Biology

Human Skeleton

The organisms with greater sizes need support to keep their body mass as one unit. This is particularly true for the organisms that live on land. We know that movement and locomotion are characteristics of animals. “Movement” is a general term meaning the act of changing place or position by entire body or by its parts.

There are two types of movements i.e. movements of body parts and locomotion. Locomotion is the movement of an animal as a whole from one place to another. We will study human skeletal system (skeleton) which is primarily responsible for support and movement.

HUMAN SKELETON

Skeletal system or skeleton is defined as the framework of hard, articulated structures that provide physical support, attachment for skeletal muscles, and protection for the bodies of animals. Like other vertebrates, the human skeleton is on the inside of body and is called endoskeleton.

The skeletal system of some invertebrates e.g. arthropods, is on the outside of the body, and is called exoskeleton.

In the living body, the skeleton is very much alive. Bones and cartilages are made of living cells and also have nerves and blood vessels in them. They grow and have the ability to repair themselves.

1. Role of Skeletal System

The big functions of skeletal system are protection, support and movements. In our body, skeleton works very closely with the muscular system to help us move. Similarly, skeleton provides protection to many internal organs e.g. skull protects brain, vertebral column protects spinal cord and ribs protect most of our other internal organs. Vertebral column also provides the main support to our body mass.

2. Bone and Cartilage

Overall, the human skeleton is made of bony framework but in certain parts, this framework is supplemented by cartilage.

a. Cartilage

Cartilage is a dense, clear blue-white firm connective tissue (but less strong than bone). The cells of cartilage are called chondrocytes. Each chondrocyte lies in a fluid space called lacuna present in the matrix of cartilage.

Recalling:

Cartilage and bone are types of connective tissue in animals. Most connective tissues contain collage fibres in a matrix.

The matrix of cartilage also contains collagen fibres.. Blood vessels do not eriler cartilage. There are three types of cartilage.

Chondrocytes in cartilage matrix
Chondrocytes in cartilage matrix

Recalling:

Tendons and ligaments are other connective tissues that contain tighty packed collagen fibres.

Types of Cartilage
Types of Cartilage

Hyaline cartilage is strong yet flexible. It is found covering the ends of the long bones, in the nose, larynx, trachea and bronchial tubes.

Elastic cartilage is similar in structure to hyaline cartilage. It is also quite strong but has elasticity due to a network of elastic fibres in addition to collagen fibres. It is found in epiglottis, pinna etc.

Fibrous cartilage is very tough and less flexible due to large number of thick collagen fibres present in knitted form. It is found in intervertebral discs.

b. Bone

Bone is the hardest connective tissue in body. Bones not only move, and protect the various parts of body but also produce red and white blood cells and store minerals.

Hyaline Cartilage
Hyaline Cartilage
 Fibrous-cartilage
Fibrous-cartilage

The hard outer layer of a bone is called compact bone while the interior of bone is soft and porous. It is called spongy bone. Spongy bone contains blood vessels and bone marrow.

Babies are born with about 300 soft bones. Some of these bones later fuse together, so that the adult skeleton has 206 hard bones.

Compact and Spongy bone
Compact and Spongy bone

Like cartilage, the matrix of bones also contains collagen. But it also contains minerals e.g. calcium and phosphate. We know that cartilage contains a single type of cell. On the other hand, bones contain different types of cell. The mature bone cells are called osteocytes.

The internal structure of bone
The internal structure of bone

Andreas Vesalius

Andreas Vesalius (1514-1564) is honoured for developing modern anatomical studies. Vesalius was born in Brussels, Belgium. He made many discoveries in anatomy, based on studies made by dissection of human dead bodies. His book contained the most accurate depictions of the whole skeleton and muscles of the human body.

3. Components of Human Skeleton

The 206 bones in the adult human skeleton are organized into a longitudinal axis i.e. axial skeleton, to which appendicular skeleton is attached.

a. Axial skeleton

Axial skeleton consists of the 80 bones in the head and trunk of body. It is composed of five parts. Skull contains 22 bones out of which 8 are cranial bones (enclosing the brain) and 14 are facial bones. There are 6 middle ear ossicles (3 in each ear). There is also a hyoid bone in neck. Vertebral column contains 26 bones (vertebrae). The chest is made of a chest bone called sternum and 24 (12 pairs) ribs.

b. Appendicular Skeleton

Appendicular skeleton is composed of 126 bones. Pectoral (shoulder) girdle is made of 4 bones. Arms have 6 bones. Both hands have 54 bones. Pelvic girdle (hips) has 2 bones. Legs have 6 bones. Both feet have 54 bones.

The thigh bone is the longest bone in our body.

The stapes is the smallest bone in the human body. The malleus is sometimes compared to a hammer, because it strikes the anvil-shaped incus.

Human-Skeleton

Human Skeleton

Do you know?

The upper jaw is fixed with the skull and is composed of two bones. The lower jaw is mobile and articulates with the skull. In lower vertebrates, the lower jaw is made up of more than one bone while in mammals, it is made of single bone. During evolution, mammals modified the lower jaw bones and incorporated four of them into the middle ear (in the form of malleus and incus in both ears). This adaptation proved beneficial for mammals. Lower jaw with single bone is stronger and the malleus and incus also improve hearing.

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