Human Skeletal System

The UPSC mains GS-3 paper syllabus has various subjects like Economics, Science and Technology. Science and technology in UPSC is mostly concerned with current Affairs. but it is necessary to understand the basics of science. Human Body consists of some of the most complex systems. Human Muscular System is helpful in the movement of the body, The muscles can move voluntarily and involuntarily.

TOPICS

• What is Skeletal system
• Bone
• Cartilage
• Joints
• Vertebral Column

WHAT IS SKELETAL SYSTEM

Skeletons are either a fluid-filled body cavity, exoskeletons, or internal skeletons. Bones, joints and muscles are part of the skeletal system of humans. The skeletal system is made of 2 parts:

• Axial Skeleton- The skeleton which makes the main axis of the body such as the skull, vertebral column and bones of the chest.
• Appendicular skeleton- It consists of bones that support appendages.

Bone

Bone is a highly mineralized tissue in which connective tissue part is 1/3rd while mineral part is 2/3rd portion. Apart from providing mechanical strength, the bones work as homeostatic reservoir for ions such as calcium, magnesium and phosphorous. Thus,bones have a very important function in acid base balance in the body. There are 270 bones in a new born baby and 206 in an adult human.

Bone as connective Tissue

Formation of bones is called Osteogenesis or Ossification.  Bones are made of three types of specialized cells called osteoblasts, osteocytes and osteoclasts. Osteoblasts make the bone while Osteoclasts break / remodel the osteous tissue. They create canals in bones. Osteocytes provide support.

The intercellular part between Osteocytes is made of casein protein and inorganic phosphates. We note here that bony tissue is highly vascular and has greater regenerative power than any other tissue of the body except Blood. Bones have narrow tubes called Haversian Canals and Volkmann’s Canals apart from the network of blood vessels.

Number of Bones

An adult human has 206 bones while a new born baby has 300 bones. 94 bones fuse as a baby grows. The total number of bones in human skull is 29. The face of a man is made up of 14 bones. Largest and longest bone is femur (thigh bone).The shortest bone in the human body is stapes or stirrup bone in the middle ear.

Cartilage

Cartilage is softer, elastic tissue that makes joints between bones, rib cage, ear, nose, bronchial tubes, intervertebral discs etc.

Joints

Joints are structures where two bones are attached so that bones can move relative to each other. Bones are held together at joints by ligaments,  which are strong, fibrous, connective tissues. Joints are classified into three groups:

• Immovable (fibrous) joints, e.g. skull bones;
• Slightly movable (cartilagenous) joints, e.g. intervertebral discs;
• Freely movable (synovial) joints, e.g. limb joints.

Synovial joints permit the greatest degree of flexibility and have the ends of bones covered with a connective tissue (synovial membrane) filled with joint (synovial) fluid.

Vertebral Column

The spinal cord runs along the dorsal side of the body and links the brain to the rest of the body.  Vertebrates have their spinal cords encased in a series of (usually) bony vertebrae that comprise the vertebral column. Our back is composed of 33 bones called vertebrae, 31 pairs of nerves, 40 muscles and numerous connecting tendons and ligaments running from the base of your skull to your tailbone. Between our vertebrae are fibrous, elastic cartilage called discs known as shock absorbers.