The Skeletal System

The Skeletal System

The bodily system that consists of the bones, their associated cartilages, and the joints, and supports and protects the body, produces blood cells, and stores minerals.

Scapula

"Scapula" is the technical name for the shoulder blade. It is a flat, triangular bone that lies over the back of the upper ribs. The rear surface can be felt under the skin. It serves as an attachment for some of the muscles and tendons of the arm, neck, chest and back and aids in the movements of the arm and shoulder. It is well padded with muscle so that great force is required to fracture it. The back surface of each scapula is divided into unequal portions by a "spine." This spine leads to a "head," which bears two processes - the "acromion process" that forms the tip of the shoulder and a "coracoid process" that curves forward and down below the clavicle (collarbone). The acromion process joins a clavicle and provides attachments for muscles of the arm and chest muscles. The acromion is a bony prominence at the top of the shoulder blade. On the head of the scapula, between the processes mentioned above, is a depression called the "glenoid cavity." It joins with the head of the upper arm bone (humerus).

Spine, Vertebra and Disk

The spine is a column of bone and cartilage that extends from the base of the skull to the pelvis. It encloses and protects the spinal cord and supports the trunk of the body and the head. The spine is made up of approximately thirty-three bones called "vertebrae." Each pair of vertebrae is connected by a joint which stabilizes the vertebral column and allows it to move. Between each pair of vertebrae is a disk-shaped pad of fibrous cartilage with a jelly-like core, which is called the "intervertebral" disk - or usually just the "disk". These disks cushion the vertebrae during movement. The entire spine encloses and protects the spinal cord, which is a column of nerve tracts running from every area of the body to the brain. The vertebrae are bound together by two long, thick ligaments running the entire length of the spine and by smaller ligaments between each pair of vertebrae. The anterior longitudinal ligament consists of strong, dense fibers, located inside the bodies of the vertebrae. They span nearly the whole length of the spine, beginning with the second vertebrae (or "axis"), and extending to the sacrum. The ligament is thicker in the middle (or "thoracic" region). Some of the shorter fibers are separated by circular openings, which allow for the passage of blood vessels. Several groups of muscles are also attached to the vertebrae, and these control movements of the spine as well as to support it. Quasimodo, the central character of Victor Hugo's novel, "The Hunchback of Notre Dame," is probably the most famous of all real or fictional sufferers of "kyphosis," an abnormal, backward curvature of the spine.

Ligaments of The Sacrum

The sacrum, at the base of the vertebral column, is wedged between the coxal bones of the pelvis and is united to them by fibrocartilage at the "sacroiliac joints." The weight of the body is transmitted to the legs through the pelvic girdle at these joints. The fibrocartilage at the front of the sacrum, which joins it to the ilium is called the "anterior sacroiliac ligament"; at the back, it is called the "posterior sacroiliac ligament." The coccyx, or tail bone, is attached by ligaments to the margins of the sacral hiatus (opening at the tip of the sacrum). These ligaments are called the "anterior" and "posterior sacrococcygeal ligaments." The "sacrospinous ligament" is a thin, triangular sheet attached by its broad base to the lateral margins of the sacrum and coccyx, where its fibers are intermingled with those of the intrapelvic surface of the "sacrotuberous ligament," and by its apex to the spine of the ischium. The sacrotuberous ligament is a broad, flat fan-shaped complex of fibers stretching from the lower back spine of the ilium, the 4th and 5th transverse tubercles and the caudal part of the lateral margin of the sacrum and coccyx to the inner margin of the tuberosity of the ischium. The "iliolumbar ligament" connects the lower lumbar vertebra process to the ilium (the largest portion of the coxal bone).

Lower Leg And Ankle Ligaments

The fibula is the long, slender bone beside the tibia. Its ends are slightly enlarged into an upper "head" and a lower "lateral malleolus." The head meets the fibula just below the lateral condyle; but it does not enter into the knee joint and does not bear any body weight. The ligaments which join the fibula to the front of the fibula are called the "anterior tibiofibular ligaments," and the "posterior tibiofibular ligaments" join them behind the knee. The lateral malleolus is joined to the ankle by the "anterior talofibular ligaments," and the "posterior talofibular ligaments." These ligaments form a prominence on the side of the ankle.

Articular Capsules

"Articular capsules" surround the joints between the cartilages of the true ribs and the sternum (breastbone). They are very thin and intimately blended with the radiate sternocostal ligaments, and are strengthened at the upper and lower parts of the articulations by a few fibers which connect the cartilages to the side of the sternum.

Sternum

The "sternum" is the medical name for the breastbone, a long, narrow, flat plate that forms the center of the front of the chest. It develops in three parts: an upper portion, or "manubrium," a middle "body," and a lower "xiphoid process" that projects down. The xiphoid process begins as a piece of cartilage. It slowly hardens into bone until, by middle life, it is usually fused to the body of the sternum. The sides of the manubrium and the body are notched where they unite with costal cartilages. It also joins the clavicles (shoulder blades) on its upper border. It usually remains a separate bone until middle age or later, when it fuses to the body of the sternum. The sternum is very strong and requires great force to fracture. The main danger in this type of injury is not the fracture itself, but the chance that the broken bone may be driven into the heart, which lies just behind it.

Tarsal Bones

The foot consists of an ankle, an instep, and five toes. The ankle is composed of seven "tarsal bones," forming a group called the tarsus. These bones are arranged so that one of them, the "talus," can move freely where it joins the tibia and fibula (lower leg bones). This is known as the "head of the talus." The remaining tarsal bones are bound firmly together, forming a mass on which the talus rests. The other bones which compose the tarsus are the "calcaneus," the largest of the ankle bones; the "talus;" the "navicular," the "cuboid," the "lateral cuneiform," the "intermediate cuneiform," and the "medial cuneiform." The "calcaneus," or heel bone, is located below the talus where it projects backward to form the base of the heel. It helps to support the weight of the body and provides an attachment for muscles that move the foot.

 

 

 Carpal Bones

The skeleton of the wrist consists of eight small "carpal bones" that are firmly bound in two rows of four bones each. The resulting mass is the "carpus." The eight bones are the "pisiform," "triangular" or "triquetrum," the "pisiform," "lunate," and "scaphoid" on the upper end of the wrist, where it connects with ligaments and the lower arm bones, and the "hamate," "capitate," "trapezoid," and "trapezium" on the lower side of the hand by the "metacarpals," or first joint of the fingers.

Condyles of The Humerus

At the lower end of the humerus (upper arm bone) and the femur, there are two smooth condyles (rounded processes of the bone): a knob-like "capitulum" on the lateral side and a pulley-shaped "trochlea" in the middle. The capitulum unites with the radius (smaller lower arm bone) at the elbow, and the trochlea is a notch which joins ligaments to the head of the ulna (larger lower arm bone). Above the condyles on either side are "epicondyles," which provide attachments for muscles and ligaments of the elbow. The one toward the center of the arm is the "medial epicondyle," and the one to the side is the "lateral epicondyle."

Capsule of The Shoulder Joint

A "capsule" is a membrane or sac enclosing a body part, usually a joint. "Capsular ligaments" are surrounded and reinforced by muscles tendons, and ligaments, which are largely responsible for keeping the adjoining parts together. The "joint capsule" of the shoulder is attached along the outside ring of the genoid cavity and the anatomical neck of the humerus. Although it completely covers the joint, the capsule is very loose and by itself would be unable to keep the bones of the joint in close contact without the aid of the fibers around it. The joint capsule of the elbow has sides which are thickened by ulnar and radial collateral ligaments. The front surface of the capsule is reinforced by fibers from a muscle (brachialis) in the upper arm.

Clavicle

The clavicle is the collarbone. There are two of these bones, each curved al little like an "f," that join the top of the breastbone (sternum) to the shoulder blade (scapula). The clavicles support the arms and transmit force from the arms into the central skeleton.

The Coccyx

The coccyx (or tail) is the lowest part of the vertebral column and is attached by ligaments to the margins of the sacral hiatus. When a person is sitting, pressure is exerted on the coccyx, and it moves forward, acting sort of like a shock absorber. Sitting down with too great a force may cause the coccyx to be fractured or dislocated.

Ligaments

A ligament is a tough band of white, fibrous, slightly elastic tissue. This is an essential part of the skeletal joints; binding the bone ends together to prevent dislocation and excessive movement that might cause breakage. Ligaments also support many internal organs; including the uterus, the bladder, the liver, and the diaphragm and helps in shaping and supporting the breasts. Ligaments, especially those in the ankle joint and knee, are sometimes damaged by injury. A "torn" ligament usually results from twisting stress when the knee is turned while weight is on that particular leg. Minor sprains are treated with ice, bandages and sometimes physical therapy, but if the ligament is torn, the joint may be placed in a plaster cast to allow time to heal or it may require surgical repairs. If a ligament is made up of several thick bands of fibrous branches, it is called a "collateral ligament." The word "ligament" comes from the Latin word, "ligamentum," meaning a band or tie.

Coracohumeral Ligament

The "coracohumeral ligament" is composed of a broad band of connective tissue that connects the coracoid process of the scapula (shoulder blade) to the greater tubercle of the humerus (upper arm bone). Its function is to strengthen the superior portion of the joint capsule. The "coracoclavicular ligament" connects the coracoid process to the clavicle (collarbone).

The Ribs

Ribs are flat, curved bones that form the framework of the chest and make up a cage to protect the heart, lungs and other upper organs. There are twelve pairs of ribs, each joined at the back of the cage to a vertebra in the spine. Between the ribs, and attached to them, are thin sheets of muscle that help to expand and relax the chest during breathing. The spaces between the ribs contain nerves and blood vessels. There are seven true ribs attached to the sternum (breastbone) directly by their costal cartilages. The remaining five pairs are called "false ribs," because their cartilages do not reach the sternum directly. Instead, the cartilages of the upper three false ribs join the cartilages attached to the ribs above, while the last rib pairs have no cartilaginous attachments to the sternum at all. These last two pairs are sometimes called "floating" ribs." The front ends of the upper ribs are linked to the sternum by cartilage, which is tough, thick and elastic. It has no blood supply of its own, but obtains nutrients from tissue fluid. The ligaments which join the costal cartilages of the ribs to the clavicle (collarbone) are called the "costoclavicular ligaments."

Extensor Retinaculum

A structure called the "extensor retinacula" consists of a group of heavy connective fibers in the tissues of the wrist. It connects the lateral margin of the radius (shorter forearm bone) with the inside border of the ulna (longer forearm bone) and with certain bones of the wrist. The retinaculum gives off branches of connective tissue to the underlying wrist bones, creating a series of sheath-like compartments through which the tendons of the extensor muscles pass to the wrist and fingers. As in the case of the wrist, the tissue formations in various regions of the ankle is thickened to form retinacula. Toward the front, for example, extensor retinacula connect the tibia and fibula (lower leg bones) as well as the calcaneus (Achilles tendon) and tissue of the sole of the foot. These retinacula form sheaths for tendons crossing the front of the ankle.

Deltoid Ligament

The deltoid ligament is a ligamentous structure that is triangular in shape and attaches to the medial malleolus of the tibia to the navicular, calcaneus, and talus (anteriorly and posteriorly) bones of the tarsus.

Phalanges

The phalanges are the small bones that make up the skeleton of the fingers, thumb and toes. Each finger and smaller toe has three phalanges; the thumb and big toe each have two. The phalange nearest the body of the hand or foot is call the "proximal" phalange; the one at the end of each digit is the "distal" phalange; and, of course, when there are three, the middle one is called the "middle" phalange.

Ligaments of The Foot

The instep is made up of five, elongated metatarsal bones that join the tarsus (the seven ankle bones). The distant heads of these bones form the ball of the foot. The tarsals and metatarsals are arranged and bound by ligaments to form the arches of the foot. A "tarsometataral ligament" joins the tarsus to the metatarsal bone. A longitudinal arch extends from the "posterior longitudinal ligament" at the heel to the "anterior longitudinal ligament" of the toe, and a transverse arch ("dorsal metatarsal ligament") stretches across the foot. These arches provide a stable, spring base for the body. At times, the tissues that bind the metatarsal become weakened and produce fallen arches or "flat feet." The "plantar ligaments" are in the sole of the foot. The "plantar calcaneonavicular ligament" joins the "navicular" bone in the ankle to the "calcaneus," or heel bone; the "plantar cuboideonavicular ligament" joins the navicular bone to the "cuboid" bone of the ankle. The "plantar metatarsal ligaments" bind the instep across the sole of the foot.

Femur

The "femur" is the thigh bone, the longest bone in the body. The lower end joins the tibia (shin) to form the knee joint. The upper end is rounded into a ball (or "head" of the femur) that fits into a socket in the pelvis to form the hip joint. Just below the head is a constriction, or neck, and two large processes - an upper, lateral "greater trochanter" and a lower, medial "lesser trochanter." These processes provide attachments for muscles of the legs and buttocks. Femoral condyles are large, rounded bumps on the distal end of the femur. They articulate (come in contact) with the condyles of the tibia and form part of the knee joint. The neck of the femur gives the hip joint a wide range of movement, but it is a point of weakness and a common site of fracture.

Fibular Collateral Ligament

The "fibular collateral ligament" consists of a strong, round cord located between the lateral condyle of the femur (thighbone) and the head of the fibula at the knee joint.

Fibula

The fibula is the outer and thinner of the two long bones of the lower leg. It is much narrower than the other bone (the shin), to which it runs parallel and to which it is attached at both ends by ligaments. The upper end of the fibula does not reach the knee, but the lower end descends below the shin and forms part of the ankle. Its main function is to provide attachment for muscles. It doesn't give much support or strength to the leg, which explains why the bone can safely be used for grafting onto other bones in the body.

Humerus

The humerus is the bone of the upper arm. The smooth, dome-shaped head of the bone lies at an angle to the shaft and fits into a shallow socket of the scapula (shoulder blade) to form the shoulder joint. Below the head, the bone narrows to form a cylindrical shaft. It flattens and widens at the lower end and, at its base, it joins with the bones of the lower arm (the ulna and radius) to make up the elbow. Some people say the "funny bone" is named because it is next to the humerus. It really isn't a bone at all, but is the ulnar nerve, which passes under a prominence of the humerus, where it is vulnerable. To find the funny bone, put the point of the right elbow on a table. Above and to the left of the point is a big knob. When it is struck, the blow pushes the nerve against this knob, causing temporary paralysis. It is no laughing matter, but it is a "funny" feeling.