Muscle fiber

“ The tracts of nerve-fibers along which those impulses pass to the muscles have been mapped out. The influence of temperature, tension and other conditions on the muscular contraction has been investigated in great detail. But we are again almost completely in the dark as to the actual nature and course of the events that take place within the envelopes of the nerve-cell, the nerve-fiber and the muscular fiber when a muscle contracts in obedience to the will. ”

“ Each fiber of striped muscle has an elastic, membranous sheath, the sarcolemma, and consists of rod-shaped cells with a nucleus along the edge, set end to end and having crosswise striations. In unstriated muscle the fibers, which have no sarcolemma, consist of oval or spindle-shaped cells, with a nucleus much smaller than that of striped muscle and situated in the middle. ”

“ When the increase of the undifferentiated protoplasm has gone on far enough, the injured muscle will produce again the muscular substance proper—the contractile fibrils. Muscular fiber, in other words, can be regenerated by itself. ”

“ The microscopic examination of each of these types of muscle shows it to be made up of fibers, these fibers to be made up of muscle cells, the muscle cell to be inclosed in a delicate tubular sheath, or membrane, called the sarcolemma. This membrane, tough and elastic, isolates each fiber. The bundles of fibers, called fasciculi, are surrounded by a fibrous sheath, which is called the perimysium internum; and the entire muscle has likewise an investing sheath of connective tissue, called the perimysium externum. ”

“ The presence of collagen fibrils varies between the adaxial and the abaxial connective tissue layers. au = auricle, bl = basal lamina, cc = central cavity, cf = collagen fibril, ci = cilium, ct = connective tissue, ec = exterior cavity, ep = epithelial cell, fa = fascicle, ic = interradial cavity, ip = interpyramidal muscle, lo = lobe, mf = muscle fiber, np = nerve process, nu = nucleus, ph = pharynx, po = postural muscle, pr = protractor muscle, pv = perivisceral coelom, py = pyramid, re = retractor muscle, to = tooth. ”

“ THE SMOOTH MUSCLE FIBERS consist of long, spindle-shaped cells, the ends of which are frequently spirally twisted, and in the center of which exists a long, rod-shaped kernel or nucleus. Unlike striated muscle, they do not form separate muscular masses, but occur scattered, or arranged in more or less dense layers or strata, in almost all organs. [Footnote: An instance of a considerable accumulation of smooth, muscle fibers is afforded by the muscle pouch of birds, which, with the exception of the outer and inner skin coverings, consists solely of these fibers collected in extensive layers.] ”

“ We do not have, then, in these organs the fine subdivision of control that there is in the skeletal muscles, for a single skeletal motor cell in the spinal cord connects with one or, at the most, a very few muscle fibers. If we consider the uses to which smooth muscles are put, we shall see that finely subdivided control is not important, as it is in the case of the skeletal muscles, where the movements have to be graded very accurately. Smooth muscles are present in the stomach and intestines and other abdominal organs which make movements. ”

“ If an impression be made at the surface of the body, the motion there occasioned is carried by the afferent fiber to the cell-substance; through this substance the motion is transferred to the efferent fiber, along which it passes to the muscle causing muscular contraction. Since the cell liberates motion, and, being much more unstable than the fiber, liberates motion freely, it often happens that a slight impression at the surface is followed by a very violent contraction of the muscle. ”

“ The Muscular System of Farm Animals. —The muscular system is too elaborate, the number of muscles too great, and their modifications for different purposes too complex for consideration in detail in the present volume. All muscles are either striped or unstriped (as examined under the microscope) , according as they are under the immediate control of the will or not. The heart muscle forms an exception, for it is striped though involuntary. The essential characteristic of muscle fibers is contractility, which they possess in high degree. ”

“ The individual muscle fascicles are formed by clusters of ciliated myoepithelial cells that are lined by a basal lamina and that sink into the underlying connective tissue during ontogenesis. The loose connective tissue separates the fascicles from each other and the epithelia [16] .
Many muscle fibers are running along the whole length of the muscle, but the muscles are innervated only from the end that faces the lantern [32] . However, the innervations of the retractor, protractor, and postural muscles are independent only to some degree. ”

“ With a little care you can pick one of the small fibres into fine threads. Now, if you look at one of these under a microscope you find that it is made of still finer fibres, which are much smaller than the threads of a spider's web. One of these smallest threads is called a muscular fibre. Many thousands of muscular fibres are required to make a muscle.
MUSCULAR
FIBRES.
5. Most of the muscles are made fast to the bones. Generally, one end is attached to one bone, and the other to another bone. Sometimes one end is made fast to a bone and the other to the skin or to other muscles. ”

“ In general, the muscles which owe their length to long fibres, have great extent and very little power of motion; whilst those with short fibres, but multiplied so as to give great length as a whole, are remarkable for an opposite character. And this is the reason: all the fibres being equally large, whatever may be their length, have the same degree of force; it is evident then that this force considered in a muscle as a whole, is measured by the number of its fibres. On the other hand, the longer a fibre is, the more it shortens in its contraction ”

“ Muscular system of the feet.—This consists of the retractors of the feet connected with the outer transverse muscle and the circular layer of muscles. In addition to these muscles there are intrinsic transverse muscles which cross the cavity of the feet in various directions (Pl. 51, fig. 20) . There is no special circular layer of fibres.
Histology of the muscle.—The main muscles of the body are unstriated and divided into fibres, each invested by a delicate membrane. Between the membrane and muscle are scattered nuclei, which are never found inside the muscle fibres. ”

“ The guide showed us a coffee-colored piece of sculpture which he said was considered to have come from the hand of Phidias, since it was not possible that any other artist, of any epoch, could have copied nature with such faultless accuracy. The figure was that of a man without a skin; with every vein, artery, muscle, every fiber and tendon and tissue of the human frame represented in minute detail. It looked natural, because somehow it looked as if it were in pain. A skinned man would be likely to look that way unless his attention were occupied with some other matter. ”

“ In some of the long muscles some of the fibres may both arise and terminate in the substance of the muscles. In such a case both ends are bevelled. All the fibres in a muscle are arranged parallel to one another.
The outer surface of each muscle fibre consists of a tough homogeneous membrane, the sarcolemma. The main muscle substance (see fig. 11) is composed of several parts, viz. the fibrillae, the sarcoplasm and the nuclei. Under the action of reagents the muscle fibre may be split into a number of longitudinal elements. These are the fibrillae. ”

“ They are attached chiefly to bones but also to cartilages, ligaments, and skin, either by means of tendons, which are cords or bands of white inelastic fibrous tissue, or by means of aponeuroses, membranous expansions of the same nature. Most voluntary muscles consist of a belly and two ends or tendons. The origin is the fixed point from which it acts while the movable point upon which it acts is known as its insertion.
Action of the Muscles.—When attached to bones, muscles are distributed in three ways: 1. When it is necessary to produce much motion rapidly, a short muscle is used. ”

“ There is provided in the central part of the body a hollow muscle invested with spiral fibres, running in both directions, the layers intersecting one another. By the contraction of these fibres, the sides of the muscular cavity are necessarily squeezed together, so as to force out from them any fluid which they may at that time contain: by the relaxation of the same fibres, the cavities are in their turn dilated, and, of course, prepared to admit every fluid which may be poured into them. ”

“ This membrane lines the structures that enclose the articulation and secretes a fluid, the synovia, that lubricates the surfaces.
The muscles are the contractile organs that move the body. The movement of the different parts of the body is rendered possible through the manner in which the skeletal muscles are inserted into the long bones, by which the lever motion is possible. A muscle originating on one bone and terminating on another either moves both bones toward each other or, if one attachment is fixed, the movable is drawn toward the fixed part. ”

“ This interpretation seems, indeed, to be directly at variance with the fact that muscle does not diminish in bulk during contraction but merely changes its shape. That which we see take place with the muscle as a whole, is said also to take place with each fibre—while it shortens it also broadens. ”

“ Fig. 53 represents the muscles of the arm after the skin and flesh are removed. They are all in smooth silky cases, laid over each other, and separated both by the smooth membranes that encase them and by layers of fat, so as to move easily without interfering with each other. They are fastened to the bones by strong tendons and cartilages; and around the wrist, in the drawing, is shown a band of cartilage to confine them in place. The muscle marked 8 is the extensor that straightens the fingers after they have been closed by a flexor the other side of the arm. ”

“ The amount of variation reported by a worker depends in large part on the degree of variation that he considers significant.
[Pg 447]
Individual variation in the muscles and in the nerves will be discussed separately; that of the muscles (excluding innervation) will be considered first.
Muscles
Considering the number, rather than degree, of variations, the most variable muscles are: Mm. flexor digitorum longus, obturator, caudofemoralis, and extensor hallucis longus. The first-mentioned muscle exhibits 14 different variations in the specimens studied. ”

“ It transmits to the other members of the body vitalizing blood, heat and spirit. Its muscular tissue, unlike ordinary muscle, is composed of three kinds of fibres, and it is not under the control of the will. ”

“ The property of the living muscle, which enables it to be the cause of motion, is this: Every muscular fibre is capable of suddenly changing its dimensions, in such a manner that it shortens and becomes proportionately thicker. Hence the absolute bulk of the fibre remains practically unchanged. From this circumstance, muscular contraction, as the change of form of a muscle is called, is radically different from the process which commonly goes by the same name in other things, and which involves a diminution of bulk. ”

“ The extent of the contractility of texture is in the muscles in proportion to the length of the fibres; hence why in amputations, the superficial part retracts more than the deep-seated; why in sleep the phenomena of contractility of texture are very apparent in the extremities, the muscles of which are very long; why, in the antagonists, nature has in general opposed muscles of proportional length; why consequently, a muscle with long fibres has rarely for a counterpoise one with short ones, and vice versa. ”

“ The split is the future body-cavity; the axial strand forms the proboscis, its sheath, the cerebral ganglion, muscles, etc., and the ligament with the contained generative organs; the outermost layer of cells forms the muscular lining to the skin. It is interesting to note that these cells destined to become muscle-fibres are at first arranged as a single layer of cubical epithelial cells lining the body-cavity; most of them become circular muscle-fibres, but a few are pushed inwards so as to lie next the body-cavity, and these become the longitudinal fibres. ”

“ So powerful and closely applied is this muscular pressure that jugglers can train themselves, with practice, to swallow standing on their heads and even to drink a glass of water in that position; while a horse or a cow always drinks "up-hill." This driving power of the food tube extends throughout its entire length; it is carried out by a series of circular rings of muscles, which are bound together by other threads of muscle running lengthwise, together forming the so-called{13} muscular coat of the tube. ”

“ Here, alone, at the distal portion of the tendon, occur muscular fibres, but these are unstriped, belonging to the category of cutaneous muscles. We have here the interesting fact that a muscle (portion of the triceps humeri of the reptiles) has been reduced to a tendon, which in a secondary way has become connected with cutaneous muscles, which, when strongly developed, represent its belly. ”