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If the bones are not connected to the brain, how is their growth controlled?

This question is not a duplicate of the question Mechanisms of bone growth, as this question deals with how bone growth is controlled, and not which bone structures or bone tissues are involved.

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  • $\begingroup$ I have edited your question to make it better to understand, feel free to roll this back, if it is not ok for you. $\endgroup$ – Chris Dec 13 '14 at 10:17
  • $\begingroup$ Your question implies that the brain directs growth - it doesn't. $\endgroup$ – rg255 Dec 13 '14 at 13:04
  • $\begingroup$ @GriffinEvo - of course it does. Where do you think Growth Hormone comes from? What do you think control thyroid hormone production? Do you think the brain has no control over anabolic steroids? $\endgroup$ – anongoodnurse Dec 13 '14 at 19:12
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    $\begingroup$ I'm mean it implies a neural connection and that growth is neurally controlled (sorry should have been more clear) you are correct that growth hormone production is in some part at least directed by the brain @anongoodnurse $\endgroup$ – rg255 Dec 13 '14 at 20:16
  • $\begingroup$ I made another edit, and as @Chris indicated, please feel free to roll back. $\endgroup$ – AliceD Dec 15 '14 at 1:57
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The developmental growth of bone tissue is hormonally controlled. It is, as far as I know, not under direct neuronal control. Before reaching adolescence, the long bones (mainly in the arms and legs) grow in the epiphyseal plate, the area of the bone where cartilage is formed and ossified on the diaphyseal side, thereby lengthening the bone. The longitudinal growth of long bones continues until early adulthood at which time the chondrocytes in the epiphyseal plate stop proliferating and the epiphyseal plate transforms into the epiphyseal line as bone replaces the cartilage (boundless website). The growth and stop of growth in adulthood is hormonally controlled. Bone tissue growth is controlled by various hormones including parathyroid hormone and growth hormone.

Growth hormone (GH) is secreted by the pituitary, in turn controlled by the hypothalamus in the brain. So although the brain is involved, it is not directly involved, in that it regulates growth, and cessation of it through hormone release. Growth hormone is probably the most important hormone and is released by the pituitary, but parathyroid hormone released by the thyroid, among other hormones, may play a role as well.

Edit: Your question implies bone growth, which at first seemed to point toward developmental growth to me. However, there is also the more dynamic control of bone mass due to the forces that act on them in everyday life, referred to as bone mass accrual. This process is controlled by the sympathetic and parasympathetic system (Bajayo et al., 2012):

direct neuroal control of bone growth

This system acts through direct neural innervation of bone tissue and stimulates bone formation when needed (after imposed strain on the skeletal system), but by default stimulates the breakdown (resorption) of bones to salvage its components for other uses (use it or loose it principle). So yes, the skeletal system is directly connected to the brain (with credits to @anongoodnurse).

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