How are muscles attached to bone? | Reference.com How are muscles attached to bone? A: Quick Answer Most muscles are attached to bones by connecting tendons. Tendons are thick, tough cords of tissue that firmly attach to both the muscle and the bone, connecting the two. A few muscles attach directly to the bone without a connecting tendon. Full Answer Tendons grow directly out of muscle fiber and connect to the outer layer of the associated bone. Many bones have lumps or protrusions where the tendon connects. This provides extra surface area for a secure join. Tendons are strong enough to withstand tension when muscles contract to move the bone. Each muscle attaches to two bones, and the push and pull of the muscle moves the bones in relationship to each other. How do muscles attach to bones? How do muscles attach to bones? Browse → Human Body → Inside the Body Our bodies have different types of tissues that are used to connect all of our different parts. Bones are connected to other bones by special tissues called "ligaments." But when bones are connected to muscles, the special tissues are called "tendons." Tendons are very strong. They are built from long strands of protein and they are not very stretchy.

When a muscle pulls, they pull too and they can move our bones. We have tendons in many parts of our bodies: wrists, elbows, thumbs, shoulders, knees, head, legs, and heels. Tendons almost always connect bone to muscle, but sometimes they connect muscle to other things, like an eyeball! Exploration Achilles Heel You can find at least one tendon in your body pretty easily. It's called the Achilles tendon and it connects your calf muscles (the back of your lower leg) to your heel. While sitting, lightly pinch the back of your leg, right above your heel. (If you were standing, you might tip over!) Wave your foot, like it was your hand. You'll feel something moving in the back of your leg. You might have thought this was a bone, but it's actually a tendon! The Achilles tendon is the strongest tendon in our bodies. Why do you think it needs to be so strong?

Sources & links Bones, Muscles, and Joints Bones, Muscles, and Joints Huesos, músculos y articulaciones The Musculoskeletal System Every time you sprint through the halls because you're late for class, score against your opponents during a game, or shoot pool with friends, you're using your bones, muscles, and joints. Without these important body parts, you'd be seriously sidelined — you'd be unable to sit, stand, walk, or do any of the activities you do every day. From our head to our toes, our bones provide support for our bodies and help form our shape. The skull protects the brain and forms the shape of our face. The spinal cord, a pathway for messages between the brain and the body, is protected by the backbone, or spinal column. The ribs form a cage that shelters the heart, lungs, liver, and spleen, and the pelvis helps protect the bladder, intestines, and in girls, the reproductive organs . Although they're very light, bones are strong enough to support our entire weight. Joints are where two bones meet. They make the skeleton flexible — without them, movement would be impossible.

Muscles are also necessary for movement: They're the masses of tough, elastic tissue that pull our bones when we move. Together, our bones, muscles, and joints — along with tendons, ligaments, and cartilage — form our musculoskeletal system and enable us to do everyday physical activities. continue What Are the Bones and What Do They Do? The human skeleton has 206 bones. Our bones begin to develop before birth. When the skeleton first forms, it is made of flexible cartilage, but within a few weeks it begins the process of ossification (pronounced: ah-suh-fuh-KAY-shun). Ossification is when the cartilage is replaced by hard deposits of calcium phosphate and stretchy collagen, the two main components of bone. It takes about 20 years for this process to be completed. The bones of kids and young teens are smaller than those of adults and contain "growing zones" called growth plates. These plates consist of columns of multiplying cartilage cells that grow in length, and then change into hard, mineralized bone. These growth plates are easy to spot on an X-ray. Because girls mature at an earlier age than boys, their growth plates change into hard bone at an earlier age.

Bone building continues throughout your life, as your body constantly renews and reshapes the bones' living tissue. Bone contains three types of cells: osteoblasts (pronounced: AHS-tee-uh-blastz), which make new bone and help repair damage; osteocytes (pronounced: AHS-tee-o-sites), which are mature bone cells that help form the new bone; and osteoclasts (pronounced: AHS-tee-o-klasts), which break down bone and help to sculpt and shape it. Osteoclasts are very active in kids and teens, working on bone as it is remodeled during growth. They also play an important role in the repair of fractures. Bones are made up of calcium, phosphorus, sodium, and other minerals, as well as the protein collagen. Calcium is needed to make bones hard, which allows them to support your weight. Bones also store calcium and release some into the bloodstream when it's needed by other parts of the body. The amounts of certain vitamins and minerals that you eat, especially vitamin D and calcium, directly affect how much calcium is stored in the bones.

The soft bone marrow inside many of our bones is where most of the blood cells flowing through our bodies are made. The bone marrow contains stem cells, which produce the body's red blood cells and platelets, and some types of white blood cells. Red blood cells carry oxygen to the body's tissues, and platelets help with blood clotting when someone has a cut or wound. White blood cells help the body fight infection. Bones are made up of two types of material — compact bone and cancellous bone. Compact bone is the solid, hard outside part of the bone. This type of bone makes up most of the human skeleton. It looks like ivory and is extremely strong. Holes and channels run through it, carrying blood vessels and nerves from the periosteum, the bone's outer membrane. Cancellous (pronounced: KAN-suh-lus) bone, which looks like a sponge, is inside the compact bone. It is made up of a mesh-like network of tiny pieces of bone called trabeculae (pronounced: truh-BEH-kyoo-lee). This is where red and white blood cells are formed in the marrow.

Bones are fastened to other bones by long, fibrous straps called ligaments (pronounced: LIG-uh-mentz). Cartilage (pronounced: KAR-tul-ij), a flexible, rubbery substance in our joints, supports bones and protects them where they rub against each other. previous continue What Are the Muscles and What Do They Do? Bones don't work alone — they need help from the muscles and joints. Muscles pull on the joints, allowing us to move. They also help the body perform other functions so we can grow and remain strong, such as chewing food and then moving it through the digestive system. The human body has more than 600 muscles. Muscles make up half of a person's body weight. They are connected to bones by tough, cord-like tissues called tendons, which allow the muscles to pull on bones. If you wiggle your fingers, you can see the tendons on the back of your hand move as they do their work. Humans have three different kinds of muscle: Skeletal muscle is attached to bone, mostly in the legs, arms, abdomen, chest, neck, and face.

Skeletal muscles are called striated (pronounced: STRY-ay-ted) because they are made up of fibers that have horizontal stripes when viewed under a microscope. These muscles hold the skeleton together, give the body shape, and help it with everyday movements (they are known as voluntary muscles because you can control their movement). They can contract (shorten or tighten) quickly and powerfully, but they tire easily and have to rest between workouts. Smooth, or involuntary, muscle is also made of fibers, but this type of muscle looks smooth, not striated. Generally, we can't consciously control our smooth muscles; rather, they're controlled by the nervous system automatically (which is why they are also called involuntary). Examples of smooth muscles are the walls of the stomach and intestines, which help break up food and move it through the digestive system . Smooth muscle is also found in the walls of blood vessels, where it squeezes the stream of blood flowing through the vessels to help maintain blood pressure. Smooth muscles take longer to contract than skeletal muscles do, but they can stay contracted for a long time because they don't tire easily. Cardiac (pronounced: KAR-dee-ak) muscle is found in the heart.

The walls of the heart's chambers are composed almost entirely of muscle fibers. Cardiac muscle is also an involuntary type of muscle. Its rhythmic, powerful contractions force blood out of the heart as it beats. previous continue Muscles and Movement Even when you sit perfectly still, there are muscles throughout your body that are constantly moving. Muscles enable your heart to beat, your chest to rise and fall as you breathe, and your blood vessels to help regulate the pressure and flow of blood through your body. When we smile and talk, muscles are helping us communicate, and when we exercise, they help us stay physically fit and healthy. The movements your muscles make are coordinated and controlled by the brain and nervous system. The involuntary muscles are controlled by structures deep within the brain and the upper part of the spinal cord called the brain stem. The voluntary muscles are regulated by the parts of the brain known as the cerebral motor cortex and the cerebellum. When you decide to move, the motor cortex sends an electrical signal through the spinal cord and peripheral nerves to the muscles, causing them to contract. The motor cortex on the right side of the brain controls the muscles on the left side of the body and vice versa.

The cerebellum (pronounced: ser-uh-BEL-um) coordinates the muscle movements ordered by the motor cortex. Sensors in the muscles and joints send messages back through peripheral nerves to tell the cerebellum and other parts of the brain where and how the arm or leg is moving and what position it's in. This feedback results in smooth, coordinated motion. If you want to lift your arm, your brain sends a message to the muscles in your arm and you move it. When you run, the messages to the brain are more involved, because many muscles have to work in rhythm. Muscles move body parts by contracting and then relaxing. Your muscles can pull bones, but they can't push them back to their original position. So they work in pairs of flexors and extensors. The flexor contracts to bend a limb at a joint. Then, when you've completed the movement, the flexor relaxes and the extensor contracts to extend or straighten the limb at the same joint: For example, the biceps muscle, in the front of the upper arm, is a flexor, and the triceps, at the back of the upper arm, is an extensor.

When you bend at your elbow, the biceps contracts. Then the biceps relaxes and the triceps contracts to straighten the elbow. previous continue What Are the Joints and What Do They Do? Joints allow our bodies to move in many ways. Some joints open and close like a hinge (such as knees and elbows), whereas others allow for more complicated movement — a shoulder or hip joint, for example, allows for backward, forward, sideways, and rotating movement. Joints are classified by their range of movement. Immovable, or fibrous, joints don't move. The dome of the skull, for example, is made of bony plates, which must be immovable to protect the brain. Between the edges of these plates are links, or joints, of fibrous tissue. Fibrous joints also hold the teeth in the jawbone. Partially movable, or cartilaginous (pronounced: kar-tuh-LAH-juh-nus), joints move a little. They are linked by cartilage, as in the spine. Each of the vertebrae in the spine moves in relation to the one above and below it, and together these movements give the spine its flexibility.

Freely movable, or synovial (pronounced: sih-NO-vee-ul), joints move in many directions. The main joints of the body — found at the hip, shoulders, elbows, knees, wrists, and ankles — are freely movable. They are filled with synovial fluid, which acts as a lubricant to help the joints move easily. There are three kinds of freely movable joints that play a big part in voluntary movement: Hinge joints allow movement in one direction, as seen in the knees and elbows. Pivot joints allow a rotating or twisting motion, like that of the head moving from side to side. Ball-and-socket joints allow the greatest freedom of movement. The hips and shoulders have this type of joint, in which the round end of a long bone fits into the hollow of another bone. previous continue Things That Can Go Wrong With the Bones, Muscles, and Joints As strong as bones are, they can break. Muscles can weaken, and joints (as well as tendons, ligaments, and cartilage) can be damaged by injury or disease. The following are problems that can affect the bones, muscles, and joints in teens: Arthritis.

Arthritis is the inflammation of a joint, and people who have it experience swelling, warmth, pain, and often have trouble moving. Although we often think of arthritis as a condition that affects only older people, arthritis also can affect children and teens. Health problems that involve arthritis in kids and teens include juvenile idiopathic arthritis (JIA, also know as juvenile rheumatoid arthritis, or JRA) , lupus , Lyme disease , and septic arthritis (a bacterial infection of a joint). Fracture. A fracture is when a bone breaks; it may crack, snap, or shatter. After a bone fracture, new bone cells fill the gap and repair the break. Applying a strong plaster cast, which keeps the bone in the correct position until it heals, is the usual treatment. If the fracture is complicated, metal pins and plates can be placed to better stabilize the fracture while the bone heals. Muscular dystrophy . Muscular dystrophy (pronounced: DIS-truh-fee) is an inherited group of diseases that affect the muscles, causing them to weaken and break down over time. The most common form in childhood is called Duchenne muscular dystrophy, and it most often affects boys.

Osgood-Schlatter disease (OSD) . Osgood-Schlatter disease is an inflammation (pain and swelling) of the bone, cartilage, and/or tendon at the top of the shinbone, where the tendon from the kneecap attaches. OSD usually strikes active teens around the beginning of their growth spurts, the approximately 2-year period during which they grow most rapidly. Osteomyelitis . Osteomyelitis (pronounced: os-tee-oh-my-uh-LIE-tus) is a bone infection that is often caused by Staphylococcus aureus (pronounced: sta-fuh-low-KAH-kus ARE-ee-us) bacteria, though other types of bacteria can cause it, too. In kids and teens, osteomyelitis usually affects the long bones of the arms and legs. Osteomyelitis often develops after an injury or trauma. Osteoporosis. In osteoporosis (pronounced: ahs-tee-o-puh-ROW-sus), bone tissue becomes brittle, thin, and spongy. Bones break easily, and the spine sometimes begins to crumble and collapse.

Although the condition usually affects older people, girls with female athlete triad syndrome and teens with eating disorders can get the condition. Exercising regularly and getting plenty of calcium when you're a kid and teen can prevent or delay you from getting osteoporosis later in life. Repetitive stress injuries (RSIs) . RSIs are a group of injuries that happen when too much stress is placed on a part of the body, resulting in inflammation (pain and swelling), muscle strain, or tissue damage. This stress generally is from repeating the same movements over and over again. Playing sports like tennis that involve repetitive motions can also lead to RSIs. Kids and teens who spend a lot of time playing musical instruments or video games are also at risk for RSIs. RSIs are becoming more common in kids and teens because they spend more time than ever using computers. Scoliosis . Every person's spine curves a little bit; a certain amount of curvature is necessary for people to move and walk properly. But three to five people out of 1,000 have a condition called scoliosis (pronounced: sko-lee-OH-sus), which causes the spine to curve too much.

The condition can be hereditary, so a person who has scoliosis often has family members who have it. Strains and sprains . Strains happen when a muscle or tendon is overstretched. Sprains are an overstretching or a partial tear of the ligaments. Strains usually happen when a person takes part in a strenuous activity when the muscles haven't properly warmed up or the muscle is not used to the activity (such as a new sport or playing a familiar sport after a long break). Sprains, on the other hand, are usually the result of an injury, such as twisting an ankle or knee. Both strains and sprains are common in teens because they're active and still growing. Tendonitis. Tendonitis (pronounced: ten-duh-NY-tus) is a common sports injury that usually happens after overusing a muscle. The tendon and tendon sheath become inflamed, which can be painful. Resting the muscles and taking anti-inflammatory medication can help to relieve this condition.

Muscular and Skeletal Systems MUSCULAR AND SKELETAL SYSTEMS Interaction of the Two Systems | Links The single-celled protozoan ancestors of animals had their weight supported by water and were able to move by cilia or other simple organelles. The evolution of large and more complex organisms (animals) necessitated the development of support and locomotion systems. Animals use their muscular and skeletal systems for support, locomotion, and maintaining their shape. Types of Skeletal Systems | Back to Top Movement is a major characteristic of animals. This movement is a result of contraction of muscles. The skeleton helps transmit that movement. Skeletons are either a fluid-filled body cavity, exoskeletons , or internal skeletons. Hydrostatic skeletons consist of fluid-filled closed chambers. Internal pressures generated by muscle contractions cause movement as well as maintain the shape of the animals, such as the sea anemone and worms. The sea anemone has one set of longitudinal muscles in the outer layer of the body, and a layer of circular muscles in the inner layer of the body. The anemone can elongate or contract its body by contracting one or the other set of muscles. Structure and function of a hydrostatic skeleton.

Images from Purves et al., Life: The Science of Biology, 4th Edition, by Sinauer Associates ( ) and WH Freeman ( ), used with permission. Exoskeletons are characteristic of the Phylum Arthropoda. Exoskeletons are hard segments that cover the muscles and visceral organs. Muscles for movement attach to the inner surface of the exoskeleton. Exoskeletons restrict the growth of the animal, thus it must shed its exoskeleton (or molt) to form a new one that has room for growth. The bulk and weight of the exoskeleton and associated mechanical problems limits the size animals can attain. Spiders use a combination of an exoskeleton for protection and fluid pressure for movement. Exoskeleton of an insect and its relation to the muscular system. Image from Purves et al., Life: The Science of Biology, 4th Edition, by Sinauer Associates ( ) and WH Freeman ( ), used with permission. Vertebrates have developed an internal mineralized (in most cases) endoskeleton composed of bone and/or cartilage. Muscles are on the outside of the endoskeleton. Cartilage and bone are types of connective tissue .

Sharks, and rays have skeletons composed entirely of cartilage; other vertebrates have an embryonic cartilage skeleton progressively replaced by bone as they mature and develop. Some areas of the human body, however, retain cartilage in the adult: in joints and flexible structures such as the ribs, trachea, nose and ears. The human endoskeleton. Image from Purves et al., Life: The Science of Biology, 4th Edition, by Sinauer Associates ( ) and WH Freeman ( ), used with permission. Functions of Muscles and Bones | Back to Top The skeleton and muscles function together as the musculoskeletal system. This system (often treated as two separate systems, the muscular , and skeletal ) plays an important homeostatic role: allowing the animal to move to more favorable external conditions. Certain cells in the bones produce immune cells as well as important cellular components of the blood. Bone also helps regulate blood calcium levels, serving as a calcium sink. Rapid muscular contraction is important in generating internal heat, another homeostatic function. The Axial and Appendicular Skeletons | Back to Top The axial skeleton consists of the skull, vertebral column, and rib cage.

The appendicular skeleton contains the bones of the appendages (limbs, wings, or flippers/fins), and the pectoral and pelvic girdles . The human skull, or cranium , has a number of individual bones tightly fitted together at immovable joints . At birth many of these joints are not completely sutured together as bone, leading to a number of "soft spots" or fontanels , which do not completely join until the age of 14-18 months. The vertebral column has 33 individual vertebrae separated from each other by a cartilage disk. These disks allow a certain flexibility to the spinal column, although the disks deteriorate with age, producing back pain. The sternum is connected to all the ribs except the lower pair. Cartilage allows for the flexibility of the rib cage during breathing. The arms and legs are part of the appendicular skeleton. The upper bones of the limbs are single: humerus (arm) and femur (leg). Below a joint (elbow or knee), both limbs have a pair of bones (radius and ulna in the arms; tibia and fibula in legs) that connect to another joint (wrist or ankle).

The carpals makeup the wrist joint; the tarsals are in the ankle joint. Each hand or foot ends in 5 digits (fingers or toes) composed of metacarpals (hands) or metatarsals (feet). Limbs are connected to the rest of the skeleton by collections of bones known as girdles. The pectoral girdle consists of the clavicle (collar bone) and scapula (shoulder blade). The humerus is joined to the pectoral girdle at a joint and is held in place by muscles and ligaments . A dislocated shoulder occurs when the end of the humerus slips out of the socket of the scapula, stretching ligaments and muscles. The pelvic girdle consists of two hipbones that form a hollow cavity, the pelvis . The vertebral column attaches to the top of the pelvis; the femur of each leg attaches to the bottom. The pelvic girdle in land animals transfers the weight of the body to the legs and feet. Pelvic girdles in fish, which have their weight supported by water, are primitive; land animals have more developed pelvic girdles.

Pelvic girdles in bipeds are recognizable different from those or quadrupeds. Bone Tissue | Back to Top Although bones vary greatly in size and shape, they have certain structural similarities. Bones have cells embedded in a mineralized (calcium) matrix and collagen fibers. Compact bone forms the shafts of long bones; it also occurs on the outer side of the bone. Spongy bone forms the inner layer. Structure of bone, a type of connective tissue. Image from Purves et al., Life: The Science of Biology, 4th Edition, by Sinauer Associates ( ) and WH Freeman ( ), used with permission. Compact bone has a series of Haversian canals around which concentric layers of bone cells ( osteocytes ) and minerals occur. New bone is formed by the osteocytes. The Haversian canals form a network of blood vessels and nerves that nourish and monitor the osteocytes. Spongy bone occurs at the ends of long bones and is less dense than compact bone. The spongy bone of the femur, humerus, and sternum contains red marrow, in which stem cells reproduce and form the cellular components of the blood and immune system .

Yellow marrow, at the center of these bones, is used to store fats. The outer layer of the bones is known as the periosteum . The inner layer of the periosteum forms new bone or modifies existing bone to meet new conditions. It is rich in nerve endings and blood and lymphatic vessels. When fractures occur, the pain is carried to the brain by nerves running through the periosteum. Bone Growth | Back to Top Endochondral ossification is the process of converting the cartilage in embryonic skeletons into bone. Cartilage is deposited early in development into shapes resembling the bones-to-be. Cells inside this cartilage grow and begin depositing minerals. The spongy bone forms, and osteoblasts attach and lay down the mineral portions of spongy bone. Osteoclasts remove material from the center of the bone, forming the central cavity of the long bones. The perichondrium , a connective tissue, forms around the cartilage and begins forming compact bone while the above changes are occurring. Blood vessels form and grow into the perichondrium, transporting stem cells into the interior. Two bands of cartilage remain as the bone develops, one at each end of the bone.

During childhood, this cartilage allows for growth and changes in the shape of bones. Eventually the elongation of the bones stops and the cartilage is all converted into bone. Growth of a long bone. Images from Purves et al., Life: The Science of Biology, 4th Edition, by Sinauer Associates ( ) and WH Freeman ( ), used with permission. Bones continue to change as adults, to adapt to the stresses generated by physical activity. Exercise can increase the diameter and strength of bone; inactivity can decrease them. Age is a factor: osteoporosis is a disease that primarily affects older, postmenopausal women. Increasing calcium intake, reducing protein intake, exercise and low doses of estrogen are effective treatments for osteoporosis. Joints | Back to Top There are three types of joints: immovable, partly movable, and synovial . Immovable joints, like those connecting the cranial bones, have edges that tightly interlock. Partly movable joints allow some degree of flexibility and usually have cartilage between the bones; example: vertebrae. Synovial joints permit the greatest degree of flexibility and have the ends of bones covered with a connective tissue filled with synovial fluid; example: hip.

The outer surface of the synovial joints contains ligaments that strengthen joints and hold bones in position. The inner surface (the synovial membrane) has cells producing synovial fluid that lubricates the joint and prevents the two cartilage caps on the bones from rubbing together. Some joints also have tendons (connective tissue linking muscles to bones). Bursae are small sacs filled with synovial fluid that reduce friction in the joint. The knee joint contains 13 bursae Joints of the human body. Images from Purves et al., Life: The Science of Biology, 4th Edition, by Sinauer Associates ( ) and WH Freeman ( ), used with permission. Skeletal Disorders Injury, degenerative wear and tear, and inflammatory disorders affect joints. Sprains are common injuries that cause ligaments to rip of separate from the bone. Tendinitis (such as tennis elbow) and bursitis are inflammations of the tendon sheaths. Osteoarthritis is a degenerative condition associated with the wearing away of the protective caps of cartilage covering the bone-ends. Bony growths or spurs develop as the cartilage degenerates, causing restriction of movement and pain.

The cause is not known and may just be wear-and-tear associated with aging. Rheumatoid arthritis is a severely damaging arthritis that begins with inflammation and thickening of the synovial membrane followed by bone degeneration and disfigurement. More women than men are affected. There may be a genetic predisposition to rheumatoid arthritis. Joint replacement may in some cases restore function. Skeletal Muscle Systems | Back to Top Vertebrates move by the actions of muscles on bones. Tendons attach many skeletal muscles across joints, allowing muscle contraction to move the bones across the joint. Muscles generally work in pairs to produce movement: when one muscle flexes (or contracts) the other relaxes, a process known as antagonism . Ligaments and tendons of the arm and leg. Images from Purves et al., Life: The Science of Biology, 4th Edition, by Sinauer Associates ( ) and WH Freeman ( ), used with permission. Muscles have both electrical and chemical activity. There is an electrical gradient across the muscle cell membrane: the outside is more positive than the inside. Stimulus causes an instantaneous reversal of this polarity, causing the muscle to contract (the mechanical characteristic) producing a twitch or movement.

Organization of a muscle. Image from Purves et al., Life: The Science of Biology, 4th Edition, by Sinauer Associates ( ) and WH Freeman ( ), used with permission. Skeletal Muscle Structure Muscle fibers are multinucleated, with the nuclei located just under the plasma membrane. Most of the cell is occupied by striated, thread-like myofibrils . Within each myofibril there are dense Z lines . A sarcomere (or muscle functional unit) extends from Z line to Z line. Each sarcomere has thick and thin filaments. The thick filaments are made of myosin and occupy the center of each sarcomere. Thin filaments are made of actin and anchor to the Z line. Fine structure of a muscle fiber. Image from Purves et al., Life: The Science of Biology, 4th Edition, by Sinauer Associates ( ) and WH Freeman ( ), used with permission. Muscles contract by shortening each sarcomere. The sliding filament model of muscle contraction has thin filaments on each side of the sarcomere sliding past each other until they meet in the middle. Myosin filaments have club-shaped heads that project toward the actin filaments.

Electron micrograph of the banding of a muscle fiber. Image from Purves et al., Life: The Science of Biology, 4th Edition, by Sinauer Associates ( ) and WH Freeman ( ), used with permission. Myosin heads attach to binding sites on the actin filaments. The myosin heads swivel toward the center of the sarcomere, detach and then reattach to the nearest active site of the actin filament. Each cycle of attachment, swiveling, and detachment shortens the sarcomere 1%. Hundreds of such cycles occur each second during muscle contraction. The roles of actin and myosin in muscle contration. Images from Purves et al., Life: The Science of Biology, 4th Edition, by Sinauer Associates ( ) and WH Freeman ( ), used with permission. Energy for this comes from ATP , the energy coin of the cell. ATP binds to the cross bridges between myosin heads and actin filaments. The release of energy powers the swiveling of the myosin head. Muscles store little ATP and so must recycle the ADP into ATP rapidly.

Creatine phosphate is a muscle storage product involved in the rapid regeneration of ADP into ATP. Calcium ions are required for each cycle of myosin-actin interaction. Calcium is released into the sarcomere when a muscle is stimulated to contract. This calcium uncovers the actin binding sites. When the muscle no longer needs to contract, the calcium ions are pumped from the sarcomere and back into storage. Contraction of a muscle fiber. Images from Purves et al., Life: The Science of Biology, 4th Edition, by Sinauer Associates ( ) and WH Freeman ( ), used with permission. Control of Muscle Contraction Neuromuscular junctions are the point where a motor neuron attaches to a muscle. Acetylcholine is released from the axon end of the nerve cell when a nerve impulse reaches the junction. A wave of electrical changes are produced in the muscle cell when the acetylcholine binds to receptors on its surface. Calcium is released from its storage area in the cell's endoplasmic reticulum . An impulse from a nerve cell causes calcium release and brings about a single, short muscle contraction called a twitch.

Skeletal muscles are organized into hundreds of motor units , each of which is a motor neuron and a group of muscle fibers. A graded response to a circumstance will involve controlling the number of motor units. While individual muscle units contract as a unit, the entire muscle can contract on a graded basis due to their organization into motor units. Contraction of Nonmuscular Cells | Back to Top Actin and myosin, whose interaction causes muscle contraction, occur in many other cells. Actin is attached to the inner surface of the plasma membrane. The interaction of cytoplasmic myosin and this actin causes contraction of the cell, such a the coordinated contractions of intestinal cells to absorb nutrients. Some fish have modified muscles that discharge electricity. These fish have electric organs consisting of modified muscles known as electroplates. The South American electric eel has more than 6000 plates arranged into 70 columns. Maximum discharge is 100 watts. Interaction of the Two Systems | Back to Top Vertebrates move by application of the principles of the lever. Levers amplify or increase the force or velocity of motion. The amount of amplification depends on the length of the lever.

There are three types of skeletal system, all interact with muscles using the lever. Tendon vs. ligament: MedlinePlus Medical Encyclopedia Image URL of this page: //medlineplus.gov/ency/imagepages/19089.htm Tendon vs. ligament Overview A tendon is a fibrous connective tissue which attaches muscle to bone. Tendons may also attach muscles to structures such as the eyeball. A tendon serves to move the bone or structure. A ligament is a fibrous connective tissue which attaches bone to bone, and usually serves to hold structures together and keep them stable. Review Date 8/17/2014 Updated by: Linda J. Vorvick, MD, Medical Director and Director of Didactic Curriculum, MEDEX Northwest Division of Physician Assistant Studies, Department of Family Medicine, UW Medicine, School of Medicine, University of Washington, Seattle, WA. Also reviewed by David Zieve, MD, MHA, Isla Ogilvie, PhD, and the A.D.A.M. Editorial team. A.D.A.M., Inc.

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Understanding Spinal Anatomy: Ligaments, Tendons and Muscles Back Pain and Spine Physicians in Colorado Telephone: (303) 762-0808 1-866-971-7940 Understanding Spinal Anatomy: Ligaments, Tendons and Muscles Ligaments and tendons are fibrous bands of connective tissue that attach to bone. Ligaments connect two or more bones together and help stabilize joints. Tendons attach muscle to bone. Tendons vary in size and are somewhat elastic and attach bones to muscles. Ligaments The system of ligaments in the vertebral column, combined with the tendons and muscles, provides a natural brace to help protect the spine from injury. Ligaments aid in joint stability during rest and movement and help prevent injury from hyperextension and hyperflexion (excessive movements). Anterior Longitudinal Ligament (ALL) A primary spine stabilizer About one-inch wide, the ALL runs the entire length of the spine from the base of the skull to the sacrum. It connects the front (anterior) of the vertebral body to the front of the annulus fibrosis.

Posterior Longitudinal Ligament (PLL) A primary spine stabilizer About one-inch wide, the PLL runs the entire length of the spine from the base of the skull to sacrum. It connects the back (posterior) of the vertebral body to the back of the annulus fibrosis. Supraspinous Ligament This ligament attaches the tip of each spinous process to the other. Interspinous Ligament This thin ligament attaches to another ligament called the ligamentum flavum that runs deep into the spinal column. Ligamentum Flavum The strongest ligament This yellow ligament is the strongest. It runs from the base of the skull to the pelvis, in front of and between the lamina, and protects the spinal cord and nerves. The ligamentum flavum also runs in front of the facet joint capsules. Tendons and Muscles Tendons are similar to ligaments, except these tension-withstanding fibrous tissues attach muscle to bone. Tendons consist of densely packed collagen fibers. Muscles, either individually or in groups, are supported by fascia. Fascia is strong sheath-like connective tissue.

The tendon that attaches muscle to bone is part of the fascia. The Skeleton and the Muscles The Skeleton and the Muscles The human skeleton is an endoskeleton (internal skeleton) made of bone and cartilage. Major Functions Support for the soft tissues and largely responsible for the shape of the human body. Movement: the strong rigid bones function as levers moved by the contraction of muscles. Protection: the tough bones protect delicate vital organs The brain is protected by the skull. The heart and lungs are protected by the rib cage. The spinal cord is protected by the backbone. ï¿½Structure ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ The skeleton is divided into: 1. Axial Skeleton: skull, backbone, ribs and sternum. ï¿½2. Appendicular Skeleton: pectoral girdle, pelvic girdle and limbs. ï¿½ Axial Skeleton 1. Skull: composed of 22 fused bones except for the mandible (lower jaw). 2. Spine or Backbone: Also known as the vertebral column.

It is composed of 33 small bones in a line - cervical (7), thoracic (12), lumbar (5), sacrum (5), coccyx (4). The vertebrae of the sacrum and coccyx are fused together. The vertebrae of the other regions can move slightly giving flexibility to the backbone. There are cartilage discs between these that act as shock absorbers. They help to protect the vertebrae. The vertebrae are held in position by ligaments. Muscles attached to their surfaces also support the vertebrae. Spinal nerves emerge in pairs from the spinal cord between the vertebrae. ï¿½ Rib Cage ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ The rib cage consists of the sternum and 12 pairs of ribs. All 12 pairs all attached to the backbone. The first seven are true ribs joining also to the sternum. The next three are the false ribs, which also join to the seventh rib. The last two are the floating ribs. They are only joined at one end to the backbone.

The sternum or breastbone is a flat thin bone at the centre of the chest wall. ï¿½ The Appendicular Skeleton The Pectoral Girdle is composed of four bones ï¿½ two clavicles (collar bones) and two scapulae (shoulder blades). The arms connect with the scapulae at a ball and socket joint. The Pelvic Girdle The Pelvic Girdle appears to be one large cylindrical bone but is actually six fused bones. The legs articulate with the pelvis at a ball and socket joint. The pelvis is securely attached to the backbone at the sacrum. Limbs ï¿½ ï¿½ Human Forelimb (arm)ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ Human Hindlimb (leg) The arms and legs have similar design. There are long upper bones. In the arm it is the humerus and in the leg it is the femur.

Also, there are two long bones in the medial region: The ulna and radius in the arm and the tibia and fibula in the leg. ï¿½ The foot and hand have similar bones. The carpals are in the wrist of the arm and the tarsals in the ankle of the leg. The metacarpals are in the palm of the hand and metatarsals in the hind foot. The phalanges are in the fingers and toes. Long Bone Structure A membrane called the periosteum encloses long bones. It contains blood vessels and nerves. The diaphysis is the shaft or long main portion of the bone. The epiphysis is at each end of the long bone and is formed separately of the diaphysis. Cartilage is found at each end of the long bones. It is made of protein called collagen. Collagen fibres are wound within the surrounding material of calcium and phosphorous salts.ï¿½ The cartilage covers the epiphyses protecting them from friction and shock at freely moveable joints. Cartilage does not have blood vessels or nerves. Useful materials enter the cartilage by diffusion. Types of Bones There are 2 types of bones: compact bone and spongy bone. 1.

Compact Bone: Is a solid bone that at microscopic level has a concentric ring structure. It is made of bone cells called osteoblasts. These cells are growing within a material that is called a bone matrix. The bone matrix is made ofï¿½ 70% inorganic salts such as calcium phosphate and 30% protein called collagen. The calcium salts give the bone strength while the protein gives it flexibility. Blood vessels as well as nerve fibres are within the bone. 2. Spongy Bone: irregular openwork of thin plates of bone. It is also known as trabecular or cancellous bone. The mineral deposits are arranged as a system of struts. Bone marrow fills the spaces between the plates. The marrow cavity is the space within the diaphysis that also contains marrow.ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ There are 2 types of bone marrow: 1.ï¿½ Red Bone Marrow: Is responsible for the formation of red blood cells, white blood cells and platelets. 2. Yellow Bone Marrow: Is responsible for energy storage in the form of lipid (fat).

This can be converted into red marrow if the body needs increased blood cell formation. It is only found in adultsï¿½ medullary cavity. Inside view of cavities within spongy bone. They are filled with red bone marrow. Bone Growth ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ The embryo is made of cartilage until about the 8th week of development. It then is replaced with bone. Osteoblasts produce the protein collagen. A hard covering of mainly calcium phosphate forms around the collagen. The osteoblasts become trapped within the calcium phosphate and become dormant bone cells. ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ The bone becomes longer as a result of growth plates found between the diaphysis and the epiphysis. At this plate, cartilage is continuously formed and then turned into bone. This process is called ossification. This stops when a person reaches the adult age.

Bone Development Even though bones stop growing in length in early adulthood, they can continue to increase in thickness or diameter throughout life in response to stress from increased muscle activity or to weight. The increase in diameter is called appositional growth. Osteoblasts in the periosteum form compact bone around the external bone surface. At the same time, osteoclasts in medullary cavity break down bone on the internal bone surface, around the medullary cavity. These two processes together increase the diameter of the bone and, at the same time, keep the bone from becoming excessively heavy and bulky. Factors that affect bone growth 1. Stress on the bones by physical activity. Osteoblasts are stimulated. More bone grows. 2. Lack of Stress causes bones to become thin. 3. Growth hormone and sex hormones increase bone size. Joints A joint is the junction between two or more bones. There are three major types of joints: 1. Fused Joints: These joints include the skull, sacrum, pelvis, and coccyx.ï¿½ As the name suggests, these joints are points where joints fuse or grow together. The place where they grow together is called the suture.

These joints provide strength, support, and protection. 2. Slightly Moveable Joints: These joints are located between the vertebrae of the upper spine. There is cartilage within the joints. They help pad and protect the bones. The bones are held together by ligaments. The ligaments are tightly bound and limit the movement of the bones. This protects the spinal cord. 3. Freely Moveable or Synovial Joints: At these joints the ends of the bones are covered with cartilage and there is a cavity that separates the bones. The bones are held in place by ligaments which stop the bones from moving too much. In addition to the ligaments the two bones are joined together by sleeve-like capsule.ï¿½ The capsule encloses the synovial cavity.

The outer layer of the capsule is composed of ligaments.ï¿½ As stated previously, the ligaments keep bones together preventing dislocation and control the range of movement.ï¿½ The inner layer of the capsule is the synovial membrane.ï¿½ The synovial membrane secretes the lubricating synovial fluid.ï¿½ Lubrication is essential to prevent frictional wear and tear.ï¿½ The cartilage at the contact ends of the bones also reduces friction. The cartilage pads also acts as shock absorbers against mechanical damage. Classes of Synovial Joints 1. Gliding: The bones of these joints move across each other, back-and-forth and side-to-side. Examples are between the carpals of the wrist and tarsals of the ankle. 2. Pivot: These joints allow a turning movement. Examples are between the first and second vertebras when turning the head, between the ulna and the radius of the lower arm when turning the palm of the hand up or down. 3. Hinge: These joints allow movement in one plane during flexion and extension. They act, as the name implies, like the hinge of a door. Examples are bending the elbow or knee. 4.

Ball and Socket: This type of joint permits movement in three planes, i.e., in all directions. Examples are the shoulder and hip joints. ï¿½ Ligaments ï¿½ï¿½ï¿½ï¿½ Ligaments are strong, slightly elastic tissues that connect bone to bone at joints. These tissues are more flexible when warm. That is why you should gently warm up before exercising. Ligaments prevent dislocation of the joint and control the range of movement of the bones at the joint. Tendons Tendons are strong inelastic cords or bands of connective tissue that connect muscle to bone. They are composed of collagen and contain blood vessels. The inelastic tendon will not stretch when the muscle contracts. Therefore the full pull is transmitted to the bone and the full range of motion is accomplished. Arthritis There are 2 types of arthritis, Osteoarthritis and Rheumatoid Arthritis. Both of these conditions involve the swelling and inflammation of the joint. See your text book page 352 for more information on this topic. Muscles There are 3 types of muscle: skeletal, smooth, and cardiac.

ï¿½ï¿½ï¿½ Skeletal Muscle Skeletal muscle, as its name implies, is the muscle attached to the skeleton. It is also called striated muscle. The contraction of skeletal muscle is under voluntary control. These muscles are mainly responsible for movement of the body. Other purposes are posture maintenance, support of the joints, and heat production.

While its contraction is fast and strong, skeletal muscle tires easily.ï¿½ ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ Smooth Muscle Smooth muscle is found in the walls of all

 the hollow organs of the body (except the heart).

Its contraction reduces the size of these structures. Thus it regulates the flow of blood in the arteries, moves your breakfast along through your gastrointestinal tract , expels urine from your urinary bladder, sends babies out into the world from the uterus, and regulates the flow of air through the lungs. The contraction of smooth muscle is not under voluntary control. It is called involuntary muscle. It contracts slowly and is slow to tire. ï¿½Cardiac Muscle ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ Your heart is made of cardiac muscle. This type of muscle only exists in your heart. Unlike other types of muscle, cardiac muscle never gets tired. It works automatically and constantly without ever pausing to rest. Cardiac muscle contracts to squeeze blood out of your heart, and relaxes to fill your heart with blood. Antagonistic Skeletal Muscles Antagonistic muscles are pairs of muscles. The action of one member is opposite to that of the other member. Muscles can contract but they do not have the ability to lengthen (stretch) themselves.

They are arranged in pairs such that after one muscle or muscle group contracts, a skeleton transfers the movement to stretch another muscle or muscle group. The pairs of muscles that stretch each other are said to be antagonistic. Example of an antagonistic muscle pair The biceps and triceps muscles of the arm are an example of an antagonistic pair. Contraction of the biceps moves the arm toward the body and stretches the triceps. Contraction of the triceps extends the arm and stretches the biceps. In this example the bicep is said to be the flexor while the tricep is the extensor. Extensors are not as strong as flexors. Muscles of the Leg (Thigh) Muscles of the Leg There are basically 32 different muscles in the leg. It is difficult to count because sometimes the muscle may be considered a hip muscle or a foot muscle. However, we are just going to look at a few of the main groups. 1. Quadriceps Femoris (or Quads) This is a group of four muscles on the front of the thigh.

One (Rectus Femoris) begins on the front of the hip/pelvic bone and the other three (Vastus Medialis, Vastus Lateralis, Vastus Intermedialis) begin at the top of the thigh bone (femur). All four cross the knee joint and attach to the top of the shin bone (tibia). The "knee cap" bone (patella) is sandwiched in the tendon at the end of the quad muscles and held over the knee joint. 2. Semimembranosis, Semiteninosus, Biceps Femoris (or the Hamstrings) All three of these are on the back of the thigh and start at the "sit bone" (ischial tuberosity), cross the knee joint and end on either side of the lower leg bone (tibia). 3. Gastrocnemius and Soleus (or Calf) This is the back of the lower leg. The gastrocs start above the knee on the thigh bone (femor) and the soleous starts below the knee on the tibia.

They merge together above the level of the ankle to become the "Achilles Tendon" which attaches tot he back of the heel bone (calcaneous) 4. Pectineus, Adductor Brevis, Adductor Longus, Adductor Magnus (or the Adductors or Inner Thigh) All of these muscles begin at the pubic ramis and attach down at various levels on the thigh bone (femor) Note: There is no "Outer Thigh" muscle group. That space is call the Iliotibial Band or ITB Main Actions: Quads: They extend or straighten the knee. The muscle fibers will pull up toward the hip causing the patella to move towrd the hip slightly, pulling on the tibia to straighten the knee. Hams: Just the opposite. They flex or bend the knee. The muscle fibers pull up toward the gluts or buttock pulling on the tibia to bend the knee. Calf: They point or plantarflex the ankle. The fibers pull up on the heel bone toward the knee pointing the ankle. Adductors: The fibers pull up towards the pubic ramus moving the leg in toward the midline of the body.

Wenning Physical Therapy

Question: What attaches muscles to bone?
Answer: Tendons