Our Skeletal System Chapter Notes | Eureka Plus Class 5: Book Solutions, Notes & Worksheets PDF Download

Many animals possess an internal structure made up of bones. This internal framework is referred to as the skeleton. The bones are organized within the animal's body in a specific arrangement.
Animals with such a bony framework are known as vertebrates. Examples of vertebrates include all types of fish (such as sharks and goldfish), amphibians (like frogs and toads), reptiles (such as snakes and lizards), birds (like sparrows and crows), and mammals (such as lions and dogs).

Skeleton and shape of an animal's body

The skeleton determines the shape of an animal's body. An animal's skeleton can help us identify it. For instance, all elephants share the same type of skeleton, and the same is true for all ostriches. However, the size of the skeleton changes depending on the animal's age.

The Human Skeleton

The human skeletal system is made up of a framework of bones. Bones are hard on the outside, but the inside of a bone is filled with a spongy material called bone marrow. Red blood cells and white blood cells are produced inside the bone marrow. An adult human skeleton has 206 bones, but the size of these bones can vary. A tall person has longer bones, while a shorter person has shorter bones.

The skeleton has three main functions: (i) It supports the body and helps maintain its shape. (ii) It protects the internal organs. (iii) It helps the body move.

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Parts of the Human Skeleton

Skull

• The skull is the bony framework of the head. It is made up of several flat, strong bones that are joined together to form an immovable shell, except for the lower jaw, which is movable. The lower jaw allows us to talk and eat. The upper and lower jaws also hold our teeth.
• The skull bones protect the brain, eyes, tongue, and the inner parts of the ears.

• The vertebral column, also known as the spine, is a strong, flexible column of bones that allows us to bend our back. It is made up of 33 bones called vertebrae, which form a hollow, tube-like structure.
• The vertebral column protects the spinal cord, which is a part of the nervous system. The spinal cord passes through the vertebral column, and this column also protects the spinal cord from shocks and jerks when we walk, run, or jump. Additionally, the vertebral column helps protect our head.

Rib Cage

• The rib cage is a protective structure in the chest made up of bones.
• It consists of flexible, curved bones called ribs that are attached to the sternum (a long bone in the center of the chest) at the front and to the vertebral column (spine) at the back.
• There are twelve pairs of ribs in the human skeleton.
• The rib cage safeguards vital organs such as the lungs and heart.

Bones of Arms and Legs

• Each arm and leg has three long bones along with several smaller bones.
• The long bones in the arms and legs are hollow and tube-like in structure.
• These bones are lightweight yet incredibly strong, allowing them to support weight and endure pressure.
• This strength is what enables us to carry our own weight, lift additional objects, and walk.

Joints

• A joint is the area where two or more bones come together. Most joints allow for movement, and these are called movable joints. For example, the joints in our arms and legs allow us to move these body parts.
• On the other hand, some joints do not permit any movement, and these are known as immovable joints. A good example of an immovable joint is the bones in the skull.
• The bones in a joint are connected by strong and flexible tissues called ligaments. Ligaments help hold the bones together and provide stability to the joint.

Ball and Socket Joint

• A ball and socket joint is a type of joint that allows movement in all directions. In this joint, the round, ball-shaped end of one bone fits into the cup-like socket of another bone.
• This design enables a wide range of motion.
• Examples of ball and socket joints in the human body include the shoulder joint and the hip joint. These joints are responsible for the ability to move the arms and legs in various directions.

Hinge Joint

• Hinge joints permit movement in a single direction, similar to the way a door hinges open and close. These joints are located in various parts of the body, including the elbows, knees, fingers, and toes. 
• The hinge joint's design allows for a back-and-forth motion, making it essential for activities such as bending and straightening limbs.

Pivot Joint

• The pivot joint is formed between the first vertebra of the spine and the skull. This joint is crucial for the movement of the neck, as it allows the head to rotate from side to side, as well as to tilt forward and backward. 
• The pivot joint provides the necessary flexibility and range of motion for the neck, enabling activities like looking around and nodding.

Gliding Joints

• Gliding joints are found in the wrists and ankles, where they allow for side-to-side and forward-and-backward movement of the hands and feet. 
• Additionally, gliding joints are present between the vertebrae in the spinal column, enabling these bones to slide against each other. This sliding motion is essential for bending the body forward, backward, and sideways, contributing to overall flexibility and mobility.

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Muscles of the Body

• Bones and joints alone cannot facilitate movement; they require the cooperation of muscles. Muscles and bones work together to enable the movement of different body parts.
• Muscles are present throughout the body, with several hundred individual muscles contributing to movement and stability. Muscles and bones also give the body its shape.
• When we want to hold something in our hand, the muscles and bones in our fingers need to work together. If either the muscle or bone in a specific body part is injured, movement in that area becomes impossible.
• Muscles are connected to bones by strong and tough tissues called tendons. The contraction and relaxation of muscles are what cause bones to move. Typically, muscles work in pairs: when one muscle contracts (pulls), the other muscle relaxes.
• For example, in the upper arm, the muscles on the front and back sides work together to move the arm. When you bend your arm, the front muscles contract (becoming shorter and thicker), and the back muscles relax (becoming longer and thinner). You can feel the muscles on top of the arm becoming stiff. When the arm is lowered, the front muscles relax, and the back muscles contract, allowing for smooth movement.

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Healthy Bones and Muscles

To keep our muscles and bones healthy, we need to eat the right food and exercise regularly. When we play, we are exercising our muscles and bones, which is why it's important to play outdoor games often.

• Foods like beans, grams, green grams, milk, cheese, wheat, eggs, and fish are beneficial for our muscles and bones. 
• It's also important to eat a variety of vegetables and fruits to keep our bodies healthy. Additionally, sunlight is good for our bones and muscles.