Glossary of Musculoskeletal System - Skeletal Terms and Terminology

The term "musculoskeletal system" includes two major and different subsystems which are the muscular system and the skeletal system. For the purpose of this review, each of these systems will be discussed and explored separately.

  • Axial bones: The majority of bones in the body which make up, for example, the skull, the ribs and the spinal column
  • Appendicular bones: The bones which make up the rest of the skeletal system after the axial bones include the bones found in the upper limbs (arms), lower limbs (legs), shoulders and the pelvis.
  • Flat bones: Flat bones like the sternum or the breast bone
  • Long bones: The bones of humerus which is the long bone of the arm and the femur which is the long bone of the leg
  • Irregular bones: Irregularly shaped bones like the sacrum and coccyx which make up the person's tail bone
  • Cancellous bone: Spongy bone which is not as strong and hard as cortical bone is
  • Cortical bone: Bone that is stronger than cancellous bone and the kind of bone that is most needed for bodily support and bodily movement
  • Periosteum: The outer layer that covers all bones with the exception of long bones
  • Endosteum: The lining around the inner most layer of the bone
  • Medullary cavity: The innermost part of the bone which holds bone marrow.
  • Osteocytes: The cells in the bone that form the inner matrix of bone tissue that gives bones their strength
  • Osteoclasts: The cells in the bone that break down bone and reabsorb it so that the bones can renew with remodeling and repair
  • Osteoblasts; The cells in the bone that build new remodeled bones by producing new collagen and building new bone minerals
  • Stem cells: The cells in the bone that are also called osteogenic cells and that form in the inner surface of the bone and they are somewhat immature osteoblasts that will later transform into osteoblasts
  • Lining cells: The cells in the bone that protect the bones and they also release calcium into the blood when the blood calcium levels are low
  • Ligaments: Connective tissue with collagen that connects bones to bones at the point where they articulate or come in close proximity to each other
  • Tendons: Connective tissue with collagen that connect bones to muscles and allow joint movement
  • Fascia: Connective tissue that connects muscles to other muscles
  • Cardiac muscle: Striated muscle like the skeletal muscles and those muscles that are restricted to only the heart
  • Myocardiocytes: Cells within cardiac muscle that contract the myocardium that are also referred to as cardiomyocytes
  • Skeletal muscle: Striated muscle that is voluntary muscle that enables the skeletal structures to move
  • Smooth muscle: Involuntary muscles that control the movements and actions of the internal organs and systems of the body
  • Abduction: Movement away from the middle of the body
  • Adduction: Movement towards the middle of the body
  • Flexion: Movement that decreases, or lessens, the angle between two muscles or joints
  • Extension: Movement that increases the angle between two muscles or joints
  • Hyperflexion: The flexion of a joint that is beyond what it normally should do
  • Hyperextension: The extension of a joint that is beyond what it normally should do
  • Rotation: The circular movement of a joint or muscle that allows the bodily part to move in a circular manner.
  • External rotation: The muscular and joint movement that entails both circular movement and also movement away from the center of the body
  • Internal rotation: The muscular and joint movement that entails both circular movement and also movement towards the center of the body
  • Circumduction: The muscular and joint movement that entails complete 3600 movement
  • Inversion: The turning of a joint inward
  • Eversion: The turning of a joint outward
  • Plantar flexion: Movement of the foot (plantar) downward
  • Dorsiflexion: Movement of the foot (plantar) upward
  • Range of motion: The specific movements or motions that each muscle is capable of.
  • Complete fracture: A fracture that involves the entire cross section of the fractured bone
  • Incomplete fracture: A fracture that affects only part of the bone and not the entire cross section
  • Stable fracture: A fracture that is stable and are not likely to be displaced
  • Unstable fracture: A fracture that has displacement from its normal alignment
  • Closed fracture: A fracture that does not break through the surface of the skin
  • Opened fracture: A fracture that breaks through the skin surface to the exterior of the body
  • Pathological fracture: A fracture that results from a disease process rather than undue stress or trauma as other fractures do.
  • Greenstick fracture: A fracture that occurs when only one side of the bone is fractured
  • Avulsion fracture: : A fracture that occurs when a fragment of the fractured bone is pulled off the bone at its tendon or ligamentous attachment
  • Comminuted fracture: A fracture that occurs when splinters and small pieces of the fractured bone occur
  • Transverse fracture: A fracture that occurs straight across the fractured bone.
  • Oblique fracture: A fracture that occurs at an angle across the fractured bone
  • Spiral fracture: : A fracture that occurs when the pattern twists around the fractured bone
  • Impacted fracture: : A fracture that occurs when a bone fragment of the fractured bone is pushed and wedged into another bone fragment of the fractured bone
  • Compression fracture: A fracture that occurs when the fractured bone collapses as occurs with vertebral spinal fractures
  • Depressed fracture: A fracture that occurs when bone fragments of the fractured bone are pushed in beyond the surrounding skin
  • Dislocation: The joints are completely separated and are no longer articulated and connected with each other
  • Subluxation: Only a partial, rather than a complete, displacement and separation of the joints or articular surfaces
  • Arthritis: One of the many types of skeletal disorders that is characterized with the inflammation of one or more skeletal joints in the body
  • Rheumatoid arthritis: A type of arthritis that affects the younger population
  • Osteoporosis:
  • Osteoarthritis: The type of arthritis that primarily affects the older population as their joints age, wear and tear.
  • Osteomyelitis: An infection of bone tissue
  • Intervertebral disc disease: A progressive degeneration of the Intervertebral discs in the spinal column
  • Fractures: The breakage of a bone

The Parts of the Skeletal System

Diagram of the front of the human skeleton.

Diagram of the rear view of the human skeleton.

Bones

The skeletal system among adult human beings has 206 bones; some of these bones, like the femur of the upper leg, are quite large and others, like the phalanges of the toes, are quite small, as shown in the picture above.

The bones of the skeleton can be categorized and classified in several ways. The bones and the human skeleton can be classified as:

  • Axial bones which make up the skull, the ribs and the spinal column
  • Appendicular bones which make up rest of the skeletal system including the bones found in the upper limbs (arms), lower limbs (legs), shoulders and the pelvis.

AND, bones can also be categorized and classified as:

  • Flat bones which are flat like the sternum or the breast bone, as shown above

Position of femur (shown in red).

Position of humerus (shown in red) from an anterior viewpoint.

  • Long bones like the humerus which is the long bone of the arm and the femur which is the long bone of the leg, as shown above

Sacrum - Pelvic Surface

A coccyx with four vertebrae below the sacrum.

  • Irregular bones which are irregular in terms of their shape like the sacrum and coccyx which make up the person's tail bone, as shown above

Right Knee

Cross section showing cancellous bone.

AND, bones can also be categorized and classified as:

  • Cancellous bone or spongy bone, as shown in the picture above, which is not as strong and hard as cortical bone is

Diagram of cross-section of cortical bone showing osteocytes and osteon.

  • Cortical bone, which is the stronger of these two types of bone, is the kind of bone that is most needed for bodily support and bodily movement.

The periosteum covers the outside of bones.

The layers of the bone, as shown in the picture above, are the:

  • Periosteum which is the outer layer that covers all bones with the exception of long bones

Endosteum covers the inside of bones, and surrounds the medullary cavity.

  • The endosteum which is the lining around the inner most layer of the bone

  • The medullary cavity which is the innermost part of the bone which holds bone marrow.

The various kinds of cells that make up bone are:

  • Osteocytes
  • Osteoclasts
  • Osteoblasts
  • Stem or osteogenic cells
  • Lining cells

These different kinds of cells that make up bone are described below:

  • Osteocytes are the cells that are the building blocks of the bone. Osteocytes form the inner matrix of bone tissue that gives bones their strength.
  • Osteoclasts perform the normal cyclical process that maintains the integrity and strength of the bones. Osteoclasts break down bone and reabsorb it so that the bones can renew with remodeling and repair.
  • Osteoblasts follow the osteoclasts in terms of the normal process that maintains the integrity and strength of the bones. Osteoblasts build new remodeled bones by producing new collagen and building new bone minerals so that the osteocyte can remain healthy and in good functioning condition.
  • Stem cells, which are also called osteogenic cells, form in the inner surface of the bone and they are somewhat immature osteoblasts that will later transform into osteoblasts.
  • Lastly, lining cells protect the bones and they also release calcium into the blood when the blood calcium levels are low.

Some of the things that are found in human bone are:

  • Minerals like calcium
  • Collagen which adds strength to bones
  • Glycoproteins like albumin
  • Proteoglycans
  • Proteins

The Role of the Skeletal System

The human skeleton and the skeletal system perform several functions.

These important roles and functions include:

  • The protection of the vital organs of the body, such as was discussed in terms of the brain being protected by the boney structure of the skull and the heart and the lungs being protected with the boney rib cage
  • The support of the human body which gives it its form and stability
  • Bodily movement as is necessary not only for mobility but also for other bodily movements that require that the bones, at the joints, have full range of motion
  • The control of some metabolic functions like the calcium and calcium storage as well as iron metabolism and iron storage in the bone marrow
  • The production of red blood cells in the bone marrow of long bones and other bones like the bones of the pelvis and sternum, or breast bone; the process of red blood cell production is called hematopoiesis
  • The regulation of blood glucose, or sugar, levels and the regulation of fat deposits

The Parts of the Skeletal System

The parts of the skeletal system include the:

  • Bones, which were discussed above in terms of their composition
  • Cartilage
  • Other tissues and structures

Cartilage

Cartilage is less hard than bones and it is more flexible than bone, however, cartilage is smooth and it forms a smooth surface. It is because of this characteristic that cartilage plays a highly important role in the protection of the ends of the bones and cartilage also gives bones a smooth surface over which bones can smoothly articulate with other bones during bodily movements. For example, the cartilage at the end of the femur provides a smooth surface so that, when it moves with the hip during ambulation for example, the cartilage enables smooth movement. You have seen cartilage many times in your life. Cartilage is seen at the end of chicken bones like the leg and the thigh of the chicken. Unlike bones, cartilage does not have a blood supply; it also does not have nerves.

Other Tissues and Structures in the Skeletal System

Sone of the tissues and structures that connect the skeletal system to the muscular system, connect the bones to the body's muscles, connect the bones to other bones, and connect muscles to muscles are:

  • Ligaments
  • Tendons
  • Fascia

Ligaments

Diagram of the right knee showing ligaments and tendons.

Ligaments, like tendons are made up of connective tissue with collagen. Ligaments connect bones to bones at the point where they articulate or come in close proximity to each other, often touching the cartilaginous ends of the bones at the point of articulation, as shown in the picture above.

Tendons

The Achilles tendon, one of the tendons in the human body.

Tendons are connective tissues with collagen that connect bones to muscles and allow joint movement, as shown in the picture above.

Fascia

The rectus sheath, an example of a fascia.

Fascia, also made of connective tissue, connects muscles to other muscles. Although fascia is technically a part of the muscular system when the muscular system is separated from the skeletal system rather than combined as the skeletomuscular system, it is being covered here because the composition of fascia is the same as that of tendons and ligaments and fascia plays a similar role in terms of bodily mobility and movement.

Skeletal Fractures

Skeletal fractures are commonly occurring skeletal injuries. Skeletal fractures are classified and described in several ways, many of which are not mutually exclusive.

A complete fracture involves the entire cross section of the fractured bone; an incomplete fracture affects only part of the bone and not the entire cross section; stable fractures are defined as fractures that are not likely to be displaced, therefore, reduction is not indicated; an unstable fracture, unlike a stable fracture, necessitates reduction because it is likely that this fracture is displaced; a closed fracture is defined as one that does not break through the surface of the skin and this type of fracture and this type of fracture is also referred to as a simple fracture; an opened fracture, on the other hand, breaks through the skin surface to the exterior of the body and, as such, an opened fracture is prone to infection because the skin lacks integrity; and a pathological fracture is one that results from a disease process rather than undue stress or trauma as other fractures do.

Fractures can also be categorized and categorized according to it pattern.

These patterns include:

  • A greenstick fracture occurs when only one side of the bone is fractured.
  • An avulsion fracture occurs when a fragment of the fractured bone is pulled off the bone at its tendon or ligamentous attachment.
  • A comminuted fracture is one that splinters the fractured bone into small fragments as a result of a traumatic force.
  • A transverse fracture is one that occurs straight across the fractured bone.
  • An oblique fracture is one that occurs at an angle across the fractured bone.
  • A spiral fracture occurs when the pattern twists around the fractured bone.
  • An impacted fracture is one that occurs when a bone fragment of the fractured bone is pushed and wedged into another bone fragment of the fractured bone.
  • Compression fractures occur when the fractured bone collapses as occurs with vertebral spinal fractures.
  • A depressed fracture occurs when bone fragments of the fractured bone is pushed in beyond the surrounding skin. This type of fracture occurs with depressed skull fractures.
  • Brief Description: Dislocations and subluxations occur as the result of a traumatic injury; a dislocation occurs when the joints, or their articular surfaces of the bones, are completely separated and are no longer articulated and connected with each other; and a subluxation is only a partial, rather than a complete, displacement and separation of the joints or articular surfaces.

Disorders Affecting the Skeletal System

  • Arthritis
  • Rheumatoid arthritis
  • Osteoporosis
  • Osteoarthritis
  • Osteomyelitis
  • Intervetebral disc disease
  • Fractures

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