What is meant by the Skeletal System?

The skeletal system is the core framework of the human body. The skeletal structure comprises bones and connective tissue, including cartilage, ligaments, and tendons. The skeletal structure of our body acts as a support structure. It maintains the body's shape and is responsible for its movement, blood cell formation, protection of organs, and mineral storage. The skeletal system is referred to as the musculoskeletal system.

The function of the Skeletal System

The skeletal system plays various important roles in the body.

• It provides shape to the body and enables different types of body movements.
• It supports the body weight and allows us to stand and move.
• The collaboration of joints, muscles and connective tissues allows body parts to move.
• Bone marrow is the main element that is found in bones. The bone marrow is the site where white and red blood cells are formed.
• The skull in the skeletal system that guards and shields the brain.
• The ribs cover and guard the lungs and heart.
• The backbone guards the spine.
• In the bones, minerals, such as calcium and phosphorus, are stored.

Components of the Human Skeletal Structure

Different components together form the skeletal system that provides support to the body. These components include bones, connective tissue, tendons, joints, and ligaments.

Bones

The bones are the hard elements that form our body's skeleton, the natural framework, which is the essential part of our skeletal system. Adults have 206 bones in their skeletons. Bone is composed of three layers: periosteum, compact or dense tissue, and spongy or soft tissue. The periosteum forms the outermost layer that surrounds and protects the bone. The dense tissue forms the middle layer and is whitish, smooth, and rigid. This tissue helps in maintaining structural integrity. The spongy tissue forms the inner layer of the bone and is porous, referred to as trabeculae.

Cartilage

The connective tissue that covers the joints (the connection between two bones) is known as cartilage. It permits bones to move freely without causing friction. The absence of cartilage creates movement issues, and movement can be uncomfortable or painful, as in arthritis.

Axial and appendicular skeleton

The human skeleton is divided into two parts: axial and appendicular. The skeleton that consists of the head and the trunk is referred to as the axial skeleton, and the bones that form the limbs, the pectoral and pelvic girdle, are referred to as the appendicular skeleton.

Axial Skeleton

The axial skeleton includes the skull, thoracic cage, laryngeal skeleton, and vertebral column.

Skull

The top and rear of the skull are made up of cranial bones, which enclose the brain. The facial part of the skull is made up of facial bones. The two parietal bones, occipital bone, two temporal bones, frontal bone, ethmoid and sphenoid, are the eight cranial bones that form the skull and protect the brain. The paired zygomatic, maxilla, palatine, lacrimal, nasal, and inferior nasal conchae bones and the unpaired mandible and vomer are the 14 facial bones that make up the facial skeleton.

Inner ear bones

The malleus, incus, and stapes are the three smallest bones in the body and they are found inside the petrous section of the temporal bone. Through these three bones, the tympanic membrane sends vibrations to the inner ear.

The bones of the vertebral column

The vertebral column is a slightly bendable column that is formed of 24 vertebrae, as well as the coccyx and sacrum. The vertebral column, often known as the spine, runs from the base of the cranium to the pelvis. It is divided into five sections: cervical (C1-C7), lumbar (L1-L5), thoracic (T1-T-12), coccygeal and sacral spines. From the foramen magnum of the skull, the spinal cord runs through the canal of the vertebral column.  

Thoracic cage

The ribs and sternum make up the thorax cage, which guards internal organs and provides connections to muscles involved in breathing and upper-limb motion. The sternum, manubrium, and xiphoid processes make up the sternum. The ribs from one to seven are called true ribs that connect directly with the sternum and eight to twelve are called false ribs.

Laryngeal skeleton

The epiglottis, cricoid cartilage, thyroid cartilage, arytenoid cartilages, corniculate cartilages, and cuneiform cartilages make up the laryngeal skeleton. The first three cartilages are unpaired, while the last three are paired. The thyroid cartilage serves as a protective barrier across the anterior section of the larynx, spanning vertically from upper to lower. It has the appearance of a partial book, with the back facing the front and two halves connecting in the middle to form the laryngeal prominence (adam’s apple).

Appendicular skeleton

The appendicular skeleton is the part of a vertebrate's skeletal structure that contains the bones that hold the appendages. There are 126 bones in total. The skeletal parts of the limbs, as well as the supportive shoulder or pectoral girdle and pelvic girdle, are all part of the appendicular skeleton.

The appendicular skeleton is organized into six primary structures:

• The clavicle and scapula make up each pectoral girdle.
• The humerus in each upper arm, the ulna and the radius in each forearm form the upper limb.
• The 16 carpals in the wrist, ten metacarpals, and 28 phalanges make up the 54 bones that form the hands.
• The pelvic girdle is made up of hip bones. Hip bones are formed by three bones (ilium, ischium and pubis).
• The femur in each thigh, the patella in each knee, tibia and fibula in each leg form the thigh and leg.

Pectoral girdle

The pectoral girdle is composed of two bones, the clavicle, and scapula that connect the upper limb to the thoracic cage. The humerus, ulna (medially), and radius (laterally) are the three regions of the upper limb. The base of the palm is made up of eight carpal bones, whereas the palm is made up of five metacarpal bones. Fourteen phalanges make up the fingers and thumb. 

Pelvic girdle

A single bone, coxal or hip bone, forms the pelvic girdle that functions as the connection point for each lower leg. The connection of each hip bone to the sacrum of the vertebral column connects it to the axial skeletal structure. Each lower limb is divided into three regions: the thigh, lower leg, and foot, and it has 30 bones (femur, patella, tibia, fibula, seven tarsal bones, five metatarsal bones, and 14 phalanges).

Context and Applications

This topic is significant in the exams of school, graduate, and post-graduate levels, especially for bachelors in life sciences/zoology and masters in life sciences/ zoology.

Practice Problems

Question 1: Pectoral girdle includes which of the following?

1. Coxal bone
2. Clavicle and scapula
3. Cuneiform cartilages
4. All of the above

Answer: Option 2 is correct.

Explanation: The pectoral girdle is a structure made up of two bones, clavicle and scapula.

Question 2: Laryngeal skeleton is a part of …………

1. Vertebral column
2. Axial skeleton
3. Appendicular skeleton
4. None of the above

Answer: Option 2 is correct.

Explanation: The skull, vertebral column, thoracic cage, and laryngeal skeleton are all part of the axial skeleton.

Question 3: The vertebral column contains the ............ number of  vertebrae

1. 12
2. 126
3. 24
4. 10

Answer: Option 3 is correct.

Explanation: The vertebral column, which is made up of 24 vertebrae, and the bones includes the coccyx and sacrum.

Question 4: Which of the following is included in the cartilages?

1. Epiglottis
2. Scapula
3. Tibia
4. All of the above

Answer: Option 1 is correct.

Explanation: The epiglottis is the cartilage found in the laryngeal skeleton. Tibia and scapula are the bones of the lower limb and pectoral girdle, respectively.

Question 5: The covering of bone is named ..............

1. Compact bone
2. Spongy bone
3. Periosteum
4. None of the above

Answer: Option 3 is correct.

Explanation: The periosteum is a strong membrane that protects and covers the bone.