Chapter 11 Review Sheet Microscopic Anatomy and Organization of Skeletal Muscle

Learning Objectives

Past the stop of this section, you will be able to:

• Compare and contrast agonist and antagonist muscles
• Describe how fascicles are bundled inside a skeletal musculus
• Explain the major events of a skeletal muscle wrinkle inside a muscle in generating force

To move the skeleton, the tension created past the wrinkle of the fibers in nigh skeletal muscles is transferred to the tendons. The tendons are strong bands of dense, regular connective tissue that connect muscles to bones. The bone connection is why this musculus tissue is called skeletal muscle.

Interactions of Skeletal Muscles in the Trunk

To pull on a bone, that is, to change the angle at its synovial joint, which essentially moves the skeleton, a skeletal musculus must also be attached to a fixed part of the skeleton. The moveable cease of the musculus that attaches to the os existence pulled is chosen the musculus'southward insertion, and the end of the muscle attached to a fixed (stabilized) bone is called the origin. During forearm flexion—angle the elbow—the brachioradialis assists the brachialis.

Although a number of muscles may be involved in an action, the master muscle involved is chosen the prime mover, or agonist. To lift a cup, a musculus called the biceps brachii is really the prime mover; however, considering it can be assisted by the brachialis, the brachialis is chosen a synergist in this action (Effigy 11.2). A synergist tin also be a fixator that stabilizes the os that is the attachment for the prime mover's origin.

Figure 11.2 Prime Movers and Synergists The biceps brachii flex the lower arm. The brachoradialis, in the forearm, and brachialis, located deep to the biceps in the upper arm, are both synergists that aid in this motion.

A muscle with the contrary action of the prime mover is called an antagonist. Antagonists play ii important roles in muscle part: (ane) they maintain trunk or limb position, such as holding the arm out or continuing erect; and (ii) they control rapid motion, as in shadow boxing without landing a punch or the power to check the motion of a limb.

For example, to extend the knee, a group of iv muscles called the quadriceps femoris in the anterior compartment of the thigh are activated (and would be called the agonists of genu extension). Still, to flex the knee joint, an opposite or combative prepare of muscles chosen the hamstrings is activated.

Equally you tin can see, these terms would also be reversed for the opposing activeness. If you consider the first action as the knee joint bending, the hamstrings would be called the agonists and the quadriceps femoris would and so be called the antagonists. Meet Table xi.1 for a list of some agonists and antagonists.

Agonist and Adversary Skeletal Musculus Pairs

Agonist	Antagonist	Movement
Biceps brachii: in the inductive compartment of the arm	Triceps brachii: in the posterior compartment of the arm	The biceps brachii flexes the forearm, whereas the triceps brachii extends it.
Hamstrings: group of three muscles in the posterior compartment of the thigh	Quadriceps femoris: group of 4 muscles in the anterior compartment of the thigh	The hamstrings flex the leg, whereas the quadriceps femoris extend information technology.
Flexor digitorum superficialis and flexor digitorum profundus: in the inductive compartment of the forearm	Extensor digitorum: in the posterior compartment of the forearm	The flexor digitorum superficialis and flexor digitorum profundus flex the fingers and the mitt at the wrist, whereas the extensor digitorum extends the fingers and the hand at the wrist.

Table xi.1

There are also skeletal muscles that do not pull against the skeleton for movements. For example, at that place are the muscles that produce facial expressions. The insertions and origins of facial muscles are in the skin, so that certain individual muscles contract to form a grinning or frown, form sounds or words, and raise the eyebrows. There also are skeletal muscles in the tongue, and the external urinary and anal sphincters that allow for voluntary regulation of urination and defecation, respectively. In addition, the diaphragm contracts and relaxes to change the book of the pleural cavities merely it does non move the skeleton to practise this.

Everyday Connection

Exercise and Stretching

When exercising, it is important to first warm up the muscles. Stretching pulls on the muscle fibers and information technology also results in an increased claret menses to the muscles being worked. Without a proper warm-upward, it is possible that you may either harm some of the muscle fibers or pull a tendon. A pulled tendon, regardless of location, results in pain, swelling, and diminished function; if information technology is moderate to severe, the injury could immobilize you for an extended period.

Recall the discussion about muscles crossing joints to create motility. Near of the joints you use during exercise are synovial joints, which take synovial fluid in the joint space between two basic. Exercise and stretching may too have a benign effect on synovial joints. Synovial fluid is a thin, merely viscous film with the consistency of egg whites. When you first get upwards and first moving, your joints feel stiff for a number of reasons. After proper stretching and warm-up, the synovial fluid may become less mucilaginous, allowing for meliorate joint function.

Patterns of Fascicle Arrangement

Skeletal muscle is enclosed in connective tissue scaffolding at 3 levels. Each muscle fiber (cell) is covered by endomysium and the entire muscle is covered past epimysium. When a grouping of muscle fibers is "bundled" every bit a unit inside the whole muscle by an additional covering of a connective tissue chosen perimysium, that bundled grouping of muscle fibers is called a fascicle. Fascicle organization past perimysia is correlated to the strength generated past a muscle; information technology likewise affects the range of motion of the muscle. Based on the patterns of fascicle arrangement, skeletal muscles can be classified in several ways. What follows are the most common fascicle arrangements.

Parallel muscles have fascicles that are arranged in the aforementioned direction as the long axis of the muscle (Figure 11.3). The majority of skeletal muscles in the torso have this type of organization. Some parallel muscles are apartment sheets that expand at the ends to make broad attachments. Other parallel muscles are rotund with tendons at one or both ends. Muscles that seem to be plump have a large mass of tissue located in the middle of the muscle, between the insertion and the origin, which is known equally the key body. A more mutual name for this muscle is belly. When a muscle contracts, the contractile fibers shorten it to an even larger bulge. For example, extend and then flex your biceps brachii muscle; the large, center section is the abdomen (Figure 11.four). When a parallel muscle has a central, large abdomen that is spindle-shaped, meaning it tapers as it extends to its origin and insertion, it sometimes is called fusiform.

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

Effigy 11.4 Biceps Brachii Muscle Contraction The big mass at the middle of a muscle is chosen the belly. Tendons sally from both ends of the belly and connect the musculus to the bones, allowing the skeleton to move. The tendons of the bicep connect to the upper arm and the forearm. (credit: Victoria Garcia)

Round muscles are also called sphincters (encounter Effigy xi.3). When they relax, the sphincters' concentrically bundled bundles of muscle fibers increment the size of the opening, and when they contract, the size of the opening shrinks to the bespeak of closure. The orbicularis oris muscle is a circular muscle that goes effectually the mouth. When it contracts, the oral opening becomes smaller, equally when puckering the lips for whistling. Another example is the orbicularis oculi, i of which surrounds each eye. Consider, for example, the names of the 2 orbicularis muscles (orbicularis oris and oribicularis oculi), where part of the first name of both muscles is the same. The first part of orbicularis, orb (orb = "circular"), is a reference to a round or circular construction; it may also brand ane think of orbit, such as the moon'due south path around the globe. The word oris (oris = "oral") refers to the oral cavity, or the mouth. The give-and-take oculi (ocular = "eye") refers to the eye.

There are other muscles throughout the trunk named by their shape or location. The deltoid is a big, triangular-shaped muscle that covers the shoulder. It is so-named considering the Greek alphabetic character delta looks like a triangle. The rectus abdominis (rector = "straight") is the straight muscle in the anterior wall of the abdomen, while the rectus femoris is the direct muscle in the anterior compartment of the thigh.

When a muscle has a widespread expansion over a sizable expanse, merely and so the fascicles come up to a single, common attachment signal, the muscle is called convergent. The attachment point for a convergent muscle could be a tendon, an aponeurosis (a flat, wide tendon), or a raphe (a very slender tendon). The large muscle on the chest, the pectoralis major, is an case of a convergent musculus because it converges on the greater tubercle of the humerus via a tendon. The temporalis muscle of the attic is another.

Pennate muscles (penna = "feathers") alloy into a tendon that runs through the central region of the muscle for its whole length, somewhat like the quill of a plumage with the muscle arranged similar to the feathers. Due to this design, the musculus fibers in a pennate musculus can only pull at an bending, and as a result, contracting pennate muscles do not movement their tendons very far. Nevertheless, because a pennate muscle more often than not tin can agree more musculus fibers within it, it can produce relatively more tension for its size. There are three subtypes of pennate muscles.

In a unipennate muscle, the fascicles are located on i side of the tendon. The extensor digitorum of the forearm is an example of a unipennate musculus. A bipennate muscle has fascicles on both sides of the tendon. In some pennate muscles, the muscle fibers wrap around the tendon, sometimes forming private fascicles in the process. This arrangement is referred to as multipennate. A common case is the deltoid muscle of the shoulder, which covers the shoulder just has a single tendon that inserts on the deltoid tuberosity of the humerus.

Because of fascicles, a portion of a multipennate muscle like the deltoid tin can be stimulated past the nervous organization to change the direction of the pull. For example, when the deltoid muscle contracts, the arm abducts (moves away from midline in the sagittal plane), just when only the anterior fascicle is stimulated, the arm will housebreak and flex (motion anteriorly at the shoulder articulation).

The Lever System of Muscle and Bone Interactions

Skeletal muscles exercise not work by themselves. Muscles are arranged in pairs based on their functions. For muscles attached to the bones of the skeleton, the connection determines the force, speed, and range of motion. These characteristics depend on each other and tin can explain the general organisation of the muscular and skeletal systems.

The skeleton and muscles deed together to move the body. Have you always used the dorsum of a hammer to remove a nail from woods? The handle acts equally a lever and the caput of the hammer acts as a fulcrum, the fixed point that the force is applied to when you lot pull back or push down on the handle. The try applied to this system is the pulling or pushing on the handle to remove the nail, which is the load, or "resistance" to the motility of the handle in the system. Our musculoskeletal system works in a similar manner, with basic being stiff levers and the articular endings of the basic—encased in synovial joints—acting as fulcrums. The load would be an object being lifted or any resistance to a movement (your head is a load when you are lifting it), and the attempt, or practical force, comes from contracting skeletal muscle.

mcmahonthempanince.blogspot.com

Source: https://openstax.org/books/anatomy-and-physiology-2e/pages/11-1-interactions-of-skeletal-muscles-their-fascicle-arrangement-and-their-lever-systems

Share this post