Development of the Musculoskeletal System

Overview

The major components of the musculoskeletal system are derivatives of mesoderm. They include bones, ligaments, tendons and joints and the skeletal muscles that move them.
Skeletal tissue, which includes bone and cartilage, arises from mesenchyme derived from 3 different sources:

  • somite (somitic) mesoderm
  • lateral plate mesoderm
  • neural crest

Muscle tissue is subdivided into three functional types, skeletal, smooth and cardiac. Cardiac and smooth muscle will be discussed with their respective viscera.
All skeletal muscles are derived from mesoderm.

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Skeletal Development - Overview

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The axial skeleton, which consists of skull, vertebral column, ribs and sternum (purple in the image) is formed mostly from somite mesoderm with the exception of the facial part of the skull (gray in the image), which is formed from mesenchyme of neural crest origin.

The appendicular skeleton of the upper and lower limbs and their girdles (blue in the image) is largely from lateral plate mesoderm as is the sternum.

Development of the skeleton commences in utero and continues to about age 20. Bone tissue forms by two different mechanisms that will be studied in depth in Microanatomy.

  • Intramembranous ossification is development of bone tissue directly within a dense connective tissue membrane; typical of development of the cranial bones, mandible and clavicle, (gold in the image).
  • Endochondral ossification involves the formation of bone within a cartilaginous model of the bone. This is typical of the remainder of the skeleton, (green in the image).

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Muscle - Overview

All muscle tissue in the body is derived from mesoderm, with the exception of a small population of smooth muscle cells in the eye which comes from neuroectoderm.
Muscle tissue is divided into three types, studied in Microanatomy.

  • Smooth Muscle - forming the wall of most visceral organs and blood vessels and located in a few other tissues such as the skin and eye.
  • Cardiac Muscle - located within the chambers of the heart.
  • Skeletal Muscle - voluntary muscle attached to the bones of the body and which produce our ability to move.

We will consider development of only skeletal muscle at this point since its development is intertwined with development of the axial and appendicular skeletons.