General Anatomy/Skeletal System

Skeleton

Introduction

There are 206 bones in the human body. A bone is made up of several tissues which work together such as bone, osseous tissue, cartilage, dense connective tissues, epithelium, adipose tissue and nervous tissue. For this reason each individual bone is classified as an organ.

Bone tissue is complex and has dynamic living qualities. The entire framework of bones, joints, cartilages and ligaments constitute the skeletal system. The skeletal system provides an internal framework for the body whilst protecting the delicate internal organs, and provides anchorage for skeletal muscles so that muscle contraction is possible, which in turn creates movement.

Bone Function

The functions of the skeletal system entail support, protection, movement, mineral storage and blood cell formation. The bones provide an internal framework which allow support and anchorage for soft organs. The leg bones support the upper body when standing and the ribs extend from the spinal cord to support thoracic contents. The brain and all internal components of the spinal cord are encased in bone and vital organs are given essential protection against accidental damage by external forces. The body has a wide and flexible range of movement because the skeletal muscles attach to bones via tendons. Bones store fat and essential minerals like calcium and phosphorus and are also the site of red blood cell formation. The bone marrow inside the hip bones produces most of the white blood cells.

A comprehensive diagram of human hematopoiesis

Bone Types

The bones in the human body can be classified into four main shapes with their names providing an indication of their shape. Long bones - longer than wide with a shaft and 2 ends. They are mostly made of compact bone but a significant amount is spongy. Nearly all the limb bones are long bones. Short bones such as the wrist and ankle are more cube shaped and are mostly spongy bone matter. Flat bones like the sternum, skull and ribs are flatter and thinner with a slight curve. Irregular bones do not fall into any of the above caterogries and include bones such as the vertebrae and hip.

Divisions of the skeleton

The skeleton is divided into two (2) main sections, the 'Axial' and the 'Appendicular'.

Axial Skeleton The axial part of the skeleton is made up of 80 bones, though the main bones are the cranial (skull) and facial bones, the vertebral column (spine) and the bony thorax (ribs and sternum), although one bone that is often forgotten is the Hyoid bone, which is situated just above the larynx. The Axial Skeleton picked up its name as it forms the 'longitudinal axis' of the body. The cranial and facial bones work together but are considered to be separate parts. The cranial bones include the frontal bone, parietal, temporal and occipital. Whereas the facial bones are made up of many smaller bones, the main ones include the mandible, maxilla, zygomatic, lacrimal, nasal, vomer, inferior nasal conchae, and the ethmoid bones. The vertebral column is made up of thirty-three (33) vertebrae, which are categorized in five (5) sections. These are the Cervical (7 vertebrae), Thoracic (12 vertebrae), Lumbar (5 vertebrae), Sacrum (5 fused vertebrae) and Coccyx (4 fused vertebrae). Lastly is the bony thorax, this is made up of the ribs and sternum. The bony thorax has twelve (12) ribs (7 true and 5 false, 2 of which are called 'floating ribs'), the ribs are fixed to the spinal column and are there to protect the body's vital organs such as the heart, lungs and kidneys. The sternum is a fusion of three (3) bones, the jugular notch, sternal angle and xiphisternal joint.

Appendicular Skeleton The Appendicular skeleton is made up of all 126 other bones in the body. Primarily it includes the shoulder girdle (including clavicle and scapula), arms (humerus, radius, ulna, carpals, metacarpals, and phalanges), the pelvic bones (pelvic girdle, including the ilium), and the legs (femur, patella, fibula, tibia, tarsals, metatarsals and phalanges). Each shoulder girdle (pectoral girdle) consists of a scapula and a clavicle (collarbone). If the clavicle is broken, the whole shoulder region will collapse, as the girdle acts as a supporting structure. The pelvic Girdle mainly consists of two 'coxal bones' (hips), which are formed by the ilium, pubic bone, ischium, iliac crest, sacroiliac joint, pelvic brim, ischial spine, acetabulum and pubic symphysis, the bones are all fused together making up a single hip.

Microscopic Structure

The structure unit within the compact bone is the Haversian system. The Lamella column like matrix tube made mostly of collagen which gives bone their strength and allow weight bearing. There is central canal which provides blood and nerve supply to the cell. A channel within each cell provides blood supply and nerve fibres that support the cell. Volkmann's canals are channels that assist with blood and nerve supply from the periosteum to the Haversian canal. Osteocytes are mature bone cells and are found within Lacunae. The Canaliculi are hair-like canals and allow all the bone cells to receive their nutrient supply.

Bone Membranes

Periosteum is a double-layered protective member covering the shaft or diaphysis. The outer fibrous layer is dense, irregular connective tissue. Its inner osteogenic layer composed of Osteoblasts (bone forming cells, responsible for new bone growth and repair) and Osteoclasts(bone-destroying cells, important for bone restoration). The delicate membrane covering the internal surface of the bone is called Endosteum.

Articulation

Articulations, also known as joints, have two major functions in the body. They hold bones together whilst allowing the bones to move. A joint can be classified in two ways, by its function and its structure. Structurally, there are the fibrous, cartilaginous and synovial joints, being classified based on whether fibrous, cartilage, or a joint cavity separated the bony regions of the joint.

Fibrous joints

These are the bones which are connected by fibrous tissues. In sutures the bones have irregular edges and they are bound tightly together by connective fibrous tissue.

Cartilaginous joints

These are bones that are connected by cartilage.

Synovial joints

Synovial Joint

Are the joints where the articulating bone ends are separated by a joint cavity which contains synovial fluid. Synovial joints account for all joints of limbs. All synovial joints have formed distinguishing features, articular cartilage which cover the ends of the bones forming the joint, fibrous articular which are joints surface which are enclosed by a sleeve or capsule of fibrous connective tissue, joint cavity the articular capsule encloses a cavity, reinforcing ligaments which is that the fibrous capsule is usually reinforced with ligaments. Types of the synovial joints are based on the shapes and can be classified as plane, hinge, pivot, condyloid,saddle and ball and socket.

• Plane: articulating surfaces are usually flat to allow slipping and gliding properties.
• Hinge: the cylindrical end of a bone fits into a trough shaped surface of another bone, like that of an elbow joint.
• Pivot: the rounded end of the bone fits into a sleeve or ring of bone.
• Condyloid: is an egg shaped surface of a bone which fits in to a concavity in another.
• Saddle: surface has both convex and concave areas.
• Ball and socket: at the end of a bone there is a spherical head and at the other there is a round socket and this creates the ball and socket movement found in such places as the hip or shoulder.

Common Problems

The skeleton can have many problems, such as fractures, abnormalities and diseases. Below are some common problems associated with the skeketal system, that are still around today.

Abnormal Spinal Curvatures

There are three main types of abnormal curvatures in the spine. They are 'Scoliosis', 'Kyphosis' and 'Lordosis'. In scoliosis, the spine is curved too far to the lateral side, having an unbalanced appearance,also making everyday movement harder. Kyphosis is the abnormal curvature of the spine in the 'cervical region', appearing as an arched back. Lordosis, is the inward curvature of the spine, causing the back to look 'caved in'. Back and chest pain can be present in these conditions, but only show in severe cases.

Fractures

The skeletal system is made of hard bone, yet when enough pressure is exerted, they can break.When a break occurs, it is called a fracture. There are many types of fractures, most are due to extreme twisting of pressure, yet old age can play a large factor, as the bones are weakened and deteriorating, making breakages easier.

Fracture Types

• Comminuted - Where the bone has fractures has resulted into many pieces
• Compressed - Where the bone has been crushed
• Depressed - The fracture leaves an indentation in the remaining bone
• Impacted - Both ends of the fracture are protruding into each other
• Spiral - The bone has a 'ragged' appearance and has been twisted
• Greenstick - The bone only fracture part way through, occurs in children
• Compound - The bone is protruding outside of the body
• Simple - The bone remains inside the body and is cracked straight through

Rickets

Rickets is a disease mainly found in children who do not have a great enough calcium or vitamin D intake. This causes the bones to fail in calcification, making the bones weak and 'bendable'. It can also occur in infants, who are being 'nursed' (breast fed) by their mothers, who do not have a enough vitamin intake themselves.

Slipped Disk

Many people these days suffer from 'slipped disks', this is due to incorrect lifting techniques or sudden movement. The disks related to this are called spinal (or vertebral) disks. Spinal herniation is where the disc protrudes outward from its normal position in the vertebral column. This can cause a great amount of pain as the disk can press on the adjacent nerves.

Authors

Nursing Class of Geraldton, Western Australia

• Jess Herriot
• Mercie Ortiz
• Michelle Stewart
• Jill Saunders
• Hamish Darby