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The Musculoskeletal System: A hidden two-way conversation

If you have read my previous blog ‘Canine Construction: Stability in Bone, Flexibility in Muscle,’ you may be thinking… Why do the skeletal and muscular systems need to have a two-way conversation? They seem to function perfectly well on their own!

 

Well, beneath your dog’s skin lies a hidden, intimate relationship between muscle and bone. Neither system could function without the other. Therefore, the systems are known collectively as the musculoskeletal system.



 

Biomechanical communication

It may come as no surprise that the primary function of the musculoskeletal system is to create movement. Whilst the immense power and movement generated by the musculoskeletal system can be easily observed when your dog runs around a field or jumps up to catch a ball, it is easy to forget the intricate movements such as the subtle twitch of the ear or eye.

 

The musculoskeletal system consists of pulleys and levers. The bones are the levers and the skeletal muscles, which attached to bone are the pulleys that create movement. Skeletal muscle often works across a synovial joint by attaching each bone on either side of the joint together. When the skeletal muscle contracts, one of the bones usually remains stationary (the anchor) while the other is levered in the direction that the joint allows, thus creating movement. For example, the ball and socket joint of the hip consists of the pelvis (anchor) and femur (lever).



Skeletal muscle can only create movement through contraction. It cannot actively extend (lengthen). Therefore, to move bones in opposite directions, pairs of muscles must work against each other. This is known as an antagonistic action. For example, the quadriceps and hamstrings work together to flex and extend the stifle (knee). When your dog flexes their stifle, the hamstrings contract and the quadriceps relax. When your dog extends their stifle the quadriceps contract and the hamstrings relax.

 


Biochemical communication

The interaction between the skeletal and muscular systems are not just mechanical. In fact, bone and muscle also participate in complex biochemical conversations through the molecules they secrete and minerals they store.

 

Bone

Bones store and supply essential nutrients and minerals that every tissue in the dog’s body requires. This includes,

  • Calcium - The skeleton houses 99% of the dog’s calcium store. Calcium is a major building-block of bone tissue, giving bones their density and strength. Calcium is also essential for the contraction of muscle, including regulating the heartbeat and is vital for the transmission of nerve impulses and blood clotting.   

  • Phosphorus – After calcium, phosphorus is the most abundant mineral in the dog’s body. 85% of phosphorus is stored in the dog’s bones. It works together with calcium to construct strong bone. Phosphorous supports the growth, maintenance and repair of all tissues and cells in the dog’s body and helps reduce muscle pain after exercise. It also helps filter out waste in the kidneys and is essential for the storage and use of energy.  

 

Building a strong dog!

Osteocytes (bone remodelling cells) maintain the correct levels of oxygen and minerals in the bone and secrete a biochemical messenger called prostaglandin E2 (PGE2). PGE2 is released when the dog’s muscular function increases as it helps to promote muscle growth, creating physically stronger and larger muscles. The osteocytes sense the increased mechanical load, and the bone adapts by becoming denser and stronger. As a result, muscle and bone work harmoniously together to build a stronger dog.

 

Muscle

When muscles contract during physical activity their cells release small messenger proteins called myokines. Some myokines support the formation and maintenance of the musculoskeletal system in the following ways,

  • Irisin - acts directly on bone by increasing the density and strength of compact bone (outer layer of bone making up 80% of the dog’s skeleton) to strengthen and prevent bending or fracture.

  • Insulin-like growth factor 1 - stimulates bone and muscle growth. This is essential for puppy development.

  • Beta-aminoisobutyric acid – helps prevent the bones osteocyte cells from dying. In return osteocytes secretes Prostaglandin E2 a molecule which stimulates muscle growth.

  • Myostatin – ensures that skeletal muscles do not grow too large and regulates bone mass.

 


Summary

As a result of biomechanical and biochemical communication the skeletal and muscular systems can work harmoniously together to build a strong dog. But like any two-way conversation it can be easily interrupted putting the musculoskeletal system at risk! Who and what can interrupt the conversation? And what may happen to the musculoskeletal system if it is interrupted? My next blog 'The Musculoskeletal System: Interrupting the conversation' discusses these very common issues and the detrimental effect this can have on your dog's wellbeing.

 


References

Black, S. (2022) Written in Bone, Penguin Books

Knowable, A. D. (2022) How Bones Communicate with the Rest of the Body, Smithsonian Magazine

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