BONES AND JOINTS. Axial Skeleton

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1 BONES AND JOINTS The adult human skeleton usually consists of 206 bones which are connected by various joints. Muscles produce force which causes movement at these joints. These bones can be grouped in two divisions: Axial skeleton and Appendicular skeleton. The 80 bones of the Axial skeleton form the vertical axis of the body. They include the bones of the skull, vertebral column, ribs and breastbone or sternum. The Appendicular skeleton consists of 126 bones and includes the free appendages and their attachments to the axial skeleton. The free appendages are the upper and lower extremities, or limbs, and their attachments that are called girdles. Axial Skeleton Skull: The skull consists of facial bones and cranial bones (cranium). The cranium is important, enclosing and protecting the brain as well as providing a site for attachment of head and neck muscles. Vertebral column: The vertebral column (spine) serves as an axial support for the trunk, protects the spinal cord, and provides attachment points for the ribs. It consists of the sacrum, coccyx and 24 individual vertebrae. These are divided into three divisions, the cervical, thoracic, and lumbar vertebrae. Cervical vertebrae: Consists of the seven vertebrae of the neck and represents as a concave (lordotic) curve. These vertebrae are numbered from the top down (superior to inferior) and are identified as C1 C7. Thoracic vertebrae: The thoracic vertebrae all articulate with the ribs. There are 12 thoracic vertebrae and are numbered T1 T12 starting where the cervical vertebrae left off. The thoracic vertebrae represents as a convex (kyphotic) curve in the middle of the back. Fit College Bones & Joints v1.1 Mar

2 Lumbar vertebrae: Also referred to as the small of the back, the lumbar vertebrae are the largest of the vertebrae in the human spine. They provide the bulk of the weight bearing function of the spine and as such account for the majority of back injuries and complaints. There are 5 lumbar vertebrae numbered L1 L5 starting where the thoracic vertebrae left off. Sacrum: Formed by 5 fused vertebrae, the sacrum articulates with L5 and with the pelvis to form the sacroiliac joints of the body. It provides support for the pelvic organs of the body. Coccyx (Tail bone): Is a small triangular shaped bone formed by 4 fused vertebrae and articulates with the sacrum. Other then providing a small amount of support for the pelvic organs, the coccyx has very little purpose. Ribs: There are 12 pairs of ribs which all articulate with the thoracic vertebrae. The first 7 ribs attach to the sternum and are referred to as true ribs. The remaining ribs are called false ribs because they either indirectly attach to the sternum or have no attachment at all. The ribs and sternum join to make up the bony thorax, which forms a protective cavity around the bodies vital organs and the thoracic cavity. Sternum: Also known as the breastbone, the sternum is the result of three bones fused together, the manubrium, the body and the xiphoid process. Manubrium: The superior portion of the sternum, the manubrium articulates with the clavicles and the first 2 ribs. Body: Forms the bulk of the sternum and articulates with the 2 nd to 7 th ribs. Xiphoid Process: Forms the inferior end of the sternum and serves as an attachment point for the muscles of the abdomen. Fit College Bones & Joints v1.1 Mar

3 Appendicular Skeleton The Appendicular skeleton consists of the bones of the limbs and their girdles and provides us with our mobility. Upper Body Clavicle: The clavicles articulate with the sternum and the scapulae, acting as a brace, holding the scapulae and arms out laterally. Scapulae: These are triangular flat bones that lie on the border of posterior surface of the rib cage between ribs 2 and 7. It articulates with the clavicle at the acromioclavicular joint and the humerus at the glenohumeral joint. Humerus: A typical long bone, the humerus articulates with the scapulae of the shoulder, and the radius and ulna of the forearm. Radius: The radius is one of two bones in the forearm. It articulates with the humerus, ulna and carpals of the wrist. In the anatomical position, the radius is positioned laterally to the ulna. Ulna: Slightly longer than the radius, the ulna is responsible for forming the elbow joint with the humerus. Carpals: The carpals are 8 small bones that make up the wrist. They articulate with each other, the metacarpals and the radius. There are 5 bones that radiate from the wrist to form the palm of the hand. Phalanges: Fingers or digits Lower Body Pelvis: The pelvis attaches the lower limbs to the axial skeleton and is secured in place with some of the strongest ligaments in the body. The pelvis articulates with the femur and sacrum. Fit College Bones & Joints v1.1 Mar

4 Femur: The longest, strongest bone in the human body, the femur articulates with the tibia, fibula and patella to also form the knee. Patella: A triangular sesamoid bone enclosed in the quadriceps tendon that secures the anterior thigh muscles to the tibia. Tibia: The tibia receives the weight of the body through the femur, transferring it to the foot. It lies anterior and medial to the fibula and articulates with the patella, femur, fibula, and tarsals. Fibula: Posterior and lateral to the tibia, it articulates with the tibia and tarsals. Tarsals: There are seven tarsal bones that make up the posterior half of the foot. Metatarsals: These are the long bones of the foot. The heads of the metatarsals make up the "ball" of the foot. The 1 st metatarsal corresponds to the big toe. The 5 th metatarsal corresponds to the smallest toe. Phalanges: There are 14 small bones that make up the toes. There are 2 phalanges in each large toe and 3 in each smaller toe. Fit College Bones & Joints v1.1 Mar

5 Structure of a long bone The shaft of a long bone is called the diaphysis and is made of thick compact bone. The ends of a long bone are called the epiphysis. The exterior of the epiphysis is made of compact bone while the interior is comprised of spongy bone. Hyaline or articular cartilage covers the epiphysis. Bone remodeling Our bones are not dormant but are continually changing. Bones can become weaker or stronger. The adult skeleton maintains itself and replaces mineral reserves by remodeling. Remodeling - recycles and renews bone matrix and involves osteocytes, osteoblasts, and osteoclasts. Bone degenerates quickly and up to 1/3 of bone mass can be lost in a few weeks of inactivity. Alcohol consumption and smoking can result in a lower bone density. Menopause which causes a decline in a females estrogen levels affects bone strength. Low body fat levels can inhibit the absorption of some fat soluble vitamins which can also weaken bones. Bones require many nutrients to stay healthy. Some of these include calcium, magnesium, protein, copper, and vitamins A, C, D and K. Vitamin C is required for collagen synthesis, and stimulates osteoblast differentiation Vitamin A stimulates osteoblast activity Vitamins K and B 12 help synthesize bone proteins A dietary source of calcium and phosphate salts plus small amounts of magnesium, fluoride, iron, and manganese are also important for normal bone growth and maintenance Hormones also influence bone growth and health Calcitriolis made in kidneys & helps absorb calcium & phosphorus from digestive tract. Calcitrolsynthesis requires vitamin D 3 (cholecalciferol) Growth hormone &thyroxine stimulate bone growth Estrogens & androgens stimulate osteoblasts Calcitonin & parathyroid hormone regulate calcium & phosphate levels Bones become thinner and weaker with age Osteopenia begins between ages 30 and 40 Women lose 8% of bone mass per decade, men 3% The epiphyses, vertebrae, & jaws are most affected resulting in fragile limbs, reduction in height, & tooth loss Osteoporosis is the result of severe bone loss and affects normal function. This normally occurs over age 45, and occurs in 29% of women & 18% of men. Fit College Bones & Joints v1.1 Mar

6 Resistance training and weight bearing exercise helps increase bone density as heavily stressed bones become thicker and stronger and the Mineral recycling allows bones to adapt to stress. Joints The weakest parts of the skeleton, joints are the point at which two bone meet. The range of movement at the joint is reliant on the structure, surrounding ligaments, tendons and muscles. As a result, joints enable movement whilst providing support against external forces (i.e. gravity) Joint types Joints can be classified according to the degree and type of movement: Fibrous (or Immovable) Joints These joints are firmly held together by a thin layer of strong connective tissue. There is no movement between the bones such as the sutures of the skull. Cartilaginous Joints: Cartilaginous joints are joints where the articular surfaces of the bones forming the joints are attached to each other by means of white fibrocartilaginous discs and ligaments. They allow only a limited degree of movement. Examples are the cartilaginous joints between the vertebrae. Synovial joints: Synovial joints make up the majority joints within the body. The articulating bones are separated by a fluid filled joint cavity. This allows synovial joints to be freely moveable. Source: Dorland's Medical Dictionary for Health Consumers Fit College Bones & Joints v1.1 Mar

7 Various kinds of joints: Fibrous: A,syndesmosis (tibiofibular); B, suture (skull). Cartilaginous: C,symphysis (vertebral bodies); D,synchondrosis (first rib and sternum). Synovial: E,condyloid (wrist); F, gliding (radioulnar); G, hinge or ginglymus (elbow); H, ball and socket (hip); I, saddle (carpometacarpal of thumb); J, pivot (atlantoaxial). Five classes of tissue make up synovial joints: Bone Cartilage Synovium Synovial fluid Tensile tissues: ligament and tendon, attached at entheses Bone The bone adjacent to a joint consists of an open spongy framework of calcified collagen in a tough outer shell. Immediately beneath articular cartilage there is a more or less continuous subchondral bony plate but this is often extremely thin. The bone can withstand thrust forces as long as it is covered in cartilage, which distributes load evenly. Without cartilage, the spongy bone collapses easily. Bone is a live tissue constantly remodelling in response to stresses. Articular Cartilage Hyaline cartilage Hyaline cartilage is the skeletal growth tissue. In many, but not all, joints a thin layer remains as the bearing surface in the adult. Hylaine cartilage is avascular. It contains type II collagen and giant molecular complexes of a proteoglycan called aggrecan. Load bearing normally occurs over small areas, varying with joint position. Cartilage does not normally wear despite decades of use, but will do if its composition or joint mechanics are abnormal. It can regenerate, and will do so at the margins of damaged joints as part of the osteochondral swellings known as osteophytes, but load bearing areas will rarely rethicken once damaged, so the tissue is unable to restore its normal shape after injury. Fibrocartilage Fibrocartilage occurs as intervertebral disc, and as discs, menisci or ring pads in many peripheral joints. It lacks the combination of collagen II and aggrecan seen in hyaline cartilage and blends in with fibrous synovial tissue. It will regenerate to fill a space e.g. in the case of repairing cartilage defects of the knee; it has lower mechanical properties compared to hialine. Fit College Bones & Joints v1.1 Mar

8 Synovium (articular capsule) Synovium is the name given to the soft tissue lining the cavities of joints, tendon sheaths and bursae. It is like other connective tissue packing, being a mixture of fatty, areolar and fibrous tissue. The surface of synovium is permeable to water, small molecules and proteins, but not to hyaluronan, which is the molecule that makes synovial fluid viscous. This allows synovium to trap synovial fluid within the cavity. Beneath the surface cell layer is a net of small blood vessels, important in the development of synovial inflammation. Joint, tendon sheath and bursalsynovium all have the same structure. Synovial Fluid Normal synovial fluid is clear, colourless and noticeably thick and stringy, like eggwhite. Hence the name syn-ovium ( with egg ). Its viscous and elastic properties are due to hyaluronan, a long chain glycosaminoglycan carbohydrate with a molecular mass of about 1 million. Synovial fluid is effectively a liquid connective tissue. Because there are no fibrous components to it, the water and the hyaluronan ground substance move around together within the synovial space, whereas in other tissues water moves and the ground substance stays put. Water diffuses in and out of the synovial cavity more easily than hyaluronan. The amount of water in a joint depends on passive equilibration of plasma with vascular and lymphatic compartments, as for all connective tissue fluid. It goes up and down with exercise and rest. Water can enter the joint rapidly during inflammation but once mixed with hyaluronan cannot leave so rapidly unless the joint ruptures. If joints are stretched suddenly, even the fluid does not fill all the space and the lining may jump into the vacuum formed, which is how people "click" their finger joints. Tendon sheaths and bursae: The synovial lining in these structures is similar to that within joints, with a slippery nonadherent surface allowing movement between planes of tissue. Synovial tendon sheaths line tendons only where they pass through narrow passages or retinacula, as in the palm, at the wrist and around the ankle. Elsewhere the tendon lies in a bed of loose fibrous tissue. Bursae occur at sites of shearing in subcutaneous tissue or between deeper tissues such as muscle groups and fascia. Many bursae develop during growth but new or adventitious bursae can occur at sites of occupational friction. Ligaments and tendons Ligaments hold bones together. They are variably elastic. Tendons transmit muscle power to bones and are inelastic (except in kangaroo legs). Joint "capsules" are composed of a basket work of independently moving ligaments and tendons associated with sheets of fascia. Some joints, such as the sacroiliac, are largely surrounded by ligament, others, such as the shoulder, with its rotator cuff, are surrounded by tendon. Tendons may also pass through joint cavities, e.g. long head of biceps. Fit College Bones & Joints v1.1 Mar