Deep fascia (or investing fascia) is a fascia, a layer of
dense connective tissue
Dense connective tissue, also called dense fibrous tissue, is a type of connective tissue with fibers as its main matrix element. The fibers are mainly composed of type I collagen. Crowded between the collagen fibers are rows of fibroblasts, fibe ...
that can surround individual muscles and groups of muscles to separate into
fascial compartment
A fascial compartment is a section within the body that contains muscles and nerves and is surrounded by deep fascia. In the human body, the limbs can each be divided into two segments – the upper limb can be divided into the arm and the forea ...
s.
This fibrous connective tissue interpenetrates and surrounds the muscles, bones, nerves, and blood vessels of the body. It provides connection and communication in the form of
aponeuroses
An aponeurosis (; plural: ''aponeuroses'') is a type or a variant of the deep fascia, in the form of a sheet of pearly-white fibrous tissue that attaches sheet-like muscles needing a wide area of attachment. Their primary function is to join muscl ...
retinacula
A retinaculum (plural ''retinacula'') is a band of thickened deep fascia around tendons that holds them in place. It is not part of any muscle. Its function is mostly to stabilize a tendon. The term retinaculum is New Latin, derived from the Latin ...
,
joint capsule
In anatomy, a joint capsule or articular capsule is an envelope surrounding a synovial joint.septa. The deep fasciae envelop all bone (
periosteum
The periosteum is a membrane that covers the outer surface of all bones, except at the articular surfaces (i.e. the parts within a joint space) of long bones. Endosteum lines the inner surface of the medullary cavity of all long bones.
Structu ...
tunica externa
The tunica externa (New Latin "outer coat"), also known as the tunica adventitia (New Latin "additional coat"), is the outermost tunica (layer) of a blood vessel, surrounding the tunica media. It is mainly composed of collagen and, in arteries, i ...
) and become specialized in muscles (
epimysium
Epimysium (plural ''epimysia'') (Greek ''epi-'' for on, upon, or above + Greek ''mys'' for muscle) is the fibrous tissue envelope that surrounds skeletal muscle. It is a layer of dense irregular connective tissue which ensheaths the entire muscle ...
,
perimysium
Perimysium is a sheath of connective tissue that groups muscle fibers into bundles (anywhere between 10 and 100 or more) or fascicles.
Studies of muscle physiology suggest that the perimysium plays a role in transmitting lateral contractile ...
perineurium
The perineurium is a protective sheath that surrounds a nerve fascicle. This bundles together axons targeting the same anatomical location. The perineurium is composed from fibroblasts.
In the peripheral nervous system, the myelin sheath of each ...
, and
endoneurium
The endoneurium (also called endoneurial channel, endoneurial sheath, endoneurial tube, or Henle's sheath) is a layer of delicate connective tissue around the myelin sheath of each myelinated nerve fiber in the peripheral nervous system. Its com ...
). The high density of collagen fibers gives the deep fascia its strength and integrity. The amount of elastin fiber determines how much extensibility and resilience it will have.
innervated
A nerve is an enclosed, cable-like bundle of nerve fibers (called axons) in the peripheral nervous system.
A nerve transmits electrical impulses. It is the basic unit of the peripheral nervous system. A nerve provides a common pathway for the e ...
chemoreceptors
A chemoreceptor, also known as chemosensor, is a specialized sensory receptor which transduces a chemical substance ( endogenous or induced) to generate a biological signal. This signal may be in the form of an action potential, if the chemorec ...
); and fluctuation in temperature (
thermoreceptors
A thermoreceptor is a non-specialised sense receptor, or more accurately the receptive portion of a sensory neuron, that codes absolute and relative changes in temperature, primarily within the innocuous range. In the mammalian peripheral nervous s ...
). Deep fascia is able to respond to sensory input by contracting; by relaxing; or by adding, reducing, or changing its composition through the process of fascial remodeling.
Fascia may be able to contract due to the activity of
myofibroblasts
A myofibroblast is a cell phenotype that was first described as being in a state between a fibroblast and a smooth muscle cell.
Structure
Myofibroblasts are contractile web-like fusiform cells that are identifiable by their expression of α-sm ...
which may play a role in wound healing.
The deep fascia can also relax. By monitoring changes in muscular tension, joint position, rate of movement, pressure, and vibration, mechanoreceptors in the deep fascia are capable of initiating relaxation. Deep fascia can relax rapidly in response to sudden muscular overload or rapid movements.
Golgi tendon organs
The Golgi tendon organ (GTO) (also called Golgi organ, tendon organ, neurotendinous organ or neurotendinous spindle) is a proprioceptor – a type of sensory receptor that senses changes in muscle tension. It lies at the interface between a musc ...
operate as a feedback mechanism by causing myofascial relaxation before muscle force becomes so great that tendons might be torn. Pacinian corpuscles sense changes in pressure and vibration to monitor the rate of
acceleration
In mechanics, acceleration is the rate of change of the velocity of an object with respect to time. Accelerations are vector quantities (in that they have magnitude and direction). The orientation of an object's acceleration is given by t ...
of movement. They will initiate a sudden relaxatory response if movement happens too fast. Deep fascia can also relax slowly as some mechanoreceptors respond to changes over longer timescales. Unlike the Golgi tendon organs, Golgi receptors report joint position independent of muscle contraction. This helps the body to know where the bones are at any given moment. Ruffini endings respond to regular stretching and to slow sustained pressure. In addition to initiating fascial relaxation, they contribute to full-body relaxation by inhibiting sympathetic activity which slows down heart rate and respiration.
When contraction persists, fascia will respond with the addition of new material. Fibroblasts secrete collagen and other proteins into the
extracellular matrix
In biology, the extracellular matrix (ECM), also called intercellular matrix, is a three-dimensional network consisting of extracellular macromolecules and minerals, such as collagen, enzymes, glycoproteins and hydroxyapatite that provide s ...
where they bind to existing proteins, making the composition thicker and less extensible. Although this potentiates the tensile strength of the fascia, it can unfortunately restrict the very structures it aims to protect. The pathologies resulting from fascial restrictions range from a mild decrease in joint range of motion to severe fascial binding of muscles, nerves and blood vessels, as in
compartment syndrome
Compartment syndrome is a condition in which increased pressure within one of the body's anatomical compartments results in insufficient blood supply to tissue within that space. There are two main types: acute and chronic. Compartments of the ...
of the leg. However, if fascial contraction can be interrupted long enough, a reverse form of fascial remodeling occurs. The fascia will normalize its composition and tone and the extra material that was generated by prolonged contraction will be ingested by macrophages within the extracellular matrix.
Like mechanoreceptors, chemoreceptors in deep fascia also have the ability to promote fascial relaxation. We tend to think of relaxation as a good thing, however fascia needs to maintain some degree of tension. This is especially true of ligaments. To maintain joint integrity, they need to provide adequate tension between bony surfaces. If a ligament is too lax, injury becomes more likely. Certain chemicals, including hormones, can influence the composition of the ligaments. An example of this is seen in the menstrual cycle, where hormones are secreted to create changes in the
uterine
The uterus (from Latin ''uterus'', plural ''uteri'') or womb () is the organ in the reproductive system of most female mammals, including humans that accommodates the embryonic and fetal development of one or more embryos until birth. The ...
and pelvic floor fascia. The hormones are not site-specific, however, and chemoreceptors in other ligaments of the body can be receptive to them as well. The ligaments of the knee may be one of the areas where this happens, as a significant association between the ovulatory phase of the menstrual cycle and an increased likelihood for an
anterior cruciate ligament
The anterior cruciate ligament (ACL) is one of a pair of cruciate ligament
Cruciate ligaments (also cruciform ligaments) are pairs of ligaments arranged like a letter X. They occur in several joints of the body, such as the knee joint and th ...
injury has been demonstrated.
It has been suggested that manipulation of the fascia by
acupuncture
Acupuncture is a form of alternative medicine and a component of traditional Chinese medicine (TCM) in which thin needles are inserted into the body. Acupuncture is a pseudoscience; the theories and practices of TCM are not based on scientif ...
needles is responsible for the physical sensation of qi flowing along meridians in the body, even though there is no physically verifiable anatomical or
histological
Histology,
also known as microscopic anatomy or microanatomy, is the branch of biology which studies the microscopic anatomy of biological tissues. Histology is the microscopic counterpart to gross anatomy, which looks at larger structures vis ...
basis for the existence of
acupuncture points
This article provides a comprehensive list of acupuncture points, locations on the body used in acupuncture, acupressure, and other treatment systems based on Traditional Chinese Medicine (TCM).
Locations and basis
More than four hundred ...