Bones And Muscles / The Skeletal System Class 5 -Notes

Points To Remember

What is a bone?

Bone is a hard and tough tissue that makes up the body’s skeleton.  

• Adults have 206 bones, while an infant has about 300 bones.

Functions of Bones in Body 

1. Provide shape and support to the body.
2. Protect the organs of the body.
3. Help us move.

Structure of Bone

• They are made of calcium, phosphorus and a substance called collagen.
• They are hard on the outside and soft on the inside.
• They can grow and repair themselves.
• There are long bones and flat bones which contain bone marrow, a fatty substance that forms blood cells.

Also Check – Bones And Muscles / The Skeletal System Class 5 – Worksheet 

Types of bones

We have different bones in our body and they differ in size and shape.

• Bones in limbs are long ,including those of the fingers and toes.
• Bones in the wrist and ankle are short.
• Skull and breast bones are flat in shape.
• Bones in hips, spine and some other parts are irregular in shape.

What is a skeletal system?

A skeletal system is the central framework of one’s body. It consists mainly of bones and connective tissues such as cartilage, tendons and ligaments. 

A skeleton has many important roles:

1. It provides shape and support to the body.
2. It protects the organs and supports the body: the skull protects the brain and ribs protect the heart and lungs.
3. Muscles are attached to the bones. Muscles and bones work together to move parts of the body.

What are the parts of a skeletal system?

A skeleton consists of five main parts:

• Skull
• Vertebral column
• Ribcage 
• Limbs
• Girdles
  

Skull

• The skull forms the head of the body. 
• It is made up of 22 bones. Out of it, 14 bones form the frame of our face and rest of the 8 bones are flat bones that are locked together like a jigsaw puzzle and form a hard hollow case known as cranium. 
• It protects the brain. 

Functions of skull  

• The skull gives shape to the face. 
• It has space for eyes, nose, ears and mouth. 
• It protects the brain, eyes, inner parts of ears and nose and tongue. 
• The lower jaw is the only movable joint of the shell and enables us to talk and eat.

Vertebral column

• It makes up the spine, or backbone. 
• The vertebral column is a long hollow column of bones. 
• The skull is joined to the spine that runs from the base of the skull down to the hip region. 
• The vertebral column has 33 small bones. Each bone is ring shaped and known as a vertebra. 
• Cartilage (a strong and elastic tissue) is present in between the vertebra and acts as a shock-absorber. 
• Out of the 33 vertebrae, the first seven are in the neck region and the last four form the tail bone.

Functions of vertebral column

• It supports the back of the body.
• It protects the spinal cord passing through it. 

Ribcage 

• The ribs are bones present in the chest region. 
• There are total 12 pairs of ribs. 
• The bones are connected to the vertebral column at the back. 
• Ten of the rib pairs are connected to the breastbone known as sternum. The sternum is a flat bone in the middle of the chest. 
• The last 2 pairs are not joined to the breastbone and they are called floating ribs.

Function of ribcage

• It protects the heart and lungs.

Limbs 

We have two pairs of limbs. Each limb has three bones.

1. Forelimbs (arm)
2. Hindlimbs (legs)

Forelimbs

1. The upper arm has a bone called humerus. 
2. The lower arm has two bones called radius and ulna. 
3. The wrist and hands are made up of many small bones. 

Hindlimbs

1. The thigh bone called femur is the longest bone in the body.    
2. The lower leg has two bones called tibia and fibula. 
3. The ankle and toes also consist many small bones. 

Girdles 

The bony structures to which limb bone is attached are girdles. 

There are two girdles in the body – 

1. Pectoral girdle
2. Pelvic girdle

• The forelimbs are attached to the pectoral girdle. Each pectoral girdle consists of a shoulder blade and a collar bone.
• The hindlimbs are attached to the pelvic girdle. 

Joints

• The place where bones connect is a joint. 
• Strong bands of tissue called ligaments hold the bones together at a joint. 

There are two kinds of joints in the body: 

• Immovable Joints
• Movable Joints

Immovable Joints

Immovable joints are simply bones that do not allow movement amongst them. Eg: joints in the skull. 

Movable Joints

Movable joints allow movement of bones. Eg: joints in arms and legs.

Movable joints are of four types. 

1. Hinge joint
2. Ball and socket joint 
3. Pivot joint 
4. Gliding joint
   

Hinge joint:

• A hinge joint allows bones to move in one direction.
• Knees are an example of hinge joint. 

Ball and socket Joint 

• A joint where one end of a bone is round like a ball to fit into another bone acting like a socket.
• The round bone moves in the socket in almost all directions.
• Hips and shoulders are example of ball and socket joints. 

Pivot joint

• This joint is present between the first and second vertebrae of the backbone.
• The skull is connected to the vertebrae through a pivot joint.
• It allows both side to side and  up and down movements. 

Gliding joint:

• This joint is present in wrists and ankles. It allows sliding movements. 

Cartilage 

• Cartilage is a strong and elastic tissue. 
• It makes the nose and ears soft and flexible.

Functions of Cartilage 

• It protects the bones from getting injured.
• It provides flexibility. 

Ligament

• Ligaments are strong bands of tissue that hold the bones together at a joint.
• There are around 900 ligaments in the body.

Function of Ligaments 

• They are strong but they allow movements of the bones.

Muscles 

• Muscles are the soft tissues in the body
• The bones of the body cannot move on their own. They move with the help of muscles. 
• The human body has around 600 different types of muscles. 
• They are present in the organs and around the bones. 
• The muscles are attached to bones with a strong fiber called tendon. 

2 types of muscles

1. Voluntary Muscles
2. Involuntary Muscles
   

Muscular System

The function of the muscular system is movement and maintenance of posture. The muscles can contract and relax.

Voluntary Muscles

• These are the muscles which work under one’s control.
• The muscles that are in the arms, legs, etc. are examples of voluntary muscles. 

Involuntary Muscles 

• These muscles do not work under one’s control.
• They work without one thinking about them.
• Eg- the stomach and heart have involuntary muscles. 

Muscles are made up of cells called muscle fibers.

3 Important Types of Muscle Fibers

1. Striated muscle fibers 
2. Smooth muscle fibers 
3. Cardiac muscle fibers
   

Striated muscle fibers

• They are an example of voluntary muscles and they are attached to the bones.
• They have dark bands running across the muscles.
• They are also known as skeletal muscles. 

Smooth muscle fibers

• These are involuntary muscles.
• They are long and narrow at the ends.
• They do not have bands.
• They can contract and relax and work for long without getting tired.
• They are found in the respiratory system organs and circulatory system organs.

Cardiac muscle fibers

• These are involuntary muscles too.
• The heart is made up of the cardiac muscle fibers.
• They have bands similar to that of striated muscle fibers.
• They are powerful and work quickly and  continuously without getting tired.