Skeletal System

The skeletal system forms the…

internal protective framework of the body

The skeleton itself is composed exclusively of _______, primarily in the form of ___________.

connective tissue; bone and cartilage

“Organs” of the skeletal system include _________, which together constitute _____________.

bones and joints; a system of levers upon which skeletal muscles work to effect movement

The skeletal system is divided into an axial skeleton, which consists of ______________, and an appendicular skeleton that includes ______________.

the skull, hyoid bone, vertebrae and ribs; the bones of the pectoral and pelvic girdles and the extremities

Bones are classified by their…

shape (e.g., long, short, flat, irregular)

What is a special type of bone?

Sesamoid bones are a special type; these typically small nodules of bone (resembling a sesame seed) are embedded within the tendons of muscles where they cross synovial joints.

Bones are composed of two types of bone tissue

compact or cortical bone, and spongy or trabecular bone

compact vs. spongy bone

• Vary with respect to their amount of solid matter and the number and size of marrow spaces they contain

• Compact bone appears as a solid mass

• Trabecular bone consists of a network of bony spicules or trabeculae delimiting spaces occupied by bone marrow

• All bones have a superficial thin layer of compact bone around a central mass of trabecular bone, except where the latter is replaced by a large marrow cavity

• Due to its density, compact bone is readily observable in conventional radiographic images

Head

• large, round articular end

• examples:  head of the femur, head of the mandible

Neck

• relatively narrow portion connecting the head to the shaft

• example:  femoral neck

Facet

• smooth flat area, usually covered with cartilage, where a bone articulates with another bone

• examples:  costal facets on thoracic vertebrae

Condyle

• knuckle-shaped region of a bone; usually associated with an articulation

• examples:  medial & lateral condyles of the femur, occipital condyles of the skull

Protuberance

• a bulge or projection of bone

• example:  external occipital protuberance

Process

• an extension or projection serving a particular purpose

• examples:  ulnar styloid process, uncinate process of cervical vertebrae, mastoid process of skull

Spine

• thorn-like process

• examples:  spine of the scapula; ischial spine of the pelvis

Crest

• ridge/edge of bone

• examples:  iliac crest, petrous crest

Line

• linear elevation, sometimes called a ridge

• examples:  soleal line of the tibia; superior nuchal line of skull

Tubercle

• small, raised eminence

• examples:  greater tubercle of the humerus, costal tubercle

Tuberosity

• large, rounded elevation

• examples:  calcaneal tuberosity, ischial tuberosity of pelvis

Foramen

• passage through a bone

• examples:  obturator foramen, foramen magnum

Fossa

• hollow or depressed area

• examples:  olecranon fossa of the humerus, iliac fossa of the pelvis, hypophyseal (pituitary) fossa of the skull

Groove

• elongated depression or furrow

• examples:  radial groove of the humerus, groove for the sigmoid sinus in the skull

Cartilage

• Located at strategic points in the skeleton

• Cartilage provides flexible support of tissues in locations such as the external nose and the thoracic cage 

• In the joints, cartilage withstands great pressures and distributes the forces generated by movement fairly evenly across its surface

• During growth, cartilage provides a means of tissue expansion in the presence of direct pressure

Joints

A joint, or articulation, is defined as the union between two or more bones.  There are three main categories of joints

Fibrous Joints

• Bones are physically connected to one another by fibrous connective tissue

• Little, if any, movement occurs at these joints

• examples include the sutures of the skull, the ligamentum flavum of the vertebral column, and the interosseous membrane between the tibia and fibula

Cartilaginous Joints

• In these joints, bones are physically connected to one another by cartilage

• examples include — intervertebral (IV) discs and the pubic symphysis, both of which are formed of fibrocartilage, and the epiphyseal plates (growth plates) of bones, which are formed of hyaline cartilage

• Little or no movement is typically allowed at these joints

Synovial Joints

• Most of the joints of the body are synovial joints

• Bones are not physically connected to one another at all —> their cartilage-covered articulating surfaces are held apposed to one another by associated connective tissues and muscles

• Synovial joints are highly movable joints

The articulating surfaces (facets) of the bones in a synovial joint (and there may be more than just two) are covered in…

articular cartilage – a specialized form of hyaline cartilage

The ends of the bones entering into a synovial joint are enclosed within a…

connective tissue capsule

This fibrous joint capsule encloses a…

sealed joint cavity that contains synovial fluid – a colorless, transparent, viscous fluid that both nourishes and lubricates the articular cartilage

some synovial joints contain…

• accessory ligaments — intrinsic and extrinsic (collateral) ligaments

• articular discs

Intrinsic Ligaments

• Part of, or within (between the fibrous capsule and the synovial membrane) the fibrous joint capsule

• Examples of intrinsic ligaments include iliofemoral, pubofemoral, and ischiofemoral ligaments of the hip joint, and the lateral ligament of the temporomandibular joint

Extrinsic (collateral) Ligaments

• outside and independent of the fibrous capsule

• Examples of extrinsic ligaments include the lateral and medial collateral ligaments of the elbow and knee

Articular discs, labra (sing. = labrum), and menisci (sing. = meniscus)

these structures, usually composed of fibrocartilage, divide or partially divide joint cavities, and modify the shape of articulating surfaces so as to enhance joint stability