Joint

∞ generated and posted on 2016.01.31 ∞

The technical term for joints, as found between bones, is articulation and associated with many joints as well as with bone growth is cartilage.

Joints, which connect together bones, may or may not move relative to each other depending on the bones involved and/or an individual's age; those joints that do move possess cartilage at the point of bone contact, where cartilage also is directly involved in bone growth; in terms of increasing movability, skeletal articulations can be classified as fibrous joints, cartilaginous joints, or synovial joints.

This page contains the following terms: Cartilage, Chondroblasts , Chondrocytes, Epiphyses, Growth plate, Axial skeleton , Joint, Articulation, Cranial sutures, Synovial joint, Synovial membrane, Synovial fluid, Ligament, Tendon, Fascia, Neuromuscular junction Osteoarthritis, Osteoporosis, Muscular dystrophy, Rheumatoid arthritis

The above video provides a nice introduction to bones and, especially, joints.



Cartilage

Highly water absorbent as well as compression-resistant connective tissue.
Cartilage is found most prominently both at the ends of bones and as an endoskeletal alternative to bone. It consists of collagen fibers, which serve to resist tearing; elastin fibers, which serve to provide flexibility; and water-absorbing ground substance, which resists compression.

Within cartilage there are no blood vessels nor innervation, since the presence of these would interfere with cartilage mechanical properties. The lack of a blood supply to the interior of cartilage results in slow healing to damaged cartilage, since without substantial access to nutrients and oxygen, as well as removal of wastes, metabolic activity and therefore rapidity of repair is limited.

Cartilage associated with bones is located at epiphyses and serves to cushion joints. Cartilage also serves as the material that is laid down during bone formation and then which is partially removed in the course of ossification.

Cartilage otherwise comes in three types termed elastic cartilage (which forms more flexible endoskeleton components such as the framework of your outer ear), fibrocartilage (as provides flexible though not highly moveable bone-like skeletal components as well as less flexible but non-bony endoskeleton such as that underlying your nose), and hyaline cartilage (which serves as endoskeletal material in its own right as well as the ends of long bones).


Links to terms of possible interest: Cartilage, Chondroitin sulfate, Collagen, Elastic cartilage, Extracellular matrix, Fibrocartilage, Glycosaminoglycan, Hyaline cartilage, Polysaccharides

The above video introduces us to cartilage and the different types of cartilage, i.e., hyaline cartilage, fibrocartilage, and elastic cartilage.

The above video introduces us to cartilage and a tiny bit about joints between bones.

The above video introduces us to hyaline cartilage.

The above video introduces us to fibrocartilage.

The above video introduces us to elastic cartilage.



Chondroblasts

Cells responsible for the formation of new cartilage matrix.
Chondroblasts are not trapped within cartilage just as osteoblasts are not trapped within bone, and chondroblasts also have a similar origin to osteoblasts. Chondroblasts in the past were referred to as cartilage cells.


Chondrocytes

Cells embedded within cartilage that are responsible for cartilage maintenance and repair.
Chondrocytes are found trapped within cartilage just as osteocytes are trapped within bone. Chondrocytes also have a similar origin to osteocytes. Indeed, both cell types, as well as osteoblasts, can form from the same precursor cells. Also equivalent to osteocytes, chondrocytes can both break down and secrete cartilage, as befitting their role in both cartilage maintenance and repair.


Links to terms of possible interest: Cartilage, Chondroblast, Chondrocyte, Perichondrium



Epiphyses

Cartilaginous ends of long bones where bone growth in length also occurs.
Epiphyses consist of cartilage as laid down by cells called chondrocytes. During the growth of long bones in length, the epiphysis beneath its leading edge grows via the formation of new cartilage. The cartilage that is in contact with existing bone, the trailing edge of epiphyseal development, then undergoes ossification. The ends of long bones during growth thus consists of existing cartilage, a middle zone of cartilage growth, and a trailing edge of bone growth. Once bone growth has terminated, as occurs in mammals during maturation, the epiphysis serves simply as the cartilaginous bone end. During bone growth, however, the growing portion of the epiphysis may be described instead as the epiphyseal growth plate. The termination of growth of a bone is described as epiphyseal closure, and different epiphyseal growth plates undergo closure at different times over the course of maturation.


Links to terms of possible interest: Epiphysis, Femur, Growth plate, Metaphysis, Red bone marrow

The quality of the above video is somewhat visually wanting but the video itself is both brief and instructive.



Growth plate

Area found between the epiphysis and metaphysis in still-lengthening bones.
The growth plate, also known as the epiphyseal plate, is found just behind the epiphysis, that is, the end of the long bone. It is technically a part of the metaphysis, which is found between the epiphysis and the shaft of the bone (the diaphysis). The growth plate is the location where new bone is laid down during bone growth. In adults – that is, individuals whose long bones have stopped lengthening – the epiphyseal plate is called instead the epiphyseal line.


Links to terms of possible interest: Cartilage, Epiphysis, Growth plate, Long bone



Axial skeleton

Combination of the bones of the skull, middle ear, neck, backbone, sternum, and ribs.
Excluded from the axial skeleton is the bulk of the pelvis, which can along with the shoulders be viewed as less central to the skeleton due to the their involvement in the support of the limbs. The term "Axial" refers to the closeness of these bones to the "Axes" or central region of the body/skeleton. Contrast with the appendicular skeleton, that is, the skeleton associated with the appendages, the arms and legs.


Links to terms of possible interest: Axial skeleton, Fibrocartilage, Hyaline cartilage, Hyoid bone, Ossicles, Rib cage, Skull, Symphyses, Synarthroses, Synchondroses, Synostoses, Vertebral column

This above video provides a nice overview of what the axial skeleton is all about.

This above video considers some comparative anatomy, in this case extremes of anatomy in terms of backbone morphology as seen in what is known as the Hero Shrew.

The above video describes the cartilaginous joints found between the vertebrae and other bones making up the axial skeleton particularly as found inferior to the skull.



Joint

Connection between two or more bones.
Joints differ in terms of the degree of movement that normally is permissible. Joints are associated with connecting as well as stabilizing connective tissue including – depending on the jointsligaments and fibrocartilage. The most fully movable joints are synovial joints which are encased by synovial membranes.


Links to terms of possible interest: Amphiarthroses, Ball and socket joint, Diarthroses, Ellipsoid joint, Hinge joint, Pivot joint, Plane joint, Saddle joint, Synarthroses

The above video introduces us to joints between bones.

The above video introduces us to joints between bones.

The above video presents the words used to describe movement relative to synovial joints. And yes, if you are studying the anatomy of the movement of joints, this stuff is important!



Articulation

Alternative name for joint between two bones.
See "Joint", above, for discussion.                                                                                                                                                                                    


Cranial sutures

Tightly interlocking joints found between the bones making up the skull.
Cranial sutures prevent movement between the bones of the skull, but only form after birth. The skull of a newborn, by contrast, consists of connective tissue between the bones of the skull, which are called fontanels. The fontanels allow the skull bones to move, to a degree, relative to each other. This movement allows the skull to change shape in response to pressure during passage down the birth canal. Towards the front-middle of an infant's head there is a particularly pronounced fontanel colloquially known as the "soft spot". Sutures more generally are rigid connections between otherwise independent hard objects associated with organisms, such between certain components of the exoskeletons of arthropods (that is, which are insects and their ilk).


Links to terms of possible interest: Amphiarthroses, Fontanel, Coronal suture, Cranial suture, Joint, Lambdoidal suture, Sagittal suture, Synarthroses, Synostoses

Reference to sutures starts at 3:29, though the above video is pretty fascinating up to that point as it walks you through the numerous bones the skull.

The above video provides an introduction to fibrous joints, including both Amphiarthroses and synarthroses (contrasting diarthroses).



Synovial joint

Highly movable articulation between bones.
The joints within our bodies that we think of as joints, that is, interactions between bones about which substantial movement can occur (e.g., our knees, our elbows, among the bones in our wrists, between the vertebrae making up our spine) are synovial joints. They possess synovial membranes, synovial fluid, and slippery, shock absorbing padding consisting of cartilage.


Links to terms of possible interest: Articular capsule, Articular cartilage, Ball and socket joint, Diarthroses, Ellipsoid joint, Hinge joint, Hyaline cartilage, Joint cavity, Pivot joint, Plane joint, Reinforcing ligament, Saddle joint, Synovial fluid, Synovial membrane, Synovial joint

The above video does a great job of describing the basic properties of a diversity of movable, that is, synovial joints.

The above video walks through the anatomy of synovial joints.

The above video is another walk through the different types of synovial joints, though does provide more detail.



Synovial membrane

Tissue that seals in the fluid that separates the surfaces of highly movable joints.
The fluid that is contained by synovial membranes is synovial fluid and those joints that possess synovial fluid are known as synovial joints. This membrane, which is a tissue membrane, is found within what is known as the joint capsule, which is a type of ligament surrounding the joint. Synovial fluid is secreted by cells found within the synovial membrane.


Links to terms of possible interest: Articular capsule, Articular cartilage, Cartilage, Connective tissue, Fibrous capsule, Hyaline cartilage, Joint cavity, Ligament, Synovial fluid, Synovial membrane



Synovial fluid

Lubrication found within highly movable joints.
Synovial fluid is a viscous fluid secreted by synovial membranes. Synovial fluid is found specifically within synovial joints and serves to lubricate the cartilaginous epiphysis separating the bones making up the joint. As a consequence, these bones can move smoothly relative to each other despite their close physical association at the joint. In addition to reducing friction, synovial fluid also contributes to the shock absorption displayed by synovial joints (that is, the synovial fluid is partially compression resistant so therefore can deform in response to sudden pressure, but not completely deform, thereby storing some of that pressure rather than transmitting it directly to the underlying cartilage). Synovial fluid is partially composed of filtered blood plasma and as such therefore contributes to the feeding of and waste removal from cartilage cells, i.e., chondrocytes.


Links to terms of possible interest: Cartilage, Femur, Synovial fluid, Synovial joint, Synovial membrane, Tibia



Ligament

Non-cartilaginous connective tissue that connects bone to bone.
Ligaments consist of dense, fibrous connective tissue with bundles of parallel collagen fibers. The bones that are connected together via one or more ligaments form a joint between those bones. In addition to connecting bones together, ligaments contribute to the stability of joints, i.e., beyond that provided by muscle and tendon.

The above video discusses ligament and ligament injury basics.

The above video gives a great illustration of how ligaments stabilize joints, what happens if they tear (particularly the ACL), and how tears can be repaired.



Tendon

Connective tissue that connects muscle to bone.
Tendons consist of dense, fibrous connective tissue with bundles of parallel collagen fibers, and are also referred to as sinew (which can be quite noticeable, for example, in the legs of turkeys as consumed during Thanksgiving). In addition to connecting muscle to bone, tendons also possess an elasticity that can be help to conserve energy during such processes as running. Ossifications can occur within tendons, the most prominent in our bodies being the patella which otherwise is known as the knee cap.

The above video does a nice job of distinguishing between what is a ligament and what is a tendon?

The above video does a nice job of talking about tendon anatomy in the first minute or so and then talks about tendonitis.



Fascia

Connective tissue that connects muscle to muscle or otherwise surrounds various soft tissues.
Fascia (or fasciae as the plural) consist of dense, fibrous connective tissue. The role of fascia consists of a combination of keeping various otherwise disparate tissue mutually associated, providing some protection (i.e., as a protective outer covering), and allowing these tissues to slide without friction relative to other tissue. Epimysium, perimysium, endomysium, and periosteum, etc., are all examples of fascia as too are also tendons and ligaments. In fact, all of those can be described as examples of what are known as deep fascia or investing fascia, contrasting superficial fascia as associated with skin, or, instead, visceral fascia or parietal fascia as associated with internal organs. The latter not only surrounds those organs but also serves to suspend organs from the walls of body cavities.


Links to terms of possible interest: Deep fascia, Epimysium, Perimysium, Periosteum, Skeletal muscle, Tendon

The above video is a little long but also is a pretty novel way to appreciate what fascia is all about.

The above video does a good if technical job of describing what fascia is all about with emphasis on the different kinds of fascia that are found in association with skeletal muscle.



Neuromuscular junction

Point of connection between muscle and the nerves that control them.
Neuromuscular junctions are equivalent to the synapses between neurons, except rather than between neurons they are between motor neurons and muscle. In either case, a fluid-filled gap exists between the two cells across which signaling molecules diffuse from upstream neuron to downstream neuron or muscle. The neurotransmitter acetylcholine serves as the signaling molecule across neuromuscular junctions in vertebrate animals. It is the binding of acetylcholine to the muscle cell across the cleft of the neuromuscular junction which initiates an action potential that ultimately is propagated down T tubules leading to release of calcium ions from sarcoplasmic reticulum, etc.


Links to terms of possible interest: Axon, Innervation, Mitochondria, Motor neuron, Myofibril, Neuromuscular junction, Neuron, Presynaptic terminal, Skeletal muscle, Synaptic cleft, Synaptic vesicle

The above video walks through the process of signal transmission across a neuromuscular junction.

The above video considers the structure and function of neuromuscular junctions in some detail.



Osteoporosis

Disease associated with progressive loss of bone mass and increased potential for bone fracture.
"Osteo" means bone and "poros" means pores, thus, bones with pores, which are bones that have been weakened in the course of loss of mineralized bone mass. This occurs when the homeostasis of bone maintenance is disrupted such that osteoclasts, which remove bone material (bone resorption), are more active than osteoblasts, which instead add bone material (ossification). While loss of bone mass is typical of aging, osteoporosis represents an excessive loss of bone mass.


Links to terms of possible interest: Bone matrix, Osteoporosis

The above video provides a nice introduction to the osteoporosis and its causes and treatment.



Osteoarthritis

Degenerative and inflammatory joint disease associated with loss of articular cartilage and bone spur formation.
Articular cartilage includes that which is associated with synovial joints. Osteoarthritis can result from genetic predispositions, joint injury, joint misalignments, obesity, and excessive overuse such as associated with athletics. It's symptoms include joint pain and stiffness. The location of the most commonly affected joints are the hands (particularly at the base of the thumb and near the ends of the fingers) hips, knees, and spine (particularly neck and lower back). Often the impact is not symmetrical, e.g., one knee may be affected but not the other.

The above video provides a nice introduction to the osteoarthritis and its causes and treatment.



Rheumatoid arthritis

Degenerative and inflammatory joint as well as more general disease that is a consequence of autoimmunity and can result in joint fusion.
Osteoarthritis is the second most common type of arthritis. The location of the most commonly affected joints are the ankles, feet, hands, and wrists but its impact is not limited to either bone or joints. In addition, its impact often is symmetrical, e.g., if one knee is affected then so is the other. The reason for this lack of focus of pathology is because rheumatoid arthritis is the result of autoimmunity rather than physical stress, i.e., contrast osteoarthritis. In addition, in rheumatoid arthritis the bones making up joints can come to grow together and if left untreated can potentially, eventually fuse, resulting in loss of joint mobility.

The above video provides a nice introduction to the rheumatoid arthritis and its causes and treatment.



Muscular dystrophy

Degenerative disease of youth involving progressive weakness and loss of ability to walk.
A number of mutations can give rise to different forms of muscular dystrophy (MD). They involve defects in muscle proteins, particularly the protein, dystrophin.

The above video presents a quick overview of myotonic dystrophy, which in adults is the most common form of muscular dystrophy.


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