1. Denervated fast extensor digitorum longus (EDL) muscles of adult rats were stimulated electrically for up to 4 months with a 'slow' pattern resembling the activity in soleus (Sol) motor units and examined with antibodies against myosin heavy chains (MHCs). 2. The normal EDL contained, on average, 45% type IIB, 29% type IIX, 23% type IIA and 3% type I fibres. All type IIB and almost all type IIX fibres disappeared during the first 3 weeks of stimulation. They were replaced by type IIA and type I fibres, whose percentages increased to about 75 and 15, respectively. Type IIA fibres remained at 75% for nearly 2 months and were then gradually replaced by type I fibres during the next 2 months. The transformation occurred sequentially in the order II BÏII X II A I, the first step (II BÏII X II A) occurring after a short delay (2 weeks) and the last step (II A I in originally IIB or IIX fibres) after a long delay (> 2 months). During the transformation coexpression of MHCs occurred. 3. It appears that the transformation to type I fibres occurred in pre-existing type II fibres since no signs of fibre damage or regeneration were observed. 4. Normal EDL was also stimulated through an intact nerve with the same pattern for up to 37 days. The effects on fibre type distributions were identical to those observed in the denervated EDL. The result indicated that the Sol-like pattern of evoked muscle activity, rather than nerve-derived trophic influences or denervation per se, was primarily responsible for the fast to slow transformation.

Although preservation of the sensitivity of the nipple and areola is an important goal in breast surgery, only scant and contradictory information about the course and distribution of the supplying nerves is found in the literature. The existing controversy might be due to the difficulty in dissecting the thin nerves and to frequent anatomic variations that bias the results if only a small number of cadavers are dissected. We dissected 28 female cadavers and found that the nipple and areola were always innervated by the lateral and anterior cutaneous branches of the 3rd, 4th, and 5th intercostal nerves. The most constant innervation pattern was by the 4th lateral cutaneous branch (79 percent) and by the 3rd and 4th anterior cutaneous branches (57 percent). The anterior cutaneous branches took a superficial course within the subcutaneous tissue and terminated at the medial areolar border in all dissected breasts. The lateral cutaneous branches took a deep course within the pectoral fascia and reached the nipple from its posterior surface in 93 percent of the dissected breasts. In 7 percent of the dissected breasts, the lateral cutaneous branches took a superficial course within the subcutaneous fat and reached the nipple from the lateral side. These findings suggest that the nerves innervating the nipple and areola are best protected if resections at the base of the breast and skin incisions at the medial areolar border are avoided.

Background: Extrafusal muscle fibers of human striated skeletal muscles are known to have a uniform innervation pattern. Motor endplates (MEP) of the ''en plaque'' type are located near the center of muscle fibers and distributed within the muscles in a narrow band. The aim of this study was to evaluate the innervation pattern of human facial muscles and compare it with that of skeletal muscles.Methods: Ten facial muscles from 11 human cadavers were dissected, the nerve entrance points located, and the dimensions measured. All muscles were stained in toto for MEPs using Acetylcholinesterase (AChE) and examined under the microscope to determine their location. Single muscle fibers were teased to evaluate the stained MEPs.Results: The length of the different facial muscles varied from 29 to 65 mm, which correlated to the length of the corresponding muscle fibers. MEP zones were found on the muscles in the immediate vicinity of the nerves' entrance points and located eccentrically. Numbers and locations varied from muscle to muscle. Three MEP zone distribution patterns were differentiated: numerous small MEP zones were evenly spread over the muscle, a predominant MEP zone and two to three small zones were spread at random, and two to four MEP zones of equal size were randomly scattered.One MEP of the ''en plaque'' type was found in 73.8% of the muscle fibers and two to five MEPs were found in 26.2%. The distances between the multiple MEPs on one muscle fiber varied from 10 to 500 µm.Conclusions: This study suggests that facial muscles differ from skeletal muscles regarding distribution and number of MEPs. The eccentric location of MEP zones and multiple MEPs suggests there is an independent mechanism of neural regulation in the facial muscle system. Anat.

Teasing preparations of cat extraocular muscles (EOM) were used to study the arrangement of muscle fibers and the distribution of the different cholinesterase-positive sites, i.e. (1) large motor endplates, (2) small motor endings of the 'en grappe' type, (3) myotendinous junctions and (4) myomyous junctions. The distribution of these cholinesterase-positive structures gives clear evidence of a complex muscle architecture of cat EOM. In the global layer of cat EOM, only multiply innervated muscle fibers run the whole length of the muscle. The focally innervated muscle fibers are generally shorter; they are usually arranged in series of two to three fibers being interconnected by myomyous junctions. Moreover, muscle fiber splitting is frequently present resulting in a netlike arrangement of muscle fibers. Most of the myomyous junctions occur between focally innervated muscle fibers, but also end-to-side connections of focally to multiply innervated muscle fibers are observed; multiply innervated muscle fi0ers have not been found connected to each other. In this layer, large motor endplates are distributed in several bands between origin and insertion. In the orbital layer all muscle fibers run from tendon to tendon, focally as well as multiply innervated ones. Here, large motor endplates are confined to a band in the middle of the muscle, and myomyous junctions are generally absent. Some functional implications of this complex architecture of cat EOM are discussed.

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