Section I. OP THB VOLUNTARY MU8CL8S. The name of muscles is frequently restricted to those bodies which are distinguished by being the active organs of motion, and by being immediately under the control of volition. The voluntary muscles constitute a large proportion of the mass of the body, especially in individuals who are engaged in laborious occupations. They are, in general, placed around the bones, and, consequently, towards the external surface; in some parts of the body they are situated more deeply, as in the mouth, chest, and abdomen. Their number, which is very great, is liable to variation: this does not so much depend on any actual difference in the muscles themselves, as on the manner according to which they have been described by anatomists; some writers considering certain muscles to be composed of several fasciculi, which others have regarded as forming so many distinct muscles. Chirnusier has admitted only three hundred and sixty-eight, while other writers extend the number to four hundred. Each muscle of the human body has received a proper name, founded on some consideration or other connected with the organ. The nomenclature of this part of anatomy is so imperfect, and so many alterations have been made in it, that there is scarcely a muscle which has not more than one name, and some have received as many as ten or twelve. Various circumstances have, at different times, regulated the application of names to muscles; a numerical order was observed, by some anatomists, to distinguish these organs, when several of them belonged to the same part, and produced the same kind of movement; OS in the instance of the extensors of the thumb, of the interossei, &c., which are called first, second, third, &c. The muscles have been more commonly named from a combination of several circumstances; for example, according to the predominance of one at other of their dimensions, from their size, from their situation in certain regions of the body, or from their connexion with different organs. Thus there are the latissimus dorsi, longissimus colli, rectus capitis posticus major, vastus internus, anterior auris, &c. The relative position has very frequently influenced the names, hence the terms anterior, posterior, internal, external, superficial, deep, &c. The name is often derived from the use of the muscle, and from the part to which it is attached; this has given rise to the terms of levator, depressor, abductor, adductor, dexter, extensor, supinator, sphincter, &c. Many muscles are distinguished by their figure, as the deltoides, rhomboideus, trapezius, scalenus, orbiculoris; othera by the straightness or obliquity of their fibres, us the rectus abdominis, rectus oculi, obliquus oculi; some by the direction of the fibres, as cervicalis descendens, obliquus abdominis ascendens, transversalis perinei; a few are named from their mode of connexion with the tendons, such as the spino-tendinosus (ligamentosus); others from the number of their origins, u the triceps and biceps. Many attempts have been made to improve the nomenclature of the muscles by modern anatomists, especially by Chaussier and Dumas. The arrangement of the former, which is founded on the principle of naming the muscles according to the connexions of their two extremities, has many advantages, and is well calculated to facilitate the study of myology, because the name of each muscle conveys to the mind the most important points of its attachment. The terms of this anatomist are generally adopted in France. The nomenclature suggested by Dumas, is a modification and extension of Chaussier's principle; the names, according to this plan, being intended to express briefly all the points to which each muscle is attached. But, as it has been judiciously remarked, where the origins and insertions are numerous, the name that pretends to enumerate them whole must often run out to the length of a sentence. In the work of Dr. Barclay, the vastness, and, in many instances, the decided incorrectness of the expressions in common use amongst anatomists, are forcibly depicted; and he has suggested new terms founded on a scientific and determined basis, which would certainly, were they generally employed, introduce great clarity and precision into anatomical descriptions. But effect so desirable an object, it is necessary that these terms should be adopted by common consent; for other- wise, they would only add to the confusion which already so much encumbers the study of anatomy. The voluntary muscles are usually disposed in pairs, but the following are single: the diaphragm, the sphincters of the mouth and anus, the arytenoides transversalis, and generally the azygos uvula. <Callout type="important" title="Muscle Pairing">The majority of voluntary muscles work in pairs for coordinated movement.</Callout> The muscles are distinguished according to their situation and connexion into those belonging to the skeleton, into those of the larynx, of the organs of the senses, and lastly of the skin. Several of the principal muscles of volition also belong to the walls of the digestive, respiratory, genital, and urinary passages, where they are insensibly confounded with the internal muscles. A useful division of the muscles, in many respects analogous with that of the bones, is founded on the relative proportions which they present in their three dimensions. According to this arrangement they are divided into three classes: the long, the wide, and the short. The long muscles are more numerous than those of the other divisions; they are almost entirely confined to the limbs, and are usually placed in strata, of which the superficial are composed of the longest muscles; while in the deeper layers the muscles are shorter, and are more slender in their situation, in consequence of being closely attached to the bones. The broad muscles generally consist of thin but expanse fibres, placed on the surface; they occupy the exterior of the great cavities of the body, and, in some instances, as in that of the abdomen, they constitute the larger part of their walls; while in others, they merely clothe the osseous particles. Several of these organs extend from the trunk to the limbs, in which case they often become considerably elongated. In the third class the muscles have their three dimensions nearly equal; they are generally triangular or oblong in form. They are, in proportion to their size, more powerful than those of the two preceding classes, and are, consequently, placed in those parts of the body where strength rather than extent of motion is required; for example, around the temporomandibular articulation, the joints of the head with the vertebral column, of the foot, hand, &c. Each of the voluntary muscles usually possesses a ventral part, called the body or belly, and two extremities, one of which is termed the head and the other the tail; the head is connected with some fixed point, which is regarded as the origin of the muscle; the lower end is attached to a more moveable part, which is considered as the insertion. This form is exemplified in several of the muscles of the limbs which are enlarged in the middle, owing to the disposition of the fleshy fibres, and contracted in the extremities, which are generally tendinous. The annular muscles, as the orbicularis oris, sphincter ani, &c., do not possess any tenosouty structure; this observation also applies to several of the small muscles, as those of the lips and of the larynx. <Callout type="important" title="Muscle Structure">The body of a muscle is its belly, while its extremities are its origin (head) and insertion (tail).</Callout> The tendons, which are usually placed at the two extremities of the muscles, are in most cases of unequal length; the one towards the origin being with few exceptions, shorter than that towards the insertion; it frequently happens that there is only one tendon which is attached sometimes to one, sometimes to the other extremity. They are always much smaller than the muscles to which they are attached; this arrangement prevents the asymmetry and form of the body, and also facilitates the complicated movements of its different parts. The fibres in the voluntary muscles are usually straight and parallel to each other; but they are sometimes radiated, as in the diaphragm, the pectoralis major, the genio-hyo-glossus, &c.; and occasionally they observe a circular course. When all the fibres run obliquely towards the tendon, they form what are called the flat or semi-penniform muscles (muscles terni pennati); when the parallel fibres pass in two directions so as to meet in the centre, they produce the complete penuiform muscle (muscle pinnatus). The rectus femoris is an instance of this disposition. There are some examples of the compound penuiform muscles, which consist of two penuiform bellies joined together; the gastrocnemius is of this order. The direction of the entire muscle, which is described by drawing a line through its centre from one extremity to the other, is frequently different from that of the fibres. When the course of the muscle and of the fibres is exactly the same, the power of the former, which in this case is equal to the sum of the forces of all the fibres, is exercised in the line of its direction; but if the fibres do not correspond with the course of the muscle or with each other, then the intensity and direction of the force will vary according to the kind of deviation. Some of the muscles are simple and distinct in their whole extent; whilst others are divided into several portions, either at their origin or at their insertion, or both these points. There are examples of the former, in the semitendinosus and gracilis. Amongst the latter or compound muscles, some have two or three distinct portions at their origin and a single insertion; such as the triceps extensor cubiti, the sternomastoideus, and the pectoralis major; others are single in their origin, and divided at their insertion, as the flexor and extensors of the toes. These divisions occasionally are not distinct, that certain muscles which are regarded by some anatomists as single, are described by others as forming several muscles; this is the case with the levator labii superioris aliaeque nasi, and the extensor digitorum manus. Again, the extensor of the leg is usually described as consisting of three separate muscles, viz. the two vasti and cruralis; whilst, by many authors, it is considered as one, called the triceps extensor cruris. Some muscles are united to each other at their origin, as the biceps cruris and semitendinosus, and also the coraco-brachialis and biceps cubiti; others are joined in their insertion, as the latissimus dorsi and teres major, the different muscles of the lips, &c. In some regions of the body, as in the sole of the foot, and the deep part of the back, the different muscles are so much confounded together that it is difficult, and in some parts impossible, to distinguish them from each other. The muscles of volition are provided with certain appendages consisting of the aponeuroses and tendinous sheaths, which increase their power and facilitate their motion; the former, by supporting the fibres in their situation and by presenting any displacement during their contraction; the latter, by lying the tendons and by allowing them at the same time to play freely within the bony canal. <Callout type="important" title="Muscle Appendages">Aponeuroses and tendinous sheaths enhance muscle power and motion.</Callout> Hitherto deferred speaking of the mechanism which is displayed in the production of animal motion, because the following observations almost exclusively apply to the voluntary muscles. The muscles are divided according to the kind of movement they produce, into associates and antagonists; the former act together and, by their combination, they cause the same kind of motion; the latter on the contrary, act in an inverse sense to each other, and thus produce dissimilar movements. The various motions of the body, with the exception of those which are very simple, are accomplished by the combined action of two or more muscles. In many instances, muscles which are opposed to each other in their single actions, are associated to produce an intermediate movement. In all these cases there is a composition of forces, each muscle losing a portion of its power; thus if the abductor and levator oculi contract but there is a compensation in the velocity and extent of motion which are acquired. The first kind of lever, in which the fulcrum is placed in the centre, is employed in certain movements requiring great force; there is an example of this in the action of the extensor muscles of the spine, which are inserted behind the fulcrum, whilst the part to be moved or the weight is placed before it. The second species of lever is rarely used in muscular action; several instances, however, might be adduced in which the weight or resistance is situated between the power and the fulcrum; thus, in depressing the lower jaw, the fulcrum corresponds to the temporomandibular articulation, the power is represented by the chin and the weight in the bone between these points: again, in raising the body on the toes, the fulcrum is at the end of the foot, the power is placed in the heel, and the resistance in the joint of the ankle. Besides the loss of power occasioned by the nature of the lever which is generally employed, and that caused by the association of the muscular contraction, the following circumstances will also produce the same effect. 1. The mode in which the muscles are inserted into the bones, and the fibres into the tendons, 2. The equal division of the muscular effort on the two points of attachment. 3. The resistance of the tonic contraction of the antagonist muscles. 4. The friction of the muscle and its tendon on the surrounding parts. 5. The muscular fibres are usually placed so as to act obliquely; this arrangement causes a loss of power; but what is lost in power is gained in the quantity of contraction; for it may be demonstrated, that a given extent of motion can be produced by a smaller quantity of contraction if oblique fibres are used than when straight ones are employed. Another great source of the laws of power is, that the tendon is generally inserted into the bone at an acute angle, whereas, in order that the power should have operated in the most advantageous manner, it ought to have acted on the lever in a perpendicular direction. As the muscles contract from their extremities towards the centre, it is evident that half the effort of the muscle is expended on the point which is fixed; thus, if the deltoid exerts a power equal to one hundred pounds, only half, or fifty pounds, will be employed in raising the arm, the other half being exerted on the scapula. This fact shows the necessity of every muscle having a fixed point during its contraction, for if both extremities were equally moveable, they would approach each other when the fibres were shortened. In order to prevent this event taking place, almost every motion is a compound one; for example, before the deltoid can effectively raise the arm, it is necessary that the trapezius, rhomboideus, &c., should secure and fix the scapula. <Callout type="important" title="Muscle Contraction">Muscles have fixed points during contraction to prevent them from shortening too much.</Callout> A third cause of the loss of power depends on the disposition of the muscular system, which is such that in general one set of muscles cannot act without experiencing the resistance arising from the tonic contraction of the antagonists. Another circumstance unfavourable to muscular action, the absence of a proper tendon and its relation, against the adjacent parts. This loss of power is considerable in those instances in which the muscle fuses over extra-joint surfaces below it by being inserted; the laxity of the cellular texture, and the provision of the bursa mucosa: tend, however, to diminish the effects of friction. All these mechanical imperfections are productive of an enormous sacrifice of power, so that it has been calculated the deltoid employs a force equal to one hundred pounds in raising the arm, but only half, or fifty pounds, is actually employed; the other half being exerted on the scapula. This fact shows the necessity of every muscle having a fixed point during its contraction, for if both extremities were equally moveable, they would approach each other when the fibres were shortened.
Key Takeaways
- Voluntary muscles are active organs of motion and under voluntary control.
- Muscles are often named based on their location, size, or function.
- The majority of voluntary muscles work in pairs for coordinated movement.
Practical Tips
- Understand the importance of muscle pairing to coordinate movements effectively.
- Recognize that the structure of a muscle includes its belly and tendons at both ends.
- Be aware of the friction between muscles and their tendons, which can reduce efficiency.
Warnings & Risks
- Be cautious when applying these principles in survival situations as they require precise control and understanding.
- Avoid overexertion without proper warm-up to prevent muscle strain or injury.
Modern Application
While the detailed anatomical descriptions may seem archaic, the fundamental principles of muscle function and coordination remain crucial for modern survival preparedness. Understanding how muscles work can help in tasks such as lifting heavy objects, performing first aid, or even crafting tools. The knowledge that muscles have fixed points during contraction is particularly useful in designing ergonomic equipment or understanding injury prevention.
Frequently Asked Questions
Q: How do the voluntary muscles differ from involuntary muscles?
Voluntary muscles are those which can be controlled by our will, such as those used for movement. In contrast, involuntary muscles, like those in the digestive system, operate automatically without conscious control.
Q: Why is it important to understand muscle pairing in survival scenarios?
Understanding muscle pairing helps ensure coordinated movements, which are essential for tasks such as lifting heavy objects or performing first aid. Proper coordination can prevent strain and injury.
Q: What role do aponeuroses play in muscle function?
Aponeuroses support the fibres of muscles during contraction and help maintain their position, enhancing overall muscle efficiency by preventing displacement.