The Musculoskeletal System
Function of the Musculoskeletal System
The musculoskeletal system consists of many different elements such as the skeleton, muscles, cartilage, tendons,
ligaments, joints, and various other connective tissues. All of these elements work together to support the body,
protect the vital organs and to allow locomotion. The bones, such as the ribs, protect the body’s internal organs such
as the heart and lungs. The skeleton also supports the weight of the body and keeps the body’s shape. The muscles’
job is to keep the bones in place and contribute to locomotion by contracting and pulling on the bones. In order for
locomotion to occur, various bones are connected by different types of joints which are connected to other bones
and muscle fibres via tendons and ligaments (connective tissues). The function of cartilage is top prevent the ends of
bones from rubbing against each other.
,
, Bone Development and Structure
A child’s skeleton is made up of flexible cartilage, which is why children tend to be more flexible and agile than
adults. Over time, the cartilage slowly ossifies (hardens) and becomes bone. This bone develops hollow centres,
which contain bone marrow. Bone marrow is required for blood cell production. The bones of the back, arms and
legs get longer as a child develops. These bones have a growth plate that is made of hyaline cartilage at either end.
Cells multiply in the growth plate and pass down the bone, forming a calcified matrix (part of the bone tissue and
forms most of the mass of the bone). Then these cells die, leaving space.
Osteoblasts are the bone cells which produce bone to fill these spaces and replace cartilage matrix. However, in
some cases osteoblasts become trapped in the matrix and become inactive cells called osteocytes. Bone consists of
an organic matrix, both secreted by osteoblasts, consisting up of collagen fibres and some ground material.
Extracellular fluid, chondroitin sulphate, proteoglycans and hyaluronic acid are found in the ground material. The
fibres of collagen line up along the lines of stress that bones sustain. This provides tensile strength for the bone.
Bone is deposited by osteoblasts, but phagocytic cells (osteoclasts) break down and absorb it. The deposition and
breakdown processes are generally in equilibrium and under the influence of certain hormones. This bone
remodelling, however, reacts to external factors, such as how much stress bones are exposed to.
The Periosteum
A two layered membrane called the periosteum covers the shaft or central part of a long bone, otherwise called the
diaphysis, of each bone. Dense, irregular connective tissue consists of the outer layer. Osteoblasts and osteoclasts
consist of the inner layer. This layer is joined to the underlying bone by knots of collagen. There are several blood
channels, lymphatic vessels, and nerve fibres in the periosteum. Via special canals, both of these join the bone
tissue.
Compact Bone
The compact bone is under the periosteum. It seems hard and dense, but it is full of Haversian canals which are
visible under a microscope that serve as passages for nerves, blood vessels and lymph vessels. The bone is a living
tissue which requires nutrients, oxygen, and waste removal.
Many structural units called osteons make up this bone. Each osteon is a cylinder. Osteons run lengthwise within the
bone, acting like thin, weight-bearing pillars. Each osteon is a group of bone matrix hollow tubes, one within the next
one. There are collagen fibres inside each matrix tunnel. Osteocytes with cytoplasmic projections are within the
bone matrix. When these cells were active osteoblasts, they were connected to other bone-forming cells.
Spongy Bone
There are more spaces between structures called trabeculae in spongy bone and it is less dense than compact bone.
Trabeculae do not have osteons, but they have osteocytes and narrow canals (canaliculi). Via these tiny canals of the
osteocytes, nutrients diffuse from the marrow. Despite the fact that they are not producing matrix, the osteocytes
