Skeleton: Overview

The skeletal system consists of the bones and joints, along with cartilage and ligaments that occur at the joints.

Function of the Skeleton

The skeleton has 5 different functions.

The skeleton supports that body.  The bones of the lower limbs support the entire body when we are standing and the pelvic girdle supports the abdominal cavity.

The skeleton protects soft body parts.  The bones of the skull protect the brain; the rib cage protects the heart and lungs.

The skeleton produces blood cells.  All bones in the fetus have red bone marrow that produces blood cells.  In the adult, only certain bones produces blood cells.

The skeleton stores minerals and fats.  All bones have a matrix that contains calcium phosphate, a source of calcium ions and phosphate ions in the bloods.  Fat is stored in yellow bone marrow.

The skeleton, along with the muscles, permits flexible body.  While articulations (joints) occur between all the bones, we associate body movements in particular with the bones of the limbs.

Anatomy of Long Bones

Bones are classified according to their shape.  Long bones are longer than they are wide.  Short bones are cube shaped- that is their lengths and widths are about equal.  Flat bones, such as those of the skull, are plate-like with broad surfaces.  Irregular bones have varied shapes that permit connections with other bones.  Round bones are circular in shape.

A long bone can be used to illustrate certain principles of the bone anatomy.  The bone is enclosed in a tough, fibrous, connective tissue covering called the periosteum, which is continuous with the ligaments and tendons that anchor bones.  At both ends of a long bone is an expanded portion called an epiphysis; the portion between the epiphyses is called the diaphysis.  The diaphysis is not solid but has a medullary cavity containing yellow marrow.  Yellow marrow contains large amounts of fat.  The epiphyses contains spongy bone.  Beyond the spongy bone are a thin shell of compact bone and, finally, a layer of hyaline cartilage called the articular cartilage.  Articular cartilage is so named because it occurs where bones articulate.  Articuation is the joining together of the bones at a joint.

Compact Bone

Compact bone, or dense bone, contains many cylinder shaped units called osteons.  The osteocytes (bone cells) are in tiny chambers called lacunae that occur between concentric layers of matrix called lamellae.

Spongy Bone

Spongy bone, or cancellous bone, contains numerous bony bars and plates, called trabeculae. Spongy bone is lighter than compact bones, but is still made for strength.

In infants, red bone marrow, a specialized tissue that produces blood cells, is found in the cavities of most bones. In adults, red blood cells, is found in the cavities of most bones. In adults, red blood cells formation, called hematopoiesis, occurs in the spongy bone of the skull, ribs, sternum, and vertebrae, and in the ends of the long bone.

Bone Growth and Repair

There are several different types of cells are involved in bone growth and repair:

Osteoprogenitor cells are unspecialized cells present in the inner portion of the periosteum, in the endosteum, and in the central canal of compact bone.

Osteoblasts are bone-forming cells derived from osteroprogenitor cells. They are responsible for secreting the matrix characteristic in bone.

Osteocytes are mature bone cells derived from osteoblast. Once the ostoblasts are surrounded by matrix, they become the oseocycle in bone.

Osteooclast are thought to be derived from monocytes, a type of white blood cell present in red bone marrow.

Bone Development and Growth

The term ossification refers to the formation of bone. The bones of the skeleton form during embryonic development in two distinctive ways- intramembranous ossification and endochondral ossification.

The intramembranous ossification, bone develops between sheets of fibrous connective tissue. Most of the bones of the human skeleton form by endochondral ossification.

After birth, the epiphyses of a long bone continue to grow, but soon secondary ossification centers appear in these regions. Here spongy bone forms and does not break down. A band of cartilage called an epiphyseal plate remains between the primary ossification center and each secondary center.

Remodeling of Bones

In an adult, bone is continually being broken down and built up again. Osteoclast derived from monocytes in red bone marrow break down bone, remove worn cells, and assist in depositing calcium in the blood. After a period of about three week, the ostroclast disappear, and the bone is repaired by the work of osteoblast. As they form, new bone, osteoblast take calcium from the blood. Eventually some of these cells get caught in the mineralized matrix they secrete and are converted to osteocytes, the cells found within the lacunae of osteons.

Bone repair

Repair of a bone is required after it breaks, or fractures. Bone repair occurs in a series of four steps:

1.Hematoma. Within six to eight hours after a fracture, blood escapes from ruptured blood vessels and forms a hematoma (mass of clotted blood) in the space between the broken bones.

2.Fibrocartilaginous callus. Tissue repair begins, and fibrocartilage fills the space between the ends of the broken bone for about three weeks.

3.Boney callus. Osteoblasts produce trabeculae of spongy bone and convert the fibrocartilaginous callus to a bony callus that joins the broken bones together and lasts about three of four months.

4.Remodeling. Osteoblasts build new compact bone at the periphery, and osteoclasts reabsorb the spongy bone, creating a new medullary cavity.

Axial Skeleton

The skeleton is divided into the axial skeleton and the appendicular skeleton. The tissue of the axial and appendicular skeletons are bone (both compact and spongy), cartilage, and dense connective tissue, a type of fibrous connective tissue.

Skull

The skull is formed by the cranium and the facial bones. These bones contain sinuses, air spaces lined by mucous membranes, that reduce the weight of the skull and give thev voice a resonant sound. The paranasal sinuses empty into the nose and are named for their locations. They include the maxillary, frontal, sphenoidal, and ethmoidal sinuses. The two mastoid sinuses drain into the middle ear. Mastoiditis, a conditions that can lead to deafness, is an inflammation of these sinuses.

Symptoms

-ear pain or discomfort

-earache

-pain behind the ear

-redness of the ear or behind the ear

-fever, may be high or spike (have sudden high increases)

-headache

-drainage from the ear

Signs and tests

An examination of the head may indicate mastoiditis. A skull X-ray or head CT scan or CT of the ear may show an abnormality in the mastoid bone. A culture of drainage from the ear may show bacteria.

Treatment

Mastoiditis may be difficult to treat because it is difficult for medications to reach deep enough into the mastoid bone. It may require repeated or long-term treatment. Antibiotics by injection, then antibiotics by mouth are given to treat the infection.

Surgery to remove part of the bone and drain the mastoid may be needed if antibiotic therapy is not successful. Surgical drainage of the middle ear through the eardrum may be needed to treat the underlying middle ear infection.

Bones of the Cranium

The cranium protects the brain and is composed of eight bones. These bones are separated from each other by immovable joints called sutured. Newborns have membranes regions called fontanels, where more than two bones meet. The largest of these is the anterior fontanel, which is located where the two parietal bones meet the two parts of the frontal bone. The fontanels permit the bones of the skull of shift during birth as the head passes through the birth canal.

Frontal Bone One frontal bone forms for forehead, a portion of the nose, and the superior portions of the orbits (bony sockets of the eyes).

Parietal Bones Two parietal bones are just posterior to the frontal bone. They form the roof of the cranium and also help form its side.

Occipital Bone One occipital bone forms the most posterior part of the skull and the base of the cranium. The spinal cord

Temporal Bones Two temporal bones are just inferior to the parietal bones on the sides of the cranium.

Spheniod Bone The sphenoid bone helps form the sides and floor of the cranium and the rear wall of the orbits.

Ethmoid Bone The ethmoid bone I anterior to the sphenoid bone and helps form the floor of the cranium.

Bones of the Face

Maxillae The two maxillae form the upper jaw

Alveolar process-the alveolar processes contain the tooth sockets for teeth: incisors, canines, premolars, and molars.

Palatine process-the left and right palatine processes form the anterior portion of the hard palate (roof of the mouth)

Palatine Bones The two palatine bones contribute to the floor and lateral wall of the nasal cavity. The horizontal plates of the palatine bones form the posterior portion of the hard palate.

Zygomatic Bones Two zygomatic bones form the sides of the orbits. They also contribute to the “cheekbones.”

Lacrimal Bones The two small, thin lacrimal bones are located on the medial walls of the orbits. A small opening between the orbit and the nasal cavity serves as a pathway for a duct that carries tears from the eyes to the nose.

Nasal Bones The two nasal bones are small, rectangular b ones that form the bridge of the nose. The ventral portion of the nose is cartilage, which explains why the nose is not seen on a skull.

Vomer bone The vomer bone joins with the perpendicular plate of the ethmoid bone to form the nasal septum..

Inferior Nasal Conchae The two inferior nasal conchae are thin, curved bones that form a part of the inferior lateral wall of the nasal cavity.

Mandible The mandible, or lower jaw, is the only movable portion of the skull. The horseshoe-shaped front and horizontal sides of the mandible, referred to as the body, form the chin.

Hyoid Bone

The U-shaped hyoid bone is located superior to the lrynx in the neck. It is the only bone in the body that does not articulate with another bone. Instead, it is suspended from the styloid processes of the temporal bones by the stylohyoid muscles and ligaments. It anchors the tongue and serves as the site for the attachment of several muscles associated with swallowing.

Vertebral Column (Spine)

The vertebral column extends from the skull to the pelvis. It consists of a series of separate bones, and vertebrae, separated by pads od fibrocartilage called the intervertebral disks.

Curvature in the spine

Vertebral Column, extends from the skull to the pelvis.

Vertebrae, consists of a series of separate bones.

Intervertebral disks, separated by pads fibrocarilage.

Lordosis, an abnormal exaggerated lumbar curvature.

Kyphosis, an in creased roundness of the thoracic curvature.

Scoliosis, an abnormal lateral (side to side) curvature.

Intervertebral Disks

The fibrocartilaginous intervertebral disks located between the vertebrae act as a cushion. They prevent the vertebrae from grinding against on another and absorb shock caused by such movements as running, jumping, and even walking.

Herniated disk, unfortunately, these disks become weakened with age, and can slip or even rupture.

Vertebrae

A typical vertebra has an anteriorly placed boy and a posteriorly placed vertebral arch. The vertebral arch forms the wall of a vertebral foramen.

Atlas and Axis, the atlas supports and balances the head and the axis has an odontoid process (also called the dens that projects in to the ring of the atlas.

Sacrum and Coccyx, the sacrum srticulates with the pelvic girdle and forms the posterior wall of the pelvic cavity and the Coccyx or tailbone, is the last part of the vertebral column.

The Rib Cage

The rib cage sometimes called the thoracic cage, is composed of the thoracic vertebrae, ribs and associated cartilages, and sternum.

The Ribs

There are twelve pairs of ribs. All twelve pairs connect directly to the thoracic vertebrae in the back.

The Sternum

The sternum, or breast bone, is a flat bone that has the shape or a blade.

Pectoral Girdle

The pectoral girdle (shoulder girdle) contains four bones: two clavicles and two scapulae.

Clavicles (collarbones)

Are slender and S- shaped.

Scapulae

Also called the shoulder blades, are broad bones that some what resemble triangles.

Acromion process, which articulates with the clavicles and provides a place of attachment for arm and chest muscles.

Coracoid process, which serves as place of attachment for arms and chest muscles.

Glenoid cavity, which articulates with the head of the arm bone (humerous). The pectoral girdle’s flexibility is also a result of the glenoid cavity being smaller than the head of humerus.

Upper Limb

The upper limb includes the bones of the arm (humerus), the forearm (radius and ulna), and the hand (carpals, metacarpals, and phalanges).

Humerus

Is the bone of the arm It is a long bone with the following features at the proximal end.

Head, which articulates with the glenoid cavity of the scapula.

Greater and Lesser tubercles, which provide attachments for muscles that, move the arm and shoulder.

Intertubercular groove, which holds a tendon form biceps brachii, a muscle of the arm.

Deltoid Tuberosity, which provides an attachment for the deltoid, a muscle that covers the shoulder joint.

Capitulum, a lateral condyle that articulates with the head of the radius.

Trochlea, a spool-shaped condyle that articulates with the head of the radius.

Coronoid fossa, a depression for a process of the ulna when the elbow is flexed.

Olecranon fossa, a depression for a process of the ulna when the elbow is extended.

Radius

The radius and ulna are bones of the forearm. The radius is on the alteral side of the forearm (the thumb side).

Head, which articulates with the capitulum of the humerus and fits into the radial notch of the ulna.

Radial tuberosity, which serves as a place of attachment for a tendon from the biceps brachii.

Ulnar notch,which articulates with the head of the ulna.

Styloid process, which serves as a place of attachment for ligaments that run to the wrist.

Ulna

The ulna is the longer bone of the forearm. Proximally, the ulna has the following features:

Coronoid Process

Olecranon Process

Trochlear Notch

Radial Notch

Head

Styloid

Hand

Each hand has a wrist, a palm, and five finger, or digits. The wrist, or carpus, contains eight small carpal bones, tightly bound by ligaments in two rows of four each.

We use our hand for most of everything that we do. It is one place in the body that most likely is guaranteed to get arthritis.

When something happens to your hand make sure you get to your family doctor right away for x-rays. If you don’t your hand may not heal right and you could have pain for the rest of your life.

Pelvic Girdle

The pelvic girdle contains two coxal bones, as well as the sacrum and coccyx. The strong bones of the pelvic girdle are firmly attached to one another and bear the weight of the body,

Coxal bones

The coxal bone has 3 parts:

Ilium-the largest part of the coxal bone

Ischium-the most inferior part of the coxal bone

Pubis-the anterior part of the coxal bone

False and True Pelvises

The false pelvis is the portion of the truck bounded laterally by the flared parts of the ilium. The true pelvis, which is inferior to the false pelvis, is the portion of the truck bounded by the sacrum, lower ilium, ischium, and pubic bones.

Sex differences

Female and male pelvises usually differ in several ways:

1. Female iliac bones are more flared than those of the male; therefore, the female has broader hips.

2. The female pelvis is wider between the ischial spines and the ischial tuberosities.

3. The female inlet and outlet of the true pelvis are wider.

4. The female pelvic cavity is more shallow, while the male pelvic cavity is more funnel shaped.

5. Female bones are lighter and thinner.

6. The female pubic arch (angle at the pubic symphysis) is wider.

Lower Limb

The lower limb includes the bones of the thigh, kneecap, the leg, and the foot.

Femur

The femur, or thighbone, is the longest and strongest bone in the body.

The femur has 10 different features:

Head

Greater and lesser trochanters

Linea aspera

Medial and lateral epicondyles

Lateral and medial condyles

Patellar surface and patella

Tibia

The tibia is the medial to the fibula. It is thicker than the fibula and bears the weight from the femur, with which it articulates.

It has the following features:

Medial and Lateral condyles

Tibial tuberosity

Anterior crest

Medial malleolus

Fibula

The fibula is lateral to the tibia and is more slender. It as a head that articulates with the tibia just below the lateral condyle.

Foot

Each foot has an ankle, and instep, and five toes. The ankle has seven tarsal bones; together they are called the tarsus. Only one of the seven bones, the talus, can move freely where it joins the tibula and fibula.

The largest of the ankle bones is the calcaneus, or heel bone. It support the weight of the body. The instep has five elongated metatarsal bones. The distal ends of the metatarsals form the ball of the foot. Along with the tarsals, thes bones form the arches of the foot. (longitudinal and transverse), which give spring to a person’s step. If the ligaments and tendons holding these bones together weaken, fallen arches, or “flat feet,” can result. The toes contain the phalanges. The big toe has only tow phalanges, but the other toes have three each.

Joint (Articulations)

Bones articulate the joints, which are often classified according to the amount of movement the allow.

Fibrous joint, are immoveable. Fibrous connective tissue joins bone to bone.

Cartilaginous joints, are slightly movable. Fibrocartilage is located between two bones.

Synovial Joints, freely movable. In these joints, the bones do not come in contact with each other.

Fibrous Joints

Some bones, such as those that make up the cranium, are sutured together by a thin layer of fibrous connective tissue and are immovable.

Coronal suture, between the parietal bones and the frontal bone.

Lambdoidal suture, between the parietal bones and the occipital bone.

Squamosal suture, between each parietal bone and each temporal bone.

Cartilaginous Joints

Slightly movable joints are those in which the bones are joined by fibrocartilage. The ribs are joined to the sternum by costal cartilages.

Synovial Joints

All synovial joints are freely movable.

Effects of Aging

When most people age they tend to get rheumatoid arthritis, the synovial membrane becomes inflamed and grows thicker cartilage, possibly due to an autoimmune reaction.