Action potentials are initiated more easily in distal than in proximal dendrites. Spike initiation in the dendrite depends on the passive cable properties of the dendritic membrane, its Na+-channel density, and local structural properties, mainly the diameter of the dendrites. Careful analysis of the threshold conditions for action potential initiation at the initial segment or the dendrites revealed that, despite the lower voltage threshold for spike initiation in the initial segment, an action potential can be initiated in the dendrite before the initial segment fires a spike. A "weakly" excitable (Na = 3 mS/cm2) dendritic membrane most accurately describes the experimentally observed attenuation of the back-propagated action potential. A high Na+-channel density of Na = 700 mS/cm2 at the axon hillock/initial segment region was required to secure antidromic invasion of the somato-dendritic membrane, whereas for the orthodromic direction, a Na+-channel density of Na = 1,200 mS/cm2 was required. on motoneurons in organotypic rat spinal cord slice cultures.
It accurately reproduces the results presented by Larkum et al. We present a model of spinal motoneurons that is consistent with observed physiological properties of spike initiation in the initial segment/axon hillock region and action potential back-propagation into the dendritic tree. Here we show that action potentials in motoneurons can be initiated in the dendrite as well, resulting in a biphasic dendritic action potential. This phenomenon has been observed in neocortical pyramidal cells as well as in cultured motoneurons.
Regardless of the site of current injection, action potentials usually originate at or near the soma and propagate decrementally back into the dendrites.
0 kommentar(er)
