Biomedical Engineering Reference
In-Depth Information
Fig. 2.5
The endoneurial stroma is non-
regenerative.
To p
: A nerve fiber before
transection, showing the axoplasm (
A
),
myelin sheath (
M
), associated Schwann
cell (
S
), as well as a very thin basement
membrane (not labeled) surround-
ing
M
and
S
. The entire nerve fiber is
surrounded by the endoneurium (
E
), a
loosely structured stroma (not clearly
visible in this photo; a clearer image
of collagen fibers in intact endoneu-
rial stroma is shown in Fig. 6.2). Scale
(
bottom right
): One half of the 1-µm
scale bar in the original photo is shown.
Bottom
: 26 months after transection the
domain previously occupied by a nerve
fiber in the distal stump is now filled
with a sheaf of collagen fibers, shown
above mostly as
dots
, that enclose
groups of Schwann cell processes
(
Büngner bands
,
Bb
) encircled by a
basement membrane. The entire sheaf of
fibers is enclosed inside a thin fibroblast
process (
arrow
). The fibroblast in the
lower right
(
fb
) has been partly trans-
formed to a perineurial cell. Microfibrils
(
m
) are observed outside the sheaf.
Scale: 1 µm. (
To p
photo from Burkitt
et al. 1993, Copyright 1993, Harcourt
Publishers Ltd.
Bottom
photo from
Bradley et al. 1998)
proximal stump. The following changes were common to both stumps: Following
transection, continuous extrusion of intrafascicular contents was observed (endo-
neurial bulge; Archibald and Fisher 1987) and a significant mass of collagen was
deposited in the stump (fibrosis; Eather et al. 1986). The collagen fibrils that were
deposited immediately outside Schwann cells in the proximal stump had an aver-
age diameter of 30 nm, compared with 50 nm in normal endoneurial stroma (Mor-
ris et al. 1972b). In the repaired proximal stump, the original uni- or difascicular
structure of the normal nerve trunk disappeared and was replaced by a collection
of small fascicles, filled with small-diameter axons, each fascicle surrounded by its
own multilaminate perineurium (compartmentation; Morris et al. 1972d). Compart-
mentation (also referred to as micro- or minifasciculation) was not observed in the
distal stump; nor was formation of Schwann cell columns observed in the proximal
stump (Morris et al. 1972d). Subdivision of a single fascicle into many was accom-
panied by significant loss in cross-sectional area occupied by endoneurial stroma
(Morris et al. 1972d). The subdivision of the injured nerve trunk into many fascicles
has been observed in early studies (Cajal 1928). Compartmentation, typically ac-
