Deep fascia (or investing fascia) is a
fascia
A fascia (; : fasciae or fascias; adjective fascial; ) is a generic term for macroscopic membranous bodily structures. Fasciae are classified as superficial, visceral or deep, and further designated according to their anatomical location.
...
, 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 extracellular matrix, matrix element. The fibers are mainly composed of type I collagen. Crowded between the collagen fibers are rows ...
that can surround individual
muscle
Muscle is a soft tissue, one of the four basic types of animal tissue. There are three types of muscle tissue in vertebrates: skeletal muscle, cardiac muscle, and smooth muscle. Muscle tissue gives skeletal muscles the ability to muscle contra ...
s and groups of muscles to separate into
fascial compartment
A fascial compartment is a section within the body that contains Skeletal muscle, muscles and nerves and is surrounded by deep fascia. In the human body, the Limb (anatomy), limbs can each be divided into two segments – the upper limb can be di ...
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 (; : aponeuroses) is a flattened tendon by which muscle attaches to bone or fascia. Aponeuroses exhibit an ordered arrangement of collagen fibres, thus attaining high tensile strength in a particular direction while being vulnerable ...
,
ligaments
A ligament is a type of fibrous connective tissue in the body that connects bones to other bones. It also connects flight feathers to bones, in dinosaurs and birds. All 30,000 species of amniotes (land animals with internal bones) have ligam ...
,
tendons
A tendon or sinew is a tough band of dense fibrous connective tissue that connects muscle to bone. It sends the mechanical forces of muscle contraction to the skeletal system, while withstanding tension.
Tendons, like ligaments, are made of ...
,
retinacula,
joint capsule
In anatomy, a joint capsule or articular capsule is an envelope surrounding a synovial joint.septa
SEPTA, the Southeastern Pennsylvania Transportation Authority, is a regional public transportation authority that operates bus, rapid transit, commuter rail, light rail, and electric trolleybus services for nearly four million people througho ...
. 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. (At the joints of long bones the bone's outer surface is lined with "articular cartila ...
and
endosteum
The endosteum (: endostea) is a thin vascular membrane of connective tissue that lines the inner surface of the bony tissue that forms the medullary cavity of long bones.
This endosteal surface is usually resorbed during long periods of malnutr ...
);
cartilage
Cartilage is a resilient and smooth type of connective tissue. Semi-transparent and non-porous, it is usually covered by a tough and fibrous membrane called perichondrium. In tetrapods, it covers and protects the ends of long bones at the joints ...
(
perichondrium
The perichondrium (from Greek and ) is a layer of dense irregular connective tissue that surrounds the cartilage of developing bone. It consists of two separate layers: an outer fibrous layer and inner chondrogenic layer. The fibrous layer conta ...
), and blood vessels (
tunica externa
The tunica externa (Neo-Latin "outer coat"), also known as the tunica adventitia (Neo-Latin "additional coat"), is the outermost tunica (biology), tunica (layer) of a blood vessel, surrounding the tunica media. It is mainly composed of collagen an ...
) and become specialized in muscles (
epimysium,
perimysium, and
endomysium
The endomysium, meaning ''within the muscle'', is a wispy layer of areolar connective tissue that ensheaths each individual muscle fiber, or muscle cell. It also contains capillaries and nerves. It overlies the muscle fiber's cell membrane: th ...
) and nerves (
epineurium
The epineurium is the outermost layer of dense irregular connective tissue surrounding a peripheral nerve. It usually surrounds multiple nerve fascicles as well as blood vessels which supply the nerve. Smaller branches of these blood vessels penet ...
,
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 comp ...
). The high density of
collagen
Collagen () is the main structural protein in the extracellular matrix of the connective tissues of many animals. It is the most abundant protein in mammals, making up 25% to 35% of protein content. Amino acids are bound together to form a trip ...
fibers gives the deep fascia its strength and integrity. The amount of
elastin
Elastin is a protein encoded by the ''ELN'' gene in humans and several other animals. Elastin is a key component in the extracellular matrix of gnathostomes (jawed vertebrates). It is highly Elasticity (physics), elastic and present in connective ...
fiber determines how much
extensibility
Extensibility is a software engineering and systems design principle that provides for future growth. Extensibility is a measure of the ability to extend a system and the level of effort required to implement the extension. Extensions can be t ...
and resilience it will have.
Examples
Examples include:
*
Fascia lata
The fascia lata is the deep fascia of the thigh. It encloses the thigh muscles and forms the outer limit of the fascial compartments of thigh, which are internally separated by the medial intermuscular septum and the lateral intermuscular sept ...
*
Deep fascia of leg
The deep fascia of leg or crural fascia forms a complete investment to the muscles, and is fused with the periosteum over the subcutaneous surfaces of the bones.
The deep fascia of the leg is continuous above with the fascia lata (deep fascia of ...
*
Brachial fascia
*
Buck's fascia
Buck's fascia (deep fascia of the penis, Gallaudet's fascia or fascia of the penis) is a layer of deep fascia covering the three erectile bodies of the penis.
Structure
Buck's fascia is continuous with the external spermatic fascia in the scro ...
Fascial dynamics
Deep fascia is less extensible than
superficial fascia
A fascia (; : fasciae or fascias; adjective fascial; ) is a generic term for macroscopic membranous bodily structures. Fasciae are classified as superficial, visceral or deep, and further designated according to their anatomical location.
Th ...
. It is essentially
avascular
Blood vessels are the tubular structures of a circulatory system that transport blood throughout many animals’ bodies. Blood vessels transport blood cells, nutrients, and oxygen to most of the tissues of a body. They also take waste and ...
, but is richly
innervated with
sensory receptor
Sensory neurons, also known as afferent neurons, are neurons in the nervous system, that convert a specific type of stimulus, via their receptors, into action potentials or graded receptor potentials. This process is called sensory transduc ...
s that report the presence of pain (
nociceptors
A nociceptor (; ) is a sensory neuron that responds to damaging or potentially damaging stimuli by sending "possible threat" signals to the spinal cord and the brain. The brain creates the sensation of pain to direct attention to the body part, ...
); change in movement (
proprioceptors
Proprioception ( ) is the sense of self-movement, force, and body position.
Proprioception is mediated by proprioceptors, a type of sensory receptor, located within muscles, tendons, and joints. Most animals possess multiple subtypes of propri ...
); change in pressure and vibration (
mechanoreceptors
A mechanoreceptor, also called mechanoceptor, is a sensory receptor that responds to mechanical pressure or distortion. Mechanoreceptors are located on sensory neurons that convert mechanical pressure into electrical signals that, in animals, ar ...
); change in the chemical milieu (
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 chemorece ...
); 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 ...
).
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 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 mus ...
operate as a feedback mechanism by causing myofascial relaxation before muscle force becomes so great that tendons might be torn.
Pacinian corpuscles
The Pacinian corpuscle (also lamellar corpuscle, or Vater–Pacini corpuscle) is a low-threshold mechanoreceptor responsive to vibration or pressure, found in the skin and other internal organs. In the skin it is one of the four main types of cuta ...
sense changes in pressure and vibration to monitor the rate of
acceleration
In mechanics, acceleration is the Rate (mathematics), rate of change of the velocity of an object with respect to time. Acceleration is one of several components of kinematics, the study of motion. Accelerations are Euclidean vector, vector ...
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 (ICM), is a network consisting of extracellular macromolecules and minerals, such as collagen, enzymes, glycoproteins and hydroxyapatite that provide structural and bio ...
where they bind to existing proteins, making the composition thicker and less extensible. Although this potentiates the tensile strength
Ultimate tensile strength (also called UTS, tensile strength, TS, ultimate strength or F_\text in notation) is the maximum stress that a material can withstand while being stretched or pulled before breaking. In brittle materials, the ultimate ...
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
Range of motion (or ROM) is the linear or angular distance that a moving object may normally travel while properly attached to another.
In biomechanics and strength training, ROM refers to the angular distance and direction a joint can move be ...
to severe fascial binding of muscles, nerves and blood vessels, as in compartment syndrome
Compartment syndrome is a serious medical condition in which increased pressure within a Fascial compartment, body compartment compromises blood flow and tissue function, potentially leading to permanent damage if not promptly treated. There are ...
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
A hormone (from the Greek participle , "setting in motion") is a class of signaling molecules in multicellular organisms that are sent to distant organs or tissues by complex biological processes to regulate physiology and behavior. Hormones a ...
, can influence the composition of the ligaments. An example of this is seen in the menstrual cycle
The menstrual cycle is a series of natural changes in hormone production and the structures of the uterus and ovaries of the female reproductive system that makes pregnancy possible. The ovarian cycle controls the production and release of eg ...
, where hormones are secreted to create changes in the uterine and pelvic floor
The pelvic floor or pelvic diaphragm is an anatomical location in the human body which has an important role in urinary and anal continence, sexual function, and support of the pelvic organs. The pelvic floor includes muscles, both skeletal and ...
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 ligaments (the other being the posterior cruciate ligament) in the human knee. The two ligaments are called "cruciform" ligaments, as they are arranged in a crossed formation. In ...
injury has been demonstrated.
Art
The continuity of the deep fasciae within the human body inspired the artistic expression seen in the Fascial Net Plastination Project
The Fascial Net Plastination Project is an anatomical research initiative established in 2018 aimed at plastinating and studying the human fascial network. The collaboration was initiated by Robert Schleip as a joint effort between Body Worlds, ...
, which is prominently displayed at the Body Worlds exhibition in Berlin.
References
{{Muscular system
Fascia