Biomedical subjects

Ichiji Tasaki

Publications and source records attributed to Ichiji Tasaki.

5 recordsLinked to original sources

PubMed2006

A note on the local current associated with the rising phase of a propagating impulse in nonmyelinated nerve fibers.

To extend our recent paper dealing with the cable properties and the conduction velocity of nonmyelinated nerve fibers (Bull. Math. Biol. 64, 1069; 2002), the behavior of the local current associated with the rising phase of a propagating action potential is discussed. It is shown that the process of charging the membrane capacity by means of the local current plays a crucial role in determining the velocity of nerve conduction. The symmetry of the local current with respect to the boundary between the resting and active regions of the nerve fiber is emphasized. It is noted that there are several simple quantitative rules governing the intensities of the capacitive, resistive and total membrane currents observed during the rising phase of an action potential.

Action Potentials↗

PubMed2005

Repetitive abrupt structural changes in polyanionic gels: a comparison with analogous processes in nerve fibers.

Repetitive abrupt structural changes can be produced in a small piece of cross-linked polyacrylate hydrogel by exchanging the divalent counter-ions in the superficial gel layer to monovalent cations. The temporal variations of the hydrostatic pressure, electric impedance and potential associated with these structural changes frequently show striking resemblance to those encountered during repetitive excitation of living nerve fibers. Common anions, such as fluoride, phosphate, aspartate, chloride, etc., produce a marked lyotropic (Hofmeister) effect on the repetitive structural changes both in synthetic polyanionic gels and in squid giant nerve fibers. Mechanical stress which brings about constraints in the polymer chains is found to facilitate the production of repetitive structural changes in the gel. In the stretched superficial layer of a synthetic polyanionic gel, a calcium-salt produces highly refractive bundles of polymer chains. In the Appendix, a crude model of ionized polymer chains that facilitates the consideration of cooperative structural changes in the gel is described.

Acrylates↗

PubMed2004

On the conduction velocity of nonmyelinated nerve fibers.

Nerve impulse conduction in nonmyelinated nerve fibers is analyzed by considering this process as a direct consequence of the coexistence of two structurally distinct regions, active and resting. Assuming that the active (i.e. swollen) region of the fiber is in direct contact with the resting (i.e. shrunken) region, a simple procedure for deriving the conduction velocity equation is described. The physico-chemical significance of the quantities in this velocity equation is briefly discussed.

Animals↗

PubMed2002

Spread of discrete structural changes in synthetic polyanionic gel: a model of propagation of a nerve impulse.

Thin fibers of cross-linked polyacrylate gel were prepared by inducing polymerization reaction inside long glass or Tygon tubings. By immersing these gel fibers in salt solutions containing both Ca(2+) and Na(+) at varying ratios, a discontinuous transition from the swollen state to the shrunken was demonstrated. A very sharp boundary was observed between the swollen and shrunken portions of the gel fiber. It was found possible to displace this sharp boundary continuously by application of a weak electric current. Based on the similarity in swelling behavior between nerve fibers and synthetic gel fibers, a non-myelinated nerve fiber carrying an impulse was treated as a cylindrical gel layer consisting of two distinct portions, a swollen (active) portion connected directly to the remaining shrunken (resting) portion. By applying the cable theory to this model of the nerve fiber, mathematical expressions describing the conduction velocity, the maximum rate of potential rise, etc. in terms of the electric parameters of the fiber were derived.

Action Potentials↗

PubMed2002

On the cable theory of nerve conduction.

Conduction of an impulse in the nonmyelinated nerve fiber is treated quantitatively by considering it as a direct consequence of the coexistence of two structurally distinct regions, resting and active, in the fiber. The profile of the electrical potential change induced in the vicinity of the boundary between the two regions is analyzed by using the cable equations. Simple mathematical formulae relating the conduction velocity to the electrical parameters of the fiber are derived from the symmetry of the potential profile at the boundary. The factors that determine the conduction velocity in the myelinated nerve fiber are reexamined.

Animals↗