Classwork Series And Exercises {JSS2- Basic Science}: The Human Body

Basic Science JSS2

Topic: The Human Body (Skeletal System and Movement)

Introduction

The human body has a bony framework known as the skeleton which gives the body shape, rigidity, support, etc. These supporting structures in the organism which helps the body in running, jumping, moving from place to place and bending to pick objects form the skeletal system. These acts of changing position from one point or position to another, or from one direction to another is known as movement.

In fact, the body of animals consists of:

1. Bones called skeletons
2. Flesh called muscles
3. Fluid called blood

The Skeletal System of Man

The skeleton is made up of two main parts:

1. Axial Skeleton
2. Appendicular Skeleton

The Axial Skeleton

The axial skeleton is made up of the skull and the vertebra, which include the spine and the chest plate. The skull refers to the bones of the head and it protects the brain. The vertebrae are otherwise referred to as backbones. These bones are placed end to end to form a hollow tube through which the spinal cord passes. The vertebra therefore protects the spinal cord.

There are 5 types of vertebrae in mammals

	Types	Position	Man	Rat	Rabbit
1	Cervical vertebra	Neck	7	7	9
	Thoracic vertebra	Chest	12	13	12
	Lumbar vertebra	Upper trunk abdomen	5	6	7
4	Sacral vertebra	Lower trunk abdomen	5	4	3-4
5	Caudal vertebra	Tall	14	27-30	16

Appendicular Skeleton

The appendicular skeleton is made up of the limbs and limb girdles which is directly concerned with movement in animals.

The limbs: There are two pairs of limbs in every animal, these are the forelimbs and the hind limbs. In man, the forelimbs are free and are called hands. In other animals except Ape and Gorilla, both the fore and hind limbs are used for walking. The forelimbs consists of the arm(humerus, ulna and radius) and the hands(carpals, metacarpals and phalanges) while the hind-limbs consists of the legs(femur, fibula and tibia) and the feet(tarsals, metatarsals and phalanges).

Limb Girdles: Generally, there are two limb girdles and they support the weight of the body. They are:

The pectoral (Shoulder) Girdles: This  is a group of large flat bones in the shoulder region to which the forelimbs are attached.

The Pelvic (Hip) Girdles: This is another group of large flat bones in the hip region to which hind limbs are attached.

What are Bones?

Bones are made of hard chemical materials called calcium (ii) Tetraoxophosphate (vi), calcium (ii) Trioxocarbonate (iv). These materials are living cells make bone from soluble compounds of calcium and phosphorus in the blood which come from the food you eat. Newly formed bone is soft and easily bent. The human body has a total of about 206 bones.

Cartilages, Ligaments, Tendons and Muscles

1. Cartilage: The end of bones have a covering materials called cartilage, which is made of a tough elastic tissue. The cartilage prevents these ends from the wears and tears (friction) that would have been caused by the movement of the bone on the other. Cartilage is a special type of connective tissue.
2. Ligament: This is the tight cord which holds bones together. Joints are held together by bones and sheets of very tough connective tissues known as ligament.
3. Tendons: The tendon is a tough fibre-like material found at the ends of muscles. It binds two neighbouring bones together and holds a fluid which serves as lubricant to reduce friction as the bones move against one another.

Muscles

Muscles are bundles of elastic substance in an animal body. Muscles are attached to bones by means of tendons. Muscles cam contract and relax to produce movement in the animal body. The skeletal and muscular systems work together to produce movement.

Muscles can contract (get shorter) and relax in order to move the bones of the body. There are muscles which can be moved voluntarily when you wish, this is called the voluntary muscle and this muscle controls the movement of the hands, legs etc. While some muscles move involuntarily of their own accord i.e. no control over them, this is called involuntary muscle. The heart muscle cannot be controlled.

Generally, there are three types of muscles namely:

1. Skeletal Muscles: Are muscles attached to the bones of the skeleton which help them move.
2. Smooth Muscles: Are muscles that lined many structures in our body such as intestine and blood vessels.
3. Cardiac Muscles: Are special striped muscles with the ability to work continuously. They form the walls of the heart.

Joints

A joint is the spot where two or more bones meet. The head, neck, legs move as a result of the presence of joint in them. There are five types of joints in the body and these joints give us different movements (they are movable joints); these are:

1. Ball and Socket Joint: This joint is for free movement in all directions e.g. in hip joint and shoulder joint.
2. Hinge Joint: This joint is for movement in one plane e.g. elbow joint and knee joint.
3. Sliding Joint: For sliding one bone over another e.g. wrist joint, ankle joint.
4. Pivot Joint: This is a joint that allows rotation of one part of the body on another. Example is found between the atlas and axis vertebrae region.
5. Suture Joint: Joint in the skull.

Reasons Human Beings Move

Movement is an act of changing position from one point or position to another, or from one direction to another. This is brought about by the action of the muscles on the bones. Muscles are attached to the bones at two points. One end of it is attached to an immovable bone (or rigid bone e.g. shoulder blade) which is the origin; and the other end to a moveable bone known as the insertion (e.g. radius). Muscles can only contract (shorten) and relax but not expand (widen). When a muscle contracts, it becomes shorter and thicker and pulls the moveable bone. When a muscle relaxes, it straightens and becomes thinner.

Most muscles act in pairs in such a way that when one of the pairs contracts, the other relaxes. Muscles acting in pairs in this manner are known as antagonistic muscles. One of the pairs is called extensor, that causes the hands to straighten out. The other part of the pair which bends the limb is called flexor. The muscles act on the bones and this brings about movement. The contraction and relaxation of the muscles also brings about movement.

Importance of Movement to Human Beings

1. Human beings need to move about because they have to:
2. Move from one place to another.
3. Escape from danger.
4. Be able to respond to stimuli.
5. Exercise the body.