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Muscles - developmental approach
Other Terms: Body
Muscles and their associated tendons come in a wide variety of shapes and sizes. The different shapes and sizes coupled with the relationships they form with one another, with the skeleton, and at the joints they cross create the large variety of musculoskeletal action that is such an integral part of the body’s function. It is also from the differences in shape and size that muscles derive their names. When the early anatomists began naming muscles they used a logical, descriptive approach. Understanding the logic behind the name can help you learn about the muscle. The characteristic features of a muscle name include adjectives and genitives that modify the noun muscle. Keep in mind that the full name of any muscle of the body begins with musculus, a masculine noun. The English language has dropped this from common usage and allows the adjective and the genitive that describe the muscle to stand alone as the English noun. For example, musculus latissimus dorsi becomes the latissimus dorsi muscle, which we often just refer to as the latissimus dorsi. Muscles were originally named by describing their various characteristics: shape, size, location, or actions. An analysis of the name musculus latissimus dorsi reveals the following: musculus = muscle the noun being described; latissimus = broadest adjective describing the noun; dorsi = of the back genitive form of dorsum referring to the part of the body where the muscle is located; Therefore, musculus latissimus dorsi literally means the broadest muscle of the back, which is an apt description of this large, flat sheet of muscle on the dorsal surface of the trunk. Using this etymological approach makes it possible to associate the somewhat foreign muscle names to terms that are more familiar, thus enhancing the memorization process through learning by association, a proven memory technique. The text associated with each muscle will assist you with this learning process. The tendinous attachments of muscles to bones, fascial connective tissues, or the integument are typically referred to as the origins and insertions of the muscles. This basic terminology is an attempt to distinguish the more stable end of a muscle from the more mobile end. When the cells of the muscle belly contract, they generate a tensile force that is transferred to the surrounding connective tissues of the muscle. This force is transferred through the muscle tendon to the bone. This muscle activity will typically produce a movement of the bone at one end of the muscle and not the other. The attachment site that does not typically move is the origin and the moveable attachment site is the insertion. Origins and insertions are most easily determined in the limbs where the origin is the proximal (stable) attachment and the insertion is the distal (mobile) attachment. Realize, however, that by stabilizing the insertion the origin can become the mobile end, but for most typical movements the typical logic of origin and insertion will apply. It is also important to understand that in many introductory anatomy texts muscle descriptions predominantly describe the muscle’s attachments to boney surfaces. While bones are the prominent attachment sites of most muscles, they are not the sole sites. Anyone who has studied muscles via dissection will quickly recognize that muscles form extensive attachments with surrounding fascial connective tissues in addition to neighboring bones. Sometimes this can become important knowledge for the assessment of muscle injury. In this software there are three levels of textual information to choose from, depending on your level of knowledge. Choose the level of muscle knowledge that best fits your needs. For a simple survey of muscle attachments, as well as other muscle information, select the beginner level. For more detailed information select the intermediate or advanced levels. In the study of muscles, it is common to describe the actions that individual muscles produce at their associated joints. While in principle it is important to recognize the movements muscles produce at the joints they cross, in reality it is important to realize that muscles do not work in isolation. Sometimes the movements attributed to a muscle are only possible for a certain range of the joint’s movement, or in combination with other muscles. Again, the program allows you to choose the level of muscle action detail that fits your learning requirements. The beginning level of text describes the primary movements produced at joints when the muscle contracts. The intermediate and advanced levels present more comprehensive information on muscle function. Each of the movements that occur at the different joints in the body have one or more muscles that produce the movements. The primary muscles responsible for a joint movement are called the prime movers. For example, the prime movers for elbow flexion are the brachialis and the biceps brachii muscles. When these muscles contract they flex, or bend, the elbow joint. You should also realize that for every joint movement there is an opposing movement. The muscles that work against the prime movers to produce an opposing movement are called antagonist muscles (anti means against and ergos means to work). For prime movers to work optimally the antagonist muscles must be relaxed. An antagonist to the brachialis and biceps brachii muscles is the strong triceps brachii on the posterior side of the arm. The triceps brachii muscle, whose prime movement is elbow extension, works against the brachialis and biceps brachii muscles. In order to produce the full range of elbow flexion, the triceps must be relaxed so that the biceps and brachialis can fully contract to flex the arm. Two additional terms used in the study of muscle action are synergist, meaning to work with or together, and fixator. These terms describe muscles that work as stabilizers of other joints, or work to eliminate actions at joints so that the prime movers can work optimally. If you look once again at the elbow joint, you can see examples of synergists and fixators. As an example, in order for the elbow to flex and lift a heavy weight that is held in the hands, the shoulder joint and wrist joint must be fixed into static positions. The antagonistic muscles around these joints must contract simultaneously, acting as fixators, to keep these joints from moving. Strong synergistic actions are occurring in the hand to allow the flexors to flex the fingers but not the wrist. As the example illustrates, it is important to recognize that even the simplest movements require the coordinated action of many muscles. One additional pedagogical feature used throughout this software is the organization of the muscles into developmental groups. This developmental grouping approach is significant because muscles that share a common embryonic origin share many things in common. Muscles with a shared developmental history, share a common areas of attachment, common actions, common nerve supply, and common blood supply. Grouping things in this way makes the learning process much easier. However, the versatility of the software also allows you to take a more traditional regional approach to the study of muscles. This approach allows you to study muscles that occupy similar regional positions in the body; for example, the muscles of the neck or muscles of the back. While this approach does not allow you to associate muscles that share common features, it does let you look at relationships of muscles in the various regions of the body.