Bones and Muscles
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
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
- They provide structural support and protect various
organs of the body.
- They produce red blood cells.
- They enable mobility by acting as levers and points of
attachment for muscles.
- They act as storage for calcium and phosphorus,
essential minerals for various cellular activities throughout the body.
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.
The human skeleton performs six major functions;
support, movement, protection, production of blood cells, warehouse of
The skull is the most complicated bony structure that
forms the head of the skeleton. It provides a protective case for the brain and
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.
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
- It forms the supporting backbone of the skeleton and
hence helps to support our body.
- It serves as protective surrounding for delicate spinal
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.
In human body there are two pairs of limbs.
- Fore limbs (arms)
- 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.
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.
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
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.
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
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
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 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.