Learning Objectives
Let's start by understanding what is the skeletal system.
The skeletal system supports and protects the body while giving it shape and form. It is composed of connective tissues including bone, cartilage, tendons, and ligaments. Nutrients are provided to this system through blood vessels that are contained within canals in the bone. The skeletal system stores minerals and fats and produces blood cells. It also provides mobility. Tendons, bones, joints, ligaments, and muscles work together to produce various body movements.
The two main components of the skeletal system are bones and cartilage. There are two types of connective tissues called tendons and ligaments that are also considered as part of the system. Ligaments connect bones to bones whereas tendons connect bones to muscles.
The human skeletal system is organized into two main divisions. An adult human skeleton contains 206 bones, 80 of which are from the axial skeleton and 126 from the appendicular skeleton.
The axial skeleton runs along the body’s central axis. It is composed of 80 bones and it consists of
The appendicular skeleton is composed of body limbs and structures that attach limbs to the axial skeleton. It consists of
The skull is made up of 22 bones joined together apart from the mandible. The 21 fused bones are not fused but separate in children to allow for the growth of the brain and the skull. These bones later fuse to give strength and protection as an adult. The mandible remains as a jaw bone that is movable. The mandible forms the only joint that is movable in the skull with the temporal bone.
Cranium is the name given to the bones of the superior portion of the skull that protects the brain from damage.
Facial bones is the name given to the bones of the inferior and anterior portion of the skull that support the eyes, mouth, and nose.
Hyoid refers to a small, U-shaped bone that is found inferior to the mandible. This is the only bone in the body that doesn’t form a joint with any other bone. It is sometimes said to be a floating bone. The function of the hyoid is to help hold the trachea open as well as forming a bony connection for the tongue muscles.
Auditory ossicles are the stapes, malleus, and incus. They are the smallest bones in the body. They are found inside the temporal bone and their purpose is to transmit as well as amplify sound from the eardrum to the inner ear.
The average person is born with 33 individual bones (the vertebrae) that interact and connect with each other through flexible joints called facets. By the time a person becomes an adult, most have 24 upper vertebrae articulating and separated from each other by intervertebral discs, and the 9 lower are fused together, 5 in the sacrum and 4 in the coccyx, or tailbone, during normal growth and development.
The sternum is also known as the breastbone. It is a thin, knife-shaped bone that is located along the midline of the anterior side of the thoracic region of the skeleton. The costal cartilage connects the sternum to the ribs. There exist 12 pairs of ribs that together with the sternum form the ribcage of the thoracic region.
The pectoral girdle is responsible for connecting the upper limb bones (arm) to the axial skeleton and is made up of the left and right clavicles as well as left and right scapula. Humerus is the name given to the bone of the upper arm.
The pelvic girdle is formed by the right and left hip bones. It connects the lower limb bones (leg) to the axial skeleton. Femur is the name given to the largest bone in the body. It is also the only bone of the thigh region (femoral).
The unique connective tissue that fills the interior of most bones is referred to as bone marrow. There are two types of bone marrow:
Bones can be classified into four types based on their shape:
Long bones – They are long and slender bones found generally in the limbs. Example: humerus, femur
Short bones – They are short bones that are smaller in size and are found in the carpals and tarsals.
Flat bones – They are thin and flat in nature and not all of them are completely flat. They provide surface area for muscle attachment. Example: scapula, sternum
Irregular bones – These bones do not have specific shapes and therefore cannot be put into any other group. Example: vertebrae
Each bone tissue is made up of two types of osseous tissues – compact bone and spongy bone.
1. Compact bone is hard and compact in nature and always found towards the outside of the bone.
2. Spongy bone is softer and more porous is found towards the center.
The function of each bone determines the ratio in which these two types of tissues exist within it
The connective tissue that is found on the outside of the bone is known as the periosteum. The periosteum is made up of cellular and fibrous tissue and plays a crucial role in the attachment to muscles and joints as it is this layer that contains tendons and ligament attachments. The endosteum is the connective tissue layer which lines the marrow cavity.
The shaft of a bone is known as the diaphysis and the swollen end is called the epiphysis. The epiphyseal line demarcates the two parts. It is the diaphysis that houses the marrow cavity which is majorly composed of loose connective tissue and is responsible for producing blood cells.
The cells that form bone matrix are known as the osteoblasts and the mature cells of the bone are called osteocytes. There is a special type of cells that help remove bone matrix and are found during bone remodeling known as osteoclasts. These are gigantic cells and are always found on the side of the bone where the matrix is being eaten away during growth and remodeling.
The matrix in bone tissue is made up of two components: the organic part contains fibers whereas the inorganic part consists of the minerals (hydroxyapatite).
Cartilage is the second component of the skeletal system. It is made up of fibers that are embedded in connective tissue or ground substance. Cartilage consists of two types of fibers – collagen and elastin fibers.
The cells that form cartilage are known as chondroblasts and the mature cells of the cartilage are known as chondrocytes. The chondrocytes lie in lacunae in the matrix. The outer layer of cartilage is known as the perichondrium. Unlike the bone, cartilage is avascular which means that it contains no blood supply. However, the perichondrium contains blood supply.
The main function of the skeletal system is that it provides a framework for the body and provides shape.
Along with the muscular system, the skeletal system helps in the movement of the body parts of the body and locomotion of the body.
The skeletal system is hard and so forms a protective layer for the softer, more delicate organs from any form of injury. The rib cage protects the heart, lungs and visceral organs, the brain is protected by the skull, etc.
It is the growth and development of bones that provide the height and width of an individual. The center of the bone consists of the bone marrow which produces blood cells and therefore hemopoietic in nature.
