Skeletal Muscle
In Chinese Medicine, the skeletal muscles are not named as such, rather there are two different tissues, called the ‘flesh’ and the ‘tendons,’ which different writers take to include skeletal muscle. TCM textbooks regard muscle as a part of the flesh, presumably because muscles do constitute a major part of the substantial fleshiness of the limbs - when eating meat, much of that flesh is muscle - but in the style of TCM textbooks this identification is offered only on authority, without justification or argument. Clinically it is true that weakness of the Earth phase (of which ‘the flesh’ is an aspect) is associated with heaviness of the limbs - a kind of weakness of the muscles. In CCM circles, many prefer to regard the muscles as a part of ‘the tendons,’ since the muscles generate motion, and this is the role of the Wood phase, to which the tendons belong. Certainly when Su Wen chapter 1 says that at the age of 56 a man’s tendons become dry and fail to be nimble, this seem to describe changes in physique that go beyond the tissues that western medicine would call tendons to include what it would call muscles. I do not find it necessary to resolve this disagreement, since both perspectives offer some useful guidance, and much of the project of integrative medicine involves learning to see things through multiple lenses.
Both of these identifications, placing the muscles in either the Earth or Wood phase, are consistent with the view in Anthroposophy, where the muscles are generally regarded as an aspect of the metabolic pole. Muscle is regarded as metabolic since it is through them that will forces are brought to bear toward the outer world, and also because of their high levels of energy consumption.
I do not disagree with these general concepts, however, there is something more interesting going on, which is not captured by just placing muscle into a pre-existing scheme of categories. Let us look more closely at the place which skeletal muscle occupies within the general motor process. First, we might regard the muscles as part of a functional group composed of muscle, tendon, and bone. Here we find that bone is certainly the formal aspect of the system, tendon is intermediate, and muscle is the most active, amorphous, and metabolically demanding of the three. On the other hand, we might see muscle as the peripheral extreme of an event which is generated within the nervous system: the depolarization and action potential propagation. Indeed, the contracting of muscle depends on its own depolarization. Muscle again appears to be a metabolic feature in relation to the informational innervation. However, if we consider muscle in relation to both bone and nerve simultaneously, we find that it is in between, and has a role of mediating between, these two different aspects of the form pole of the body. In Chinese Medicine terms, we could say that muscle is positioned within and between the taiyang and shaoyin aspects of the water phase. Then again most of the body could be located between taiyang and shaoyin, so this does not yet offer us much to clarify how we might want to classify skeletal muscle.
Nerve and bone are both clear representatives of the formal/informational pole, at the same time their natures are so different that they could be opposites. Bone and nerve display a yin-yang, internal-external inversion: Bone is extremely slow, while nerve is extremely fast. Bone displays maximum stability, even through generations, while nerve is extremely flexible, the most adaptable feature of human functioning. Bone is outwardly formal, while nerve is inwardly informational. Nerve is the center of consciousness, while bone is even more remote from personal consciousness than the will forces of muscle. Nerve provides a locus for our personal consciousness while bone represents a kind of geological pondering, or at least a geological level testament to our nature. It is the task of skeletal muscle to mediate between these two, and in this light skeletal muscle seems very interesting.
The place and importance of this mediation can be recognized experientially by tensing all of one’s muscles, holding them tensed, and then trying to think. One may be able to form a few thoughts in one’s mind, but one immediately recognizes that one’s ability to think is severely impaired. When the skeletal muscle hardens, it becomes more formal, bringing the nerve and bone aspects into closer contact. If this persists for too long, they begin to invade each other’s proper realms. This invasion manifests quickly in the realm of thought, but if it persists for long enough a muscle which is pulling excessively on a bone can also lead to inappropriate bone growth or deformation, leading to bunions and bone spurs. When a muscle softens, it becomes relatively amorphous and metabolic imposing a kind of insulation between the two aspects of the formal pole.
Structure
When we turn to the structure of skeletal muscle cells, we find an extreme degree of order, precision, and longitudinal elements, which would be surprising for a purely metabolic aspect of the body. It is here that the skeletal muscle reveals its proximity and relationship to the formal pole.
The structure which is most directly responsible for the muscle’s ability to contract are the sarcomeres. Each sarcomere, is bounded on two sides by Z discs, where the sarcomere is joined in series to further sarcomeres, the chain of which constitute a myofibril. Proceeding from each Z disc, toward the center of the sarcomere, are numerous strands of actin. Interdigitating with the actin are strands of myosin, which, when the muscle contracts, attach to the actin, and pull the actin from both directions toward the center of the sarcomere, drawing the two Z discs closer together, shortening the sarcomere. The length of the actin and myosin strands are precise, so that each sarcomere has completely regular dimensions. As a side note, the sarcomere is hexagonal in cross-section.
Let us look more closely at the structure of the actin and myosin. Actin is a yin element of this system. It is passive, but not inert. For contraction to occur, it needs to make itself receptive to the myosin, which will then attach and pull. The body of the actin strand is composed of two chains of the protein F-actin, which wrap around each other in a helix. Attached to the F-actin at regular intervals are molecules of ADP (adenosine diphosphate) which serve as the active sites where the myosin attaches. However, when the muscle is at rest, these active sites are covered by the protein tropomyosin, which also forms a chain and spirals with the F-actin. There is a third protein, called troponin, distributed at regular intervals. Troponin has a high affinity for calcium, and in the presence of calcium undergoes a conformational change which pulls the tropomyosin in such a manner that the active sites are uncovered.
Myosin is the yang element in this pair. It does the work of pulling on the actin strands, and it is continuously in motion during contraction. A strand of myosin is composed of numerous myosin molecules. The body of each myosin molecule consists of two heavy chains which, like the F-actin, wrap around each other, forming a double helix. This portion of the molecule is called the tail. At one end of the tail, the two chains diverge, forming “arms” which project away from the tail, and terminate in structure called the “head.” Thus there are two heads: one from each chain. Attached to each head are two light chains which are involved in the process of binding with the actin. Taken together, the arms and heads are called cross-bridges. The cross-bridges can bend at the point where they depart from the body of the myosin and also where they attach to the actin. This flexibility allows the cross-bridges to reach out and then pull inward. This action will happen spontaneously, whenever the active sites are exposed and ATP is available.
Now that we understand the structure of a sarcomere, we can scale up rather easily to the macroscopic level of muscle tissue. Numerous sarcomeres are attached in series, forming a chain called a myofibril. Numerous myofibrils run parallel to each other within each muscle fiber, which is a single, long, multi-nucleated cell.
There is one other feature of the skeletal muscle cell which we must discuss, namely the structures which signal the proper time for contraction. With only a few exceptions, each muscle fiber is innervated at a single point, called the neuromuscular junction, located near the center of the fiber. The neuromuscular junction is formed by a depression or pocket in the surface of the muscle into which a nerve terminal is inserted, forming a very direct connection. These nerves release acetylcholine (ACh) to stimulate muscular contraction. At the neuromuscular junction, the muscle fiber has a number of acetylcholine gated ion channels, which, when they bind two molecules of ACh, will open, allowing primarily sodium, but also potassium and calcium (all positive ions), to enter from the extracellular matrix. This leads to a local depolarization of the cell membrane. This depolarization is propagated outward in both directions along the membrane of the muscle fiber, in much the same way as a membrane depolarization is propagated along nerve fiber. Unlike in a nerve cell, where the signal mostly needs to travel from one end of the cell to the other, in a muscle cell the signal carried by depolarization needs to reach the interior of the cell. This requirement is met with a special challenge because muscle cells have a much thicker body than a nerve cell. The depolarization on the surface of the cell would not be nearly strong enough to signal into the center of the cell. The muscle cell is thus perforated through-out by transverse tubules (T-tubules). These are little tubes which run from the membrane, through the body of the cell, to the other side. They are open to and filled with extracellular fluid, and hence they function as an internal continuation of the cell membrane, allowing depolarization to effect the whole cell.
The signal then reaches the sarcoplasmic reticulum, which is basically a large repository of calcium which is spread through-out the cell. This calcium is released on encountering the depolarization and is the direct antecedent to changes in the actin which allow cross-bridges to begin pulling on the actin and shortening the sarcomeres, as discussed above.
These signaling mechanisms again demonstrate the importance of the form/information pole when interpreting muscle cells. First, the muscle cell propagates membrane depolarization like a nerve cell. Second, through the t-tubules it ensures that the whole cell is pervaded by this informational element. Third, it contains as well an internal signaling feature (i.e. the sarcoplasmic reticulum).
Energy
The energy required for muscle contraction is derived from energy stored in three forms. First, there is substance in the muscle called phosphocreatine. Energy is released from cleaving the phosphate bond of this molecule. This works in much the same way as in the release of energy when ATP becomes ADP. This energy is available very quickly, but there is a very small amount available - only enough to power a muscle for a few seconds. Phosphocreatine is another sign pointing toward an affinity in skeletal muscle toward the form-pole. Phosphocreatine is formal energy: it is energy stored in a structure which requires a minimum of metabolic activity to release. Moreover, the other major place that phosphocreatine is found is in the brain.
The second energy source is glycolysis. This is a process of breaking down glycogen, a carbohydrate-based energy-bearing substance stored in the muscle cell. This process is more metabolically demanding than the breakdown of phosphocreatine (glycolysis requires the involvement of 10 different enzymes) and is not as quick as the breakdown of phosphocreatine, but it can supply more energy - enough for about one minute of contraction. Two important facts about glycolysis are that it does not require oxygen and that it leads to a build-up of metabolic by-products, which, if they are not metabolized or removed from the cell, become a source of toxicity.
If enough oxygen is available, then oxidative phosphorylation picks up where glycolysis leaves off, using many of the glycolytic end-products in the production of further energy/ATP.
Functionality
Through much of this essay, I have emphasized the form-pole features of skeletal muscle. My point in doing so has not been to argue that skeletal muscle should be regarded simply as a form-pole aspect of the body. Rather the muscle mediates between two aspects of the form pole. This mediation depends in part on the skeletal muscle’s ability to establish distance and insulation between the two aspects of the form pole, and this insulation occurs by virtue of the metabolic qualities of the muscle. On the other hand, this mediation also requires the muscle to allow regulated closeness and communication between the nerve and bone. Regarded as a mediating feature, we expect to find rhythmic or alternating qualities in the muscle, and indeed we do find these.
This alternating quality appears most immediately and macroscopically in the muscle’s ability to move between contracted and flaccid states. When the muscle contracts, it hardens, thereby acquiring a definite form. This hardening also limits blood flow reducing the metabolic potentials of the muscle. In this state the nerve pulls, through the muscle, on the bone. When the muscle softens, it becomes more amorphous, which is a quality of the metabolic pole. Metabolic process come to the fore as greater blood flow is restored and the muscle cell begins to rebuild phosphocreatine, etc. In the softened state, the nerve and bone have reduced influence on each other.
In the legs, where walking is the most characteristic motion, this alternation tends to take on a fairly simple periodicity. In the arms, which have a closer relation to the head-pole, the tendency is to produce motions which communicate meanings (such as speech gesturing, writing, playing instruments, or forming mudras) or which impart form to an external material (such as hammering nails or grating cheese), but these motions also have a rhythmic quality.
The rhythmic quality of muscle contraction also appears on the microscopic level. When a muscle contracts, it does so in “twitches,” almost like a pulse, containing both a contraction and relaxation phase. As the signal from the nerves for a muscle to contract increases, these twitches come more and more frequently, so that soon the contraction of one twitch comes before the previous twitch has finished the relaxation phase of its cycle, nevertheless, muscular tension never becomes totally stable, but contains tiny twitch rhythms of relaxation and tension within a given level of tension. The twitch principle can become quite apparent when trying to hold a stable posture (such as the universe stance) after the muscles have become fatigued.
Pathology and Treatment
I do not intend to discuss here all muscular pathologies, or anything even approaching that. Rather, I just want to look at a couple of nearly universal conditions for which a new understanding follows directly from the preceding discussion.
First is tetany or spasm, the familiar “knots” in our muscles. This is a muscle which does not soften appropriately, i.e. it is stuck in formal state, usually because it is excessively under the influence of the nerve pole, and often facial tissues have been recruited to hold the tension. In spasm, the polarity between nerve and bone breaks down, and they begin invading each other’s realms. I can think of three possible treatment approaches: The first approach is directly inducing or introducing metabolic activity into the muscle. This metabolic activity may be in the form of acute inflammation (picture an acupuncture needle giving the muscle a working over), which could help to waken the muscles and restore to them their full function, or it may be in the form of herbs which directly strengthen the metabolic pole. The second approach is to induce a rhythm into the muscle. This approach seeks to remind the muscle of the full range of its function or to co-operate with the muscle in breaking the lock which holds the muscle in one state without denying the muscle the ability to take up the formal state as necessary. The third approach, which we could call the most homeopathic, is to recognize that the muscles are probably locked in a formal state because they are being recruited by the nerves, which feel are experiencing some kind of weakness. In this approach our goal is to tonify the formal pole, both the nerves and the bones, so that they will have adequate stability and strength, without needing to use the muscles to take their place. I think a good treatment can include at least two, and perhaps all three of these principles.
The second pathology to consider here is muscular soreness, including both the familiar soreness after beginning a new exercise routine as well as problems such as fibromyalgia. This is usually not a problem located in the muscle cell itself, but is primarily due to inadequate circulation (shaoyang & jueyin) to the cells, inhibiting their ability to breathe (taiyin/metal) and to clear themselves of their toxins (yangming/metal). If this state persists, the the lack of circulation (a rhythmic process), leads to a weakening of the muscle cell’s ability to perform its own rhythmic function, not because it is locked in one position, as in the case of spasm, but because it becomes deficient, not having the vitality to fully perform either formal or metabolic functions.
In the second part of this essay, we will examine and compare smooth muscle. In a third section we will look at a few herbs which are of signal importance in treating common muscular complaints, particularly we will look at bai shao (white peony) and black cohosh (a close relative of sheng ma), and perhaps solomon seal (relative of huang jing and yu zhu).
