ANATOMY KEY CONCEPTS CH 6.1-6.12

6.6 Key Concepts

A bone marking (surface feature) is an area on the surface of a bone with a specific function. Bone markings can be used to describe and identify specific bones. The axial skeleton can be subdivided into the skull and associated bones (including the auditory ossicles, or ear bones, and the hyoid); the rib cage, composed of the ribs and sternum; and the vertebral column. The thoracic cage consists of the rib cage and thoracic vertebrae. The appendicular skeleton includes the bones of the upper and lower limbs and the pectoral and pelvic girdles.

6.2 Key Concepts

Bone, or osseous tissue, is a supporting connective tissue with a solid matrix. General categories of bones are long bones, short bones, flat bones, and irregular bones. The features of a long bone include a diaphysis, two epiphyses, and a central marrow cavity. The two types of bone tissue are compact bone and spongy (trabecular) bone. A bone is covered by a periosteum and lined with an endosteum. Both types of bone tissue contain osteocytes in lacunae. Layers of calcified matrix are lamellae, interconnected by canaliculi. The basic functional unit of compact bone is the osteon, containing osteocytes arranged around a central canal. Spongy bone contains trabeculae, often in an open network. Compact bone is located where stresses come from a limited range of directions. Spongy bone is located where stresses are few or come from many different directions. Cells other than osteocytes are also present in bone. Osteoblasts synthesize the matrix in the process of ossification. Osteoclasts dissolve the bony matrix through the process of osteolysis or resorption.

6.8 Key Concepts

Each arm articulates with the trunk at a pectoral girdle, or shoulder girdle, which consists of a scapula and a clavicle. The clavicle and scapula position the shoulder joint, help move the arm, and provide a base for arm movement and muscle attachment. Both the coracoid process and the acromion are attached to ligaments and tendons. The scapular spine crosses the posterior surface of the scapular body. The humerus articulates with the scapula at the shoulder joint. The greater tubercle and lesser tubercle of the humerus are important sites for muscle attachment. Other prominent landmarks include the deltoid tuberosity, the medial and lateral epicondyles, and the articular condyle. Distally, the humerus articulates with the radius and ulna. The medial trochlea extends from the coronoid fossa to the olecranon fossa. The radius and ulna are the bones of the forearm. The olecranon fossa accommodates the olecranon process during extension of the arm. The coronoid and radial fossae accommodate the coronoid process of the ulna. The bones of the wrist form two rows of carpal bones. The distal carpal bones articulate with the metacarpal bones of the palm. The metacarpal bones articulate with the proximal phalanges, or finger bones. Four of the fingers contain three phalanges; the pollex, or thumb, has only two. The pelvic girdle consists of two hip

6.12 Key Concepts

Growth and maintenance of the skeletal system is supported by the integumentary system. The skeletal system also interacts with the muscular, cardiovascular, lymphatic, digestive, urinary, and endocrine systems.

6.10 Key Concepts

Important terms that describe movements at synovial joints are flexion, extension, hyperextension, abduction, adduction, circumduction, and rotation. The bones in the forearm permit pronation and supination. Movements of the foot include inversion and eversion. The ankle undergoes flexion and extension, also known as dorsiflexion and plantar flexion, respectively. Opposition is the thumb movement that enables us to grasp and hold objects. Reposition is the opposite of opposition. Protraction involves moving a part of the body forward; retraction involves moving it back. Depression and elevation occur when we move a structure inferiorly and superiorly, respectively. Major types of synovial joints include plane (gliding) joints, hinge joints, pivot joints, condylar joints, saddle joints, and ball-and-socket joints.

6.9 Key Concepts

Joints, or articulations exist wherever two bones interact. Immovable joints are synarthroses, slightly movable joints are amphiarthroses, and those that are freely movable are called diarthroses. Examples of synarthroses are a suture, a gomphosis, and a synchondrosis. Examples of amphiarthroses are a syndesmosis and a symphysis. The bony surfaces at diarthroses, or synovial joints, are covered by articular cartilages, lubricated by synovial fluid, and enclosed within a joint capsule. Other synovial structures include menisci, fat pads, bursae, and various ligaments.

6.3 Key Concepts

Ossification is the process of converting other tissues to bone. Intramembranous ossification begins when stem cells in connective tissue differentiate into osteoblasts and produce spongy or compact bone. Endochondral ossification begins with the formation of a cartilage model of a bone that is gradually replaced by bone. In this process, bone length also increases. Bone diameter increases through appositional growth. The timing of epiphyseal closure differs among bones and among individuals. Normal ossification requires a reliable source of minerals, vitamins, and hormones

6.11 Key Concepts

The articular processes of adjacent vertebrae form plane (gliding) joints. Symphyseal joints connect adjacent vertebral bodies and are separated by intervertebral discs. The shoulder joint is formed by the glenoid cavity and the head of the humerus. This ball-and-socket joint is extremely mobile and, for that reason, it is also unstable and easily dislocated. Bursae at the shoulder joint reduce friction from muscles and tendons during movement. The elbow joint permits only flexion and extension. It is extremely stable because of extensive ligaments and the shapes of the articulating bones. The hip joint is formed by the union of the acetabulum with the head of the femur. This ball-and-socket joint permits flexion and extension, adduction and abduction, circumduction, and rotation. The knee joint is a complicated hinge joint. The joint permits flexion-extension and limited rotation

6.7 Key Concepts

The cranium encloses the cranial cavity, which encloses the brain. The frontal bone forms the forehead and superior surface of each orbit. The parietal bones form the upper sides and roof of the cranium. The occipital bone surrounds the foramen magnum and articulates with the sphenoid, temporal, and parietal bones to form the back of the cranium. The temporal bones help form the sides and base of the cranium and fuse with the parietal bones along the squamous suture. The sphenoid bone acts like a bridge that unites the cranial and facial bones. The ethmoid bone stabilizes the brain and forms the roof and sides of the nasal cavity. Its cribriform plate contains perforations for olfactory nerves, and the perpendicular plate forms part of the bony nasal septum. The left and right maxillae, or maxillary bones, articulate with all the other facial bones except the mandible. The palatine bones form the posterior portions of the hard palate and contribute to the walls of the nasal cavity and to the floor of each orbit. The vomer forms the inferior portion of the bony nasal septum. The zygomatic bones help complete the orbit and together with the temporal bones form the zygomatic arch (cheekbone). The nasal bones articulate with the frontal bone and the maxillary bones. The lacrimal bones are within the orbit on its medial surface. The inferior nasal conchae inside the nasal cavity aid the superior and middle nasal conchae of the ethmoid bone in slowing incoming air. The nasal complex includes the bones that form the superior and lateral walls of the nasal cavity and the sinuses that drain into them. The nasal septum divides the nasal cavities. Together, the frontal, sphenoidal, palatine, maxillary sinuses, and ethmoidal cells make up the paranasal sinuses. The mandible is the bone of the lower jaw. The hyoid bone is suspended below the skull by ligaments from the styloid processes of the temporal bones. Fibrous tissue connections called fontanelles permit the skulls of infants and children to continue growing. The vertebral column consists of the vertebrae, sacrum, and coccyx. We have 7 cervical vertebrae, 12 thoracic vertebrae, and 5 lumbar vertebrae. The sacrum and coccyx consist of fused vertebrae. The spinal column has four spinal curves, which accommodate the unequal distribution of body weight and keep it in line with the body axis. A typical vertebra has a body and a vertebral arch; it articulates with other vertebrae at the articular processes. Adjacent vertebrae are separated by an in

6.5 Key Concepts

The effects of aging on the skeleton can include osteopenia and osteoporosis.

6.4 Key Concepts

The organic and mineral components of bone are continuously recycled and renewed through the process of remodeling. The shapes and thicknesses of bones reflect the stresses applied to them. Mineral turnover enables bone to adapt to new stresses. Calcium is the most abundant mineral in the human body, with roughly 99 percent of it located in the skeleton. The skeleton acts as a calcium reserve. A fracture is a crack or break in a bone. Closed fractures are internal. Open fractures project through the skin. Repair of a fracture involves the formation of a fracture hematoma, an external callus, and an internal callus

6.1 Key Concepts

The skeletal system includes the bones of the skeleton and the cartilages, ligaments, and other connective tissues that stabilize or interconnect bones. Its major functions include structural support, storage of minerals and lipids, blood cell production, protection, and leverage.