Extracellular electrical signals in a neuron-surface junction: model of heterogeneous membrane conductivity

Signals recorded from neurons with extracellular planar sensors have a wide range of waveforms and amplitudes. This variety is a result of different physical conditions affecting the ion currents through a cellular membrane. The transmembrane currents are often considered by macroscopic membrane models as essentially a homogeneous process. However, this assumption is doubtful, since ions move through ion channels, which are scattered within the membrane. Accounting for this fact, the present work proposes a theoretical model of heterogeneous membrane conductivity. The model is based on the hypothesis that both potential and charge are distributed inhomogeneously on the membrane surface, concentrated near channel pores, as the direct consequence of the inhomogeneous transmembrane current. A system of continuity equations having non-stationary and quasi-stationary forms expresses this fact mathematically. The present work performs mathematical analysis of the proposed equations, following by the synthesis of the equivalent electric element of a heterogeneous membrane current. This element is further used to construct a model of the cell-surface electric junction in a form of the equivalent electrical circuit. After that a study of how the heterogeneous membrane conductivity affects parameters of the extracellular electrical signal is performed. As the result it was found that variation of the passive characteristics of the cell-surface junction, conductivity of the cleft and the cleft height, could lead to different shapes of the extracellular signals

Nicotinic Acetylcholine Receptor Kinetics of the Neuromuscular Junction Simulated Using SPICE: An Illustration of Physiological Process Simulation with Conventional Circuit Simulation Software

With the advent of modern day computational power, there is a great deal of interest in the simulation and modeling of complex biological systems. A significant effort is being made to develop generalized software packages for the simulation of cellular processes, metabolic pathways and complex biochemical reaction systems. The advantages to being able to implement and simulate complex biological systems in a virtual environment are several. Simulations of this type, if sufficiently detailed, provide experimental physiologists with the ability to visualize the dynamics of a given biological system of interest. The validity of hypotheses related to the system under study can be tested in a virtual environment prior to carrying out experimental studies. We discuss a systematic approach by which certain reaction balance equations can be transformed into equivalent circuit models that may then be implemented and simulated using SPICE (Simulation Program with Integrated Circuit Emphasis). To introduce the methodology, we develop a simulation for a single ligand-receptor interaction and then we utilize this framework to implement a simulation of nicotinic acetylcholine receptor kinetics at the postsynaptic membrane of the neuromuscular junction. Although the example studies that we present are specific to biochemical reaction systems associated with cellular processes, the procedure is equally applicable to any biochemical or chemical process for which analogous systems of mass balance equations exist that have an equivalent circuit analog. The overall approach described above is useful from the biomedical engineering educational perspective because SPICE simulators are readily accessible to students in freeware versions that they can use to simulate and visualize relatively complex physiological processes such as neurotransmitter/receptor dynamics

Analysis of fatal-serious accidents and dangerous vehicle movements at access points on Malaysian Rural Roads

raffic accidents have been recognized as one of the major causes of human and economic losses in both developed and developing countries. In 20 l 0, Malaysia recorded a total of 414,421 accidents, resulting in an average of 19 deaths from road accidents every single day. This research analyzed the factors relevant to fatal and serious accidents on rural federal roads in Malaysia. The objective was to identify the dangerous vehicle movements and factors posing significant risks for fatal-serious accidents at access points (non-signalized minor junctions) and to suggest countermeasures. This research consists of seven Chapters. Firstly, Chapter l provides a discussion of accident trends and traffic studies in general. In Chapter 2, the scope was then narrowed down to focus on the accident black spot in order to identify the hazardous or black spot sections. Chapter 3 further examines the quantitative accident records and traffic characteristics for each of the selected sections. Next, Chapter 4 focuses on vehicle movements at non-signalized intersections. Chapter 5 provides the methodology and procedures adopted in the development of accident prediction models. Chapter 6 focuses on the development of gap acceptance model. Finally, Chapter 7 provides the development of serious conflict model. This research carries out numerous surveys to observe various traffic movements, including right and left turns, from minor and major roads, in addition to many other characteristics, in order to construct accident analysis models. One of the findings is that right-turn motorcycles caused serious conflicts and right tum movement was considered o be the most dangerous movement. Based on this finding, this research further examines the driver behavior of gap acceptance and serious conflicts using the proposed four gap patterns for a right-turn vehicle from minor to major roads at access points in Road Section 10 of the Federal Road 50 (Unchannelized intersection connected 2-lane minor and 4-lane major roads). In addition, further analysis is perfon:ned to identify the gap pattern and the factors relevant to serious conflicts. The results demonstrated thal right-turning vehicles, especially motorcycles, apparently intended to start turning right in a very short gap and the approaching speed and the gap between a pair of vehicles from opposite directions in the mainstream were the critical factors causing serious conflicts to the right-turn vehicles. In addition, this research studies more on the other two non-signalized intersections located in Road Sections 2 (Channelized intersection connected 2-lane minor and 6-lane major roads) and 9 (Unchannelized intersection connected 2-lane minor and 4-lane major roads with a traffic signal in close proximity) of the Federal Road 50. The results found that the existence of channelization on the intersection encouraged the right-tum vehicle to accept a longer gap. Furthermore, the combined analysis of all the three un-signalized intersections (Road Sections 2, 9 and 0), reveals that angular serious conflict, nose-tail conflict, and if the second vehicle in he pair in the mainstream is a motorcycle or a passenger car, can significantly influence the right-tum vehjcles to accept a short gap. On the other hand, a traffic light located in a relatively close distance to the access point, as well as channelization on the intersection can cause the right-tum vehicles to accept longer gaps

Analysis of fatal-serious accidents and dangerous vehicle movements at access points on Malaysian Rural Roads

raffic accidents have been recognized as one of the major causes of human and economic losses in both developed and developing countries. In 20 l 0, Malaysia recorded a total of 414,421 accidents, resulting in an average of 19 deaths from road accidents every single day. This research analyzed the factors relevant to fatal and serious accidents on rural federal roads in Malaysia. The objective was to identify the dangerous vehicle movements and factors posing significant risks for fatal-serious accidents at access points (non-signalized minor junctions) and to suggest countermeasures. This research consists of seven Chapters. Firstly, Chapter l provides a discussion of accident trends and traffic studies in general. In Chapter 2, the scope was then narrowed down to focus on the accident black spot in order to identify the hazardous or black spot sections. Chapter 3 further examines the quantitative accident records and traffic characteristics for each of the selected sections. Next, Chapter 4 focuses on vehicle movements at non-signalized intersections. Chapter 5 provides the methodology and procedures adopted in the development of accident prediction models. Chapter 6 focuses on the development of gap acceptance model. Finally, Chapter 7 provides the development of serious conflict model. This research carries out numerous surveys to observe various traffic movements, including right and left turns, from minor and major roads, in addition to many other characteristics, in order to construct accident analysis models. One of the findings is that right-turn motorcycles caused serious conflicts and right tum movement was considered o be the most dangerous movement. Based on this finding, this research further examines the driver behavior of gap acceptance and serious conflicts using the proposed four gap patterns for a right-turn vehicle from minor to major roads at access points in Road Section 10 of the Federal Road 50 (Unchannelized intersection connected 2-lane minor and 4-lane major roads). In addition, further analysis is perfon:ned to identify the gap pattern and the factors relevant to serious conflicts. The results demonstrated thal right-turning vehicles, especially motorcycles, apparently intended to start turning right in a very short gap and the approaching speed and the gap between a pair of vehicles from opposite directions in the mainstream were the critical factors causing serious conflicts to the right-turn vehicles. In addition, this research studies more on the other two non-signalized intersections located in Road Sections 2 (Channelized intersection connected 2-lane minor and 6-lane major roads) and 9 (Unchannelized intersection connected 2-lane minor and 4-lane major roads with a traffic signal in close proximity) of the Federal Road 50. The results found that the existence of channelization on the intersection encouraged the right-tum vehicle to accept a longer gap. Furthermore, the combined analysis of all the three un-signalized intersections (Road Sections 2, 9 and 0), reveals that angular serious conflict, nose-tail conflict, and if the second vehicle in he pair in the mainstream is a motorcycle or a passenger car, can significantly influence the right-tum vehjcles to accept a short gap. On the other hand, a traffic light located in a relatively close distance to the access point, as well as channelization on the intersection can cause the right-tum vehicles to accept longer gaps