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BTEC Structure and Function of the Skeletal System (Barry Comp)

Alun Jones
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Alun Jones

on 26 September 2012

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Transcript of BTEC Structure and Function of the Skeletal System (Barry Comp)

The Structure and Function of the Skeletal System Structure of the Skeletal System You need to know:

the difference between the axial and appendicular skeleton
the five different types of bone
the location of the major bones The AXIAL skeleton is the main supporting frame of the skeleton, consisting of the skull, vertebral column and ribcage. The APPENDICULAR skeleton is the bones of the skeleton that make up the limbs and their associated girdles (hip and shoulder). There are 5 types of bone:

long bones
short bones
flat bones
irregular bones
sesamoid bones Function of the Skeletal system You need to know that the skeleton provides the following functions:

It provides support
It provides protection
It provides an attachment for skeletal muscles and therefore movement
It is a source of blood cell production
It is a store of minerals. Support

The skeleton provides a rigid framework to theee body, giving it shape and providing suitable sites for the attachment of skeletal muscle. Protection

The skeleton provides protection for the internal organs. E.g. the vertebral column protects the spinal cord; the cranium protects the brain; and the ribcage principally protects the heart and lungs. Attachment for Skeletal Muscles

The bones of the skeleton provide a large surface area for the attachment of muscles - the engines of movement. The long bones, in particular, provide a system of levers against which the muscles can pull. Blood Production

Within the bones, bone marrow produces both red and white blood cells. Red blood cells are generally produced at the end of long bones such as the humerus (arm) and the femur (thigh), and in some flat bones such as the pelvis and the sternum (breastbone). White blood cells are usually produced in the shafts of long bones. Mineral Storage

The bones of the skeleton have storage capabilities for vital minerals such as calcium and phosphorus, which can be distributed to other parts of the body when required. Joints You need to know about the 3 types of joint:

Fixed
Slightly moveable
Synovial / Freely moveable

You also need to know the types, structures and movement at synovial joints. A FIXED joint is very stable and allows no observable movement. Bones are often joined by strong fibres called sutures, such as the sutures of the cranium (skull). A SLIGHTLY MOVEABLE joint is joined by a tough, fibrous cartilage which provides stability and possesses shock-absorption properties. However, a small amount of movement usually exists. E.g. between the lumbar bones, intervertebral discs of cartilage occur, allowing some movement. Synovial Joints SYNOVIAL or freely moveable joints are the most common type of joint in the body, and the most important in terms of physical activity, because of the wide range of movement. The joint is enclosed in a fibrous joint capsule, which is lined with a synovial membrane. Lubrication is provided by synovial fluid, which is secreted into the joint by the synovial membrane. In addition, where the bones come into contact with each other, they are lined with smooth yet hard-wearing hyaline or articular cartilage. Synovial joint stability is provided by the strength of the muscles crossing the joint, which are supported by ligaments that may be inside or outside the capsule. Ligaments are very elastic and lose effectiveness to some degree when torn or stretched. Some synovial joints possess sacs of synovial fluid known as bursae, which are sited in areas of increased pressure or stress and help to reduce friction as tissues and structures move past each other. Pads of fat help to absorb shock and improve the ‘fit’ of the articulating bones. This is particularly true in the knee joint, to help the articulation of the femur and tibia. There are six different examples of synovial joints:

• Hinge Joint
• Ball-and-socket Joint
• Pivot Joint
• Ellipsoid Joint
• Gliding Joint
• Saddle Joint A SADDLE joint is biaxial and generally occurs where concave and convex surfaces meet. E.g. the carpo-metacarpal joint of the thumb. A GLIDING joint is formed where flat surfaces glide past one another. Although mainly biaxial, they may permit movement in all directions. E.g. in the wrist, the small carpal bones move against each other. The BALL-AND-SOCKET joint allows the widest range of movement. They occur where a rounded head of a bone fits into a cup-shaped cavity. E.g. in the hip and shoulder. An ELLIPSOID joint is biaxial, allowing movement in two planes. E.g. the radiocarpal joint of the wrist allows movement back and forth as well as side to side. A HINGE joint is a uniaxial joint, which only allows movement in one plane. E.g. the knee joint only allows movement back and forth. Strong ligaments exist in order to prevent any sideways movement. Similar to a hinge joint, a PIVOT joint is also uniaxial and only allows rotation. E.g. in the cervical vertebrae, the axis rotates on the atlas. Flexion occurs when the angle between the articulating bones is decreased. For example: by raising the lower arm up to touch the shoulder, the angle between the radius and the humerus at the elbow has decreased. A muscle that causes flexion is known as a 'flexor'. In the instance at the elbow, the bicep brachii is the flexor muscle. Movement at a Joint There are a number of different types of joint movement:

Flexion / Extension
Abduction / Adduction
Circumduction
Rotation
Pronation / Suppination
Plantarflexion / Dorsiflexion
Inversion / Eversion
Hyperextension Flexion Extension Extension of a joint occurs when the angle of the articulating bones is increased. For example: when standing up from a seated position, the angle between the femur and tibia increases, thus causing extension at the knee joint. Extreme extension, usually at an angle of greater than 180° is known as HYPEREXTENSION. A muscle that causes extension is known as an 'extensor'. In the example of the knee joint, the quadricep femoris group is the extensor. Abduction This is movement of a body part away from the midline of the body or other body part. For example:
if arms are placed by the sides of the body and then raised laterally, abduction has occurred at the shoulder joint;
if fingers are spread out, movement has occured away from the midline of the hand and abduction has occured. Adduction Adduction is the opposite of abduction and concerns movement towards the midline of the body or body part. For example, by lowering the arm back to the sides of the body, movement towards the midline has occurred and is termed adduction. Circumduction Circumduction occurs where a circle can be described by the body part and is simply a combination of flexion, extension, abduction and adduction. True circumduction can only really occur at ball and socket joints of the shoulder and hip. Pronation occurs at the elbow and involves internal rotation between the radius and humerus. It typically occurs where the palm of the hand is moved from facing upwards to facing downwards. Supination is the opposite of pronation and again takes place at the elbow. This time the movement is lateral rotation between the radius and humerus and generally occurs when the palm of the hand is turned so that it faces upwards. Pronation Suppination Rotation Rotation of a joint occurs where the bone turns about its axis within the joint. Rotation towards the body is termed internal or medial rotation, while rotation away from the body is called external or lateral rotation.

To explain this further attempt the following exercise:

1.Grip a ruler at the bottom with your right hand.
2.Now raise your arm up in front of your body and move the ruler in an anticlockwise movement. Medial rotation has occurred at the shoulder joint.
3.Now move the ruler clockwise so that it ends up pointing to the side. This is lateral rotation and has once again occurred at the shoulder. Plantarflexion Dorisflexion Plantarflexion occurs at the ankle joint and is typified by the pointing of the toes. This also occurs at the ankle when the foot is raised upwards towards the tibia. Inversion Eversion This occurs when the sole of the foot is turned inwards towards the midline of the body. Eversion occurs when the sole of the foot is turned laterally outwards.
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