An approximation method for the determination of diffusion and permeability coefficients in nerve trunks

A recently introduced approximation method is applied in order to obtain an expression for the amount of a substance remaining within a nerve at any time, the nerve having been soaked for a long time in a solution containing the substance until the time zero when it is bathed in the same solution but without the substance. The case of a uniform nerve without a sheath leads to substantially the same results as previously obtained by A. V. Hill (1928) for this case. A solution is given for the case of a nerve without sheath but having fibers which are permeable. In this case it is shown how an effective diffusion coefficient for the interstitial fluid can be obtained, as well as the effective inward and outward fiber permeabilities. A solution is given for the case of a nerve with a sheath in which the substance considered does not penetrate the fibers, and it is shown how the effective diffusion coefficients of the sheath and the interstitial fluid can be obtained.     

On the effects of a constant sub-threshold conditioning stimulus upon the response to a constant current test stimulus

The strength of a test stimulus, which is just adequate to produce a response after a sub-threshold conditioning stimulus, is calculated on the basis of Rashevsky's two-factor theory as a function of the strength and duration of the conditioning stimulus. The results are compared with available data for one of a family of curves and found to be in satisfactory agreement.     

Some conditions for sustained oscillations in biochemical chains with feedback inhibition

A chain ofn reactions is considered in which the last substance inhibits the production of the first with degreep, p being the order of the inhibition. Maintained oscillations are possible for certain values of the parameters under the following conditions: (1) If there is no time delay, then there must be at least three compartments (n=3) and either the degree of inhibition is sufficiently large (p>8 forn=3) or there must be enzymatic removal from the first compartment, in which casep≥1. (2) If there are time delays, but there is no enzymatic removal, the degree of the inhibition must be greater than or equal to 2 for any value ofn. (3) If there is a time delay in addition to enzymatic removal, one compartment with simple first order inhibition is sufficient. Conditions on the parameters necessary for maintained oscillations are given for many of the cases discussed.     

Note on the Donnan equilibrium

The solution for the spatial distribution of ions in a Donnan equilibrium has been given by J. H. Bartlett and R. A. Kromhout (1952). The present note gives an explicit solution for the case in which the length of the region containing the membrane is large; in biological situations this requires only that the length considered should be greater than a few hundred Ångstrom units. The Donnan equilibrium may be considered to be a special case of a situation in which forces other than electrical act upon the ions; in particular, it represents the case in which only one ion is acted upon and the energy difference on the two sides of the membrane is infinite. An expression is given for the difference in energy of theith in terms of the electrical potential and of the ion concentrations. As an illustration, the results are applied to nerve membrane potentials.     

A statistical consequence of the logical calculus of nervous nets

A formal method is derived for converting logical relations among the actions of neurons in a net into statistical relations among the frequencies of their impulses.     

A mathematical analysis of elongation and constriction in cell division

An equation for the rate of elongation of a dividing egg is integrated and generalized. The rates of elongation and constriction of a number of eggs under various conditions are analyzed and compared with the theoretical predictions. The theory accounts rather well for a large body of data on elongation and constriction. The general shapes of the elongation and constriction curves are predicted and the orders of magnitude of the parameters are satisfactory. One of the parameters for the elongation curves is related theoretically to the parameter of the constriction curves, and the correct order of magnitude is obtained if one parameter is predicted from the other.     

On the relationship between response time and dosage of a drug as a function of its mode of entry

Theoretical studies have been carried out to determine the effect of the route of entry and the temporal sequence of dosage on the response. On the basis of continuity equations applied to a schematized system, equations relating the dosage and response time have been derived for some special cases, and the form of this relatinship is discussed. This paper is based in part on work done for the Office of Scientific Research and Development under Contract NDCrc-132 with the University of Chicago.     

A note on the interpretation of perseveration in discrimination

The effect of one judgment upon the next judgment in a discrimination situation is considered to be the result of two types of perseveration. One arises from the judgment itself. The other results from a persistence, from one trial to the next, of a transient bias. It is shown that the resulting perseveration can then be a function of the difficulty of the first of the pair of choices. Expressions are derived from which the extent of each effect can be measured from observed proportions of responses.     

Structural coupling of the EF hand and C‐terminal GTPase domains in the mitochondrial protein Miro

Miro is a highly conserved calcium‐binding GTPase at the regulatory nexus of mitochondrial transport and autophagy. Here we present crystal structures comprising the tandem EF hand and carboxy terminal GTPase (cGTPase) domains of Drosophila Miro. The structures reveal two previously unidentified ‘hidden’ EF hands, each paired with a canonical EF hand. Each EF hand pair is bound to a helix that structurally mimics an EF hand ligand. A key nucleotide‐sensing element and a Pink1 phosphorylation site both lie within an extensive EF hand–cGTPase interface. Our results indicate structural mechanisms for calcium, nucleotide and phosphorylation‐dependent regulation of mitochondrial function by Miro.