Adductor muscle

“ There are two adductor muscles. The first and largest is already well known; it has been described by all writers who have made the teredo an object of study. It extends (Fig. 11, m) between the two valves in the form of a muscular mass, relatively quite large, and occupies about two-thirds of the length of the shell and one-third of its width. ”

“ The spot will slowly move to the right as the muscle dies, but we need not wait for this. I need hardly say that a dead muscle gives no current. What would happen if we made the muscle contract? Would the contraction increase or diminish the current, or would it have no effect? To answer this question, I shall ask Mr. Brodie to lay the nerve still attached to the muscle over the wires coming from the induction coil, and, as he has a key in the circuit, I ask him by closing it to throw the muscle into tetanus while it remains on the pads. ”

“ Granting electric discharge to be the cause of muscle-contraction, what is its origin? That it is not carried to the muscle by the nerves follows from the fact that a muscle will still contract when deprived of all its nerve-fibers. It must therefore be generated within the muscle itself. To reach a solution of the problem we must obviously follow the analogies of its production elsewhere. ”

“ It is a brief extension of the limb at the knee-joint, due to a simple contraction of the extensor muscle, elicited by a tap or other short mechanical stimulus applied to the muscle fibres through the tendon of the muscle. The jerk is obtainable only from muscle fibres possessed of neural tonus. If the sensory nerves of the extensor muscle be severed, the “jerk” is lost. The brevity of the interval between the tap on the knee and the beginning of the resultant contraction of the muscle seems such as to exclude the possibility of reflex development. ”

“ Most of the muscles act upon the bones, so as to produce the effects of a lever of the third kind, as it is termed by mechanics, where the power acts between the centre of motion and the weight; hence it has a mechanical disadvantage; as an instance of this, the muscle which bends the forearm, is inserted about one eighth or one tenth of the distance from the centre of motion that the hand is, where the weight or resistance is applied; hence the muscle must exert a force eight or ten times greater than the weight to be raised. ”

“ Motor Phenomena.—There is immediate and complete loss of voluntary power in the muscles supplied by the divided nerve. The muscles rapidly waste, and within from three to five days, they cease to react to the faradic current. When tested with the galvanic current, it is found that a stronger current must be used to call forth contraction than in a healthy muscle, and the contraction appears first at the closing of the circuit when the anode is used as the testing electrode. ”

“ But if the muscle is found in one of the two extreme positions, for example in adduction, abduction, flexion, extension, &c. then there will be an inequality of action in the antagonists, as it respects the contractility354 of texture; the one most stretched, will make in order to contract itself, an effort much greater than that which is already contracted. To maintain the equilibrium, it is necessary then that the vital forces continue to influence the contracted muscles. ”

“ The current of the cut muscle at rest is not of so much importance as the current of the same muscle in action. There are strong reasons for holding that the resting current is due to the death or dying of the layer of muscle-substance laid bare by the transverse section. Dying muscle-substance, it would appear, becomes negative to living substance. But the negative variation current, or the action current, as we may well term it, indicates changes happening in the muscle, changes that are somehow connected with the phenomena of contraction. ”

“ It cannot be used to affect the deep-lying structures, such as the brain, spinal cord, etc. The current-strength is not measured by a milliampere meter. It will produce muscular contraction only through the motor nerve supplying the muscle. ”

“ How the Muscles do their Work.—A tiny nerve [Pg 143] thread runs from the spinal cord or brain to every muscle thread. Messages sent through the nerve threads to the muscles make them act. A muscle can act in only two ways (Fig. 84) . It can become shorter or longer. When it gets shorter, we say it contracts. When it stretches out, it is said to relax.
A muscle cannot contract more than one fourth of its length. To pull the forearm up, the brain sends a message to the muscle fixed by one end at the shoulder and by the other end to a bone at the elbow. ”

“ There can be no doubt that when we firmly contract a muscle and maintain the contraction, the muscle is in a state of tetanus, in which the quivers of the partial contractions can be seen. We all know how difficult it is to keep the hand or arm quite steady. They tremble, and we can feel the vibration. ”

“ When the nerve discharges its influence into the muscles, a very rapid molecular change takes place in the substance contained in the cartouches or muscular boxes, which contract, pressing their ends close together. Scarcely has the action of the nerves ceased than they relax and resume their previous form. It is well known, that when a muscle contracts, it becomes thicker and shorter; it suffices to take hold of the arm a little above the elbow and then to bend it in order to feel how the biceps muscle swells and hardens. ”

“ If this should fail, attention should be paid to the various actions of the limb, the attendant symptoms arising from parts affected, and what may be called the general anatomy of the whole circle of injury. A muscle, in the act of contraction, may oppose an obstacle to the passage of an instrument in the direction the ball has taken, especially if it should have passed between tendons or surfaces loosely connected by cellular membrane; as by the side of, or between the great blood-vessels, which by their elasticity may make way for the ball, and yet impede the progress of a sound. ”

“ There are but few motions in the economy that are simple, but few muscles that can contract separately. Almost every sort of contraction supposes another, and for this reason; the two points to which a muscle is ordinarily attached are both capable of being moved; if one of them was not fixed, both would then be put in motion when the muscle contracted; thus in the contraction of its extensors, the leg if it was not fixed would approach the foot as much as the foot approached the leg ”

“ He considers that a muscle is a machine for the conversion of potential energy into mechanical force; that the mechanical force of the muscles is derived chiefly, if not entirely, from the oxidation of matters either contained in the blood or deposited around the muscular fibres, and not from the oxidation of the muscles themselves; that in man the chief materials used for the production of muscular power are non-nitrogenous ”

“ 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. ”

“ 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. ”

“ There are almost no motions performed by single muscles. Most activity results from the contraction of a group of muscles and these are usually in delicate balance with other groups of muscles which either assist or prevent overaction. The delicate adjustment of muscle groups, which is normally present, results in co-ordinated movements. Following nerve disease or, for that matter, the immobilization of joints and muscles, co-ordination is usually lost to more or less degree. Muscles must be re-trained to work together. ”

“ 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. ”

“ This gives the muscle greater play than in us, and enables it to lift, more slowly perhaps, but more efficiently, for the arm-bone between the joint and the place where the muscle is attached, is the long arm of a lever which is shorter in man. Below the globular head of the arm-bone is the shaft or cylindrical part of the bone which gives origin to the three-headed muscle called triceps, and is covered by the two-headed one (biceps) already mentioned, besides the deltoid. ”

“ When these forces cease to be in action, immediately the contractility of texture of the elongated muscle, which had a tendency to exert itself, but was prevented, exerts itself, becomes efficacious, and draws back the moveable part to the middle position, a position in which the equilibrium is restored. Hence why in all the cases in which the cerebral influence has no power over the muscles, in which they are not irritated by stimulants, the limbs are uniformly found in a medium position between extension and flexion, abduction and adduction, &c. ”

“ While lifting, grip and contract every muscle of the arm and hand out to the finger-tips. This is much like the contraction placed upon the muscles of the body and of the throat by the conscious-breathing, local-effort school. Lift the arm again from the side, and in lifting have the thought or sensation of letting go all contraction of the muscles. Make the arm light and flexible, and use just enough strength to lift it, and hold it in a horizontal position. This should be the condition of all the muscles of the body under the influence of correct, lift, expand, and let go. ”

“ Of course this possibility of variation is of great advantage in our use of our muscles. It depends upon the very large number of individual fibers of which even our smallest muscles are made up. Whenever any single fiber contracts, it pulls to its full extent; if only a few become active, the pull of the whole muscle will be slight; as more come into action, more force will be exerted; the muscle will show its utmost power when all the fibers are contracting at once. We are conscious of greater mental effort when we make a powerful muscular contraction. ”

“ 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. ”

“ These cases are generally accompanied by round shoulders and flat chest, protrusion of the abdomen, and rotation of the vertebræ.
A muscle can be developed only by the active contraction and relaxation of its fibers. Continuous tension quickly tires and lowers its tone, so that exercises given for increasing muscular power should be comparatively quick and frequently repeated, while those that aim at the stretching of muscles and ligaments should be slow and long maintained. ”

“ The fourth state of muscular contraction is when the muscle is doing negative work, i.e. when work is being done on it, as for instance when we go downstairs, or when a descending weight forces down the opposing arm which attempts to support it. ”

“ After a bone has been moved by the contraction of a muscle, it is brought back to its position by the contraction of another muscle on the opposite side, the former muscle meanwhile being relaxed. Muscles thus acting in opposition to each other are called antagonistic. Thus the biceps serves as one of the antagonists to the triceps, and the various flexors and extensors of the limbs are antagonistic to one another. ”

“ From these facts, as well as from the great force with which the muscle contracts, one must conclude that the muscle is a transformer of energy—that within its protoplasm, chemical changes take place whereby the potential energy of oxygen and food is converted into the kinetic energy of motion.
Fig. 113—Capillaries of muscles. Plan of Using Muscular Force.—Two difficulties have to be overcome in the using of muscular force in the body. The first of these is due to the fact that the muscles exert their force only when they contract. They can pull but not push. ”