Introduction To The Skeleton

Introduction to the skeleton.
The skeleton is essentially what holds the human body together. However the body has many other functions apart from just shaping.
Support: The skeleton provides a framework for the body that supports itself and keeps organs in their place. The pelvis and leg muscles are thick and strong to support the weight of the body.
Levers: The system uses the bones with joints to provide movement to the body. The bones are held together by ligaments and tendons. The tibia and femur act as levers so a footballer can kick.
Attachment: Bones provide a surface that the muscles can attach to, forming the human shape. A material called periosteum provides a surface that muscle tendons attach to.
Protection: The skeleton encases organs in hard bones to stop them being damaged easily. Bones such as the cranium and ribs protect the body’s vital organs from boxing blows or rugby tackles.
Blood Cell Production: The bone marrow inside the bone allows for production of red and white blood cells. Red blood cells are produced in the long bones of the body. This is crucial for a cyclist who need a lot of oxygen delivered in these red blood cells.
The Axial and Appendicular skeleton There are two types of skeleton which make up the 206 bones that the body has; The axial skeleton and the appendicular skeleton.
Axial skeleton:
Appendicular Skelton:
Skull
Shoulder girdle
Vertebral column
Bones of the arms
Sternum
Hands
Ribs
legs

feet

The axial skeleton consists of 80 bones and forms the head and trunk of the human skeleton. It protects the vital organs such as the brain, heart and lungs.The appendicular skeleton is formed of 126 bones and forms limbs so therefore has a much larger range of movement than the axial skeleton. types of bone:
Compact and Cancellous bone:
Compact bone is the dense rigid bone that forms a cylinder around the cancellous bone to protect it. The bone provides structural support and flexibility to the bone through haversian systems which are a series of canals which create a honeycomb like structure. The cancellous bone is much lighter and weaker but provides flexibility. It is usually found at the ends of long bone or at the joints and it much less dense than compact bone.
There are 5 types of bone.
1) The Long bone such as the femur which produce red bloods cells and allow for movement. Long bones are made out of compact bone and cancellous bone. There are also the epiphyseal plates or growth plates. In the middle of the bone is the medullary cavity. This is hollow and containing red and yellow bone marrow.
2) The Short Bones are as wide as they are long and provide no movement but do provide stability. An example of a short bone is the tarsals in the foot.
3) Flats bones protect a delicate are of the body or allow muscles to attach. An example of this type of bone is the cranium that will protect the brain from a boxing punch or the ribs that would protect vital organs such as the heart and lungs from a cycling fall. Flat bones consist of two layers of compact bone with a variable amount of cancellous bone inbetween.
4) Irregular bones have very specific jobs such as the vertebrae allowing movement and protection of the spine. The diagram shows that there are three different types of vertebrae. The cervical vertebrae are the vertebrae in the neck and allow a comparatively large amount of movement such as nodding. The thoracic vertebrae increases in size further down the spine. Humans have 11 of these and their main purpose is to support the ribs and to maintain posture. The Lumbar vertebrae are the largest of the three types and allows backwards and forwards bending.
5) The final type of bone is the sesamoid bone which has a tendon attached to it such as in the hand or knee. These do not heal easily if injured as there is a very limited blood supply so therefore a sportsperson will have to be extra careful. The bone allows the movement of the joint.

Holding together all the bones are 3 types of joints: fibrous, cartilaginous and synovial.
Fibrous joints are fixed and can not move. The bones which make up the skull are connected through fibrous joints. There is no joint cavity in this type of joint and the bones are connected through fibrous tissue.
Cartilaginous joints are connected simply by cartilage and nothing else. These provide more movement than a fibrous joint but less than a synovial joint. An example of this is the joints connecting the vertebrae.
Structure and function of synovial joints
Synovial joints contains a two layered joint capsule that has a tough fibrous outer layer called the fibrous capsule and a inner synovial membrane. These strengthen the joint so the bones are not pulled apart and also secretes synovial fluid. This is filled with synovial fluid which reduces friction and allows for movement. This joint is covered by a layer of spongy hyaline cartilage which covers all the internal joint surfaces with the exception of the articular cartilage. This absorbs compression to avoid the bone ends from being crushed and also prevents friction between the articulating bones. Also in the joint is the ligament which connects the two articulating bones. Its function is to provide stability to the joint.
There are 6 different types of synovial joints: Ball&Socket, condyloid, hinge, pivot, gliding and saddle.
Ball and socket joints are round shaped joints where one articulating bone creates a socket in which the other bone joins into to allow a greater range of movement in joints like the shoulder or hip.
Hinge Joints are cylindrical in shape in which one bone with a protrusion articulates with a bone that has a depression. This means that movement is restricted to only bending or straightening like a knee or ankle joint.
When one bone arcticulates with another that has a ring like structure a pivot joint is created. An example of this is the atlas/axis joint and it is restricted to only rotation.
A condyloid joint such as the wrist has a flatter oval articulating surfaces causing a much flatter surface than the ball and socket joint although it is similar. This means that it has the second greatest range of movement.
The vertebrae and spine are an example of a gliding joint in which the articulating surfaces are mainly the same size and are also basically flat. This means that it creates a “gliding” motion in all directions.
The final type of joint is the saddle joint which has both concave and convex areas and is similar to the condyloid joint. The concave surface of one bone articulates with the convex surface of another. An example of this is the thumb and it allows a degree of movements in all directions.