Some researchers have proposed that connective tissue constitutes a body-wide signalling network. This body-wide signalling network connects and informs other physiological systems and is thought of as a metasystem.
This body-wide signalling network is realised by the physical continuity of connective tissue throughout the body. Signalling is direct and fast – this contrasts with other physiological systems which rely on indirect chemical, hormonal and neurological messaging.
This ancient body-wide signalling network is embedded with more recent, in evolutionary terms, neuroanatomical structures – specifically the free nerve endings associated with both mechanobiology and interoception.
The effects of signalling and ongoing remodelling of connective tissue is not confined to the musculoskeletal system. Extensive communication between connective tissue and other systems is mediated through material continuity within the body and the nervous system. Connective tissue infiltrates every space within the body. This body-wide signalling network can not be separated from the organism as a whole.
HOW THIS BODY-WIDE SIGNALLING WORKS ACROSS DIFFERENT SCALES
Connective tissue forms a dynamic, interconnected and seamless tensional network. Connective tissue is the scaffold for everything else in the body and is capable of remodelling. Connective tissue undergoes continuous material turn over in response to mechanical and biochemical activity. The composition and continuity of connective tissue is dependent on location and function, and can range anywhere between soft (loose) and hard (dense).
Soft continuity refers to diffuse and ubiquitous connective tissue which is loosely arranged – like the loose wrappings around muscles, subcutaneous connective tissue and the loose sheets around abdominal organs. Hard continuity refers to dense, localised, organised and mechanically connected elements of the tensional network – like ligaments, tendons and muscles.
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Connective tissue is composed of extracellular matrix (ECM). ECM is embedded with specialised cells called fibroblasts which synthesise collagen, regenerate damaged collagen fibres and/or lay down entirely new fibres in response to mechanical forces (e.g. physical training or injury) – this is referred to as remodelling. The activity of fibroblasts is sensitive to the the physiology of the organism as a whole.
A certain class of fibroblasts called myofibroblasts have the ability to actively contract and pre-tension ECM. This pre-tension is transmitted to the entire connective tissue network – sometimes referred to as the fascial body. This is an example of body-wide signalling, occurring across different physical scales from molecules to cells to gross anatomical structures – a distinctive characteristic of biotensegrity.
Tensional equilibrium of the fascial body is achieved through various mechanisms which act over different time scales. These mechanisms include instantaneous streaming electrical signals, as well as slower cellular and extracellular remodelling. The interplay of these processes regulates the long term organisation and physical properties of ECM – these processes influence the stiffness and elasticity of the fascial body.
In addition to being innervated and contractile – capillaries and lymphatic vessels also pass through ECM. Consequently immune function, interstitial fluid and lymphatic flow are influenced by injury, mechanical load, emotional states, breathing patterns, blood biochemistry (e.g. pH), et cetera. These influences may distort or alter the tensional equilibrium of the entire fascial body. It has been proposed that some of the earliest signs of disease and pathology are manifested as inertia and stasis in the ECM and dysfunction within this body-wide signalling network.
FEATURED IMAGE:
H. Wiig et al. Interaction between the extracellular matrix and lymphatics – consequences for lymphangiogenisis and lymphatic function (2010).