Biomedical subjects

D E Wooldridge

Publications and source records attributed to D E Wooldridge.

8 recordsLinked to original sources

PubMed1984

Movement of ions through fixed pores in the neural membrane.

A simple configuration is first proposed for the pores used by sodium and potassium ions in moving through the neural membrane. The voltage dependence of the ion current through a system of such pores is then derived from diffusion theory and shown not to agree well with experimental observation. Good agreement is obtained, however, when the end segments of the pores are modified to include constrictions and ion-specific trapping centers.

Animals↗

PubMed1984

A "convertible pore" model of neural membrane conductance.

Instead of the single-channel pore proposed earlier [Wooldridge, D. E. (1984) Proc. Natl. Acad. Sci. USA 81, 5609-5612] for the transit of conductance ions through the neural membrane, a pore with a second channel for "influence ions" of calcium or magnesium is considered in this paper. By entering trapping centers at the closed inner ends of the new channels, the influence ions are postulated to alter the rates of chemical reactions that change the configurational state of the gates guarding the inner ends of the nearby conductance channels. This makes the permeability of the conductance channels strongly dependent on voltage. Using a four-state reaction scheme for both the sodium and potassium pore systems, a computer model of the membrane conductance is constructed. When suitable values are assigned to its parameters, the model closely reproduces the results of the Hodgkin-Huxley voltage-clamp and action potential experiments.

Action Potentials↗

PubMed1980

Memory neuron: operating characteristics for the memory component of a neuroconnective brain model.

In this paper an attempt is made to deduce the principal operating operating characteristics that a neuron would need in order to qualify as the basic memory component of a sensory memory system. The required characteristics are found to include the possession of many--perhaps more than 100--separately innervated "recording connections," in each of which the constituent synapses can be put in a persisting state of (inhibitory) effectiveness or of ineffectiveness depending on whether the input axon is inactive or is carrying spikes at the time a triggering "recording command" comes to the memory neuron. The synapses of the recording connections must also respond to an "erasing command" by assuming a common prerecording state unaffected by previous history. At other times a synapse-regeneration feature must operate, to counter any decay of effectiveness of connections that have been left by recording in an effective state as well as any acquisition of effectiveness by connections that have been left in an ineffective state.

Brain↗

PubMed1980

Memory neuron: synapse microchemistry for the memory component of a neuroconnective brain model.

This paper examines the synaptic microchemistry required if a memory neuron is to have the operating characteristics previously attributed to it [Wooldridge, D.E. (1980) Proc. Natl. Acad. Sci. USA, 77,2305-2308]. It is concluded that the requirements can be met by a combination of membrane mechanisms not very different from those that are commonly postulated to explain the properties of known types of neurons.

Brain↗

PubMed1976

Spike-forming model of neural membrane: computer simulation of additional perfused axon experiments.

In this paper a physical model of the neural membrane that I developed is tested for its ability to account for the details of the action potential spikes observed in squid giant axons, when perfused with sodium- and potassium-free fluids and surrounded by a calcium chloride solution. The near-zero resting potential of these perfused axons is accounted for by the model. The sizes, shapes, and conductances of the spikes observed with a number of different perfusates are also accounted for, when suitable values are assigned to the so-far unmeasured membrane constants that control the model properties. The three papers comprising the series are summarized at the end of this paper.

Action Potentials↗

PubMed1976

Spike-forming model of the neural membrane: improvement in the parameter values.

A new set of values is presented for the reaction rate and ionic conductance parameters that determine the properties of the previously developed model of the neural membrane [Wooldridge, D.E. (1975) Proc. Natl. Acad. Sci. USA 72, 3468-3471]. The resulting improvement in the extent of the agreement between theory and experiment is briefly described.

Action Potentials↗

PubMed1975

Spike-forming model of the neural membrane: computer simulation of some perfused axon experiments.

This paper is an attempt to account for the action potential spikes observed when the normal axoplasm of a squid giant neuron is replaced by a postassium-free, sodium-rich fluid, and the axon is immersed in a potassiumand sodium-free, calcium-rich bath. For this purpose a recently described model of the neural membrane [Wooldridge, D. E. (1975) Proc. Nat. Acad. Sci. USA 72, 3468-3471] is extended. Allowances are made for the flow of Ca++, Cl-, and Na+ ions through some of the membrane pore configurations, as well as for some electron conductance, all of amounts too small to be significant in the normal neuron. It is also postulated that the nature of the perfusing fluid affects the rates of some of the reactions that change the convertible gates from one configuration to another, as well as the ionic permeabilities of the resulting configurations. The result of the modifications is a single membrane model that accounts for the 3-sec, 15 muA/cm2 action potential spikes of the perfused axon as well as for the 0.5-msec, 1 mA/cm2 spikes of the normal neuron.

Action Potentials↗

PubMed1975

A spike-forming model of the neural membrane.

A model of the neural membrane is described, based on a set of "convertible gates" on its inner surface. The atomic arrangement of a gate is specified to be subject to modification by a set of chemical reactions, sometimes permitting sodium ions, sometimes potassium ions, sometimes neither, to have access to the transmembrane channel it guards. Reaction rate and current/voltage equations are developed, values assigned to the parameters, and computer solutions obtained. Under pulse or continuous stimulating current the model is found to generate action potential spikes closely similar in height and shape to those of real neurons. Other electrical properties are also relatively neuron-like.

Action Potentials↗