what is a sheet-like connective tissue that connects muscle to another muscle or to a bone?

Interactions of Skeletal Muscles

Skeletal muscles interact to produce movements by fashion of anatomical positioning and the coordinated summation of innervation signals.

Learning Objectives

Explain the summation interactions of skeletal muscles and how they affect move

Key Takeaways

Fundamental Points

• Muscle contractions tin be termed twitch, summation or tetanus.
• A twitch contraction is the
  period of contraction and relaxation of a muscle after a single stimulation.
• Summation is the
  occurrence of boosted twitch contractions before the previous twitch has completely relaxed.
• Summation can exist accomplished past increasing the frequency of stimulation, or by recruiting boosted muscle fibers within a musculus.
• Tetanus
  occurs when the frequency of muscle wrinkle is such that the maximal force is tension is generated without whatever relaxation of the muscle.

Cardinal Terms

• tetanus: When the frequency of musculus contraction is such that the maximal force is tension is generated without whatever relaxation of the muscle.
• summation: The occurrence of additional twitch contractions before the previous twitch has completely relaxed.
• twitch: The period of contraction and relaxation of a muscle subsequently a unmarried stimulation.

Skeletal muscle contractions can be grouped based on the length and frequency of contraction.

Twitch

When stimulated by a single action potential a muscle contracts and and so relaxes. The time between the stimulus and the initiation of contraction is termed the latent period, which is followed by the contraction period. At peak contraction the musculus relaxes and returns to its resting position. Taken all together these three periods are termed a twitch.

Muscle Twitch Contraction: The time between stimulation and contraction is termed the latent menstruum. Later wrinkle the muscle relaxes dorsum to a resting level of tension. Together these three periods grade a single musculus twitch,

Summation

If an boosted activeness potential were to stimulate a muscle contraction before a previous musculus twitch had completely relaxed so it would sum onto this previous twitch increasing the total amount of tension produced in the muscle. This addition is termed summation. Inside a muscle summation can occur across motor units to recruit more muscle fibers, and as well within motor units by increasing the frequency of wrinkle.

Multiple fiber summation

When a weak signal is sent by the central nervous system to contract a muscle, the smaller motor units, existence more excitable than the larger ones, are stimulated first. As the strength of the signal increases, more than (and larger) motor units are excited. The largest motor units have as much as 50 times the contractile strength every bit the smaller ones; thus, every bit more and larger motor units are activated, the force of muscle contraction becomes progressively stronger. A concept known as the size principle allows for a gradation of muscle force during weak contraction to occur in small steps, which become progressively larger as greater amounts of forcefulness are required.

Frequency summation

For skeletal muscles, the force exerted by the muscle tin can be controlled by varying the frequency at which action potentials are sent to muscle fibers. Activeness potentials do non get in at muscles synchronously, and, during a contraction, only a certain percentage of the fibers in the musculus will exist contracting at whatever given fourth dimension. In a typical circumstance, when a human is exerting equally much muscular force as they are consciously able, roughly one-third of the fibers in that muscle volition be contracting at once. This relatively low level of wrinkle is a protective machinery to prevent damage to the musculus tissue and attaching tendons and structures.

Tetanus

If the frequency of action potentials generated increases to such a betoken that musculus tension has reached its superlative and plateaued and no relaxation is observed then the muscle contraction is described as a tetanus.

Summation and Tetanus Contractions: Repeated twitch contractions, where the previous twitch has not relaxed completely are chosen a summation. If the frequency of these contractions increases to the point where maximum tension is generated and no relaxation is observed then the contraction is termed a tetanus.

How Skeletal Muscles Are Named

The anatomical arrangement of skeletal muscle fascicles tin exist described every bit parallel, convergent, pennate, or sphincter.

Learning Objectives

Differentiate amid parallel, pennate, convergent, and sphincter muscle types

Central Takeaways

Key Points

• Parallel muscles are the well-nigh abundant and typical, with fascicles arranged parallel to one some other.
• Convergent muscles are similar to parallel muscles in attachment, although fascicles exercise not run parallel to one another, producing a broader musculus.
• In a pennate muscle the tendon runs through the length of the muscle, with the fascicles attaching at an angle.
• Sphincter muscles are characterized past a circular arrangement of fascicles around an opening. With contraction, the opening becomes smaller.

Fundamental Terms

• Parallel: A muscle with a common signal of attachment, with fascicles running parallel to each other.
• Round: A ring similar ring of muscle that surrounds a bodily opening, constricting and relaxing to control flow.
• Pennate: A feather shaped musculus with fascicles that attach obliquely (at an angle) to a central tendon.
• Convergent: A muscle with a mutual point of attachment, although private fascicles practise not necessarily run parallel to each other.

Skeletal muscle can be categorised into four groups based on its anatomical arrangement.

Parallel

Parallel muscles are characterized past fascicles that run parallel to one another, and contraction of these musculus groups acts as an extension of the contraction of a unmarried muscle fiber. Well-nigh skeletal muscles in the trunk are parallel muscles; although they tin be seen in a variety of shapes such as apartment bands, spindle shaped, and some can take large protrusions in their center known equally the abdomen of the muscle.

Parallel muscles can be divided into fusiform and not-fusiform types based on their shape. Fusiform muscles are more than spindle shaped (their bore at the center is greater than at either terminate), whereas, non-fusiform muscles are more rectangular with a constant diameter.

The biceps brachii is an example of a  fusiform parallel muscle, and is responsible for flexing the forearm.

Convergent

Convergent muscles accept a common bespeak of zipper, from which the muscle fascicles extend outward, not necessarily in a specific spatial design, allowing the muscle to cover a broad surface. These muscles do non tend to exert every bit much force on their tendons. Muscle fibers can often exert opposing effects during contraction, such equally not pulling in the same management depending on the location of the muscle cobweb. Covering a broad surface these fibers permit for more than versatile types of move. Because the fascicles pull on the tendons at an bending, they practice not move the tendon as far as their parallel muscle counterparts. Despite this they generate greater tension considering they possess a greater corporeality of muscle fibers than similarly sized parallel muscles.

The pectoralis major found in the chest is an example of a convergent muscle, and is responsible for flexing the upper arm.

Pennate

In Pennate muscles, the tendon runs through the length of the musculus. Fascicles pull on the tendon at an angle, thus not moving every bit far at the parallel muscles during a wrinkle. However, these muscles tend to accept relatively more muscle fibers than similarly sized parallel muscles, and thus behave more than tension.

If all the fascicles of a pennate musculus are on the same side of the tendon, the pennate muscle is chosen unipennate. If the fascicles lie to either side of the tendon the muscle is called bipennate. If the central tendon branches within a pennate muscle, the muscle is called multipennate.

The rectus femoris found in the thigh, and responsible for its flexion, is an instance of a bipennate muscle.

Circular

The fibers of the circular or sphincter muscles are arranged concentrically around an opening or recess. As the musculus contracts, the opening it circumvents gets smaller. For this reason, these muscles are often found at the entrances and exits of external and internal passageways. Skeletal circular muscles are different from smooth musculus equivalents due to their construction and because they are under voluntary control

The orbicularis oris which controls the opening of the oral fissure is an instance of a circular muscle.

Types of muscle in the torso: The four types of musculus; parallel (fusiform and not-fusiform), circular, convergent and pennate (uni, bi and multi).

How Skeletal Muscles Produce Movements

Muscles are arranged in groupings of agonist, antagonist, and synergists that produce and modulate movement.

Learning Objectives

Differentiate between agonist and antagonist muscles

Cardinal Takeaways

Central Points

• Agonist muscles shorten with wrinkle to produce a movement.
• Following wrinkle, the antagonist musculus paired to the agonist muscle returns the limb to the previous position.
• Synergist muscles deed around a movable articulation to produce motion similar to or in concert with agonist muscles, allowing for a range of possible movements.

Central Terms

• antagonist: This blazon of muscle acts equally opposing musculus to agonists, usually contracting as a means of returning the limb to its original resting position.
• agonist: These muscles are typically assembly with the movement itself, and are sometimes referred to as prime movers. They contract while another muscle relaxes.
• synergist: This type of muscle acts around a movable articulation to produce motion similar to or in concert with agonist muscles.

Muscles exist in groupings that work to produce movements by muscle contraction. Muscles are classified co-ordinate to their actions during contractions equally agonists, antagonists, or synergists.

For musculus pairings referred to every bit combative pairs, one musculus is designated as the extensor muscle, which contracts to open up the joint, and the flexor muscle, which acts opposite to the extensor musculus. These pairs be in places in the body in which the torso cannot return the limb back to its original position through unproblematic lack of contraction. Typical muscle pairings include the biceps brachii and triceps brachii, which act to flex or extend the forearm.

Agonist Muscles

Agonist muscles are those we typically associate with movement itself, and are thus sometimes referred to as prime movers. Agonist muscles produce the principal motility or series of movements through their own contractions. To generate a movement, agonist muscles must physically exist arranged so that they cantankerous a joint by way of the tendon. Wrinkle will motion limbs associated with that articulation. In this sense, the bone acts as a lever with the attached muscle fiber's contraction, driving movement.

During flexing of the forearm the biceps brachii is the agonist muscle, pulling the forearm up towards the shoulder.

Antagonist Muscles

The majority of muscles are grouped in pairs, with an antagonist to each agonist muscle. Exceptions include those muscles such as sphincter muscles that human activity to contract in a fashion that is reverse to the resting state of the musculus. Adversary muscles deed equally opposing muscles to agonists, ordinarily contracting equally a means of returning the limb to its original, resting position.

During flexing of the forearm, the triceps brachii is the antagonist muscle, resisting the movement of the forearm upward towards the shoulder.

Synergist Muscles

Synergist muscles deed around a moveable joint to produce motion similar to or in concert with agonist muscles. They often act to reduce excessive force generated by the agonist muscle and are referred to as neutralizers. Synergists are useful because they fix certain joints to allow a range of contractions, in dissimilarity with the sheer power of an agonist contraction that limits the range of possible movements.

During flexing of the forearm, the brachioradialis and brachialis act every bit synergist muscles, aiding the biceps brachii in pulling the forearm up towards the shoulder. The muscles of the rotator gage are also synergists in that they fix the shoulder joint allowing the bicepps brachii to exert a greater force.

Flexing of the forearm by the biceps brachii: The biceps brachii is the agonist, or primer mover, responsible for flexing the forearm. The triceps brachii (not shown) acts every bit the antagonist. The brachioradialis and brachialis are synergist muscles, and the rotator cuff (non shown) fixes the shoulder joint allowing the biceps brachii to exert greater force.

Muscle Attachment Sites

Tendons are composed of connective tissue that attaches muscle to os.

Learning Objectives

Describe the role of tendons

Fundamental Takeaways

Key Points

• Tendons have elasticity, which allows them to withstand tension and human activity equally springs.
• Tendons mainly consists of closely-packed collagen fibers running parallel to the force generated past the muscle to which they are attached.
• Tendons also contain elastin fibers to improve the elastic backdrop and proteoglycans, which maintain tendon organisation during extension and compression.
• Aponeuroses are big apartment sheets of connective tissue similar to tendons. They are responsible for binding muscle to bone and to the fascia of other muscles.

Cardinal Terms

• tendon: A tough band of gristly tissue that commonly connects a muscle with a bone.
• aponeuroses: A tough flat sail of gristly tissue that connects musculus with bones or with the fascia of other muscles.

Most skeletal muscle attaches to os in order to produce movement. However, some skeletal muscle attaches straight to other muscles, fascia, or tissues such as the skin.

Tendons

Achilles Tendon: The Achilles tendon provides stability and limits the range of motion at the ankle joint. It is the thickest and strongest tendon in the body. Tendons are a mutual tissue that connect muscle to os.

A tendon is a cord-like, fibrous connective tissue that connects muscle to bone and is capable of withstanding tension. At either end of the tendon, its fibers intertwine with the fascia of a muscle or the periosteum (a dense fibrous covering of a os), assuasive force to be dissipated across the bone or muscle.

Tendons mainly consists of closely-packed collagen fibers running parallel to the force generated past the muscle to which they are attached. Intertwined with the collagen fibers are elastin molecules, which better the tendons' elasticity, and various proteoglycans, proteins to which many saccharide molecules are fastened. These proteins play a key role in maintaining the organization of the tendon, particularly during compression and extension.

Tendons were once thought to play just a passive connective role. However, enquiry into their elastic properties has demonstrated that they can also act every bit springs. The elasticity of tendons allows them to passively store energy for later release. The most widely-researched example is the Achilles tendon which stores and releases elastic energy during walking, improving efficiency and reducing musculus load.

Aponeuroses

Not all muscle attaches via tendons. Aponeuroses are big, sheet-like layers of connective tissue with a similar limerick to tendons. Aponeuroses tin as well attach to os, equally in the scalp aponeuroses, and to the fascia of other muscles or tissues, such every bit the anterior abdominal aponeuroses. Their large form and shape provides construction and distributes tension across a wider area or large number of muscle groups.

Other Attachments

Muscles can also attach direct to other tissues, which is most axiomatic in the confront. The skeletal muscles involved in controlling expression attach directly onto the fascia of the skin.

Arrangement of Fascicles

Skeletal muscles are grouped into fascicles, which are bunches of muscle fibers surrounded by a perimysium.

Learning Objectives

Outline the construction of a muscle fascicle

Cardinal Takeaways

Key Points

• Skeletal muscle is surrounded past a thick connective canvass termed the fascia
• Underneath this is some other layer of connective tissue called the epimysium, which extends inwards every bit the perimysium into the musculus, splitting fibers into bundles termed fascicles.
• Each fascicle is surrounded by another layer of connective tissue termed the endomysium.
• This structure separates and protects the muscle and also acts to spread forcefulness throughout the muscle, preventing damage.

Key Terms

• perimysium: The continuation of the epimysium into the muscle, splitting fibers into fascicles.
• epimysium: A canvass of connective tissue lying below the fascia, likewise surrounding a muscle.
• fascia: A sheet of thick connective tissue which surrounds a muscle.
• endomysium: A sheet of connective tissue which wraps each fascicle.
• fascicle: A grouping of musculus of fibers surrounded by the perimysium.

Musculus Fascia

Muscle Structure: Skeletal muscle is surrounded by a thick outer layer of connective tissue termed the fascia. Within this is a layer termed the epimysium which splits inwards into the musculus as the perimysium dividing muscle fibers into groups termed fascicle. Each fascicle is surrounded by another layer of connective tissue termed the endomysium.

Skeletal muscle tissue is composed of numerous muscle fibers which are separated from adjacent muscles and other tissues by a layer of dense, rubberband connective tissue termed the fascia. This fascia can project across the end of the muscle and attach to bones, other muscles, and other tissues. Key musculus groups and the associated vascular and nervous systems can too be separated from other tissue, such as in the upper arm. These groupings are chosen fascial compartments.

This fascia is interlinked with a serious of fascia constitute throughout the body, including the superficial fascia which is the lowermost layer of the skin and the visceral fascia which surrounds internal organs. The fascia surrounding a muscle or muscle grouping does not contain many blood vessels, just is rich with sensory receptors.

Muscle fascia is predominately equanimous of cross-linked collagen and elastin fibers oriented parallel to the management of muscle forcefulness, making them able to resist loftier-tension forces while remaining somewhat elastic.

Fascicles

Beneath the fascia in skeletal musculus is another layer of connective tissue termed the epimysium which is closely associated with the fascia. Information technology extends inwards and becomes the perimysium, then into the muscle separating muscle fibers into small bundles termed fascicles. Fascicles tin can be arranged in a multifariousness of anatomical positions inside a muscle, producing different movements.

Each private fiber inside a fascicle is surrounded by a thin connective layer termed the endomysium, which helps maintain close association between the musculus fiber and associated vascular and nervous systems.

The organization of connective tissue throughout and around a musculus provides strength and flexibility while distributing the force evenly. Information technology too maintains the shut association of the vascular and nervous system with the muscle, which is required to deliver necessary metabolites and nervus impulses.

Cardiac and Smooth Muscle Tissue

Whilst both cardiac and smooth muscles are as well wrapped in connective tissue, they are not differentiated in the same way as skeletal muscles.

Lever Systems

Arrangement of muscles allows them to movement relative to one some other, while the insertion articulation acts as the pin bespeak for a lever system.

Learning Objectives

Differentiate between flexors and extensors and between adductors and abductors

Central Takeaways

Key Points

• A simple lever organisation can be used to describe skeletal muscle activeness. Levers are composed of a pivot, a fixed rod, and a load to which a force is applied.
• The relative positions of the pivot, load, and strength determine the type of lever and subsequent activity.
• Flexors and extensors piece of work to arrange the angle between two trunk parts. Flexion decreases the angle and extension increases the bending.
• Abduction and adduction are movements relative to the midline of the body. Abduction is the movement away from this midline while adduction is movement towards the midline.
• Internal rotation brings the distal portions of the limbs inwards towards the midline. External rotation is the opposite movement, pointing the distal portion of limbs away from the midline.
• The acme of a limb or body office moves it in a superior direction, while low moves body parts in an junior management.

Key Terms

• abduction: Motion abroad from the midline of the body.
• rotation: The act of turning around a middle or an axis.
• offset class lever: Strength and load to either side of the pivot.
• second-class lever: Load between force and pivot.
• third-class lever: Strength between pivot and load.
• origin: The relatively immovable point of attachment for a musculus.
• insertion: The movable point of attachment for a muscle.
• flexion: Reduces the angle betwixt two trunk parts.
• extension: Increases the angle between two body parts.
• adduction: Move towards the midline of the trunk.

Skeletal muscle is ordinarily attached to a relatively immovable function of the body at one end and more than mobile region on the other stop of a articulation. The attachment at the immovable end is referred to equally the origin and at the moveable terminate, the insertion. Upon contraction, the insertion is pulled towards the origin. This movement can exist described using a unproblematic lever organization. Muscles can have multiple origins and insertions which modulate the type of motion they produce.

Levers

A lever is equanimous of three parts: a fixed rod which is attached to a fulcrum (pivot) and a load. Depending on the relative position of the 3 components, levers can movement heavy loads or move loads further or faster when a strength is practical.

If a load is close to a pin and the forcefulness is applied far from the pivot, then the lever is said to operate at mechanical advantage. A big just relatively small-scale forcefulness can movement a heavy object. The classic case of such a lever is a auto jack. With large movements of the lever, the heavy car is lifted in small increments off the ground.

If a load is far from a pin and a force is applied near to the pivot, then the lever is said to operate at a mechanical disadvantage. A big force is required to movement a relatively pocket-sized load, but the speed and distance at which that load can exist moved is greatly increased. An example of this is a spade combined with forceful movements of the muscles in the arm, which results in large movements of the spade head.

In muscles, the joints are the pivots and the basic are the stock-still rods. The load is the weight of the os, associated tissues, and other objects being moved, and the force is practical past the muscle at its insertion point.

Classes of Levers

Levers can also vary based on the relative position of the load, pivot and point of force application. Classes of levers include:

Get-go-class Lever

In a first course lever, the load and strength sit down on either side of the pin like a seesaw. First-class levers are relatively uncommon in the torso, but i instance is the triceps brachii muscle of the upper arm which acts to extend the forearm. The force is applied at its betoken of insertion on the ulna in the forearm, the elbow is the pivot, and the load is the humerus in the upper arm. Thinking of the relative distance between the points of attachment, the triceps brachii can be said to human activity at a mechanical disadvantage.

Second-class Lever

In a 2nd-class lever, the forcefulness is practical at one end with the pin at the other and the load in between. Second-class levers are also relatively uncommon in the body. One example is raising yourself up on your toes. The pin is based at the forepart of the foot, the load is the weight of the body, and the force is practical through the Achilles tendon in the heel. All 2nd-class levers in the body deed at a mechanical advantage since the strength is ever applied closer to the load than to the pivot.

Third-course Lever

In a 3rd-course lever the force is practical between the load and the pivot. The majority of muscles in the trunk are third-class levers and all human activity at a mechanical disadvantage as the force is practical closer to the pin than the load. An example of a third-class lever in the body is the biceps brachii, which flexes the forearm towards the shoulder. Originating at the scapula, the pivot is the elbow, with the force practical immediately after the elbow at the signal of insertion on the radius of the forearm. The load is the forearm and any objects a person carries.

Types of Motility

Working together using the lever principles discussed above, skeletal muscles tin can induce a wide range of movements.

Flexors and Extensors

Flexors and extensors adapt and alter the angle between two body parts. Flexion decreases the bending and extension increases the angle. For example, extension of the arm opens the angle of the elbow joint, while flexion allows for the bending of the arm. Flexion can likewise move in towards the torso or forward, such as with hips or shoulders. Extension in this instance moves the limbs towards the posterior side of the body lever.

Abduction and Adduction

Abduction and adduction are movements relative to the midline of the body. Abduction is the movement away from the midline of the body and adduction is movement towards this line. For example, moving artillery or legs laterally away from the body is abduction, and bringing the limbs dorsum to the midline is adduction.

Internal Rotation

Internal or medial rotation is specific to the shoulder or hip and brings the distal portions of the limbs inwards towards the midline. Internal rotation can too move the humerus and femur inward. External or lateral rotation is the reverse move, pointing the distal portion of limbs also as the humerus and femur away from the mid-line.

Low and Elevation

A limb or a torso office tin be moved upward (or in a superior management) through elevation. For instance, the trapezius elevates the apex of the shoulder upward. Depression is the opposite of summit, or moving body parts in an junior management.

Types of body movements: Muscle positioning around a articulation determines the blazon of motion that is produced.

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Source: https://courses.lumenlearning.com/boundless-ap/chapter/overview-of-the-muscular-system/

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