THE SKELETAL SYSTEM

Human Skeleton, Anterior Vie. Photo credit, Biology Discussion

  QUESTION: Explain the functions of the skeleton

Skeleton is the bony frame work of the body in vertebrates’ .The major functions are

A. Gives shape and rigidity to the body.

B. Anchor muscles and protects internal organs such as the lung, heart, and brain.

C. The body frame work, allows movements in all body plain by acting as a system of levers.

D. Critical in the production of blood cells.

E. Skeleton serves as the store house of calcium, phosphates and other ions.

       TYPES OF SKELETAL SYSTEM

A.       Hydrostatic skeleton

B.       Exoskeleton

C.      Endoskeleton 

A.      Hydrostatic skeleton: Hydrostatic skeleton is found in many cold blooded organism and soft bodied animals, it consist of fluid filled cavity, the “coelom”, surrounded by muscles. The pressure of the fluid and the action of surrounding circular longitudinal muscles helps the organism to change shape and produce movement, such as burrowing or swimming. An example is the earthworms.

B.     Exoskeleton: Is the external skeleton that support and protect an animal’s body, it occur in insects, crab, snail, spider etc. Examples of exoskeleton are cuticle, shell and chitin.

C.     Endoskeleton: This is an internal support structure of an animal, composed of mineralized tissues. It develops within the skin or the deeper body tissue. The vertebrate is basically on endoskeleton made up of tissue, bone and cartilage. 

Q     QUESTION: Differentiate between cartilage and bone

The difference between cartilage and bone

           CARTILAGE                                                               BONE

1.    Is a tough elastic connective tissue	Is a hard living and growing tissue
2.    Composed of specialized cells called Chondrocytes	Made up of collagen
3.    They do not communicate with one another	Communicates with one another at positions called joints.
4.    Is not a vascular tissue	Is a vascular tissue
5.    Soft and do not break easily	Hard and breaks easily.

Question: What is a joint?

Joints (articulations), are unions or junctions between two or more bones or rigid parts of the skeleton. Simply put, it is a place where two or bones meet. Joints are constructed to allow movement (except for skull bone) and provide mechanical support. They perform different types of movement and also carry out different functions. Some articulations does not allow any movement for example the epiphysis and diaphysis of growing long bone, others allows only limited movement, such as the  teeth within their socket, some are freely moveable, for example the shoulder joint.

Types of joints

There are three types of joints based on the type of material by which the articulating bones are made of,

1- Fibrous joint: this type of joint is united by fibrous tissue. The amount of movement occurring at this junction depends in most cases on the length of the fiber uniting the articulating bone. The sutures of the cranium are good examples. Fibrous joints are close together interlocking, wavy or overlapping, the interosseous membrane in the forearm is a sheet of fibrous tissue that joins the radius and ulna in syndesmosis. A dentoaveolar syndesmosis, is another example, a peg-like process fits into a socket articulating between the root of the teeth and the alveolar process of the jaw. Movement of this type of joint (a loose tooth) indicates a pathological condition.

2- Cartilaginous joint: These are united by hyaline or fibrous cartilage, there are two types, the primary and the secondary.

Primary cartilaginous joint: These are also known as synchondroses, the bones are held together by hyaline or cartilage which allow slight bending during early life, they are usually temporal, example are the development of the long bone where bony epiphysis and the shaft are joined by an epiphysal plate.

·         Secondary cartilaginous joint: These are also known as symphyses, they are strong and slightly moveable joints held together by fibro cartilage, the fibro cartilage intervertebral disc between the vertebrates consist of bending connective tissue that joins the vertebrae together. This type of joints provide strength and act as shock absorber, and also provide some degree of flexibility to the vertebral column(spine).

3- Synovial joint: Synovial joints held in position by articular capsule, made up of outer fibrous layer lined by a serous synovial membrane enclosing an articular cavity. An example is the joint of the knee, a space that contains some amount of lubricating synovial fluid secreted by the membrane inside the capsule. Articular cartilage covers the articulating surface of the bone, all other space are covered by the synovial membrane.

This joint is the most common type in the body; it allows free movement between bones and is regarded as the joint of locomotion, typical of all limb joints.  It is classified into six depending on the type of movement they produce and the shape of the articulating surface.

·       Plane joint: Plane joints permits sliding or gliding movement in the plane of the articular surface, the opposing surface of the bone are flat or almost flat, with movement limited by the tight capsule, an example is the acromioclavicular joint between the acromion of the scapular and the clavicle.

·       Ball and socket joint: This is a multi axial joint; it permits movement in multiple axis and plane, flexion and extension, medial and lateral rotation, abduction and adduction, and circumduction. Ball and socket joints are highly movable; the spheroidal surface of one bone moves within the socket of another, an example is the hip joint, in which the spherical head of the femur rotates within the socket formed by the acetabulum of the hip bone.

·       Hinge joint: Permits flexion and extension only, (Movement in one plane (Sagital) around a single axis that run transversely, thus, they are uni-axial. The capsule of these joint is thin and lax interiorly where movement occur. The elbow joint, joined by strong ligament is an example of hinge joint.

·       Saddle joint: Is a biaxial joint that allow movement in two plane, abduction and adduction as well as flexion and extension, (sagital and frontal), Saddle joint also permit movement in a circular sequence (circumduction). The opposing articular surfaces are shaped like a saddle, that is to say they are reciprocally concave and biconcave, an example is the Carpometacarpal joint at the base of the first digit (Thumb).

·        Pivot Joint:This permits rotation around a central axis, and is therefore a  uni-axial joint,  In pivot joints, a round process of bone rotates within a sleeve or ring, the medium atlantoaxial joint is an example, is the atlas (a vertebrate)  rotates around a finger like process (C₂  vertebrate) during rotation of the head.

·       Condyloid joints: permits flexion and extension as well as abduction and adduction, this means that condyloid joints are also biaxial. However, movement in one plane (sagital) is usually greater (free) than in other plane. Circumduction which is more restricted than in other joints is also possible. An example is metacarpophalengeal joint. (Knuckle joints).

DEFINITION OF TERMS

• · Coelum: Main body cavity of many triploblastic animals, in which gut is suspended, situated in the mesoderm and lined by epithelium. It contains fluid which unlike blood is not circulated by muscle cells but contract to allow the organism produce movement.

• · Epiphysial plate: The cartilage disc between the metaphysic and the epiphysis of an immature long bone permitting growth in length.

• · Cranium: Skull of vertebrate

• ·  Suture: A type of fibrous joint in which the two bones formed in membrane are united by a fibrous membrane continuous with the perioseum, the material that hold or bind two surfaces together.

• ·    Serous: Containing or producing serum or watery substance.

• ·     Ulna: The media and the larger of the two bones of the fore arms.

• ·       Radius: the lateral and the shorter of the two bones of the forearm.

• ·       Syndesmosis: A type of fibrous joint in which opposing surfaces that are relatively far apart are held together by ligament.

• ·       Synchondrosis: A union between two bones formed either by hyaline cartilage or fibro cartilage.

• ·  Intervertebral disc: A disc interposed between the bodies of adjacent vertebrate composed of outer fibrous part that surrounds a central gelatinous mass.

• · Acetabulum: A cup shaped depression on the external surface of the hip bone with which the head of the femur articulate (Cotyloid cavity)

• ·  Abduction: Movement of the body part away from the median plane of the body.

• · Adduction: Movement of the body part towards the median plan of the body,

• · Diaphysis: Shaft of a long limb bone, or central portion of mammalian vertebrate.

·       REFERENCES

·       Clinically Oriented Anatomy, 6TH edition, by Keith L. Moore. Arthur F.   Dalley and Ann M.R Agar.

·       Basic Histology, Text and Atlax