells from the cochlea of the guinea‐pig were isolated and their motile properties studied in short‐term culture by the whole‐cell variant of the patch recording technique, concluding that interaction between actin and myosin, although present in the cell, is unlikely to account for the cell motility.
Abstract: 1. Outer hair cells from the cochlea of the guinea-pig were isolated and their motile properties studied in short-term culture by the whole-cell variant of the patch recording technique. 2. Cells elongated and shortened when subjected to voltage steps. Cells from both high- and low-frequency regions of the cochlea responded with an elongation when hyperpolarized and a shortening when depolarized. The longitudinal motion of the cell was measured by a differential photosensor capable of responding to motion frequencies 0-40 kHz. 3. Under voltage clamp the length change of the cell was graded with command voltage over a range +/- 2 microns (approximately 4% of the length) for cells from the apical turns of the cochlea. The mean sensitivity of the movement was 2.11 nm/pA injected current, or 19.8 nm/mV membrane polarization. 4. The kinetics of the cell length change during a voltage step were measured. Stimulated at their basal end, cells from the apical (low-frequency) cochlear turns responded with a latency of between 120 and 255 microseconds. The cells thereafter elongated exponentially by a process which could be characterized by three time constants, one with value 240 microseconds, and a second in the range 1.3-2.8 ms. A third time constant with a value 20-40 ms characterized a slower component which may represent osmotic changes. 5. Consistent with the linearity shown to voltage steps, sinusoidal stimulation of the cell generated movements which could be measured at frequencies above 1 kHz. The phase of the movement relative to the stimulus continued to grow with frequency, suggesting the presence of an absolute delay in the response of about 200 microseconds. 6. The electrically stimulated movements were insensitive to the ionic composition of the cell, manipulated by dialysis from the patch pipette. The responses occurred when the major cation was K+ or Na+ in the pipette. Loading the cell with ATP-free solutions or calcium buffers did not inhibit the response. 7. It is concluded that interaction between actin and myosin, although present in the cell, is unlikely to account for the cell motility. Instead, it is proposed that outer hair cell motility is associated with structures in the cell cortex. The implications for cochlear mechanics of such force generation in outer hair cells are discussed.
801 citations
350 citations
TL;DR: Using MRI, it is found that a slowly diffusing water pool was expanding upon activation on the human visual cortex at the detriment of a faster diffusing pool, reflecting early biophysical events that take place in the activated cells, such as cell swelling and membrane expansion.
Abstract: Using MRI, we found that a slowly diffusing water pool was expanding (1.7 ± 0.3%) upon activation on the human visual cortex at the detriment of a faster diffusing pool. The time course of this water phase transition preceded the activation-triggered vascular response detected by usual functional MRI by several seconds. The observed changes in water diffusion likely reflect early biophysical events that take place in the activated cells, such as cell swelling and membrane expansion. Although the exact mechanisms remain to clarify, access to such an early and direct physiological marker of cortical activation with MRI will provide opportunities for functional neuroimaging of the human brain.
252 citations
TL;DR: In this paper, the authors demonstrated that a propagated nerve impulse in a crab nerve produced an outward movement of 50 to 100 angstroms of the nerve surfce and a rise in swelling pressure on the order of 5 dynes per square centimeter.
Abstract: Swelling of nerve fibers during the action potential was demonstrated by three different methods. Generation of a propagated nerve impulse in a crab nerve produced an outward movement of 50 to 100 angstroms of the nerve surfce and a rise in swelling pressure on the order of 5 dynes per square centimeter. In squid giant axons, the amplitude of the observed outward movement of the surface was small.
224 citations
Australian Catholic University1, Cardiff University2, University College London3, National University of Singapore4, University of Nottingham5, Brighton and Sussex Medical School6, King's College London7, Engineering and Physical Sciences Research Council8, University of Manchester9, University of Oxford10
TL;DR: Ten advantages of ultra‐strong gradients for microstructural imaging are described, and how the increase of the accessible measurement space compared to a lower‐gradient systems can accelerate developments in the areas of axon diameter distribution mapping, tumour characterisation, and quality enhancement of images acquired on lower‐ gradient systems.
145 citations