Support and also Movement The Muscular mechanism The Muscular device advent

Figure 11.1 A body in Motion The muscular system allows us come move, flex and also contort our bodies. Practicing yoga, together pictured here, is a great example of the voluntary usage of the muscular system. (credit: Dmitry Yanchylenko)


After researching this chapter, you will be may be to:

Describe the actions and also roles of agonists and also antagonistsExplain the structure and also organization the muscle fascicles and also their function in generating forceExplain the criteria used to name skeletal musclesIdentify the skeletal muscles and also their plot on the skeleton and soft organization of the bodyIdentify the origins and insertions of skeleton muscles and also the prime movements

Think about the things that you do each day—talking, walking, sitting, standing, and running—all the these tasks require motion of details skeletal muscles. Skeletal muscles are also used during sleep. The diaphragm is a sheet of bones muscle that has to contract and also relax because that you to breathe day and night. If girlfriend recall native your research of the bones system and also joints, body movement occurs approximately the joints in the body. The emphasis of this chapter is on bones muscle organization. The device to surname skeletal muscles will be explained; in some cases, the muscle is called by that is shape, and in other instances it is named by its ar or attachments to the skeleton. If you understand the an interpretation of the surname of the muscle, regularly it will aid you psychic its location and/or what the does. This chapter additionally will explain how bones muscles room arranged to accomplish movement, and also how various other muscles might assist, or be arranged on the skeleton to stand up to or bring out the opposite movement. The actions of the skeleton muscles will be spanned in a local manner, working from the head under to the toes.

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by the finish of this section, you will be may be to:Compare and contrast agonist and also antagonist musclesDescribe just how fascicles room arranged in ~ a skeleton muscleExplain the major events that a skeletal muscle contraction in ~ a muscle in generating force

To move the skeleton, the tension created by the contraction of the yarn in most skeletal muscles is transferred to the tendons. The tendons are strong bands that dense, continuous connective tissue that connect muscles to bones. The bone connection is why this muscle tissue is called skeletal muscle.

Interactions the Skeletal muscles in the Body

To traction on a bone, the is, to readjust the edge at that synovial joint, which essentially moves the skeleton, a bones muscle must also be attached come a fixed component of the skeleton. The moveable finish of the muscle that attaches come the bone being pulled is called the muscle’s insertion, and also the end of the muscle attached come a addressed (stabilized) bone is called the origin. Throughout forearm flexion—bending the elbow—the brachioradialis assists the brachialis.

Although a variety of muscles might be associated in an action, the principal muscle involved is called the prime mover, or agonist. To lift a cup, a muscle referred to as the biceps brachii is actually the prime mover; however, because it deserve to be helped by the brachialis, the brachialis is called a synergist in this action (Figure 11.2). A synergist can also be a fixator that stabilizes the bone that is the attachment because that the prime mover’s origin.


Figure 11.2 Prime Movers and Synergists The biceps brachii flex the reduced arm. The brachoradialis, in the forearm, and brachialis, located deep come the biceps in the top arm, room both synergists that assist in this motion.

A muscle with the opposite activity of the prime mover is called an antagonist. Antagonists pat two necessary roles in muscle function: (1) they maintain body or body position, such as holding the eight out or stand erect; and also (2) they manage rapid movement, together in zero boxing without landing a punch or the capacity to check the motion of a limb.

For example, to prolong the knee, a group of four muscles called the quadriceps femoris in the anterior compartment of the thigh space activated (and would be referred to as the agonists of knee extension). However, to flex the knee joint, an the contrary or antagonistic collection of muscles called the hamstrings is activated.

As you deserve to see, these terms would likewise be reversed because that the the opposite action. If you consider the first action together the knee bending, the hamstrings would certainly be called the agonists and also the quadriceps femoris would then be called the antagonists. See Table 11.1 for a list of some agonists and antagonists.

Agonist and Antagonist skeleton Muscle Pairs

Biceps brachii: in the anterior compartment the the armTriceps brachii: in the posterior compartment the the armThe biceps brachii flexes the forearm, vice versa, the triceps brachii extends it.
Hamstrings: group of 3 muscles in the posterior compartment of the thighQuadriceps femoris: group of four muscles in the anterior compartment the the thighThe hamstrings flex the leg, conversely, the quadriceps femoris prolong it.
Flexor digitorum superficialis and also flexor digitorum profundus: in the anterior compartment that the forearmExtensor digitorum: in the posterior compartment the the forearmThe flexor digitorum superficialis and flexor digitorum profundus flex the fingers and also the hand in ~ the wrist, whereas the extensor digitorum extend the fingers and also the hand in ~ the wrist.

Table 11.1

There are also skeletal muscle that execute not pull versus the skeleton because that movements. For example, there room the muscle that create facial expressions. The insertions and origins of face muscles are in the skin, for this reason that details individual muscle contract to kind a smile or frown, type sounds or words, and also raise the eyebrows. There additionally are skeletal muscle in the tongue, and the outside urinary and also anal sphincters that allow for voluntarily regulation the urination and also defecation, respectively. In addition, the diaphragm contracts and also relaxes to readjust the volume that the pleural cavities yet it go not move the skeleton to do this.


Exercise and also Stretching

When exercising, the is essential to very first warm increase the muscles. Stretching pulls top top the muscle fibers and it additionally results in an increased blood circulation to the muscles gift worked. Without a suitable warm-up, that is feasible that you might either damages some of the muscle fibers or pull a tendon. A traction tendon, regardless of location, results in pain, swelling, and also diminished function; if the is moderate to severe, the injury can immobilize you for an extensive period.

Recall the discussion around muscles crossing joints to develop movement. Many of the joints girlfriend use throughout exercise room synovial joints, which have synovial fluid in the joint room between two bones. Exercise and also stretching may also have a helpful effect on synovial joints. Synovial fluid is a thin, but viscous film with the consistency the egg whites. As soon as you an initial get up and also start moving, her joints feel stiff because that a variety of reasons. After suitable stretching and also warm-up, the synovial fluid may come to be less viscous, permitting for much better joint function.

Patterns that Fascicle Organization

Skeletal muscle is attached in connective organization scaffolding at 3 levels. Each muscle fiber (cell) is covered by endomysium and the whole muscle is spanned by epimysium. Once a team of muscle fibers is “bundled” as a unit within the totality muscle by an additional covering of a connective tissue referred to as perimysium, that bundled group of muscle yarn is referred to as a fascicle. Fascicle setup by perimysia is associated to the pressure generated by a muscle; it also affects the selection of motion of the muscle. Based upon the trends of fascicle arrangement, skeletal muscles can be classified in number of ways. What complies with are the most typical fascicle arrangements.

Parallel muscles have fascicles that room arranged in the same direction as the long axis the the muscle (Figure 11.3). The majority of skeletal muscle in the body have this kind of organization. Part parallel muscles are flat sheets that expand at the ends to make large attachments. Various other parallel muscles are rotund with tendons in ~ one or both ends. Muscles the seem to it is in plump have a huge mass of tissue located in the center of the muscle, between the insertion and the origin, i m sorry is known as the central body. A more common surname for this muscle is belly. Once a muscle contracts, the contractile fibers shorten it come an also larger bulge. Because that example, extend and also then flex your biceps brachii muscle; the large, middle section is the ship (Figure 11.4). Once a parallel muscle has a central, large belly that is spindle-shaped, meaning it tapers as it extends come its origin and insertion, it occasionally is called fusiform.


Figure 11.3 Muscle Shapes and Fiber Alignment The skeletal muscles of the body typically come in seven various general shapes.


Figure 11.4 Biceps Brachii Muscle Contraction The huge mass in ~ the center of a muscle is called the belly. Tendons arise from both end of the belly and also connect the muscle come the bones, allowing the skeleton come move. The tendons the the bicep attach to the upper arm and the forearm. (credit: Victoria Garcia)

Circular muscles are likewise called sphincters (see Figure 11.3). Once they relax, the sphincters’ concentrically arranged bundles of muscle fibers rise the dimension of the opening, and also when castle contract, the size of the opening shrinks come the suggest of closure. The orbicularis oris muscle is a circular muscle the goes approximately the mouth. Once it contracts, the dental opening becomes smaller, as once puckering the lips because that whistling. An additional example is the orbicularis oculi, among which surrounds every eye. Consider, for example, the name of the 2 orbicularis muscle (orbicularis oris and also oribicularis oculi), where part of the very first name that both muscles is the same. The first part that orbicularis, orb (orb = “circular”), is a reference to a round or circular structure; the may also make one think the orbit, such together the moon’s path roughly the earth. The word oris (oris = “oral”) describes the dental cavity, or the mouth. Words oculi (ocular = “eye”) describes the eye.

There are other muscles transparent the body named by their shape or location. The deltoid is a large, triangular-shaped muscle the covers the shoulder. It is so-named since the Greek letter delta looks prefer a triangle. The rectus abdomis (rector = “straight”) is the straight muscle in the anterior wall of the abdomen, when the rectus femoris is the straight muscle in the anterior compartment the the thigh.

When a muscle has actually a widespread expansion over a sizable area, however then the fascicles involved a single, typical attachment point, the muscle is called convergent. The attachment allude for a convergent muscle could be a tendon, one aponeurosis (a flat, large tendon), or a raphe (a an extremely slender tendon). The big muscle top top the chest, the pectoralis major, is an example of a convergent muscle due to the fact that it converges ~ above the higher tubercle the the humerus via a tendon. The temporalis muscle that the cranium is another.

Pennate muscles (penna = “feathers”) blend into a tendon the runs with the main region of the muscle because that its entirety length, somewhat prefer the quill of a feather through the muscle arranged similar to the feathers. Because of this design, the muscle yarn in a pennate muscle deserve to only traction at one angle, and as a result, contracting pennate muscles perform not relocate their tendons really far. However, due to the fact that a pennate muscle usually can hold an ext muscle fibers in ~ it, that can produce relatively an ext tension for its size. There space three subtypes that pennate muscles.

In a unipennate muscle, the fascicles are located on one side of the tendon. The extensor digitorum the the forearm is an instance of a unipennate muscle. A bipennate muscle has actually fascicles top top both sides of the tendon. In some pennate muscles, the muscle yarn wrap roughly the tendon, sometimes forming individual fascicles in the process. This setup is referred to as multipennate. A typical example is the deltoid muscle the the shoulder, i beg your pardon covers the shoulder but has a solitary tendon that inserts on the deltoid tuberosity that the humerus.

Because of fascicles, a part of a multipennate muscle choose the deltoid can be engendered by the nervous device to change the direction the the pull. For example, when the deltoid muscle contracts, the arm abducts (moves away from midline in the sagittal plane), but when only the anterior fascicle is stimulated, the arm will abduct and flex (move anteriorly at the shoulder joint).

The lever System the Muscle and also Bone Interactions

Skeletal muscles execute not work-related by themselves. Muscles are arranged in pairs based upon their functions. For muscles attached come the skeletal of the skeleton, the connection determines the force, speed, and range of movement. These qualities depend on every other and also can define the basic organization that the muscular and skeletal systems.

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The skeleton and also muscles act together to relocate the body. Have actually you ever used the back of a hammer to remove a pond from wood? The handle acts together a lever and the head of the hammer acts as a fulcrum, the fixed suggest that the pressure is applied to once you pull back or push down on the handle. The effort used to this device is the pulling or pushing on the handle to remove the nail, i beg your pardon is the load, or “resistance” come the motion of the take care of in the system. Our musculoskeletal system works in a comparable manner, with bones being stiff levers and also the articular end of the bones—encased in synovial joints—acting as fulcrums. The fill would be things being lifted or any kind of resistance to a movement (your head is a fill when you room lifting it), and the effort, or applied force, comes from contracting bones muscle.