Ronald A. Bergman, Ph.D., Adel K. Afifi, M.D., Paul M. Heidger,
Peer Review Status: Externally Peer Reviewed
A. Human, 10% formalin, H. & E., 435 x.
B. Frog, glutaraldehyde-osmium fixation, toluidine blue stain, 1416 x.
This plate shows some of the histological features of neuromuscular spindles as seen in the human tongue (A) and frog sartorius (B). Note that the neuromuscular spindle is surrounded by skeletal muscle fibers (extrafusal fibers). Each spindle contains several small muscle fibers (the intrafusal fibers), myelinated nerve fibers enclosed within a connective tissue capsule, which is pierced by the nerve fibers reaching the spindle. Nerve fibers of the spindle are both sensory and motor. Information conveyed from and to the muscle spindle is not consciously received but is important in reflex regulation of muscle tone. Intrafusal muscle fibers of the spindle receive axons of the gamma motor neurons in the spinal cord, whereas the extrafusal muscle fibers receive axons of the larger alpha motor neurons. See Plates 120 and 121.
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