NERVE FIBER TERMINATIONS
Figure 8­63
Downloaded
by
[Rutgers
University
130.219.8.11]
at
[04/08/15].
Copyright
©
McGraw-Hill
Global
Education
Holdings,
Within skeletal muscle and tendons are two types of encapsulated nerve terminations that function as stretch re-
ceptors. In tendon, these receptors are known as Golgi tendon organs; in muscle, they are known as muscle
LLC.
spindles.
Not
Muscle spindles (arrowhead) are enclosed by a connective tissue capsule and are situated between the normal
to
skeletal muscle cells, which are called the extrafusal fibers (arrows). Within the capsule is an area filled with
be
redistributed
lymph, containing two to ten smaller skeletal muscle cells, or intrafusal fibers. Innervation to the extrafusal fibers
is provided by axons terminating in motor end plates (curved arrows), neuromuscular junctions, or myoneural junc-
tions, three different terms for the same structure.
or
This image shows several extrafusal muscle fibers and a muscle spindle in the center of the field. The connective
modified
tissue capsule is not shown in this specimen. The primary sensory endings (annulospiral endings) are wrapped sev-
eral times around the intrafusal fibers. Details of the nuclear structure and striation pattern are lost in this example.
in
At the ends of the spindle are the secondary or flower spray endings that terminate on the striated portions of the
any
intrafusal muscle fibers. For higher magnifications of this image, see the next two micrographs in this lesson set.
way
without
No single histologic preparation can capture all of the details of the muscle spindle; therefore, you should refer to
texts or atlases for a more complete morphologic picture.
permission.
420

---