Multi-scale Physiological Systems

Wednesday, June 16 at 05:45pm (PDT)
Thursday, June 17 at 01:45am (BST)
Thursday, June 17 09:45am (KST)

SMB2021 SMB2021 Follow Wednesday (Thursday) during the "MS15" time block.
Note: this minisymposia has multiple sessions. The second session is MS14-NEUR (click here).

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Saeed Farjami (University of Surrey, United Kingdom), Anmar Khadra (McGill University, Canada)


Many physiological systems in neurophysiology, immunology and cell biology possess different time scale at the single cell and population levels. The interaction of such time scales allow these systems to exhibit interesting and complex dynamics that are essential for their function. The use of slow-fast analysis to study these muti-scale systems is essential for deciphering their underlying dynamics. In this minisymposium, speakers will present their work on how such approaches allowed us to determine the implications of the presence of different time-scales on functions in many physiological systems in health and disease.

Anmar Khadra

(McGill University, Canada)
"Characterizing the spatiotemporal patterns produced by an excitable fish keratocyte model"
The spatiotemporal dynamics of self-organizing lamellipodium in crawling keratocytes have been previously studied using a partial differential equation model to understand the three main patterns of activity observed in such cells, including stalling, waving and smooth motility. The model consisted of three key variables: the density of barbed actin filaments, nascent adhesions (NAs) and VASP, an anti-capping protein that gets sequestered by NAs during maturation. Using parameter sweeping, the distinct regimes of behaviour associated with the three activity patterns were identified. By converting the PDE model into an ODE model, we successfully examined the excitability properties of this system and determined all of its patterns of activity. Our results revealed that there are two additional regimes not previously identified: bistability and type IV excitability. We found that these regimes are also present in the PDE model. Applying slow-fast analysis on the ODE model as well as machine-learning based image analysis showed that the ODE model exhibits a canard explosion through a folded-saddle and that rough motility seen in keratocytes is likely due to noise-dependent motility governed by dynamics at the interface of bistability and type IV excitability. The two parameter bifurcation suggested that the increase in the proportion of rough motion is due to a shift in activity towards the bistable and type IV excitable regimes induced by a decrease in NA maturation rate. In this talk, I will provide a summary of these findings.

Theodore Vo

(Monash University, Australia)
"Big Ducks in the Heart"
Early afterdepolarizations (EADs) are voltage oscillations observed during the repolarization phase of the cardiac action potential, and are a potentially lethal source of cardiac arrhyth- mia. Experiments have shown that the production of EADs can depend on the complex interplay between cellular ion channel properties, the extrinsic chemical environment, and the rate of sinoa- trial pacing. However, the mechanisms by which alterations in these qualities induce EADs are not well understood. In this work, we analyse a canonical model of the electrical activity in a cardiac cell using geometric singular perturbation techniques. We demonstrate that the EADs are canard-induced mixed-mode oscillations, and explain the essential role that canards play in producing the rich set of model EAD behaviours, some of which have also been observed in experiments. This dynamical viewpoint gives predictive power that is beyond that of the bio- physical explanation alone while also uncovering a common mechanism for phenomena observed in experiments on both atrial and ventricular cardiac cells.

Sushmita John

(University of Pittsburgh, USA)
"Transitions in neuronal bursting types"
Bursting patterns that fall into an intermediate category between square-wave (fold-homoclinic burst) and pseudo-plateau bursting (fold-subcritical Hopf. burst) have been observed in the voltage recordings of many bursting neurons. Existing research shows that certain mathematical models for these neurons exhibit a transition between square-wave and pseudo-plateau bursting patterns with small parameter changes. However, this transition may be dysfunctional for neurons that necessarily need to spike during the burst. In this work, we study in detail the transition from square-wave to pseudo-plateau bursting patterns seen in neuronal models. We explore properties and parameters of different models to identify the features of currents that affect this transition. The analysis is done using numerical simulations and dynamical systems methods such as fast/slow analysis, bifurcation theory and phase-plane analysis. This approach also helps us to fully characterize intermediate bursting patterns and compare them to the activity seen in bursting neuron types such as respiratory neurons. This is joint work with Dr. Jonathan Rubin.

André Longtin

(University of Ottawa, Canada)
"Multi-delay control, communication and complexity"
Physiological control is inherently slow with delays that can easily exceed the overall response time of a system’ components to time-varying inputs. It is also the case that control may encompass many subunits that act in concert, and that this involves multiple delays that can span milliseconds to seconds. It is generally assumed that the combination of nonlinearity and delays can lead to oscillatory and even more complex behaviour such as chaos or hyperchaos. But there is a point when multiple delays are present where one starts to think in terms of distributions of delays, and of their simplifying action on network dynamics via the integro-differential formulation of the dynamics. This talk will discuss this transition, and show how complexity collapses when there is a low density of delays. We will also discuss these results in the context of understanding the response properties of such multi-delay systems.

Hosted by SMB2021 Follow
Virtual conference of the Society for Mathematical Biology, 2021.