Bones and Muscles

What is bone?

Can you see your bones? No, but we can feel some of them underneath our skin. Bones are living tissue.

Bones have hard outer layer called cortical (compact) bone, which is strong, dense and tough and spongy inner layer called trabecular (cancellous) bone, which is lighter compared to compact bone. They have their own blood supply as well as nerves, which help them to grow and repair themselves. That is how they grow as we get older.

Bones are composed of calcium, phosphorus, and a fibrous substance known as collagen. Bones are strong but light in weight as they are hollow from inside. The long bones of the arms and legs, such as the femur (thigh bone), have a central cavity containing bone marrow. Bone marrow is the flexible tissue in the interior of bones. In humans, red blood cells are produced by bone marrow.

Usually child is born with 300 soft bones. With the growth of child, these bones fuse together and an adult person has 206 bones. The smallest bone is stapes which is present inside our ear.

Major function of bones

      1.   They provide structural support and protect various organs of the body.

      2.   They produce red blood cells.

      3.   They enable mobility by acting as levers and points of attachment for muscles.

      4.   They act as storage for calcium and phosphorus, essential minerals for various cellular activities throughout the body.

The Skeletal system

The skeletal system is made up of 206 bones and includes all of the bones and joints in the body. The skeleton is a framework of bones that provides protection, gives the body proper shape, and helps in the movement. The human skeleton is divided into the axial skeleton and the appendicular skeleton. The axial skeleton includes the vertebral column, the rib cage, the skull and other associated bones. The appendicular skeleton, which is attached to the axial skeleton, includes the shoulder girdle, the pelvic girdle and the bones of the upper and lower limbs.

Function

The human skeleton performs six major functions; support, movement, protection, production of blood cells, warehouse of important minerals.

The Skull

The skull is the most complicated bony structure that forms the head of the skeleton. It provides a protective case for the brain and supports the structures of the face. The skull is composed of two parts: the cranium and the mandible.

The human skull contains 22 bones. Out of these 8 bones form a rigid hollow case called cranium which protects the brain. Other 14 bones form the face and are called facial bones and support the eyes, nose and mouth. All the bones of the skull except the lower jaw bone form a rigid structure. There is a fluid filled space in between the skull and the brain that protects the brain from shocks and jerks.

If we observe our face carefully, we will notice hole where our nose should be. Nose does not have bones; instead, it is made of a material called cartilage, which make nose soft and flexible. Cartilage is strong elastic connective tissue which is flexible than bones.

The Spine

A long flexible column of bones extending from neck to the end of the back is called the backbone or vertebral column or spine or spinal column. Human being is born with 33 vertebrae: 24 presacral vertebrae (7 cervical, 12 thoracic, and 5 lumbar) followed by the sacrum (5 fused sacral vertebrae) and the coccyx (4 frequently fused coccygeal vertebrae).Adult spine has 24 separate vertebrae due to fusion of certain vertebrae with development of the body. Between each pair of vertebrae is a disc of cartilage that cushions the bones during movement. The top two vertebrae are different from others, first, called the atlas, rotate around stout vertical peg on the second, the axis. This helps skull to move freely up and down, and from side to side.

Function of spine

      1.   It forms the supporting backbone of the skeleton and hence helps to support our body.

      2.   It serves as protective surrounding for delicate spinal cord.

Rib Cage

The ribs are delicate bones that enclose and protect the chest cavity, where organ such as heart and lungs are located. The human rib cage is made up of 12 paired rib bones; each are symmetrically paired on a right and left side, forming a cage. The last 2 lowest pairs of ribs are only attached to the spine at the back. Hence they are called the floating ribs.

The ribcage forms part of the body’s respiratory system and helps in expansion of the chest cavity so that the lungs can expand and breathe in oxygen.

Limbs

In human body there are two pairs of limbs.

      1.   Fore limbs (arms)

      2.   Hind limbs (legs)

Fore limbs: The bones of shoulder or pectoral girdle are attached to our backbone. The fore limb can be divided into upper arm, the forearm, and the hand. The upper arm of the body extends from the shoulder to the elbow and provides strength for pulling and lifting. The forearm is the part of the fore limb between the wrist and the elbow. The muscles in the forearm help the wrist to extend, rotate, and flex. Hand includes 5 fingers that allow humans to do much more complicated tasks.

The upper arm has single long bone called humerous, till elbow. The lower arm is made up of two bones. There are 27 bones in our hand and wrist.

Hind limbs:

At the bottom of the backbone, there are flat bones which form the pelvic girdle. Our leg bones are connected to pelvic girdle. The leg consists of upper leg, knee, lower leg, ankle, and foot. The femur is the thigh bone, which is the largest bone in the body. The base of the femur makes up part of the knee. The knee is a pivot-like hinge joint, the largest joint that connects the bones in the upper and lower leg. The lower leg has two bones. The ankle and foot contains 26 bones.

The leg gives support to the body when we are standing and help us to do other movements such as walk, run, and jump.

Joints

A joint is junction where two or more bones meet. Different parts such as bone, muscles, synovial fluid, cartilage and ligaments work together which enable us to bend, stretch, twist and turn easily. Most of our joints are move only in certain directions.

The ends of our bones are covered with a thin layer of cartilage. This cushions the joint. Stretchy straps called the ligaments help to hold the joint together and prevent it dislocating.

Immovable joints

An immovable joint or fixed joint is a place in the body where two bones are joined together but show very little or no movement. This includes joints between the bones of the skull, joints in the pelvis and joints between the teeth and the mandible, or lower jaw, and the maxilla, or upper jaw.

Movable joints

The joints that provide free movement to the body are called movable joints. This type of bones is found in the arms, leg, hip and shoulder. Cartilage is found within all movable joints which make movements easier.  

There are different types of movable joints in the body:

Hinge joint: This type of joint moves only in one direction like a hinge of a door. Joints in elbows, knees, fingers and toes have hinge joints.

Ball and Socket joint: This type of joint allows movement in all direction and found in hip and shoulders.

Pivot joint: This type of joint is found between our head and neck and allows side to side movement.

Gliding Joint: Gliding joints allow the bones to glide past one another in any direction along the plane of the joint – up and down, left and right, and diagonally. This type of joint is found in wrist and ankle.

Muscles

Muscles are soft, fleshy but strong tissues that are attached to the bones by tough bands called tendons. The muscular system is responsible for the movement of the human body.

Types of muscles

Voluntary or Skeletal Muscles – This muscles can be consciously controlled. Human has more than 600 skeletal muscles. These type of muscles are attached either directly or indirectly to the bones and work in opposing pairs i.e. one muscle in the pair contracts while other relaxes to produce movement. These are found in arms, legs, eyes, tongue etc. Thus while reading, writing, walking or running, we use voluntary muscles.

Smooth muscles – These muscles are found in the internal body organs and works automatically. They perform action such as forcing food through intestine.

Cardiac Muscles – These are found only in heart. These are involuntary muscles responsible for pumping blood throughout the body.

Interesting thing is that it takes 43 muscles to frown and only 17 muscles to smile.