Biomedical subjects

R R Poznański

Publications and source records attributed to R R Poznański.

4 recordsLinked to original sources

PubMed1996

Subthreshold response to white-noise current input in a tapering cable model of a neuron.

The expectation (mean) and variance of the depolarization in the absence of a threshold for action-potential generation is obtained in a neuron model represented by a tapering equivalent cable with a random (white noise) synaptic input current at a point along the dendrites. The results show that the introduction of a taper in the equivalent-cable representation of the neuron produces larger values for both the expectation and variance which are neither insensitive nor symmetrical with respect to the location of the input. It is also shown that taper extends the invariance of the variability in the steady-state somatic response to proximally located random inputs, implying that only small changes in the noisiness of the somatic response occur for a random input located in the dendrites.

Animals↗

PubMed1990

Analysis of a postsynaptic scheme based on a tapering equivalent cable model.

An analytic solution of a modified cable equation with reversal potentials is used to explore nonlinear synaptic effects in passive dendritic trees of arbitrary geometry. It is shown that shunting inhibition can be effective when located off the direct path between the excitation and the soma. It is also shown that a peripherally placed excitatory input juxtaposed with a shunting inhibitory input may produce a voltage-peak minimum at the soma in order to suppress the initiation of an action potential at the axon hillock. The applicability of this postsynaptic scheme as a basis for a directionally selective signal generation in the retina is discussed.

Animals↗

PubMed1988

Membrane voltage changes in passive dendritic trees: a tapering equivalent cylinder model.

An exponentially tapering equivalent cylinder model is employed in order to approximate the loss of the dendritic trunk parameter observed from anatomical data on apical and basilar dendrites of CA1 and CA3 hippocampal pyramidal neurons. This model allows dendritic trees with a relative paucity of branching to be treated. In particular, terminal branches are not required to end at the same electrotonic distance. The Laplace transform method is used to obtain analytic expressions for the Green's function corresponding to an instantaneous pulse of current injected at a single point along a tapering equivalent cylinder with sealed ends. The time course of the voltage in response to an arbitrary input is computed using the Green's function in a convolution integral. Examples of current input considered are (1) an infinitesimally brief (Dirac delta function) pulse and (2) a step pulse. It is demonstrated that inputs located on a tapering equivalent cylinder are more effective at the soma than identically placed inputs on a nontapering equivalent cylinder. Asymptotic solutions are derived to enable the voltage response behaviour over both relatively short and long time periods to be analysed. Semilogarithmic plots of these solutions provide a basis for estimating the membrane time constant tau m from experimental transients. Transient voltage decrement from a clamped soma reveals that tapering tends to reduce the error associated with inadequate voltage clamping of the dendritic membrane. A formula is derived which shows that tapering tends to increase the estimate of the electrotonic length parameter L.

Animals↗

PubMedDate not supplied

Nonlinear summation of junction potentials in a three-dimensional syncytium.

A three-dimensional "cable" equation with reversal potentials is derived for an infinite syncytium. Its solution is found analytically by using Green's function methods for the special case of two impulsive conductance changes activated at different "points" in space. It is shown that junction potentials generated at different sites in the syncytium do not in theory sum linearly.

Action Potentials↗