The Muscular Skeletal System

How bone cells integrate with other systems to maintain homeostasis.

The Haversian System

Arrangements of a calcified matrix and cells in a circular fashion; osteon.  Each osteon contains Haversian canals that run parallel to the long axis and contains nerves and blood vessels

As bone accounts for up to 98% of the body’s stored calcium, it must be able to lay down bone or calcium as well as release calcium back into the blood.  This is a vital homeostatic mechanism; as the levels of blood calcium must always be maintained to ensure the efficient transmission of nerve impulses, blood clotting and the contraction of cardiac and skeletal muscles.

Parathyroid Hormone

If levels of blood calcium are detected to drop by the parathyroid then parathyroid hormone is released into the blood.  This highly important hormone travels around the vascular system into the Haversian canals and then penetrates into the osteoclasts in the fluid filled lacunae.

  • Osteoblasts = stem cells that give rise to osteocytes = builds bone matrix.
  • Osteocytes = mature bones cells that have trapped themselves in the bone matrix so have stopped forming new matrix.
  • Osteoclasts = large cells that break down and dissolve bone matrix.

The parathyroid hormone then stimulates these bone cells to initiate the ‘break down’ of the surrounding bone tissue and cause the reabsorption of calcium back into the blood, thus raising the blood-calcium level back up to an acceptable level.

Although bone is often seen as an inactive dense tissue.  It is in fact one of the most highly active tissues in the body, with its constant resorption and ossification of calcium to maintain the required homeostatic levels of calcium in the blood.

The main structure and bones of the axial skeletal and appendicular skeleton.

The anatomy of muscles and how they are specialised to produce movement.

  • Skeletal muscles allow us to be mobile as well as providing much of the tensegrity structure that holds us up.  Furthermore these structures need to be finely conducted by the CNS (cerebellum) so that controlled and accurate movement is possible.

 Skeletal muscle is a highly specialised form of connective tissue.  It functions to provide movement of the entire body or it parts.  It produces heat and provides posture so that we can sit, stand, run, walk, and remain stable.

In order to carry out these vital functions, skeletal muscles have 3 specific characteristics:

  1. Excitability – or irritability.  They can be stimulated by nerve signals.
  2. Contractility – they can shorten, thus producing body movement
  3. Extensibility – they can stretch, which means that contracted muscles can return to their normal resting state.

Muscle groups

Skeletal muscles almost always act in groups.  for one seemingly simple action, many different muscles may be involved.

  • Prime mover – responsible for movement instigation
  • Antagonists reverse this action – return to normal
  • Synergists enhance the accuracy of movement
  • Fixator muscles add strength and stability of ten maintain posture.

Calcium is used to contract skeletal muscles and other muscles such as cardiac muscles for heartbeat as well as for making bone matrix.  So calcium needs to be able to move in and out of the bones and around the body according to where it is needed.

The major waste product from this activity is heat. This surplus heat plays a major role in  maintaining  constant body temperature.  If the hypothalamus detects a drop in core body temperature (37)It will initiate an emergency response from the skeletal muscles to start shivering, producing more ‘wasteheat to restore the body temperature.


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