Chapter 9 The body and its movement

Transcription

1 Chapter 9 The body and its movement 1) All living things are made up of cells. 2) Cells make up tissues, tissues make up organs, organs make up organ system and organ systems make up the human body. 3) The main organ systems in the human body are skeletal, muscular, circulatory, nervous, respiratory, digestive, excretory and reproductive. 4) The skeleton gives support and protection, helps in the movements and makes blood cells. 5) The human skeleton can be divided into four main parts skull, backbone, ribs and limbs. Functions of the skeleton The skeleton has four main functions: (a) Support skeleton provides framework and holds us upright. (b) Protection the bones protect the soft organs of our body. The brain is protected by the skull, the heart and the lungs by the thin long bones in your chest called the ribs. (c) Movement though the individual bones are hard, several of them move at places where they are joined to other bones. (d) Making blood cells bones are hard from outside but they are soft and spongy in the inside. The inside of bones contains a soft substance called the bone marrow. Blood cells are made in the bone marrow. (a) The skull Structure of the human skeleton The skull is the bony structure that surrounds and protects the brain. The upper part is made up of 8 flat bones joined together. The face and jaw 1 Page

2 contains 14 bones. The lower jaw bones are the only movable bone in the skull. (b) The backbone or spine The backbone consists of 33 small bones called the vertebrae. The vertebrae are joined to each other. The joints allow slight movement if the vertebrae. This is why you can bend and twist your back. The backbone is attached to the base of the skull. It forms the central supporting rod for the skeleton. Each vertebra has a hole in it. The delicate organ of your body called the spinal cord passes through these holes. Thus, the backbone protect the delicate organ spinal cord. (c) The rib cage The ribs are thin, flat, curved bones that form a protective cage around the organs in the upper part of the body. This is called the rib cage. The rib cage consists of 24 bones arranged in 12 pairs. All of them are joined to the backbone at the back. Most of them are joined to the breast bone at the back. The last two pairs that are not joined to the breast bone are called floating ribs. The rib cage protects the heart and the lungs. (d) The limbs (arms and legs) The longest bone of your body is the thigh bone or the femur. The ankles and the feet have a number of small bones. The upper arm has one long bone called the humerus. (a) Hinge joint JOINTS The elbow, knee and finger joints allow movement in one plane only, that is, up and down, or backward and forward, like the hinges of a door. Such joints are therefore called hinge joints. (b) Ball and socket joint 2 Page

3 The shoulder and hip joints allow movements in all directions. In such joints, the end of one of the bones is round as a ball. It fits into a hollow part (or socket) in the other bone. (c) Pivot joint The neck joint also allows movement in all directions. It allows you to move your head up and down, left and right and also to rotate it. In such joints, one of the bones ends in a rounded or conical surface that fits into a dent in the other bone. Such a joint is called a pivot joint. (d) Gliding joint The wrist or ankle joints have flattened ends of bones that can move (or glide) against each other. These joints allow side to side as well as backward and forward movement. Movements (a) (b) (c) Earthworms have liquid skeletons. To move, the earthworm first extends the front part of its body, keeping the rear part fixed to the ground. Next, it fixes the front part and shortens it, thus pulling the rear end forward. It carries out such expansion and contraction of muscles repeatedly to move forward. Skeleton this is outside the body is known as an exoskeleton. Crabs and insects such as cockroaches also have exoskeleton. The snail has a thick structure called a foot. It is made up of strong muscles. It produces a series of wave like movements that push the snail's body forward. The skeleton of a human body is inside the body. Such an skeleton is known as endoskeleton. Fish, amphibians, reptiles, birds and mammals have endoskeletons. Muscles that enable the fish to move are found on either side of the backbone. These muscles contract on one side and expand on the other. 3 Page

4 Chapter 13 ELECTRIC CURRENT AND CIRCUITS BULB An electric bulb have an outer case made up of glass.the outer case is fixed on a metallic base. The wire inside the glass case is made of tungsten. It serves as filament of the bulb.the inside of the bulbs filled with mixture of inert gases. The filament is fixed to two thicker wires. One touches the bottom of the bulb and the other touches the metal casing. These acts as two terminals of the bulb Positive and Negative. They are fixed in such a manner that they do not touch each other. WORKING When the two terminals are joined to an electric cell the electric current flows through the filament which gets heated up and starts glowing. ELECTRIC CURRENT Electric current is a form of energy, that is electrical energy which gets converted to heat and light energy when it flows through an electric bulb. ELECTRIC CIRCUIT When we connect the terminals of an electric cell to an electric bulb through connecting wires,then the bulb starts glowing.it is joined in such away that the electric current can flow along a closed loop. ELECTRIC SWITCH Switch is a simple device that is used for making and breaking the circuit. The starting and stopping of electric current in an electric circuit is controlled by an electric switch. ELECTRIC CONDUCTORS AND INSULATORS The materials that allow electric current to pass through them are called conductors.all metals carbon (in the form of graphite), salt solution and impure water are some conductors of electricity. The materials that do not allow electric current to pass through them are called insulators. Wood, plastic, wool, rubber, distilled water, are some insulators. 4 Page

5 WHAT IS A FUSED BULB? When the filament of a bulb breaks, the electric circuit is no more complete. There is a break in the path of the electric current as no electric current can pass through the filament, the bulb does not glow and is thus called a fused bulb. 5 Page