FASCIAS, FASCIAL COMPARTMENTS,BURSAE, AND POTENTIAL SPACES- 1
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Fascias (L. fasciae) constitute the wrapping, packing, and insulating materials of the deep structures of the body.Underlying the subcutaneous tissue (superficial fascia) almost everywhere is the deep fascia. The deep fascia is a dense, organized connective tissue layer, devoid of fat, that covers most of the body parallel to (deep to) the skin and subcutaneous tissue.
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Extensions from it internal surface invest deeper structures, such as individual muscles (when it may also be called epimysium—see and neurovascular bundles, as investing fascia. Its thickness varies widely. For example, in the face, distinct layers of deep fascia are absent.
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In the limbs, groups of muscles with similar functions, usually sharing the same nerve supply, are located in fascial compartments. These compartments are separated by thick sheets of deep fascia, called intermuscular septa that extend centrally from the surrounding fascial sleeve to attach to bones. These compartments may contain or direct the spread of an infection or a tumor.
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In a few places, the deep fascia gives attachment (origin) to the underlying muscles (although it is not usually included in lists or tables of origins and insertions); but in most places, the muscles are free to contract and glide deep to it.
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However, the deep fascia itself never passes freely over bone; where deep fascia contacts bone, it blends firmly with the periosteum (bone covering). The relatively unyielding deep fascia investing muscles, and especially that surrounding the fascial compartments in the limbs, limits the outward expansion of the bellies of contracting skeletal muscles.
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Blood is thus pushed out as the veins of the muscles and compartments are compressed. Valves within the veins allow the blood to flow only in one direction (toward the heart), preventing the backflow that might occur as the muscles relax. Thus, deep fascia, contracting muscles, and venous valves work together as a musculovenous pump to return blood to the heart, especially in the lower limbs where blood must move against the pull of gravity.
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Near certain joints (e.g., wrist and ankle), the deep fascia becomes markedly thickened, forming a retinaculum (plural = retinacula) to hold tendons in place where they cross the joint during flexion and extension, preventing them from taking a shortcut, or bow stringing, across the angle created.
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Subserous fascia, with varying amounts of fatty tissue, lies between the internal surfaces of the musculoskeletal walls and the serous membranes lining the body cavities. These are the endothoracic, endoabdominal, and endopelvic fascias; the latter two may be referred to collectively as extraperitoneal fascia.
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Bursae (singular = bursa; Mediev. L., a purse) are closed sacs or envelopes of serous membrane (a delicate connective tissue membrane capable of secreting fluid to lubricate a smooth internal surface).
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Bursae are normally collapsed. Unlike three-dimensional realized or actual spaces, these potential spaces have no depth; their walls are apposed with only a thin film of lubricating fluid between them that is secreted by the enclosing membranes. When the wall is interrupted at any point, or when a fluid is secreted or formed within them in excess, they become realized spaces; however, this condition is abnormal or pathological.