Overview of Osteology, Arthrology, and Myology

Posted on Aug 28, 2024 in Biology

ITEM 3. OVERVIEW OF OSTEOLOGY

Classification of Bones

  • Long Bones: Typical of limbs, their length reflects both the speed and power of motion. One axis predominates over the other two. They are subject to great traction. Their tubular shaft with a central medullary cavity widens (metaphysis) towards the expanded articular ends (epiphysis), which have separate ossification centers and are often multiple.
  • Short Bones: Characterized by no axis predominating over the others. They are subject to compressive forces and can withstand much pressure, so they usually have a thin crust of compact bone supported by an inner zone entirely trabecular. We usually find them in the carpus and tarsus. Examples: Vertebrae, cuboid, navicular.
  • Irregular Bones: These include any bone not easily assignable to the above groups. They are usually at the base of the face.

Both the shape and bone structure are affected by genetic, metabolic, and mechanical factors. Each bone represents the result of a long history through countless functional successive generations.

Depressions and elevations disrupt the bone surfaces.

  • A pit is called a depression. Long depressions are known as furrows.
  • A notch is an indentation, and a real gap is a gap.
  • A large projection is called apophyses. If long and thin, it’s a spine, and if pointed, it’s called a process.
  • A rounded projection is a tuberosity or tubercle.
  • Long elevations are called ridges.
  • Epicondyle: A projection located near a condyle that usually serves as an insertion point for collateral ligaments.
  • The expanded proximal end of many long bones is commonly referred to as the head.
  • A hole is an opening in a bone. Holes are known as channels when they are long.
  • Fist-shaped condyles
  • Groove-shaped pulley: trochlea

Bone surfaces are smooth, tailored to the movement of joints, and covered by articular cartilage, covering the actual surfaces of synovial joints.

Main Function

Living tissue is very consistent, shock-resistant, pressure and tension-resistant, but also elastic. It serves as a barrier against external aggression, as a lever arm and anchor point for muscles and tendons. The bone case protects vital organs like the heart, lungs, and brain. It also allows movement in body parts to perform work or activities by establishing the displacement of the individual.

Bones form the musculoskeletal system or the bony skeleton and are lined with muscles depending on their location.

They act as a reservoir of calcium (essential for muscle contractions, while involved in hemostasis) and are involved in hematopoiesis (blood cell formation).

Bone Composition

Composed of organic matter (64%), inorganic (34%), and H2O (2%).

  • Fibers: 95% of the organic matter.
    • Collagen I: Formed through tropocollagen. They are distinguished because they are placed parallel and have an elliptical shape.
  • Fundamental Substance: Matter in gel form. Established by:
    • H2O
    • Proteoglycans: Glycosaminoglycans sulfur (hyaluronic acid, keratin, and chondroitin)
    • Minerals: Tricalcium phosphate, calcium carbonate, and calcium citrate.
    • Ions: Ca, Fl, Fe, Zn, Na, K, Mg.

Mature Bone Structure

In the concentric lamellae are two types of bone tissue (compact and spongy).

  • Compact Bone Tissue: Found in the middle of long bones and wrapping the spongy bone. It forms the shaft (elongated portion of long bones left in the middle of the epiphysis or distal portions thereof). It appears as a continuous solid mass, and its structure is only visible under an optical microscope. The lamellae are arranged in three ways:
    • Concentrically around a longitudinal vascular canal (called the Haversian canal), which contains capillaries, postcapillary venules, and sometimes arterioles, forming cylindrical structures called osteons or Haversian systems visible by light microscopy.
    • Between osteons, lamellae are arranged at an angle, forming the interstitial systems of osteons, separated by cement lines (a poor bone matrix layer of collagen fibers traversed by tubules or lacking vascular elements, all observable by light microscopy).
    • Beneath the periosteum on its inner surface and below the endosteum, lamellae are located around the circumference of the shaft in an extended form, called the outer and inner circumferential lamellae (parallel to the surface).
  • Haversian canals communicate with each other, the surface, or the marrow cavity by transverse or oblique channels called Volkmann canals. These canals have vessels coming from the periosteum and endosteum, larger than those of osteons. Light microscopy makes them difficult to recognize because they are surrounded by concentric lamellae.
  • Spongy Bone Tissue: Found in the epiphysis of long bones and in short and flat bones. It consists of disorganized osteons. Hematopoiesis occurs inside the spongy tissue (this place is called red marrow).

Ossification of the Bones

Two types of ossification:

  • Intramembranous ossification (mesenchymal)
  • Ossification intracartilaginous (endochondral)

Intramembranous Ossification (Mesenchymal)

Direct mineralization consists of a highly vascular connective tissue that stretches from regular ossification centers in the mesenchymal cells. Cells undergo a differentiation phase of intense proliferation around a capillary network.

Ossification Intracartilaginous (Endochondral)

The majority of human bones are preformed in cartilage during early fetal life. A long bone is prefigured by a rod of hyaline cartilage, which replaces a similar rod of condensed mesenchyme, and both predict the shape of the bone early.

Bone Growth

The majority of human bones are preformed by hyaline cartilage, some condensed in the mesenchyme. The first is a soft tissue, gradually transformed into bone at the beginning of osteogenesis, often from a center that expands to form the complete skeletal element.

These centers of ossification appear over a long period, many during embryonic life. Most bones ossify from several centers, and ossification progresses from that point towards the ends, which are cartilaginous at birth.

The shaft is ossified by a primary center while the cartilaginous epiphyses ossify secondary centers. As the epiphysis increases in size, almost all the cartilage is replaced by bone, except for a layer of hyaline cartilage that persists in the articular surface and a thicker zone between the diaphysis and epiphysis.

The persistence of the epiphyseal plate allows the bone to grow in length until it reaches its usual dimensions at maturity.

ITEM 4. OVERVIEW OF ARTHROLOGY

Arthrology is the study of the functional topography and temporal variation of joints.

Joints exhibit differences in growth and transmission of outside movements.

Solid joints (not synovial) are routinely called synarthroses and are grouped according to the major type of intermediate tissue: fibrous and cartilaginous joints. Both types of synarthrosis characterize nearly all cranial joints.

Cavitated joints (synovial) are called synovial joints and, with few exceptions, are located between the ends or other defined areas of endochondral bones.

  • Gomphosis: The dentoalveolar joint is a specialized fibrous joint, limited to fixing teeth in the alveolar bone of the upper and lower jaws.
  • Syndesmosis: A fibrous joint in which the bony surfaces are united by an interosseous ligament and routinely allows a little movement.

Synovial Joints

Participating bones are united by a fibrous capsule, and the bone surfaces are not continuous. They are covered with articular cartilage, a specialized hyaline cartilage layer with precise thickness and variable types. Contact is established between these cartilage surfaces, which have a very low friction coefficient. Sliding contact is facilitated by synovial fluid, which acts as a lubricant.

The fibrous capsule completely surrounds the joint. The capsule is lined by synovium, which also covers all non-articular surfaces, including non-articular bone surfaces, and the tendons and ligaments partially or wholly within the fibrous capsule, such as in the shoulder and knee.

Another structure covered by the intra-articular synovium is the meniscus.

Articular Surfaces

Formed mostly by a special variety of hyaline cartilage. Articular cartilage has a wear-resistant surface with low friction. It is lubricated, somewhat compressible, and elastic, making it ideally suited to move easily and stop on a similar surface while absorbing large compressive forces.

Fibrous Capsule of Fibrous Joints

  • Synovial Membrane: Lines the non-articular areas of synovial joints, bags, and tendon sheaths. All regions where movement occurs between opposing surfaces are lubricated by a liquid similar to egg white and absorbed through the membrane.
  • Synovial Intima (Synovial Sheath): Formed by synoviocytes. The functions of synovial intimal cells include removing debris from the joint cavity and synthesizing some components of the synovial fluid. The synovial fluid composition suggests a blood plasma dialysate that contains protein derived mainly from blood, plus mucin, mostly hyaluronate.

Synovial fluid functions include providing a fluid environment with little variation in pH. In the case of joint surfaces, it provides nutrition to articular cartilages, discs, and menisci, along with lubrication and decreased erosion.

Classification and Movement of Synovial Joints

  • Complexity of Form: Most synovial joints have two surfaces (male and female) and are simple joints. In some, one surface is completely convex (male) and larger than the opposite concave surface (female).
  • Degrees of Freedom: Joints moving on a single axis have one degree of freedom of movement. Those moving on two axes have two degrees of freedom of movement, and those with three axes have three degrees of freedom. Rotation about an axis: Uniaxial: 1 degree of freedom. Independent movements around an axis: Biaxial: 2 degrees of freedom. Some joints may have up to 3 degrees of freedom.

General Classification of Synovial Joints

  1. Plane Joints: This involves the apposition between nearly flat surfaces, usually with a slight curvature (e.g., cervical vertebral arch section).
  2. Hinge or Ginglymus Joints: Articular surfaces are pulley-shaped, hollow and solid, limiting movement to one plane.
  3. Trochoid Joints (Pivots): One bone pivots in a ring. This osteoligamentous joint only allows rotation around the pivot axis.
  4. Condyloid Joints: Biaxial. The articular surface is shaped like a solid ellipse in two axes of space, articulating with a surface also shaped like a hollow ellipse in two axes. Bicondylar Joints: Uniaxial.
  5. Saddle or Sellar Joints: Biaxial. They have concavoconvex surfaces, convex in one axis and concave in the perpendicular axis.
  6. Spheroid or Ball-and-Socket Joints: Formed by a head and an opposing glenoid cavity. Multiaxial.

Menisci and Labrums

These fibrous structures join the joint capsule, providing vascularization and innervation. Menisci divide joints into:

  • Complete Meniscus: A meniscus completely divides the joint capsule.
  • Incomplete Meniscus: Does not divide the joint capsule.

Labrums are also linked to the joint capsule, and their secretion is triangular. The meniscus allows a greater range of motion in certain joints and distributes forces and pressures on the joint.

Joint Capsule

A fibrous cuff that links the pieces of bone and inserts on the periphery of the articular surfaces. The capsule is continuous with the periosteum.

ITEM 5. OVERVIEW OF MYOLOGY

Myology studies the mechanical response to the contraction of contractile proteins. Muscle tissue has a limited capacity for regeneration and is replaced by fibers when damaged.

A muscle cell is known as a muscle fiber or muscle cell.

  • Smooth Muscle Tissue: Composed of fusiform fibers with a central nucleus. Found in the walls of viscera. These muscles are involuntary (autonomic).
  • Cardiac Muscle: Formed by longitudinal fibers with a striated appearance. Each fiber has a single core. It exists only in the middle layer of the heart.
  • Skeletal Muscle: Comprised of longitudinal fibers with a striated appearance. Each fiber has multiple cores located on the periphery. Found in the musculoskeletal system. Controlled by the nervous system (voluntary contraction). Performs significant mechanical work. Very rich in mitochondria.

Skeletal Muscle

Muscle fibers are bundled together to form larger bundles, ultimately forming the muscle. The fiber has a circular or elliptical section and a diameter of 10-100 microns.

Characteristics of Muscle Fibers

Nuclei are observed near the periphery of the fibers.

  • The cytoplasmic membrane is called the sarcolemma.
  • The cytoplasm is called sarcoplasm.
  • The fiber consists of myofibrils, characterized by a striated appearance (repeated along the entire length).

Within a myofibril are:

  • A dark band: A band
  • A clear band: I band
  • The A band is divided by a clear H band.
  • The dark area of the H band consists of two types of contractile proteins:
    • Actin: Fine filaments bound to each Z band.
    • Myosin: Thick filaments. Myosin (55%) is the most abundant protein and forms longitudinal filaments. Each strand consists of about 180 molecules grouped in a head shape.

Muscle contraction occurs through the interaction of actin and myosin (actomyosin).

Actin (23%) is divided into:

  • F-actin
  • G-actin
  • Tropomyosin B: Makes up 6% of the myofibrillar proteins.
  • Troponin: Represents 6% of the contractile proteins of the myofibrils. Formed by three units or molecules:
    • Troponin T: Binds to tropomyosin.
    • Troponin I: Inhibits an enzyme called ATPase, allowing ATP to become ADP.
    • Troponin C: Binds calcium ions.

Other Structural Proteins

  • Alpha-actinin: Links actin molecules.
  • Myomesin: Links myosin filaments, leading to the M band.
  • C protein: Links actin molecules.
  • I protein: Associated with magnesium.

Relaxed Muscle

Tropomyosin is interposed between actin and the myosin head. Calcium is needed for contraction. Thanks to calcium uptake by troponin C, calcium ion concentration increases, activating the other two troponin molecules. Troponin I‘s power produces ATP and ADP, and troponin T binds and displaces tropomyosin. This connects the myosin head with actin, and the energy release causes angulation of the myosin head.

Classifications of Muscles

  1. Shape
    • Long Muscles: One axis predominates over the other two. They allow for large movements and have great power. Example: Sartorius
    • Wide Muscles: Two axes predominate over the other, forming walls. They are abundant in the abdomen.
    • Short Muscles: No axis predominates over the others. They perform precise maneuvers and have great power. Example: Quadratus femoris muscle, supraspinatus
  2. Belly Shape
    • Strap Muscles: Fibers are usually parallel, forming a more or less thick belly. They cause large displacements but have little force of contraction.
    • Fusiform Muscles: Spindle-shaped fibers form a belly wider at the center than at the ends. They cause large movements and have a large but not very intense force of contraction. Example: Coracobrachialis.
    • Triangular Muscles: Fibers run obliquely. Example: Adductor longus.
  3. How Fibers Join the Tendon
    • Pennate Muscles: Fibers come from both sides to form the tendon and belly. Example: Rectus femoris.
    • Unipennate Muscles: Fibers only attach to the tendon on one side. These muscles are very powerful.
    • Muscles with fibers positioned in a spiral allow movement in a single plane.
    • Digastric Muscles: Some fibers attach to an intermediate tendon and then continue to their insertion. Example: Omohyoid
    • Polygastric Muscles: Have more than one intermediate tendon.
  4. Origin
    • Biceps: Two origins or heads.
    • Triceps: Three origins or heads.
    • Quadriceps: Four origins or heads.
  5. Insertion
    • Bicaudal: Two insertions.
    • Tricaudal: Three insertions.
    • Polycaudal: More than three insertions.

Specialized Structures at the Insertion


· · Tendon: Structure structure composed of collagen fibers that are placed parallel to the axis of the tendon and the fibers are placed so that they are not flexible and low resistance to the extension.
· Among them we find a loose connective tissue and cells (tenocitos)
· The set is called endotendon, which are involved in a pod (Peritenomio). Peritenomio prolongation is continuous with the periosteum to be confused and at the other end with the perimysium.
· There tendinous fibers get into the bone and calcify when there is a union between tendon and bone, known as Sharpey’s fibers.
• The tendon has an outer sleeve that protects it, which consists of the parietal layer and an inner layer which is a visceral synovial layer. Between them there is a space filled with synovial fluid.
• The tendon transmits muscle force to bone, is highly resistant, has low extensibility and is capable of sliding.
· Aponeurosis:
· · They are sheets of fibrous connective tissue, mainly collagen fibers.
• Acting as tendons crushed.
· They can be attached to the bone, fascia or other skin.
· From one extreme to another leaving muscle fibers.