| Comments |
"The most direct measurements of action potential latencies
and conduction velocities come from dual somatic
and axonal intracellular recordings. Because of the small
size of most CNS glutamatergic axons, such intracellular
recordings have been possible only in the axon initial
segment region or in distal axon by recording from axon
“blebs,” the balled ends of axons created by the slicing
procedure. These recordings have allowed direct identification
of the arrival/development of the action potential
peak in the soma and at various points along the axon of
layer 5 neocortical neurons. The recordings thus predict conduction velocities, measured as the arrival of the action
potential peak, that are slower in the antidromic direction
than in the orthodromic direction (Shu et al., 2006,
2007a,b Kole et al., 2007) (Table 1). The recordings also
verify axonal initiation, showing that the action potential
normally develops first in the initial segment of the axon
(Shu et al., 2007b Schmidt-Hieber et al., 2008)...The propagation time for an action potential traveling
from the axonal action potential initiation site to a presynaptic
bouton could be up to several milliseconds for both
myelinated and unmyelinated axons. Table 1 shows the
orthodromic conduction velocities for a variety of neurons
studied with recent single-fiber techniques." |