CHAPTER 6 Musculoskeletal System^263
cortex. Blood supply for the bone travels through small blood vessels within
haversian canals located longitudinally within the cortical bone area. The inner layer
is more spongy, cancellous tissue which has spaces filled with marrow. Production
of blood cells occurs within the red bone marrow. Yellow bone marrow is composed
primarily of fat cells. Osteoblasts (bone-building cells) and osteoclasts (bone-resorb-
ing cells) are found in the outer layer of the bone.
Joints are the areas where two or more bones come together. Joints are described
as being freely movable (synovial joints like the hip), partially movable (pelvic
bones), or immovable (suture lines in the skull). Synovial joints are lined with syn-
ovium. This membrane secretes synovial fluid to lubricate the joint and act as a
shock absorber during motion or weight bearing. Synovial joints have a variety of
range of motion including flexion, extension, rotation, circumduction, supination,
pronation, abduction, adduction, inversion, and eversion. Partially movable joints
have specific small amounts of motion that are typical of the joint space. Pelvic
bones and individual joints between the vertebral bones are partially movable. Im-
movable joints are areas where bones come together, but no movement is allowed.
Muscles work in groups, with one set of muscles relaxing as another set con-
tracts to create motion. A small amount of muscle contraction is typical to main-
tain muscle tone within the muscles. Skeletal muscle is striated and voluntary.
Connective tissues are the pieces that hold other parts together. Tendons attach
muscles to bones; ligaments attach bones to bones. Cartilage provides a smooth
surface within joints to ease movement and provide cushioning to weight-bearing
joints. Bursa are small fluid-filled sacs, within joint areas or adjacent to bone
which provide cushioning at points of friction.
Just the Facts
Carpal Tunnel Syndrome
WHAT WENT WRONG?
The median nerve that passes through the carpal tunnel in the anterior wrist is
compressed, resulting in pain and a numb sensation in the thumb, index finger,
middle finger, and lateral aspect of the fourth finger in the hand. This is often the
result of repetitive hand motions and may be work- or hobby-related. Carpal tunnel
syndrome tends to be more common in women.
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