9.1 Introduction of Human Skeleton

• The skeleton is the framework of the human body, much like the structural framework required for constructing a house.

• It consists of 206 bones of different shapes (long, small, flat, and unequal), giving the body its shape and protecting vital internal organs such as the heart, lungs, brain, stomach, and intestines.

• In children, the number of bones is greater than in adults, as some bones fuse as a person matures.

• The skeleton consists of bones and associated parts, working together to maintain the body’s shape and function.

Key Bones in the Human Skeleton

1. Skull: Includes Maxilla (upper jaw), Cranium (brain case), Mandible (lower jaw).

2. Limbs:

• Upper Limb: Humerus (upper arm), Radius and Ulna (forearm), Carpal (wrist), Metacarpal (hand), Phalanges (fingers).

• Lower Limb: Femur (thigh), Patella (knee cap), Tibia and Fibula (shin), Tarsal (ankle), Metatarsal (foot), Phalanges (toes).

3. Ribcage: Sternum (breastbone), Rib (protecting thoracic organs).

4. Vertebral Column: Consists of vertebrae (backbones), Sacrum, Coccyx (tailbone).

5. Pelvic Girdle: Ilium, Pubis (pelvic bones).

Bones and Bone Joints

• Bones are interconnected by joints, which allow for movement. Joints are held together by ligaments and are attached to muscles for movement. The skeletal system also includes tendons, cartilage, and muscles.

Classification of Skeleton

1. Exoskeleton: External parts of the body such as nails and hair.

2. Endoskeleton: The internal skeleton, made up of bones and cartilage.

9.1.1 Role of Skeleton in Firmness and Locomotion

The skeleton plays several critical roles in the body:

• Structure and Firmness: Provides the body with a rigid structure and shape, joining different parts of the body.

• Protection and Weight Carrying: Protects internal organs (brain, heart, lungs) and supports the body’s weight, with muscles attached to bones to aid in movement.

• Movement and Locomotion: Facilitates movement, especially through the attachment of muscles to bones in limbs and girdles.

• Production of Red Blood Cells: Bone marrow produces red blood cells.

• Storage of Mineral Salts: Stores calcium, potassium, phosphorus, and other minerals, maintaining bone strength.

9.1.2 Bone, Cartilage, and Joint

Bone

• Structure: Bone is the strongest form of connective tissue and consists of a matrix made of organic and inorganic compounds like phosphorus, sodium, potassium, and calcium.

• Cell Composition: Bone cells are distributed within the matrix. Bone tissue continuously undergoes decay and development.

• Bone Formation: Vitamin D and calcium are essential for bone development, and adequate sunlight is necessary for vitamin D synthesis. Lack of these can cause bone growth issues.

Cartilage

• Properties: Cartilage is softer, more flexible, and elastic than bone. It serves as a type of connective tissue.

• Structure: Cartilage cells (chondrocytes and chondroblasts) are found within a matrix called chondrin, which is semi-transparent and light blue.

• Types: Cartilage is found in structures like the ears, joints, and on bone articulating surfaces.

Bone Joint (Articulation)

• Definition: The connection between two or more bones, held together by ligaments, which prevent dislocation.

• Types of Joints:

• Fixed Joint: No movement, e.g., the joints in the cranium.

• Slightly Movable Joint: Allows some movement, e.g., intervertebral joints.

• Freely Movable Joint: Allows free movement, e.g., hinge joints, ball and socket joints.

Synovial Joint

• Definition: A type of joint where the ends of bones are covered with cartilage and connected by a fibrous capsule containing synovial fluid, which reduces friction and allows for smooth movement.

Types of Synovial Joints

1. Ball and Socket Joint:

• Allows movement in all directions. Example: Shoulder joint, hip joint.

2. Hinge Joint:

• Allows movement in only one plane (like a door hinge). Example: Elbow, knee, finger joints.