Khullakitab.comClass 9 Science Note
Skeletal System
Skeleton system is a supporting framework of the body made by the combination of various bones.
There are 206 bones in our body.
Functions of bones
a. It gives definite shape and size to the body.
b. It protects delicate organs such as heart, lungs, kidneys etc.
c. RBC is formed in the red marrow of bones.
d. Muscles are attached to the body which helps in moving different body parts.
Bones are divided into two groups
Axial skeleton: It includes bones of head, thorax ribs and vertebral column.
Appendicular skeleton: It includes the bones of limbs, shoulder and pelvic girdle.
Skull
Skull is a bony structure of the head in the skeleton, which supports the structures of the face and forms a cavity for the brain.
There are eight bones in the skull. They are
i. Frontal
ii. Parietal
iii. Temporal
iv. Ethmoid
v. Sphenoid
vi. Occipital
There are 14 pieces of bones in the face. They are:
i. Mandible
ii. Maxilla
iii .Zygomatic Bone
iv. Nasal Bone
v. Lacrimal Bone
vi. Vomer Bone
vii .Palatine Bone
viii. Inferior nasal conchae bone
Larynx
Hyoid bone: It supports the tongue-base situated just below the mandible.
Ear ossicles : There are three ear bones: malleus ,incus and stapes
Trunk bone
Trunk bones consists of vertebral column and thorax
Vertebral column consists of:
a. Cervical vertebrae (7 pieces)
b. Thoracic vertebrae (12 pieces)
c. Lumbar vertebrae (5 pieces)
d. Sacral vertebrae or sacrum
e. Coccygeal vertebrae or coccyx
Thoracic bone
This helps to protect the vital organ such as lungs and heart.
Appendicular skeleton
They are divided into two parts
Upper parts
Shoulder gridle:
The bones in our hand are:
Humerus: The long bone extending from shoulder to elbow is called humerus.
Radius and Ulna: The part between elbow and wrist consists of two bones called radius and ulna. The ulna lies towards the little finger and the radius lies towards the thumb.
Carpals: There are 8 carpals in the wrist. They lie as two rows, four in each row.
Metacarpals: Each hand consists of five metacarpals. They are attached to carpals at one side and two fingers at the other side.
Phalange: The five fingers consist of 14 pieces of bones called phalanges. The thumb consists of two bones and the remaining four fingers consist of three bones each.
Lower parts:
Pelvic girdle: The two bones connected to the thigh bones and vertebrae together are called pelvic gridle.It helps to protect the organ like stomach, urinary bladder and intestine.
The bones at legs are:
Femur: The largest and the strongest bone of the body is femur. It is attached to the tibia and fibula bone at the lower part.
Fibula and Tibia: They are two long bones below the knee. One is fibula which is thin and weak. It does not the support the load of the body. The other is tibia which is thick and strong. It supports the load of the body.
Tarsals and Metatarsals: There are 7 bones in the tarsals whereas metatarsals are made up of five bones. Tarsals are round and are arranged in three rows. Metatarsals are straight and long.
Phalanges: The toes consist of 14 pieces of bones as in the hands. The first toe consists of two bones and the rest consist of three bones each.
Joint
The joining of two or more bone is called joint.
There are four types of joint in a body. They are as follows:
a. Gliding joint: The bones slide one above the other. Example: Joints found in carapals and tarsals.
b. Hinge joint: The bone can be moved in one direction only. Example: Joints found in elbow, knee and fingers.
c. Pivot joint: The joint between the first and second bone of the neck, and the joint between ulna and radius are examples of pivot joint. This joint can rotate around the bone.
d. Ball and socket joint: In this joint, the bone can easily be dislocated. Because of this joint, we can move.