Physiology

General overview

fascia_flow_chart
 

Figure 3.1 Overview of fascia subgroups.

 

As described before in the introduction,  fascia is a form of connective tissue that surrounds all of the body’s inner structures (muscles, organs and bones) (see fig. 3.1). This gives the human body its shape and also provides support.

Fascia is often described as being viscoelastic, which may be interpreted as a liquid or gel like substance that provides both resistance and friction. This viscoelasticity is also a form of plastoelasticity, meaning an object has both plasticity and elastic properties (Zorn et al., 2007). Depending on which layer of the fascia is being observed, one may encounter slight changes in the types of cells and fibers that make up the different layers..

subcutaneous layer of fascia that connect directly to the compression fascia

Figure 3.2 Superficial fascia.

 

Fascia itself is primarily made up of several types of cells namely fibroblasts, adipocytes and white blood cells (Kumka et al., 2012). Adipocytes are more commonly referred to as lipids or fat cells and are most abundant in the subcutaneous layers of fascia (fig 3.2).

Considering that the fascia surrounds and covers each muscle (fig 3.3), it is prone to several forces such as gravity and general contractile forces. The most predominant force acting on the fascia is known as friction, which is described as “the force resisting the relative motion of solid surfaces, liquids and material elements sliding over each other”                                                                         (Leonardo tribology center, 2012).

Perimysium

Figure 3.3 Perimysium surrounding the large muscles of the quadriceps.

 

The motion that occurs between the surfaces of musculature and other soft tissues in the body can be further defined as ¨lubricated friction¨. Lubricated friction is the movement of two solid surfaces with a layer of lubricant between the layers (S.T.L.E. 2008). This lubrication is essential to prevent excessive wear on the fascia, which when compromised may lead to a loss of its tensile integrity (fig 3.4) and may therefore result in an injury to the body.

The substances that provide the lubrication for sustained muscle activity are glycoproteins, which are primarily found in the extracellular matrix (ECM). Along with providing lubrication between muscles, glycoproteins of the ECM play a fundamental role in cell recognition, migration and proliferation (Kwaitkowska et al., 1999).

*Video 3.1 Dissection of the perimysium to reveal bundles of muscle fibers that are surrounded also by fascia.

Epimysium

Figure 3.4 Disruption of muscle fibre bundles causing rupture in the intramuscular connective tissue/ fascicular fascia.

 

The primary components that give integrity to the ECM are forms of proteins that are produced by fibroblast cells (Frantz et., al 2010). Fibroblasts are responsible for producing collagens, glycosaminoglycans glycoproteins (Encyclopedia Britannica, 2015) and tropoelastin, which is the soluble precursor of elastin (Sephel et al., 1986). These are all found in the ECM. The type of fascia observed in the body may present different characteristics depending on the byproduct produced by the fibroblasts cells. These cell products metabolize into the collagen (fig 3.5) and elastin fibers that give the fascia its form and function (Anatomy Trains, 2014). These fibers may be easily observed in separating fascia and are surrounded by adipose/fat tissue. However the deeper fascial layers have dense layers of collagen and elastin fibers, which give it a more fibrous and interwoven sheet-like appearance.

3.4 Thick white collogen-fibers of the retinacum
Figure 3.5 Thick white collagen fibers of the retinaculum.

According to Mithieux (2005), ¨Elastin is a key ECM protein that is critical to the elasticity and resilience of many vertebrate tissues, including large arteries, lung, ligament, tendon, skin, and elastic cartilage¨. Essentially stating that elastin is factually everywhere in the body and is seen to have connections with all of the bodies major systems, respiratory (lungs), vascular (arterial walls), nervous (Golgi Tendons) systems.

3.5 High abundance of elastin fibers make the superficial fascia capable of stretching more then the more rigid fascia seen in fig.3.4

Figure 3.6 Superficial fascia contains a high number of elastin fibers which give it its characteristic stretching capabilities.

 

Mosby’s medical dictionary describes collagen as ¨a fibrous insoluble protein consisting of bundles of tiny reticular fibrils that combine to form the white glistening inelastic fibers of tendons, ligaments and fascia. It is found in connective tissue, including skin, bone, ligaments, and cartilage and it represents 30% of the body’s total protein¨ (Mosby, 2009). Collagen can be subdivided into approximately 28 different types, however not all of these are found in the fascia. The types of collagen found in the fascia are namely, collagen I, III, IV, V, VI, XI, XII, XIV, XXI (Kumka et al., 2012). Collagen I is one of the most abundant molecules in humans constituting major parts of the ECM, thus providing structural integrity and mechanical resilience to the fascia (Stamov et al., 2012).

*Video 3.2 demonstrates the integrity of the compression fascia covering the upper leg

The main difference between collagen and elastin fibers is that collagen fibers build a structural framework for cells and tissues, whereas elastin fibers help with stress distribution (fig 3.6) (Ushiki et al., 2012). These attributes give the fascia a degree of pliability. However, this is not to be mistaken for integrity, which suggests the point at which a tissue may rupture due to excessive loading. According to Kerr (1999), a collagenous tendon will only stretch to approximately 110% of its normal length as opposed to elastin, which may stretch up to 230% of its resting length. By having these properties the fascia can act like a net, which has the integrity to keep all of the tissues in the body in a predetermined place. This net like property is made possible by two factors: 1. The network of collagen fibers, which provides high tensile strength to the fascia; 2. The elastin fibers allow the net to stretch, which can allow tissues to have the capability of contraction and elongation (Kumka et al., 2012). This provides the fascia with enough integrity to withstand high forces and also the ability to adapt to activities that we peruse on a daily basis, for example running, weightlifting or cycling.

* Please read the following paragraph before going further with this page .

Fascial layers.

1. Separating Fascia
          1a. Superficial Fascia
          1b. Visceral Fascia
          1c. Parietal Fascia
2. Compression Fascia
3. Fascicular Fascia
4. Linking Dynamic Fascia
5. Linking Passive Fascia


Due to the different physiological characteristics of the fascia and the different functions it serves in the body it can be subdivided into several different categories. For the purpose of this site the categories will be labeled from 1-5 as it will make it easier to reference the different layers affected by a particular form of therapy. These therapies all focus on fascial manipulation on different layers, however the parietal and visceral fascia will not be discussed in the therapies section as they are not generally treated/manipulated by the physiotherapist.
Massage therapy (effleurage and petrissage) concentrates primarily on the superficial and compression fascia. Craniosacral therapy works primarily on the linking fascia. The other therapies are generally used to manipulate the fascicular fascia (Triggerpoint, Dry Needling, PNF and Rolfing therapy).

1. The Separating Fascia (Superficial/Visceral/Peritoneal)

Visceral Fascia
Figure 3.7 Visceral fascia under tension. 

The separating fascia has been described as an arrangement of visible sheets that divide the body into layers of different fibers, which in turn allows the body to take up forces and friction in all directions. However, even though the main function of this fascia is to allow more effective sliding of tissues over each other it is still prone to adhesions caused from previous injury or invasive procedure (Hedley et al., 2010).

Reticular Type III collagen fibers and elastic fibers are the major components of separating fascia, with small amounts of collagen Types V, VII (Gelsa et al., 2003). While the reticular fibers provide a supporting framework for the cellular components of fascia, the elastic fibers form a three dimensional network to allow separating fascia to respond to stretch and distention (fig 3.7 & video 2.3) (Ross et al., 2011). Due to the depth of the of the adipose layer in some cadavers, the superficial fascia can be more easily observed as a 3 dimensional matrix as opposed to the deeper fascia that surrounds muscle and attaches to bone.

This separating fascia has previously been described as 3 different types of fascia known as the Superficial, Visceral and Peritoneal fascia. These original terms were denominated due to the different locations in the body where these types of fascia have been observed. With this in mind, due to their locations in the body, they appear to have very different characteristics and textures however they are in fact all made of essentially the same components.

Below they will be described as three separate entities and their positions and function in the body.

1a. Superficial fascia

The term superficial fascia (fig 3.6) is a generic term for a structure that in fact is not limited to the subcutaneous tissues. Hedley et al. (2008) describes this as ¨a complex connective tissue matrix, surrounding everything from body cavities to individual organs. It separates, supports, and compartmentalizes organs and regions in order to maintain proper structural and functional relationships throughout the body. This group of fascia has a unique appearance and texture upon observation, ranging from transparent woven sheets to a fuzzy cotton-like consistency¨ (Hedley et al., 2008). This layer can vary greatly in individuals depending on body type and presence of fatty tissue. This superficial layer, when observed in a cadaver, may be dissected and presented as a sheath that fully encapsulates the body, which even when dissected keeps its integrity (Hedley et al., 2008).

1b. Visceral Fascia

*Video 3.3 This video demonstrates the integrity of the visceral fascia

Visceral fascia (fig 3.7) is a term used for the fascia that lies directly outside the visceral layer of the serosae surrounds the viscera (FICAT, 2013). In some instances, it also joins structures together and also separates other structures from one another (Farlex, 2012). It also has the role of suspending the organs in space and helps to ensure that they stay in their predetermined locations (Hedley, 2006).

1c. Parietal fascia

SONY DSC
Figure 3.8b Pericardium held away from the heart.
3.7 Epicardium being held away from the heart.
Figure 3.8a Pericardium held back against the heart.

The peritoneal fascia (fig. 3.8a, 3.8b) lies outside the parietal fascia layer of the serosae for example the pericardium (FICAT, 2013). This fascia acts as durable membrane that is found in the areas of the body that are vulnerable. This may be observed in the deep parietal fascia of the abdominal wall. The peritoneal fascia is found behind the abdominal wall where it separates the inner organs from the surrounding musculature. An example of when this structure has been compromised may be seen in a hernia in the groin area or the lower abdominal region. Without this structure, it would essentially be impossible for the body to be in an upright position without the internal structures putting pressure on and eventually damaging surrounding musculature. This fascia keeps the organs of the body in their designated compartments. Pericardium, pleura and peritoneum are other areas where this fascia may be encountered.

2. Compression Fascia 

3.8a Compression fascia of the lower arm
3.9a Compression fascia of the lower arm.

This fascia (fig 3.9a, 3.9b) can be observed when the superficial/separating fascia has been removed and may be seen throughout the body .

The compression fascia acts like a stocking which envelopes the extremities and keeps muscle groups together. The composition of the compression fascia is a mixture of dense layers of collagenous tissue interwoven with tendons and joint capsules. The primary features of this fascia are collagen type I fibers and elastin fibers (Kumka et al., 2012). In some areas of the body compression fascia interweaves with the fascicular fascia, forming the epimysium. This connection between fascicular and compression fascia can be observed in the quadriceps between the vastus lateralis and the vastus medialis forming a thick septum of fascia that separates these two muscles (Fourie et al., 2007).

3.8b Compression fascia covering the entire leg.
3.9b Compression fascia covering the entire leg.
Saphenous vein coming fromdeep to superficail layers through the fascia
3.10 Saphenous vein coming through the compression fascia into the superficial layers.

The main characteristic of this type of fascia is that the arrangement of the collagen fiber varies between the layers of the fasciae. Between the layers there is loose connective tissue that allows the layers to slide against each other, which in turn allows each individual layer of the fascia to respond more effectively to stimuli (Stecco et al., 2009). The compression fascia plays a significant role in ambulation and venous return (fig 3.10) because of its influence on compartmental pressure, muscle contraction and force distribution (Kumka et al., 2012). The influence that fascia has on venous return was observed by Caggiati et al., (2000) while performing a comparative study about ¨Fascial relations and structure of the tributaries of the saphenous veins¨.

3. Fascicular Fascia 

*Video 3.4 highligts the integrity of the fascia surrounding the rhomboids

Fascicular fascia is more exploratory than the previous types of fascia discussed, it covers all parts of the muscles, tendons, and nerves (Kumka et al., 2012). This fascia is mainly constructed of Collagen fibers type I and III but also contains small amounts of collagen type V, VI, XII, and XIV fibers (Kumka et al., 2012).

3.8 Thick bands of fascia joining to form an aponeurosis in the upper leg muscles
3.11a Thick bands of fascia joining to form an aponeurosis in the upper leg muscles.
3.11b continuation of the gracilis tendon into the compression fascia
3.11b Continuation of the gracilis tendon into the compression fascia

It can be seen in human specimens that thick bands form along the edges of individual muscles that are in contact with each other. Normally these bands of fascia run down to the bone where they attach to the periosteum (fig 3.11a) (Kumka et al., 2012). With this in mind, the fascicular fascia essentially keeps our musculature firmly attached to the bones. This type of fascia has a significant influence on growth, transmission of mechanical signals to muscle cells and co-ordination of forces between muscle fibers (Purslow et al., 2002). A review by ¨Huijing et al, (2007)¨has shown myofascial force transmission happens between all muscles within a limb segment. From the muscle, the fascia integrates with the tendon at the myotendinous junction where it transitions from the epimysium to the epitenon (fig. 3.11b) and then typically integrates into joint capsules. It is at these points where the fascia is highly innervated by Golgi tendons (Kumka et al., 2012). As we look deeper in to the structures that are enveloped by the deep fascia, it is seen that each component of the given structure is encased in these sheets of connective tissue.

*Table 1 gives the appropriate terminology in regards to its location and terms used to describe it.

Summary of fascial characteristic
* Adapted from Kumka et al., 2012.

4/5. Linking Fascia

Linking fascia is the last type of fascia and completes the connections and continuity of the fascial system encapsulating the body. It consists primarily of unilateral densely packed, parallel collagen type I fibers. This provides the fascia with substantial integrity and therefore it may withstand high forces, however the fascia has enough elasticity to adapt to an un-regulatory environment (Kumka et al., 2012). Due to the high integrity of the linking fascia it is seen in muscular aponeurosis, tendinous arches and neurovascular sheaths (Terminologia Anatomica, 2015).

This group may be subdivided further into passive and dynamic linking fascia.

4. Linking Dynamic Fascia

Linking Dynamic fascia is named due to its role in movement coordination and stability shown by its characteristically high concentration of contractile and proprioceptive fibers (Kumka et al., 2012). Due to the high innervation of this fascia it is distinctly different from the others permitting it to play a significant role in nociception and proprioception (Yahia et al., 1992). This can be observed in the thoracolumbar fascia as it has a function in spinal stability and makes strong connections between the outer extremities and torso (Vleeming et al., 1995). According to Vleeming et al. (1995) ¨anatomic structures normally described as hip, pelvic, and leg muscles interact with so-called arm and spinal muscles via the thoracolumbar fascia¨. It has also been hypothesized that the thoracolumbar fascia plays a significant neurosensory role in the lumbar spine mechanism (Yahia et al., 1992). With this in mind it may therefore also be hypothesized that injury to this dynamic linking fascia may attribute to lower back pain, even if the injury itself is not actually located in the lower back.

5. Linking Passive Fascia

ankle

Figure 3.13 Passive fascia seen in the planter fascia.

 

Linking Passive fascia acts as a connector between sections of the body that do not have a high abundance of soft tissue and may be found in areas such as the head and neck (ligamentum nuchae & ligamentum flavum), retinaculum and some tendinous arches (plantar fascia fig 3.13) (Van der Wal et al., 2009). It also makes up the rectus sheath, which in conjunction with the peritoneal fascia compartmentalizes the abdomen and provides protection against external forces that may otherwise damage organs (Kumka et al., 2012). The differences between passive and dynamic fascia is that passive can only transmit force when it is being loaded or stretched, for example, the plantar fascia (van der Wal et al., 2009). If you can compare the passive fascia to an elastic band in the sense that without an external force acting on it, the fascia cannot spontaneously contract or relax.

Innervation

In various studies it has been noted that fascia is populated by sensory neural fibers (van der Wal 2009.,  Yahia et al., 1995, Stecco et al., 2007). For this reason it can be suggested that fascia may contribute to proprioception and nociception and may respond to manual pressure, temperature, and vibration (Kumka et al., 2012). Some of the receptors in the fascia serve as both a mechanoreceptor and a nociceptor (types III and IV receptors). These receptors are responsible for the detection of pain in muscles, tendons, ligaments and bone (Kiernan et al., 2009). There has been research done suggesting that there are high amounts of encapsulated nerve endings found in fascia that respond to mechanical stress and deformation. These include: Golgi receptors, Pacinian corpuscles, and Ruffini’s corpuscles (Schleip et al., 2003; Stecco et al., 2007; Yahia et al., 1992).

Definitions

*All definitions have been obtained from the online Miriam Webster dictionary unless stated otherwise

      • Adipocytes: a fat-containing cell of adipose tissue— also called adipocyte, lipocyte

      • Collagen: the chief constituent of the fibrils of connective tissue (as in skin and tendons) and of the organic substance of bones

      • Elastin: a protein that is similar to collagen and is the chief constituent of elastic fibers

      • Endomysium: the delicate connective tissue surrounding the individual muscular fibers within the smallest bundles

      • Endotenon: fine connective tissue between the strands in a tendon (Farlex, 2012)

      • Epimysium: the external connective-tissue sheath of a muscle

      • Epineurium: the external connective-tissue sheath of a nerve trunk

      • Epitenon: The white fibrous sheath surrounding a tendon (Farlex, 2012)

      • Extracellular matrix (ECM): tissue that usually provides structural support to the animal cells in addition to performing various other important functions (Farlex, 2012)

      • Fascia: a sheet of connective tissue (as an aponeurosis) covering or binding together body structures

      • Glycoproteins: a conjugated protein in which the non protein group is a carbohydrate—called also glucoprotein

      • Golgi tendon: a spindle-shaped sensory end organ within a tendon that provides information about muscle tension called also neurotendinous spindle

      • Innervation: the distribution of nerves to or in a part

      • Mechanoreceptor: a neural end organ (as a tactile receptor) that responds to a mechanical stimulus (as a change in pressure)

      • Nociceptor: a receptor for injurious or painful stimuli : a pain sense organ

      • Pacinian corpuscles: a pressure-sensitive mechanoreceptor that is an oval capsule terminating some sensory nerve fibers especially in the skin (as of the hands and feet)

      • Perimysium: the connective-tissue sheath that surrounds a muscle and forms sheaths for the bundles of muscle fibers

      • Perineurium: the sheath of connective tissue that surrounds a bundle of nerve fibers

      • Peritendon: tissue surrounding the Achilles tendon; note: the Achilles tendon does not have a synovial sheath (Maffulli et al., 2004)

      • Proprioception: the reception of stimuli produced within the organism.

      • Reticular Fiber: any of the thin branching fibers of connective tissue that form an intricate interstitial network ramifying through other tissues and organs

      • Ruffini’s corpuscles: any of numerous oval sensory end organs occurring in the subcutaneous tissue of the fingers called also Ruffini’s brush, Ruffini’s end organ

Flowchart 1

Figure 3.1

Please click here for a full list of references

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