Movement (Cont’d)
“Be yourself, people don’t have to like you and you don’t have to care that they don’t.”
– Peanuts
HOW ARE you this week, my fellow travellers? Welcome to another in our series of lessons on movement. I hope that you have been finding the lessons helpful. Please feel free to provide your feedback.
This week, we will begin by looking at joints, their structure and how they assist the bodyin movement. First, we will look at the structure of bone.
Bone is made up of the following:
■ Minerals, e.g., calcium phosphate and small amounts of magnesium salts. These make bone very hard.
■ Collagen fibres – These give the bone some degree of elasticity. Do you remember the type of molecule to which collagen belongs? Did you say protein? If you did, then you are correct; collagen is a type of protein.
■ Living cells – These receive food and oxygen from blood vessels present in the bone. These cells are arranged in rings around the blood vessels.
The hardest part of the bone is known as the compact bone and is found on the outside. Underneath this is the spongy bone – this has spaces in it and these spaces help to lessen the weight of the bone. In the centre of the bone is the bone marrow, which is very soft and is provided with a good supply of blood. Remember that this is where red blood cells, some white blood cells and platelets are manufactured. The ends of the bones are covered with cartilage. Cartilage contains collagen but it does not contain much mineral salts, so it is softer than bone. It allows the ends of adjacent bones to move over each other at a joint. See Figure 1.
JOINTS
Joints are formed where two bones meet. Joints exist to both give mobility to the skeleton as well as to hold it together. They are classified based on the type of connective tissue joining the bones and whether or not there is a joint cavity present. These factors determine the motility of the joint.
There are three main types of joints. These are:
1. Fibrous joints – immoveable
2. Cartilaginous – partially moveable
3. Synovial joints – fully moveable
FIBROUS JOINTS
These are found where bones are joined quite closely by fibres and no joint cavity exists. Sometimes the joints are so close, they cannot move at all; for example, the joints of the cranium. These joints are called sutures and are immoveable.
CARTILAGINOUS
These are found in the pelvis and the wrist (carpals) and ankle (tarsals); some movement occurs between the joints. These joints are said to be partially moveable and are described as gliding joints.
SYNOVIAL JOINTS
These are moveable joints and are found where bones need to move freely. The bones meeting at the joint are separated by a fluid-filled joint cavity.
There are two types:
1. The hinge joint, e.g., elbow, knee. These bones move freely in one plane.
2. Ball and socket, e.g., shoulder and the hip. These bones allow movement in all planes.
3. Pivot. This joint between the atlas and the axis vertebrae is also classified as a synovial joint. This joint is called a pivot joint.
The bones of a synovial joint have between them a small amount of thick fluid, known as the synovial fluid. The fluid is made and kept in place by the synovial membrane. The fluid serves to lubricate the joint, enabling the bones to move freely.
STRUCTURES ASSOCIATED WITH A TYPICAL JOINT STRUCTURE IMPORTANCE
■ Ligament
Joins one bone to another and has the ability to stretch as the bones move away and towards each other.
■ Muscle
These can contract or relax, and when they are attached to the bone, they can pull up or extend the bone.
■ Tendon
These join the muscles to the bone. They are non-elastic, so muscle contraction or relaxation affects the bone directly.
■ Synovial fluid
This is the fluid found in the joint and helps to reduce friction when the bones move.
Be reminded that you may be asked to identify types of joints in the exam, as well as be asked to label and give the function(s) of labelled parts. This means that you need to study the different diagrams! You have been warned!
See you next week!