Tissues of the musculoskeletal system

Question 1

What is the most abundant protein in the body?

Answer 1

Collagen

Question 2

What characterizes the features of connective tissue generally?

Answer 2

Relative abundance of extracellular matrix as compared with cellular mass

Question 3

What is the tertiary structure of collagen?

Answer 3

Triple helix made up of three separate polypeptide molecules called alpha chains

Question 4

What are the primary components of the extracellular matrix?

Answer 4

Collagen, proteoglycans, elastin

Question 5

What is the basic structure of proteoglycans?

Answer 5

Core protein with one or more covalently attached glycosaminoglycan side chains

Question 6

What are the two major families of proteoglycans?

Answer 6

Large aggregating and small leucine rich

Question 7

What is the composition of elastic fibers?

Answer 7

Composed mainly of elastin. The monomeric component of elastin is tropoelastin

Question 8

How much elastic deformation can elastic fibers undergo?

Answer 8

70% of the resting length (maximum extension of 220% before loss of resting length)

Question 9

What other components of the extracellular matrix are essential for elastin formation?

Answer 9

Presence of fibrillin microfibrils and fibronectin

Question 10

What cells comprise the basic multicellular unit of bone?

Answer 10

Osteoblasts, osteoclasts, osteocytes

Question 11

Where does most bone remodelling occur?

Answer 11

On cortical or trabecular surfaces

Question 12

What are the two predominant forms of bone in the adult?

Answer 12

Cancellous and cortical

Question 13

Where do osteoblasts, osteoclasts and osteocytes reside?

Answer 13

Osteoblasts: periosteal and endosteal membranes.
Osteocytes: are terminally differentiated osteoblasts encased in bone
Osteoclasts: exist on the bone surface

Question 14

What is the water, mineral and organic matter content of bone?

Answer 14

Low water content (5-10%), high mineral content (70%), remainder is inorganic matter

Question 15

What accounts for the majority of the organic matrix in bone?

Answer 15

Collagen (90%). Predominantly type 1

Question 16

What is the primary mineral component of bone?

Answer 16

Calcium hydroxylapatite

Question 17

What components of bone provide stiffness and strength to resist compressive and tensile stresses?

Answer 17

Compressive stresses: mineral component.
Tensile stresses: organic component (hence why bone is week in tension)

Question 18

What are the two types of bone formation?

Answer 18

Lamellar bone and woven bone

Question 19

What is the water content of articular cartilage?

Answer 19

70%

Question 20

On a dry weight basis what is the composition of articular cartilage?

Answer 20

50% collagen, 35% proteoglycans, 10% other glycoproteins. Chrondrocytes make up 5-10% of articular cartilage by volume

Question 21

What is the predominant type of collagen in articular and fibrocartilage?

Answer 21

Articular: type 1
Fibrocartilage: type 2

Question 22

What are the layers of articular cartilage?

Answer 22

Unmineralized zones:
Zone 1: Superficial zone: chondrocytes are small and axes are parallel to joint surface. Collagen is fibrils are densely packed and also parallel.

Zone 2: Transitional zone: chondrocytes are larger and rounded. Collagen fibrils form a mesh like structure.

Zone 3: Radiate zone: chondrocytes and collagen fibrils are larger and orientated perpendicular to the joint surface.

Tide mark: separates the unmineralized and mineralized zones.

Zone 4: Calcified cartilage/mineralized zone

Question 23

Are proteoglycans more or less abundant with depth in the articular cartilage?

Answer 23

More abundant deeper, and provide resistance to compressive stresses. Tensile stresses are predominantly mitigated by collagen fibrils.

Question 24

Does fibrocartilage contain a high or low quantity of proteoglycans?

Answer 24

Relatively low quantity. Characterized by chrondrocytic cells suspended in a dense ECM

Question 25

What are the three different types of tendon in the body?

Answer 25

Aponeuroses, positional tendons (stiff) and energy storing (most elastic)

Question 26

What is the composition of ligaments or tendons?

Answer 26

Tenocytes or ligamentocytes are elongated fibroblastic cells that are aligned with collagen fibers. ECM predominantly composed of type 1 collaged. Numerous proteoglycans.

Question 27

What are the biomechanical characteristics of tendons/ligaments?

Answer 27

Anistrophic, viscoelastic (creep recovery and stress relaxation)

Question 28

What are the two types of entheses?

Answer 28

Fibrous (incorporated into periosteum) or fibrocartilaginous (bony attachment via a fibrocartilaginous precursor)

Question 29

What is the major cellular component of muscle?

Answer 29

Intracellular myofibrillar proteins (ECM makes up a small proportion)

Question 30

What are the basic functional units of muscle?

Answer 30

Myofiber is made up of myofibrils that are composed of sarcomeres (overlapping regions of actin and myosin that longitudinally slide in response to stimulation from a motor axon - release of calcium from sarcoplasmic reticulum in response to ACh binding on sarcolemma).

The cell membrane of myofibers is the sarcolemma, with nuclei positioned immediately adjacent. The sarcoplasmic reticulum surrounds myofibrils within a myofiber.

Myofibers are then bundled into muscle fibers (surrounded by endomysium). Then fasicles (surrounded by perimysium). Then muscle bellies (surrounded by epimysium). These connective tissue structures compose the ECM of skeletal muscle.

Question 31

What are the two basic types of muscle fibers?

Answer 31

Slow twitch (type 1): relies predominantly on oxidative metabolism.
Fast twitch (type 2): variable reliance on oxidative metabolism

Question 32

What connective tissue structure is predoninantly responsible for transmission of muscle force?

Answer 32

Perimysium