How is skeletal muscle connected to bone

How Do Bones Grow? 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 , mature bone cells which help continue new born formation osteoclasts pronounced: AHS-tee-o-klasts , which break down bone and help to sculpt and shape it What Are Muscles and What Do They Do? Humans have three different kinds of muscle: Skeletal muscle is attached by cord-like tendons to bone, such as in the legs, arms, 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 help hold the skeleton together, give the body shape, and help it with everyday movements known as voluntary muscles because you can control their movement. They can contract shorten or tighten quickly and powerfully, but they tire easily.

Smooth, or involuntary, muscle is also made of fibers, but this type of muscle looks smooth, not striated. We can't consciously control our smooth muscles; rather, they're controlled by the nervous system automatically which is why they're 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 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. How Do Muscles Work? 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 move slightly during birth and then fuse together as the skull finishes growing.

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 — such as those 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. Three kinds of freely movable joints 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. They range from extremely tiny strands such as the stapedium muscle of the middle ear to large masses such as the muscles of the thigh. Some skeletal muscles are broad in shape and some narrow. In some muscles the fibers are parallel to the long axis of the muscle; in some they converge to a narrow attachment; and in some they are oblique.

Each skeletal muscle fiber is a single cylindrical muscle cell. An individual skeletal muscle may be made up of hundreds, or even thousands, of muscle fibers bundled together and wrapped in a connective tissue covering.

Each muscle is surrounded by a connective tissue sheath called the epimysium. Fascia , connective tissue outside the epimysium, surrounds and separates the muscles.

Portions of the epimysium project inward to divide the muscle into compartments. The skeleton is divided into the:. Coordinated movement is made possible through the combination of purposeful and synchronised movements across the relevant muscles and bones to create articulation of the joints. The configuration of the joint surface determines the movement possible. Planes of movement include flexion, extension, abduction, adduction, rotation and circumduction Table 1. The joints are the articulating surfaces between two bones and may be classified according to how much movement they allow:.

They can also be classified according to the components that unite the bones such as fibrous structures, cartilaginous structures and synovial structures , as shown below. Fibrous joints are articulating surfaces linked together with tough fibrous connections. One example is the suture lines in the skull, where bones that were initially separate have become fused together synostosis to form one bone Danning, As the suture line does not permit movement once fusion has occurred, this is considered to be a synarthrotic joint.

Syndesmoses are another type of fibrous joint, in which ligaments and interosseous membrane connect the joint to create a firm structure. One example is the inferior tibiofibular joint, in which interosseous, tibiofibular and transverse ligaments connect the distal tibia and fibula of the lower leg.

Another is the radioulnar joint, where an intraosseous membrane connects the distal radius and ulnar bones of the forearm. This can also be classified as an amphiarthrotic joint as it permits some movement to allow for pronation and supination of the hand and forearm.

These joints are connected by tough cartilage between the bone and can be classified as primary synchondroses or secondary symphyses. Synchondroses Synchondroses are cartilaginous joints formed of hyaline cartilage, and are mainly found in the growing skeleton as the ossification centres of growing bone that will ossify over time synostosis , such as the epiphyseal growth plate.

Cartilaginous joints are usually immobile but, in a rare condition in children and adolescents, the attachment of the epiphysis loosens, allowing the femoral head to slip down the femoral neck.

This is known as a slipped upper femoral epiphysis and often presents with the child developing an unexpected limp Robson and Syndercombe Court, In the mature skeleton, an example of a synchondrosis is the first sternocostal joint between the first rib and the manubrium ; all other sternocostal joints are synovial.

The intervertebral discs between the vertebral bodies of the spine are an example of bones connected by fibrocartilage. These fibrous joints allow relatively limited movement individually but extensive movement can be achieved collectively across the whole spine.

Another example of a symphysis is the symphysis pubis in the pelvis, which helps maintain pelvic stability. In pregnancy, the symphysis pubis is softened by hormones to allow for expansion during delivery. As symphyses allow slight movement between the articulating surfaces, they are considered to be amphiarthroses. Synovial joints are designed to allow free movement of the joint and are classified as diarthroses.

Characterised by a gap between the articulating bones, they are held in close proximity by a joint capsule. Contraction of the infrastructure of muscles around the joint maintains movement, while stability is maintained through the use of soft tissue structures, such as ligaments, labra, fat pads and menisci Danning, The joint has an outer fibrous capsule that encapsulates the entire joint and is attached to the periosteum, allowing movement, maintaining tensile strength and helping to prevent dislocation.

This layer also contains the synovial membrane synovium , which is composed of synoviocytes of which there are two types:. Synovial fluid The synovial fluid helps protect the joint from mechanical injury and contains hyaluronic acid and lubricin Danning, In a healthy joint, the synovial fluid is very viscous and clear, and is either colourless or a pale straw colour. Water is able to enter the joint very easily during inflammation but, once it mixes with hyaluronic acid, it cannot leave as quickly Robson and Syndercombe Court, — as such, although it may only take a few hours for the joint to swell, it can take a few days for that swelling to subside.

The synovial fluid may become infected by a haematogenous blood-borne spread of bacteria, extension of an adjacent infection or direct inoculation following trauma or an invasive procedure. This is known as septic arthritis and can damage the synovium or cartilage. Rheumatoid arthritis This is an autoimmune inflammatory arthropathy that affects the synovium.

It occurs more often in smokers and is three times more common in women than men Ralston and McInnes, Clinical onset is characterised by the abnormal production of cytokines and inflammatory mediators such as interleukin 1, interleukin 6, interleukin 15 and tumour necrosis factor Ralston and McInnes, This causes the synovium to become inflamed and hypertrophied so the synovial villi become thickened and fuse together to form a pannus.