Types Of Joints, Meaning And Structures – ss1

Hi, welcome to this hall on the types of joints, meaning and structure of a joint In biology ss1.

Table Of Contents

1. Meaning of joints
2. Types Of joints
3. Structure of a joint
4. Revision question

Meaning Of Joint: A joint is a point or place or region where two or more bones meet or articulate. Movement of the body or parts of the body is made possible with the aid of joints and muscles. Joints are held together firmly by ligaments which are made of stiff, partially elastic fibres. Ligaments join bonds to bones.

Types Of Joints

There are two main types of joints in mammals. These are immovable or fixed joints and movable joints.

A Movable Or Fixed Joints

Immovable joints are joints or regions where two or more bones are firmly attached to one another or are firmly fixed by ligaments in such a way that movement of these bones are not possible.

Examples of places in the body where immovable joints are found are the skull and pelvic girdle. Immovable joints of the skull are called sutures.

Movable Joints

Movable joints are joint or regions where two or more bones meet in such a way that the bones move over each other, making movement possible. Most of the bones in the body are held by movable joints.

Types Of Movable Joints

There are four main types of movable joints. These are:

1. Ball and socket joints
2. Hinge joints
3. Glinding or sliding joints
4. Pivot joint.

1. Ball and socket joints: Ball and socket joints allow movement in all planes or direction (i.e up to 360°). This joint is found in the shoulder and the hip joint. In the shoulder joint, the head of the humerus is a ball-like structure which fits into the glenoid cavity of the scapula (pectoral girdle). This allows movement in all directions. Similarly, in the hip joint, the round head of the femur fits into the acetabulum of the pelvic girdle to form a freely articulating joint.

2. Hinge joints: Hinge joint allows movement in one plane or direction Only (i.e up to 180°). Examples of Hinge joints are found in the elbow and knee joint. The elbow joint is found between the humerus and the ulna/radius. Similarly, the knee joint is found between the femur and tibia/fibula. As the name implies, each set of bones making up the hinge joint functions like one half of a hinge.

3. Gliding or Sliding joints: The gliding joint allow the sliding of bones over one another. Examples of these joint are found at the wrist and ankle. They allow the hand and foot to be moved up and down or rotated slightly.

4. Pivot or rotating Joints: Pivot joint allows nodding or rotation of one part of the body on another. It is found between the atlas and axis vertebra. The odontoid process of the axis act as a pivot which allows the rotation of the head on the vertebra: (i.e the atlas and the skull together rotate about the odontoid process).

How The Structure Of A Joint Adapts It To Its Function

• In movable joints, there is the presence of cartilage of reduce friction between two bones in contact.
• The ligaments also help to hold the bones together.
• The synovial membrane secretes the synovial fluid.
• The synovial fluid lubricates the joint thereby minimizing shock and friction leading to easy movement of joint.

Structure Of A Joint

The main part of a joint consist of the following structures:

1. Ligaments: These are tough, partly elastic bands of tissue. They hold two bones together at a joint. In other words, they join one bone to another. They are able to accommodate movement at the joints because of their elastic nature.
2. Tendons: Tendons are extension of connective tissue which surround the muscles. Unlike ligaments, they are non-elastic in nature. They connect muscles to bones.
3. Articular cartilage: These are found at the surface of bones at joints. They play the role of cushioning the bones by protecting them from wear and tear during movement. They prevent the articulating (touching) surface from being worn out due to friction.
4. Synovial membrane: Synovial membrane is responsible for the secretion of synovial fluid.
5. Synovial fluid: This is the fluid secreted by the synovial membrane. It lubricates the joints and thus reduce shock as well as friction between two bones.
6. Capsule: Capsule is the space or sack which contains the synovial fluid.

How Muscles Act On Bones To Cause Movement

Muscles are bundles of long, thin cells enclosed in sheaths of connective tissue. Muscles are attached to the bones at two points. One of the points of attachment is called origin of the muscles. This is where the muscles are attached to an immovable or rigid bone, e.g,. shoulder blade. The other point of attachment is called insertion. This is where the muscles are attached to a movable bone, e.g, radius. Muscles are attached to the bones by means of non-elastic, tough, whitish cord of fibrous materials called tendons. Muscles can only contract and relax but they cannot lengthen or expand. When a muscle contract, it become shorter and thicker. Thus a pulling force is exerted on the bone in which it is attached. When a muscle relaxes, it lengthens and becomes Thinner. Most muscles act in a pairs called antagonistic pairs so that while one member is contracting, the other is relaxing. One member is called extensor and this tend to extend or straighten the limb by its contraction; the other member is called flexor, this bends or flexes the limb.

Movement Of Fore Limb Or Able Joints

The muscles of the upper arm or humerus are referred to as biceps and triceps. Bicep muscles are found at the front of the humerus and are attached to the scapula by means of two tendons. The tricep muscles are found at the back of the humerus. The contraction and relaxation of this muscles bring about bending and straightening of a limb.

The muscles are antagonistic muscles, that is, they work together in pairs in opposite ways. When an impulse is received from the central nervous system, the biceps (flexors) contract by becoming shorter and thicker, and at the same time, the triceps (extensors) relax. Since the tendon do not stretch, the shortening of the biceps results in a pull of the radius and as a result, the arm is bent.

On the other hand, when the triceps muscles (extensor muscles) contract, becoming shorter and thicker at the same time, the bicep muscle (flexors) relax, a force is exerted on the ulna and the arm is straightened as a result. Energy is involved in the movement of limbs. The muscular energy comes from the oxidation of glycogen which is stored within the muscles (i.e tissue respiration).

READ ALSO: Types of Muscles and their Functions in Human Body

Revision Questions

1. What is joint?
2. Outline and explain the types of joints mentioned above.
3. (a) Briefly list and explain the structure of a joint (b) how the structure of a joint adapt it to its function.