Biomedical Engineering Reference
In-Depth Information
Fig. 6.4
The conduction velocity of a regenerated nerve is typically lower than that of the normal
nerve. Electrophysiological behavior of nerve trunk regenerated across a 10-mm gap bridged by a
collagen tube filled with nerve regeneration template (NRT) matrix. Oscilloscope tracings of the
amplitude of A-fiber and B-fiber nerve action potentials for normal rat sciatic nerve and regener-
ated nerve trunk. A-fiber action potential probably represents signal carried only by axons larger
than about 6 µm in diameter; it corresponded to conduction velocities of about 50 ± 2 m/s for the
regenerated nerve and 67 ± 3 m/s for the normal control. B-fiber potential was observed only in
regenerated trunks, corresponding to velocities of about 10-25 m/s. Conduction velocities were
calculated from the measured distance between electrodes and from the latency, i.e., the time
lag between the electrical stimulus (
arrow
) and the peak in amplitude. (From Chamberlain et al.
1998b)
6.4.8
Long-Term Evidence for Synthesis of a Conducting
Nerve Trunk
In the preceding sections we used an assay based on short-term data (i.e., data on
percent reinnervation across a gap obtained within generally less than 20 weeks).
This assay reports on the presence of myelinated axons along the nerve trunk; no
direct information was supplied, however, on the ability of the nerve trunk to func-
tion as a conducting organ.
Data obtained after about 20 weeks, sufficient time for bridging of many tubu-
lated gaps, frequently include electrophysiological data. An example of such data
appears in Fig.
6.4
. Functional information of this type is useful because it strongly
suggests the presence of at least one regenerated fascicle, a structural unit com-
prising a bundle of nerve fibers embedded in the endoneurium and encased in the
perineurium. Since, however, electrophysiological data have not been confidently
