Fibrous bands or cords of CONNECTIVE TISSUE at the ends of SKELETAL MUSCLE FIBERS that serve to attach the MUSCLES to bones and other structures.
Human Skeletal Muscle with Tendon and Ligament
Image by TheVisualMD
Tendon
Tendons
Image by NCI / NIH
Tendons
Commonly, the epimysium, perimysium, and endomysium extend beyond the fleshy part of the muscle, the belly or gaster, to form a thick ropelike tendon or a broad, flat sheet-like aponeurosis. The tendon and aponeurosis form indirect attachments from muscles to the periosteum of bones or to the connective tissue of other muscles. Typically a muscle spans a joint and is attached to bones by tendons at both ends. One of the bones remains relatively fixed or stable while the other end moves as a result of muscle contraction.
Image by NCI / NIH
Tendon
To move the skeleton, the tension created by the contraction of the fibers in most 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 muscle tissue is called skeletal muscle.Tough, fibrous, cord-like tissue that connects muscle to bone or another structure, such as an eyeball. Tendons help the bone or structure to move.
Exercise and Stretching
When exercising, it is important to first warm up the muscles. Stretching pulls on the muscle fibers and it also results in an increased blood flow to the muscles being worked. Without a proper warm-up, it is possible that you may either damage some of the muscle fibers or pull a tendon. A pulled tendon, regardless of location, results in pain, swelling, and diminished function; if it is moderate to severe, the injury could immobilize you for an extended period.
Recall the discussion about muscles crossing joints to create movement. Most of the joints you use during exercise are synovial joints, which have synovial fluid in the joint space between two bones. Exercise and stretching may also have a beneficial effect on synovial joints. Synovial fluid is a thin, but viscous film with the consistency of egg whites. When you first get up and start moving, your joints feel stiff for a number of reasons. After proper stretching and warm-up, the synovial fluid may become less viscous, allowing for better joint function.
About Tendons
A tendon is a flexible band of tissue that connects muscles to bones.
Tendons can be small, like those found in the hand or ankle, or large, like the Achilles tendon in the heel.
Tendons help create movement by making the muscles push or pull the bones in different ways.
National Institute of Arthritis and Musculoskeletal and Skin Diseases (NIAMS)
Source: CNX OpenStax
Additional Materials (12)
Achilles tendon
Image by TheVisualMD
Tendon
Image by : Picture of the palmaris longus tendon visible on the anterior aspect of the wrist when the wrist is flexed while touching the 1st and 5th digits together.
Strains and Sprains OUCH! - Avoid Painful Muscle, Tendon or Ligament Injury - Safety Training Video
Safety Memos/YouTube
4:45
Trigger Finger
Dartmouth-Hitchcock/YouTube
1:35
Is Your Problem Really Tendinosis
Lee Health/YouTube
1:07
Tendons - What Are Tendons - Functions Of Tendons - Tendonitis
Whats Up Dude/YouTube
2:21
Does Stretching/Warming Up Actually Help?
AsapSCIENCE/YouTube
Basic measurements of the plantaris muscle
Ł. Olewnik, G. Wysiadecki, M. Podgórski, M. Polguj, and M. Topol/Wikimedia
Dense connective tissue
Extensor tendonitis
Image by Injurymap.com
Extensor tendonitis
Image by Injurymap.com
Dense Connective Tissue
Dense connective tissue contains more collagen fibers than does loose connective tissue. As a consequence, it displays greater resistance to stretching. There are two major categories of dense connective tissue: regular and irregular. Dense regular connective tissue fibers are parallel to each other, enhancing tensile strength and resistance to stretching in the direction of the fiber orientations. Ligaments and tendons are made of dense regular connective tissue, but in ligaments not all fibers are parallel. Dense regular elastic tissue contains elastin fibers in addition to collagen fibers, which allows the ligament to return to its original length after stretching. The ligaments in the vocal folds and between the vertebrae in the vertebral column are elastic.
In dense irregular connective tissue, the direction of fibers is random. This arrangement gives the tissue greater strength in all directions and less strength in one particular direction. In some tissues, fibers crisscross and form a mesh. In other tissues, stretching in several directions is achieved by alternating layers where fibers run in the same orientation in each layer, and it is the layers themselves that are stacked at an angle. The dermis of the skin is an example of dense irregular connective tissue rich in collagen fibers. Dense irregular elastic tissues give arterial walls the strength and the ability to regain original shape after stretching.
DISORDERS OF THE…
Connective Tissue: TendinitisYour opponent stands ready as you prepare to hit the serve, but you are confident that you will smash the ball past your opponent. As you toss the ball high in the air, a burning pain shoots across your wrist and you drop the tennis racket. That dull ache in the wrist that you ignored through the summer is now an unbearable pain. The game is over for now.
After examining your swollen wrist, the doctor in the emergency room announces that you have developed wrist tendinitis. She recommends icing the tender area, taking non-steroidal anti-inflammatory medication to ease the pain and to reduce swelling, and complete rest for a few weeks. She interrupts your protests that you cannot stop playing. She issues a stern warning about the risk of aggravating the condition and the possibility of surgery. She consoles you by mentioning that well known tennis players such as Venus and Serena Williams and Rafael Nadal have also suffered from tendinitis related injuries.
What is tendinitis and how did it happen? Tendinitis is the inflammation of a tendon, the thick band of fibrous connective tissue that attaches a muscle to a bone. The condition causes pain and tenderness in the area around a joint. On rare occasions, a sudden serious injury will cause tendinitis. Most often, the condition results from repetitive motions over time that strain the tendons needed to perform the tasks.
Persons whose jobs and hobbies involve performing the same movements over and over again are often at the greatest risk of tendinitis. You hear of tennis and golfer’s elbow, jumper's knee, and swimmer’s shoulder. In all cases, overuse of the joint causes a microtrauma that initiates the inflammatory response. Tendinitis is routinely diagnosed through a clinical examination. In case of severe pain, X-rays can be examined to rule out the possibility of a bone injury. Severe cases of tendinitis can even tear loose a tendon. Surgical repair of a tendon is painful. Connective tissue in the tendon does not have abundant blood supply and heals slowly.
While older adults are at risk for tendinitis because the elasticity of tendon tissue decreases with age, active people of all ages can develop tendinitis. Young athletes, dancers, and computer operators; anyone who performs the same movements constantly is at risk for tendinitis. Although repetitive motions are unavoidable in many activities and may lead to tendinitis, precautions can be taken that can lessen the probability of developing tendinitis. For active individuals, stretches before exercising and cross training or changing exercises are recommended. For the passionate athlete, it may be time to take some lessons to improve technique. All of the preventive measures aim to increase the strength of the tendon and decrease the stress put on it. With proper rest and managed care, you will be back on the court to hit that slice-spin serve over the net.
Source: CNX OpenStax
Additional Materials (7)
Tendon
Image by : Picture of the palmaris longus tendon visible on the anterior aspect of the wrist when the wrist is flexed while touching the 1st and 5th digits together.
Image by Hwilms
Ligaments, tendons, and joints | Muscular-skeletal system physiology | NCLEX-RN | Khan Academy
Video by khanacademymedicine/YouTube
Pain on the back of the heel
Achilles tendinitis, also known as achilles tendinopathy, occurs when the Achilles tendon, found at the back of the ankle, becomes inflamed. The most common symptoms are pain and swelling around the affected tendon.
Image by Injurymap.com
Pain under your heel
Image by Injurymap.com
Achilles tendon tendonitis
Achilles tendon tendonitis
Image by Δρ. Χαράλαμπος Γκούβας
Sprained ankle
Sprains are injuries or tears in ligaments. Strains are injuries to muscles or tendons. Ankle sprains or strains occur when the ankle joint twists abnormally. This can happen when playing sports, jumping, or even walking on an uneven surface. Symptoms of a sprained ankle include pain, swelling, bruising, and difficulty walking or bearing weight. Tendonitis (strained ankle tendon) produces pain, swelling, and warmth. A severe tear creates weakness and instability as well.
Image by OdraciRRicardo
Tendinitis
Tendinitis is disorder when tendons (thick fibrous cords that attach muscles to bones) become inflamed.
Image by www.scientificanimations.com
Tendon
Hwilms
2:47
Ligaments, tendons, and joints | Muscular-skeletal system physiology | NCLEX-RN | Khan Academy
khanacademymedicine/YouTube
Pain on the back of the heel
Injurymap.com
Pain under your heel
Injurymap.com
Achilles tendon tendonitis
Δρ. Χαράλαμπος Γκούβας
Sprained ankle
OdraciRRicardo
Tendinitis
www.scientificanimations.com
Structural Features of Synovial Joints
Synovitis
Image by TheVisualMD
Synovitis
Synovitis
Image by TheVisualMD
Structural Features of Synovial Joints
Structural Features of Synovial Joints
Synovial joints are characterized by the presence of a joint cavity. The walls of this space are formed by the articular capsule, a fibrous connective tissue structure that is attached to each bone just outside the area of the bone’s articulating surface. The bones of the joint articulate with each other within the joint cavity.
Friction between the bones at a synovial joint is prevented by the presence of the articular cartilage, a thin layer of hyaline cartilage that covers the entire articulating surface of each bone. However, unlike at a cartilaginous joint, the articular cartilages of each bone are not continuous with each other. Instead, the articular cartilage acts like a Teflon® coating over the bone surface, allowing the articulating bones to move smoothly against each other without damaging the underlying bone tissue. Lining the inner surface of the articular capsule is a thin synovial membrane. The cells of this membrane secrete synovial fluid (synovia = “a thick fluid”), a thick, slimy fluid that provides lubrication to further reduce friction between the bones of the joint. This fluid also provides nourishment to the articular cartilage, which does not contain blood vessels. The ability of the bones to move smoothly against each other within the joint cavity, and the freedom of joint movement this provides, means that each synovial joint is functionally classified as a diarthrosis.
Outside of their articulating surfaces, the bones are connected together by ligaments, which are strong bands of fibrous connective tissue. These strengthen and support the joint by anchoring the bones together and preventing their separation. Ligaments allow for normal movements at a joint, but limit the range of these motions, thus preventing excessive or abnormal joint movements. Ligaments are classified based on their relationship to the fibrous articular capsule. An extrinsic ligament is located outside of the articular capsule, an intrinsic ligament is fused to or incorporated into the wall of the articular capsule, and an intracapsular ligament is located inside of the articular capsule.
At many synovial joints, additional support is provided by the muscles and their tendons that act across the joint. A tendon is the dense connective tissue structure that attaches a muscle to bone. As forces acting on a joint increase, the body will automatically increase the overall strength of contraction of the muscles crossing that joint, thus allowing the muscle and its tendon to serve as a “dynamic ligament” to resist forces and support the joint. This type of indirect support by muscles is very important at the shoulder joint, for example, where the ligaments are relatively weak.
Additional Structures Associated with Synovial Joints
A few synovial joints of the body have a fibrocartilage structure located between the articulating bones. This is called an articular disc, which is generally small and oval-shaped, or a meniscus, which is larger and C-shaped. These structures can serve several functions, depending on the specific joint. In some places, an articular disc may act to strongly unite the bones of the joint to each other. Examples of this include the articular discs found at the sternoclavicular joint or between the distal ends of the radius and ulna bones. At other synovial joints, the disc can provide shock absorption and cushioning between the bones, which is the function of each meniscus within the knee joint. Finally, an articular disc can serve to smooth the movements between the articulating bones, as seen at the temporomandibular joint. Some synovial joints also have a fat pad, which can serve as a cushion between the bones.
Additional structures located outside of a synovial joint serve to prevent friction between the bones of the joint and the overlying muscle tendons or skin. A bursa (plural = bursae) is a thin connective tissue sac filled with lubricating liquid. They are located in regions where skin, ligaments, muscles, or muscle tendons can rub against each other, usually near a body joint (Figure 9.9). Bursae reduce friction by separating the adjacent structures, preventing them from rubbing directly against each other. Bursae are classified by their location. A subcutaneous bursa is located between the skin and an underlying bone. It allows skin to move smoothly over the bone. Examples include the prepatellar bursa located over the kneecap and the olecranon bursa at the tip of the elbow. A submuscular bursa is found between a muscle and an underlying bone, or between adjacent muscles. These prevent rubbing of the muscle during movements. A large submuscular bursa, the trochanteric bursa, is found at the lateral hip, between the greater trochanter of the femur and the overlying gluteus maximus muscle. A subtendinous bursa is found between a tendon and a bone. Examples include the subacromial bursa that protects the tendon of shoulder muscle as it passes under the acromion of the scapula, and the suprapatellar bursa that separates the tendon of the large anterior thigh muscle from the distal femur just above the knee.
Figure 9.9 Bursae Bursae are fluid-filled sacs that serve to prevent friction between skin, muscle, or tendon and an underlying bone. Three major bursae and a fat pad are part of the complex joint that unites the femur and tibia of the leg.
A tendon sheath is similar in structure to a bursa, but smaller. It is a connective tissue sac that surrounds a muscle tendon at places where the tendon crosses a joint. It contains a lubricating fluid that allows for smooth motions of the tendon during muscle contraction and joint movements.
Source: CNX OpenStax
Additional Materials (4)
Shoulder external rotator
Shoulder external rotator (infraspinatus and teres minor)
Image by Young Lae, Moon M.D. Chair of 3D Based Medical Application Working group. Chairman and Professor of Orthopaedics, Chosun University Hospital, Korea.
Synovial Joints
Video by Medic Tutorials - Medicine and Language/YouTube
Joint
Diagram of a typical synovial (diarthrosis) joint
Image by Madhero88
Glenohumeral Joint
The glenohumeral (shoulder) joint is a ball-and-socket joint that provides the widest range of motions. It has a loose articular capsule and is supported by ligaments and the rotator cuff muscles.
Image by CNX Openstax
Shoulder external rotator
Young Lae, Moon M.D. Chair of 3D Based Medical Application Working group. Chairman and Professor of Orthopaedics, Chosun University Hospital, Korea.
8:04
Synovial Joints
Medic Tutorials - Medicine and Language/YouTube
Joint
Madhero88
Glenohumeral Joint
CNX Openstax
Interactions of Skeletal Muscles
The three major types of muscle tissue are cardiac, skeletal, and smooth
Image by TheVisualMD
The three major types of muscle tissue are cardiac, skeletal, and smooth
The three major types of muscle tissue are cardiac, skeletal, and smooth. The cardiac muscle cells are located in the walls of the heart, appear striated, and are under involuntary control. Attached to bones by tendons is the skeletal muscle, associated with the body's voluntary movements. The smooth muscle tissue appear spindle-shaped, also under involuntary control, are located in the walls of hollow internal structures such as blood vessels, digestive tract, and many other organs.
Image by TheVisualMD
Interactions of Skeletal Muscles
To move the skeleton, the tension created by the contraction of the fibers in most 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 muscle tissue is called skeletal muscle.
Interactions of Skeletal Muscles in the Body
To pull on a bone, that is, to change the angle at its synovial joint, which essentially moves the skeleton, a skeletal muscle must also be attached to a fixed part of the skeleton. The moveable end of the muscle that attaches to the bone being pulled is called the muscle’s insertion, and the end of the muscle attached to a fixed (stabilized) bone is called the origin. During forearm flexion—bending the elbow—the brachioradialis assists the brachialis.
Although a number of muscles may be involved in an action, the principal muscle involved is called the prime mover, or agonist. To lift a cup, a muscle called the biceps brachii is actually the prime mover; however, because it can be assisted by the brachialis, the brachialis is called a synergist in this action (image). A synergist can also be a fixator that stabilizes the bone that is the attachment for the prime mover’s origin.
A muscle with the opposite action of the prime mover is called an antagonist. Antagonists play two important roles in muscle function: (1) they maintain body or limb position, such as holding the arm out or standing erect; and (2) they control rapid movement, as in shadow boxing without landing a punch or the ability to check the motion of a limb.
For example, to extend the knee, a group of four muscles called the quadriceps femoris in the anterior compartment of the thigh are activated (and would be called the agonists of knee extension). However, to flex the knee joint, an opposite or antagonistic set of muscles called the hamstrings is activated.
As you can see, these terms would also be reversed for the opposing action. If you consider the first action as the knee bending, the hamstrings would be called the agonists and the quadriceps femoris would then be called the antagonists. See image for a list of some agonists and antagonists.
Agonist and Antagonist Skeletal Muscle Pairs
Agonist
Antagonist
Movement
Biceps brachii: in the anterior 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 four muscles in the anterior compartment of the thigh
The hamstrings flex the leg, whereas the quadriceps femoris extend it.
Flexor digitorum superficialis and flexor digitorum profundus: in the anterior 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 hand at the wrist, whereas the extensor digitorum extends the fingers and the hand at the wrist.
There are also skeletal muscles that do not pull against the skeleton for movements. For example, there 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 smile 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 volume of the pleural cavities but it does not move the skeleton to do this.
Patterns of Fascicle Organization
Skeletal muscle is enclosed in connective tissue scaffolding at three levels. Each muscle fiber (cell) is covered by endomysium and the entire muscle is covered by epimysium. When a group of muscle fibers is “bundled” as a unit within the whole muscle by an additional covering of a connective tissue called perimysium, that bundled group of muscle fibers is called a fascicle. Fascicle arrangement by perimysia is correlated to the force generated by a muscle; it also 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 same direction as the long axis of the muscle (image). The majority of skeletal muscles in the body have this type of organization. Some parallel muscles are flat 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 as the central body. A more common 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, middle section is the belly (image). When a parallel muscle has a central, large belly that is spindle-shaped, meaning it tapers as it extends to its origin and insertion, it sometimes is called fusiform.
Circular muscles are also called sphincters (see image). When they relax, the sphincters’ concentrically arranged bundles of muscle fibers increase the size of the opening, and when they contract, the size of the opening shrinks to the point of closure. The orbicularis oris muscle is a circular muscle that goes around the mouth. When it contracts, the oral opening becomes smaller, as when puckering the lips for whistling. Another example is the orbicularis oculi, one of which surrounds each eye. Consider, for example, the names of the two 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 structure; it may also make one think of orbit, such as the moon’s path around the earth. The word oris (oris = “oral”) refers to the oral cavity, or the mouth. The word oculi (ocular = “eye”) refers to the eye.
There are other muscles throughout the body named by their shape or location. The deltoid is a large, triangular-shaped muscle that covers the shoulder. It is so-named because the Greek letter delta looks like a triangle. The rectus abdomis (rector = “straight”) is the straight muscle in the anterior wall of the abdomen, while the rectus femoris is the straight muscle in the anterior compartment of the thigh.
When a muscle has a widespread expansion over a sizable area, but then the fascicles come to a single, common attachment point, the muscle is called convergent. The attachment point for a convergent muscle could be a tendon, an aponeurosis (a flat, broad tendon), or a raphe (a very slender tendon). The large muscle on the chest, the pectoralis major, is an example of a convergent muscle because it converges on the greater tubercle of the humerus via a tendon. The temporalis muscle of the cranium is another.
Pennate muscles (penna = “feathers”) blend into a tendon that runs through the central region of the muscle for its whole length, somewhat like the quill of a feather with the muscle arranged similar to the feathers. Due to this design, the muscle fibers in a pennate muscle can only pull at an angle, and as a result, contracting pennate muscles do not move their tendons very far. However, because a pennate muscle generally can hold more muscle 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 one side of the tendon. The extensor digitorum of the forearm is an example of a unipennate muscle. A bipennate muscle has fascicles on both sides of the tendon. In some pennate muscles, the muscle fibers wrap around the tendon, sometimes forming individual fascicles in the process. This arrangement is referred to as multipennate. A common example is the deltoid muscle of the shoulder, which covers the shoulder but 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 can be stimulated by the nervous system 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), but when only the anterior fascicle is stimulated, the arm will abduct and flex (move anteriorly at the shoulder joint).
The Lever System of Muscle and Bone Interactions
Skeletal muscles do 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 movement. These characteristics depend on each other and can explain the general organization of the muscular and skeletal systems.
The skeleton and muscles act together to move the body. Have you ever used the back of a hammer to remove a nail from wood? The handle acts as a lever and the head of the hammer acts as a fulcrum, the fixed point that the force is applied to when you pull back or push down on the handle. The effort applied to this system is the pulling or pushing on the handle to remove the nail, which is the load, or “resistance” to the movement of the handle in the system. Our musculoskeletal system works in a similar manner, with bones being stiff levers and the articular endings of the bones—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 effort, or applied force, comes from contracting skeletal muscle.
Overview
Skeletal muscles each have an origin and an insertion. The end of the muscle that attaches to the bone being pulled is called the muscle’s insertion and the end of the muscle attached to a fixed, or stabilized, bone is called the origin. The muscle primarily responsible for a movement is called the prime mover, and muscles that assist in this action are called synergists. A synergist that makes the insertion site more stable is called a fixator. Meanwhile, a muscle with the opposite action of the prime mover is called an antagonist. Several factors contribute to the force generated by a skeletal muscle. One is the arrangement of the fascicles in the skeletal muscle. Fascicles can be parallel, circular, convergent, pennate, fusiform, or triangular. Each arrangement has its own range of motion and ability to do work.
Source: CNX OpenStax
Additional Materials (2)
Muscle Interactions
Video by Interactive Learning/YouTube
Myology - Skeletal Muscle Contraction
Video by Armando Hasudungan/YouTube
1:05
Muscle Interactions
Interactive Learning/YouTube
7:39
Myology - Skeletal Muscle Contraction
Armando Hasudungan/YouTube
Skeletal Muscle - Tendons
Human Skeletal Muscle Involved in Throwing
Image by TheVisualMD
Human Skeletal Muscle Involved in Throwing
Computer generated series of five superimposed images of the muscular action involved in the act of throwing. Muscles and the bones to which they are attached act as levers. To raise the forearm, for instance, the biceps pulls against the elbow, the arm's fulcrum, which magnifies the movement so effectively that the muscle has to contract just slightly to move the forearm several inches.
Image by TheVisualMD
Skeletal Muscle - Tendons
The best-known feature of skeletal muscle is its ability to contract and cause movement. Skeletal muscles act not only to produce movement but also to stop movement, such as resisting gravity to maintain posture. Small, constant adjustments of the skeletal muscles are needed to hold a body upright or balanced in any position. Muscles also prevent excess movement of the bones and joints, maintaining skeletal stability and preventing skeletal structure damage or deformation. Joints can become misaligned or dislocated entirely by pulling on the associated bones; muscles work to keep joints stable. Skeletal muscles are located throughout the body at the openings of internal tracts to control the movement of various substances. These muscles allow functions, such as swallowing, urination, and defecation, to be under voluntary control. Skeletal muscles also protect internal organs (particularly abdominal and pelvic organs) by acting as an external barrier or shield to external trauma and by supporting the weight of the organs.
Skeletal muscles contribute to the maintenance of homeostasis in the body by generating heat. Muscle contraction requires energy, and when ATP is broken down, heat is produced. This heat is very noticeable during exercise, when sustained muscle movement causes body temperature to rise, and in cases of extreme cold, when shivering produces random skeletal muscle contractions to generate heat.
Each skeletal muscle is an organ that consists of various integrated tissues. These tissues include the skeletal muscle fibers, blood vessels, nerve fibers, and connective tissue. Each skeletal muscle has three layers of connective tissue (called “mysia”) that enclose it and provide structure to the muscle as a whole, and also compartmentalize the muscle fibers within the muscle (Figure 10.3). Each muscle is wrapped in a sheath of dense, irregular connective tissue called the epimysium, which allows a muscle to contract and move powerfully while maintaining its structural integrity. The epimysium also separates muscle from other tissues and organs in the area, allowing the muscle to move independently.
Figure 10.4 Muscle Fiber A skeletal muscle fiber is surrounded by a plasma membrane called the sarcolemma, which contains sarcoplasm, the cytoplasm of muscle cells. A muscle fiber is composed of many fibrils, which give the cell its striated appearance.
Inside each skeletal muscle, muscle fibers are organized into individual bundles, each called a fascicle, by a middle layer of connective tissue called the perimysium. This fascicular organization is common in muscles of the limbs; it allows the nervous system to trigger a specific movement of a muscle by activating a subset of muscle fibers within a bundle, or fascicle of the muscle. Inside each fascicle, each muscle fiber is encased in a thin connective tissue layer of collagen and reticular fibers called the endomysium. The endomysium contains the extracellular fluid and nutrients to support the muscle fiber. These nutrients are supplied via blood to the muscle tissue.
In skeletal muscles that work with tendons to pull on bones, the collagen in the three tissue layers (the mysia) intertwines with the collagen of a tendon. At the other end of the tendon, it fuses with the periosteum coating the bone. The tension created by contraction of the muscle fibers is then transferred though the mysia, to the tendon, and then to the periosteum to pull on the bone for movement of the skeleton. In other places, the mysia may fuse with a broad, tendon-like sheet called an aponeurosis, or to fascia, the connective tissue between skin and bones. The broad sheet of connective tissue in the lower back that the latissimus dorsi muscles (the “lats”) fuse into is an example of an aponeurosis.
Every skeletal muscle is also richly supplied by blood vessels for nourishment, oxygen delivery, and waste removal. In addition, every muscle fiber in a skeletal muscle is supplied by the axon branch of a somatic motor neuron, which signals the fiber to contract. Unlike cardiac and smooth muscle, the only way to functionally contract a skeletal muscle is through signaling from the nervous system.
Source: CNX OpenStax
Additional Materials (2)
Skeletal Muscle Revealing Actin and Myosin
Visualization of the cellular and molecular structure of human skeletal muscle. The contraction of skeletal muscles is accomplished, on a molecular level, by the interaction of two long parallel-running proteins - one ropelike, the other more like a ladder studded regularly with sticky heads. The proteins (myosin and actin) touch, swing past each other, release, then repeat the motion, "generating force" - turning chemical energy into physical energy. Pooled and concentrated, they produce enough torque to contract the whole arm.
Image by TheVisualMD
Three distinct types of muscles (L to R): Smooth (non-striated) muscles in internal organs, cardiac or heart muscles, and skeletal muscles
Three distinct types of muscles (L to R): Smooth (non-striated) muscles, cardiac or heart muscles, and skeletal muscles.
Image by Scientific Animations, Inc.
Skeletal Muscle Revealing Actin and Myosin
TheVisualMD
Three distinct types of muscles (L to R): Smooth (non-striated) muscles in internal organs, cardiac or heart muscles, and skeletal muscles
Scientific Animations, Inc.
Achilles Tendon
Achilles Tendon
Image by Ryan Johnson
Achilles Tendon
calcaneal tendon
Image by Ryan Johnson
Achilles Tendon
Calcaneal Tendon (also, Achilles tendon) strong tendon that inserts into the calcaneal bone of the ankle
The lateral compartment of the leg includes two muscles: the fibularis longus (peroneus longus) and the fibularis brevis (peroneus brevis). The superficial muscles in the posterior compartment of the leg all insert onto the calcaneal tendon (Achilles tendon), a strong tendon that inserts into the calcaneal bone of the ankle. The muscles in this compartment are large and strong and keep humans upright. The most superficial and visible muscle of the calf is the gastrocnemius. Deep to the gastrocnemius is the wide, flat soleus. The plantaris runs obliquely between the two; some people may have two of these muscles, whereas no plantaris is observed in about seven percent of other cadaver dissections. The plantaris tendon is a desirable substitute for the fascia lata in hernia repair, tendon transplants, and repair of ligaments. There are four deep muscles in the posterior compartment of the leg as well: the popliteus, flexor digitorum longus, flexor hallucis longus, and tibialis posterior.
Muscles of the Lower Leg
The muscles of the anterior compartment of the lower leg are generally responsible for dorsiflexion, and the muscles of the posterior compartment of the lower leg are generally responsible for plantar flexion. The lateral and medial muscles in both compartments invert, evert, and rotate the foot.
Source: CNX OpenStax
Additional Materials (2)
Achilles Tendon Rupture | Complete Anatomy
Video by 3D4Medical From Elsevier/YouTube
Achilles Tendon : Anatomy of the Achilles Tendon
Video by ehowhealth/YouTube
1:24
Achilles Tendon Rupture | Complete Anatomy
3D4Medical From Elsevier/YouTube
0:46
Achilles Tendon : Anatomy of the Achilles Tendon
ehowhealth/YouTube
Shoulder Joints
Clavicle and Head of Humerus Showing Arthritis of Shoulder Joint
Image by TheVisualMD
Clavicle and Head of Humerus Showing Arthritis of Shoulder Joint
Computer generated image of a human shoulder joint based on segmented human data. The cutaway of the deltoid muscle reveals arthritis of the shoulder joint. The round head of the humerus bone is no longer smooth due to the degeneration of the bone. Pain and a decrease in a motion are common symptoms of arthritis of the right shoulder.
Image by TheVisualMD
Shoulder Joints
The shoulder joint is called the glenohumeral joint. This is a ball-and-socket joint formed by the articulation between the head of the humerus and the glenoid cavity of the scapula (image). This joint has the largest range of motion of any joint in the body. However, this freedom of movement is due to the lack of structural support and thus the enhanced mobility is offset by a loss of stability.
Glenohumeral Joint
The glenohumeral (shoulder) joint is a ball-and-socket joint that provides the widest range of motions. It has a loose articular capsule and is supported by ligaments and the rotator cuff muscles.
The large range of motions at the shoulder joint is provided by the articulation of the large, rounded humeral head with the small and shallow glenoid cavity, which is only about one third of the size of the humeral head. The socket formed by the glenoid cavity is deepened slightly by a small lip of fibrocartilage called the glenoid labrum, which extends around the outer margin of the cavity. The articular capsule that surrounds the glenohumeral joint is relatively thin and loose to allow for large motions of the upper limb. Some structural support for the joint is provided by thickenings of the articular capsule wall that form weak intrinsic ligaments. These include the coracohumeral ligament, running from the coracoid process of the scapula to the anterior humerus, and three ligaments, each called a glenohumeral ligament, located on the anterior side of the articular capsule. These ligaments help to strengthen the superior and anterior capsule walls.
However, the primary support for the shoulder joint is provided by muscles crossing the joint, particularly the four rotator cuff muscles. These muscles (supraspinatus, infraspinatus, teres minor, and subscapularis) arise from the scapula and attach to the greater or lesser tubercles of the humerus. As these muscles cross the shoulder joint, their tendons encircle the head of the humerus and become fused to the anterior, superior, and posterior walls of the articular capsule. The thickening of the capsule formed by the fusion of these four muscle tendons is called the rotator cuff. Two bursae, the subacromial bursa and the subscapular bursa, help to prevent friction between the rotator cuff muscle tendons and the scapula as these tendons cross the glenohumeral joint. In addition to their individual actions of moving the upper limb, the rotator cuff muscles also serve to hold the head of the humerus in position within the glenoid cavity. By constantly adjusting their strength of contraction to resist forces acting on the shoulder, these muscles serve as “dynamic ligaments” and thus provide the primary structural support for the glenohumeral joint.
Injuries to the shoulder joint are common. Repetitive use of the upper limb, particularly in abduction such as during throwing, swimming, or racquet sports, may lead to acute or chronic inflammation of the bursa or muscle tendons, a tear of the glenoid labrum, or degeneration or tears of the rotator cuff. Because the humeral head is strongly supported by muscles and ligaments around its anterior, superior, and posterior aspects, most dislocations of the humerus occur in an inferior direction. This can occur when force is applied to the humerus when the upper limb is fully abducted, as when diving to catch a baseball and landing on your hand or elbow. Inflammatory responses to any shoulder injury can lead to the formation of scar tissue between the articular capsule and surrounding structures, thus reducing shoulder mobility, a condition called adhesive capsulitis (“frozen shoulder”).
Source: CNX OpenStax
Additional Materials (13)
Shoulder Joint Displaying Humerus and Scapula
3D visualization based on segmented human data of the shoulder joint. The shoulder, the most freely moving joint of the body, is an example of a ball and socket joint. The hemispherical head of the humerus fits into the small, shallow cavity of the scapula allowing a great range of motion
Image by TheVisualMD
Skeletal Anatomy of Shoulder
The humerus (the upper arm bone), the scapula (shoulder blade), and the clavicle (collar bone) are the bones that make up the shoulder.
Image by TheVisualMD
Shoulder Joint
Deltoid Muscle Revealing Shoulder Joint : Computer generated image of a human shoulder joint based on segmented human data. The cutaway of the deltoid muscle reveals the shoulder joint. The round head of the humerus bone is surrounded by several ligaments and a bursal sac. The acromium and coracoid process of the scapula bone are also depicted.
Image by TheVisualMD
Shoulder Joint
Illustration of Shoulder Joint
Image by OpenStax College
Shoulder Joint
Shoulder Joint. See a full animation of this medical topic.
Shoulder Joint Displaying Humerus, Clavicle, Rotator Cuff and Scapula : Computer generated image of a human shoulder joint based on segmented human data. The coronal section of the humerus bone shows the spongy core of cancellous bone surrounded by the a dense compact area. Some muscles of the shoulder joint are shown in section. The clavicle bone articulates with the sternum and the acromial process of the scapula.
Image by TheVisualMD
Humerus
Left Shoulder Displaying Scapula and Humerus : Posterior view of left shoulder of skeleton : proximal part of humerus, scapula, acromion process of clavicle. The articulations between the bones of the shoulder make up the shoulder joints. The glenohumeral joint is the main joint of the shoulder formed by the articulation between the head of the humerus and the lateral scapula.
Image by TheVisualMD
Rotator cuff
Human right shoulder joint, seen from lateral side. Bones drawn are scapula and humerus. Muscles shown are subscapularis muscle (shown at right), infraspinatus muscle (shown at upper left), teres minor muscle (shown at bottom left).
Image by Young Lae, Moon M.D. Chair of 3D Based Medical Application Working group. Chairman and Professor of Orthopaedics, Chosun University Hospital, Korea
Rotator cuff
This illustration shows the main structures of the shoulder. The bursa, rotator cuff tendons, humerus, biceps muscle, clavicle, and scapula are labeled.
Image by Young Lae, Moon M.D. Chair of 3D Based Medical Application Working group. Chairman and Professor of Orthopaedics, Chosun University Hospital, Korea
Shoulder joint: Movements, bones and muscles - Human Anatomy | Kenhub
Video by Kenhub - Learn Human Anatomy/YouTube
Muscles of the upper arm and shoulder blade - Human Anatomy | Kenhub
Young Lae, Moon M.D. Chair of 3D Based Medical Application Working group. Chairman and Professor of Orthopaedics, Chosun University Hospital, Korea
Rotator cuff
Young Lae, Moon M.D. Chair of 3D Based Medical Application Working group. Chairman and Professor of Orthopaedics, Chosun University Hospital, Korea
20:28
Shoulder joint: Movements, bones and muscles - Human Anatomy | Kenhub
Kenhub - Learn Human Anatomy/YouTube
15:52
Muscles of the upper arm and shoulder blade - Human Anatomy | Kenhub
Kenhub - Learn Human Anatomy/YouTube
6:53
Shoulder Anatomy Animated Tutorial
Randale Sechrest/YouTube
10:26
Rotator Cuff | 3D Anatomy Tutorial
AnatomyZone/YouTube
Knee Joint
All
Anterior Cruciate Ligament
Ligaments
Menisci
Posterior Cruciate Ligament
1
2
3
4
5
Knee Joint
Interactive by TheVisualMD
All
Anterior Cruciate Ligament
Ligaments
Menisci
Posterior Cruciate Ligament
1
2
3
4
5
Knee Joint
The ligaments that hold the bones of your knee joint in place benefit from slow, careful stretching. Keeping the surrounding muscles flexible and strong helps protect the entire joint. Slowly flexing the knee while standing, by holding your foot in your hand behind you for 30 seconds, will stretch your quadriceps and increase the range of motion in your ACL. Slowly stretching forward while seated, like the woman pictured, will stretch your hamstrings and keep the PCL flexible.
Interactive by TheVisualMD
Knee Joint
The knee joint is the largest joint of the body (Figure). It actually consists of three articulations. The femoropatellar joint is found between the patella and the distal femur. The medial tibiofemoral joint and lateral tibiofemoral joint are located between the medial and lateral condyles of the femur and the medial and lateral condyles of the tibia. All of these articulations are enclosed within a single articular capsule. The knee functions as a hinge joint, allowing flexion and extension of the leg. This action is generated by both rolling and gliding motions of the femur on the tibia. In addition, some rotation of the leg is available when the knee is flexed, but not when extended. The knee is well constructed for weight bearing in its extended position, but is vulnerable to injuries associated with hyperextension, twisting, or blows to the medial or lateral side of the joint, particularly while weight bearing.
At the femoropatellar joint, the patella slides vertically within a groove on the distal femur. The patella is a sesamoid bone incorporated into the tendon of the quadriceps femoris muscle, the large muscle of the anterior thigh. The patella serves to protect the quadriceps tendon from friction against the distal femur. Continuing from the patella to the anterior tibia just below the knee is the patellar ligament. Acting via the patella and patellar ligament, the quadriceps femoris is a powerful muscle that acts to extend the leg at the knee. It also serves as a “dynamic ligament” to provide very important support and stabilization for the knee joint.
The medial and lateral tibiofemoral joints are the articulations between the rounded condyles of the femur and the relatively flat condyles of the tibia. During flexion and extension motions, the condyles of the femur both roll and glide over the surfaces of the tibia. The rolling action produces flexion or extension, while the gliding action serves to maintain the femoral condyles centered over the tibial condyles, thus ensuring maximal bony, weight-bearing support for the femur in all knee positions. As the knee comes into full extension, the femur undergoes a slight medial rotation in relation to tibia. The rotation results because the lateral condyle of the femur is slightly smaller than the medial condyle. Thus, the lateral condyle finishes its rolling motion first, followed by the medial condyle. The resulting small medial rotation of the femur serves to “lock” the knee into its fully extended and most stable position. Flexion of the knee is initiated by a slight lateral rotation of the femur on the tibia, which “unlocks” the knee. This lateral rotation motion is produced by the popliteus muscle of the posterior leg.
Located between the articulating surfaces of the femur and tibia are two articular discs, the medial meniscus and lateral meniscus (see Figureb). Each is a C-shaped fibrocartilage structure that is thin along its inside margin and thick along the outer margin. They are attached to their tibial condyles, but do not attach to the femur. While both menisci are free to move during knee motions, the medial meniscus shows less movement because it is anchored at its outer margin to the articular capsule and tibial collateral ligament. The menisci provide padding between the bones and help to fill the gap between the round femoral condyles and flattened tibial condyles. Some areas of each meniscus lack an arterial blood supply and thus these areas heal poorly if damaged.
The knee joint has multiple ligaments that provide support, particularly in the extended position (see Figurec). Outside of the articular capsule, located at the sides of the knee, are two extrinsic ligaments. The fibular collateral ligament(lateral collateral ligament) is on the lateral side and spans from the lateral epicondyle of the femur to the head of the fibula. The tibial collateral ligament(medial collateral ligament) of the medial knee runs from the medial epicondyle of the femur to the medial tibia. As it crosses the knee, the tibial collateral ligament is firmly attached on its deep side to the articular capsule and to the medial meniscus, an important factor when considering knee injuries. In the fully extended knee position, both collateral ligaments are taut (tight), thus serving to stabilize and support the extended knee and preventing side-to-side or rotational motions between the femur and tibia.
The articular capsule of the posterior knee is thickened by intrinsic ligaments that help to resist knee hyperextension. Inside the knee are two intracapsular ligaments, the anterior cruciate ligament and posterior cruciate ligament. These ligaments are anchored inferiorly to the tibia at the intercondylar eminence, the roughened area between the tibial condyles. The cruciate ligaments are named for whether they are attached anteriorly or posteriorly to this tibial region. Each ligament runs diagonally upward to attach to the inner aspect of a femoral condyle. The cruciate ligaments are named for the X-shape formed as they pass each other (cruciate means “cross”). The posterior cruciate ligament is the stronger ligament. It serves to support the knee when it is flexed and weight bearing, as when walking downhill. In this position, the posterior cruciate ligament prevents the femur from sliding anteriorly off the top of the tibia. The anterior cruciate ligament becomes tight when the knee is extended, and thus resists hyperextension.
Knee Joint
(a) The knee joint is the largest joint of the body. (b)–(c) It is supported by the tibial and fibular collateral ligaments located on the sides of the knee outside of the articular capsule, and the anterior and posterior cruciate ligaments found inside the capsule. The medial and lateral menisci provide padding and support between the femoral condyles and tibial condyles.
Source: CNX OpenStax
Additional Materials (26)
Knee Joint
A simple (and yes rather crappy) diagram showing an unfolding suprapatellar synovial recess in a flexing knee.
Image by Addingrefs
Human Leg
Human Leg
Image by TheVisualMD
Knee Anatomy Animated Tutorial
Video by Randale Sechrest/YouTube
Clinical Anatomy - Knee mensicus and knee joint
Video by Armando Hasudungan/YouTube
Q Angle Of The Knee - Everything You Need To Know - Dr. Nabil Ebraheim
Video by nabil ebraheim/YouTube
Knee Ligament Anatomy Animation
Video by BertramZarinsMD/YouTube
Knee anatomy and patellofemoral pain
Video by BioSkinBracing/YouTube
Clinical Anatomy - Knee
Video by Armando Hasudungan/YouTube
The Knee Joint
Video by Medic Tutorials - Medicine and Language/YouTube
How to stretch knee muscle | A Episode 67
Video by Pain Relief Expert/YouTube
How to improve knee health | A Episode 76
Video by Pain Relief Expert/YouTube
Knee Joint - Part 1 - 3D Anatomy Tutorial
Video by AnatomyZone/YouTube
Anatomy Of The Knee - Everything You Need To Know - Dr. Nabil Ebraheim
Medial view of the knee showing anatomical features.
Image by National Institute of Arthritis and Musculoskeletal and Skin Diseases (NIAMS)
Knee
Rendering of the human knee anatomy
Image by Kari Stammen
Knee Joint
Frontal view of Knee Joint anatomy
Image by Image by Blausen.com staff. \"Blausen gallery 2014\". Wikiversity Journal of Medicine. DOI:10.15347/wjm/2014.010. ISSN 20018762
Knee Joint
Knee Anatomy. See a related animation of this medical topic.
Image by Blausen.com staff (2014). \"Medical gallery of Blausen Medical 2014\". WikiJournal of Medicine 1 (2). DOI:10.15347/wjm/2014.010. ISSN 2002-4436
Healthy meniscus in the knee
Healthy meniscus in the knee
Image by BruceBlaus / Andrewmeyerson
Knee Joint
A close-up illustration shows a knee joint, visible from mid-thigh to mid-calf. Leg muscles are visible, along with the bones, cartilage and ligaments that form the intricate knee joints. Knees are a common site of overuse injuries among athletes at all levels of fitness, as they support much of the body's weight during any weight-bearing exercise.
Image by TheVisualMD
Right Knee
Computer generated image of the medial side of the right knee. The knee is a hinge joint and its primary movements are flexion and extension, as well as slight medial and lateral rotation.
Image by TheVisualMD
Anterior cruciate ligaments
Anterior cruciate ligament : Right knee.
Image by Mysid
Knee, Ankle Joints and Running Leg
Knee, Ankle Joints and Running Leg
Image by TheVisualMD
Knee with Ruptured Anterior Cruciate Ligament (ACL)
Image of a knee highlighting a ruptured Anterior Cruciate Ligament (ACL) - one of the two main stabilizing ligaments in the knee. An ACL becomes torn when it's stretched beyond its normal range of elasticity. Generally, the injury occurs during exercise or sports, although a torn ACL doesn't usually result from contact between players. Once the ligament tears, it doesn't heal - it remains loose. Injuries to the ACL are among the most common of all sports-related knee injuries.
Image by TheVisualMD
Normal Knee
The knee joint, the largest joint in the body, connects the femur (thigh bone), tibia (shin bone), fibula (outer shin bone), and patella (kneecap). Although it is a hinge joint, with a limited range of motion, the knee joint is very complex. It is composed of three compartments that permit its sliding, slightly rotating motion. The knee joint has an extensive network of muscles, ligaments, and tendons that hold it together, stabilize it, and permit it to move. Unlike the hip joint, the knee doesn't gain any stability from its bone structure. It depends completely on its ligaments, muscles, tendons and cartilage-and that's one reason it's so prone to injury. Because it carries most of the body's weight, and because that load is compounded with each step, the knee requires a great deal of cushioning. It contains two types of cartilage: fibrocartilage (the menisci) and hyaline cartilage. Three fluid sacs called bursae surround the knee joint and provide a smooth sliding surface for tendons. Large blood vessels pass through the area behind the knee, called the popliteal space. Like all synovial joints, the knee joint is bathed in synovial fluid. The large muscles of the thigh, the hamstrings and quadriceps muscles, move the knee. They also play a vital role in stabilizing the knee joint.
Image by TheVisualMD
Three Views of the Knee and leg
Three Views of the Knee and leg
Image by TheVisualMD
Knee Joint
Addingrefs
Human Leg
TheVisualMD
10:57
Knee Anatomy Animated Tutorial
Randale Sechrest/YouTube
8:24
Clinical Anatomy - Knee mensicus and knee joint
Armando Hasudungan/YouTube
3:00
Q Angle Of The Knee - Everything You Need To Know - Dr. Nabil Ebraheim
nabil ebraheim/YouTube
2:09
Knee Ligament Anatomy Animation
BertramZarinsMD/YouTube
3:14
Knee anatomy and patellofemoral pain
BioSkinBracing/YouTube
15:08
Clinical Anatomy - Knee
Armando Hasudungan/YouTube
6:15
The Knee Joint
Medic Tutorials - Medicine and Language/YouTube
3:20
How to stretch knee muscle | A Episode 67
Pain Relief Expert/YouTube
3:17
How to improve knee health | A Episode 76
Pain Relief Expert/YouTube
6:58
Knee Joint - Part 1 - 3D Anatomy Tutorial
AnatomyZone/YouTube
7:23
Anatomy Of The Knee - Everything You Need To Know - Dr. Nabil Ebraheim