Skeletal System – Class 11 | Chapter – 20 | Biology Short Notes Series PDF

Skeletal System: Skeletal system is composed of all the bones in the body along with the associated connective tissues. It is the basic internal framework of the human body. Skeletal system along with its associated tissues supports the structure of the body and allows movement. Depending upon the species, the skeletal system of the living beings differs from each other. There is a lot of difference between the skeleton of terrestrial and aquatic animals.

Joints are an important component of skeletal system. They allow for movement of different body parts. A skeleton mainly includes all the rigid components of the body associated with each other through various connective tissues like tendons, ligaments, cartilage etc.

Functions of Skeletal System

The skeletal system performs a wise range of functions for the human body. While its main functions is to provide structure and allow movement of body parts, it also helps in production of blood cells and storage of minerals. The various functions perform by the body are as follows:

  • Support to the Body – Skeletal system provides an internal rigid framework to the body which helps support its internal organs. It also provides a shape to the body. 
  • Movement of Body Parts – Movement is the key functions of the skelatal system. There are different types of joints formed by the skeleton. These joints allow the movement of the different body parts. Without the joints, the body would have been a stiff, rigid structure with no movement. 
  • Protection of Internal Organs – The skeletal system serves to protect the internal, delicate organs of the body. For example, skull protects the brain, thoracic cage protects the heart and the lungs etc. 
  • Storage of Minerals – Skeleton also serves to store various essential minerals required for growth and repair of the cells. These minerals are stored in the bone matrix and released into the blood whenever required. 
  • Production of Blood Cells – The bone marrow present inside the bones is responsible for producing the red and white blood cells in our body. 

Diseases of Skeletal System

There are different types of diseases associated with the skeletal system. The most common diseases of the skeletal system includes:

  • Osteoporosis – In this condition, the strength of the bone gradually decreases at a rate higher than that of the bone growth. It can be due to genetic reasons and lack of essential nutrients like calcium or vitamin D.
  • Osteoarthritis – It refers to the condition in which the cartilage that protects the ends of the bones in joints gets broken down. Because of the absence of the cartilage at the joints, the rubbing of bones occurs leading to pain and damage to the bones. 
  • Leukemia – Leukemia is a type of cancer in bone marrow and the lymphatic system. It affects blood cells and other body functions. 

Anatomy of Skeletal System

Skeletal System

Human body consists of 206 bones arranged in a specific pattern in the body. This arrangement allows the body to perform its different functions including locomotion and movement. The skeletal system of humans is mainly divided into two categories:

  • Axial Skeleton
  • Appendicular Skeleton

Axial Skeleton

The axial skeletal system is present along the body’s central axis i.e. on its longitudinal axis. It includes the skull, spine, sternum, auditory ossicles, hyoid, and ribs. The axial skeleton of an adult is composed of 80 different bones. Some of the bones of the axial skeleton are as follows:

  • Skull – The skull acts as the protective cage for the brain. Since the brain is a delicate part, it is well protected by the skull. Skull mainly contains 22 bones divided into two types – Cranial and Facial. A skull with 2 occipital condyles is named dicondylic. Human skull is dicondylic. 
  • Auditory Ossicles – The bones of the auditory ossicles are found in the inner ear canal. It consists of 6 small bones, three on each side of the head. The bones are named malleus, incus and stapes. These bones helps in transmission of sound waves from outside to the inner ear. 
  • Hyoid – It is the U-shaped bone present at the base of the jaw. It serves to attach muscles and ligaments in the neck.
  • Vertebral Column – The vertebral column or spine is made up of 26 bones including 24 vertebrae and two other bones sacrum and coccyx. The sacrum and coccyx bones are made of fused vertebrae. 
  • Thoracic Cage – It includes the sternum and the ribs. There are 12 pairs of ribs in a human body. Thoracic cage act as a protective covering for the organs like heart and lungs. 

Vertebral Column

The vertebral column is composed of 26 bones which encloses the spinal cord and supports head. It is divided into 5 regions mentioned below:

  • Cervical Vertebrae – These are 7 in number and are found in the neck region. 
  • Thoracic Vertebrae – They are 12 found in the upper region of the back. 
  • Lumbar Vertebrae – The next 5 bones make up the lumbar vertebrae region. It supports the lower part of the back. 
  • Sacral Vertebrae – The next 5 vertebrae fuses to form the sacral region. 
  • Coccygeal Vertebrae – It is made up of 4 fused vertebrae. 

Both sacral and coccygeal vertebrae support the weight of the body while sitting.

Appendicular Skeleton

The appendicular skeletal system comprises of 126 bones which includes limbs, pelvic girdle, and pectoral girdles. These bones make up the arms and legs of the humans. 

  • Pectoral Girdle – It is the region where the bones of the arms gets attached to the axial skeleton. This region is made up of two bones for each arm – Clavicle and Scapula. 
  • Pelvic Girdle – Pelvic girdle forms the hip region. It is the region where legs attach to the axial skeleton. The bones of the pelvic girdle includes Ilium, Ischium, and Pubis. 
  • Limbs – There are different bones that makes up the upper and the lower limb. The upper limbs (or the arms) includes bones known as humerus, radius, ulna, carpals, metacarpals and phalanges. The bones of the lower limb (legs) are femur, tibia, fibula, patella, tarsals, metatarsals and phalanges. 

Upper Limb

The bones of the upper limb are as follows:

  • Upper arm – Humerus – 1
  • Forearm – Radius – 2
  • Ulna
  • Wrist – Carpals – 8
  • Palm – Metacarpals – 5
  • Fingers – Phalanges – 14

To remember phalanges, its formula for the human hand is 2,3,3,3,3.

Lower Limb

In each lower limb, 30 bones are found. These are – 

  • Thigh – Femur – 1
  • Shank – Tibia – 2
  • Fibula
  • Ankle – Tarsals – 7
  • Instep – Metatarsals – 5
  • Toes – Phalanges – 14
  • Knee joint – Patella – 1

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By Team Learning Mantras