1. Basic Concepts In MSK - Bone

Question 1

What are the three major components of the MSK?

Answer 1

Bone, skeletal muscle, connective tissues`

Question 2

From which of the germ layers do the three major components of the MSK derive from?

Answer 2

Mesoderm

Question 3

What are the 6 functions of bone?`

Answer 3

• Support
• Protection
• Metabolic
• Storage
• Movement (i.e.
joints)
• Haematopoiesis

Question 4

Describe the function of bone to support

Answer 4

The skeleton provides the framework for maintaining our body posture, with the limbs acting as pillars to support the trunk in space, and the rib cage supporting the thoracic wall.

Question 5

Describe the function of bone as protection

Answer 5

• The ribs protect the lungs and heart;
• the skull protects the brain;
• the vertebrae protect the spinal cord
• the pelvic structures are protected by the bony pelvis

Question 6

Describe the metabolic function of bone

Answer 6

• Bone is a living, actively-metabolising tissue; it is not inert.
• The metabolic functions of bone largely involve the homeostasis of calcium and phosphate.

Question 7

Describe the storage function of bone

Answer 7

• the skeleton is the main body reservoir for calcium and phosphate.
• bone also contains a large amount of protein (e.g. collagen) and the bone marrow is rich in fat.
• The skeleton is the primary site of storage of some growth factors and cytokines e.g. insulin like growth factors, transforming growth factors and bone morphogenetic proteins (BMPs).

Question 8

Describe the function of bone in movement

Answer 8

• Movement occurs at joints between bones.
• The bones act as an attachment site for the muscles and tendons, which use the bones as levers.
• The shape of the articulating surfaces determines the range of
motion.

Question 9

Describe the haemopoietic function of bone, including where it occurs in children and adults

Answer 9

• This takes place within the cavities of the bones.
• In children, the long bones such as the femur and
tibia are important sites of haematopoiesis
• in the adult the residual sites are mainly the pelvis, skull, vertebrae and the sternum.

Question 10

What are the 6 functions of skeletal muscle?

Answer 10

1) LOCOMOTION: Contraction of muscles acting across a joint lead to movement of that joint
2) POSTURE: Postural muscles enable us to maintain equilibrium e.g. when standing upright
3) METABOLIC: fast-twitch and slow-twitch
4) VENOUS RETURN: The muscles in the leg compress deep veins and help to propel venous blood back up towards the heart.
5) HEAT PRODUCTION: Shivering results in an increase in the metabolic rate of muscle, which in turn results in the generation of heat (thermogenesis) and an increase in body temperature
6) CONTINENCE: The muscles of the pelvic floor are responsible for the maintenance of urinary and faecal continence

Question 11

What are the different types of connective tissue?

Answer 11

Tendons
Ligaments
Fascia
Cartilage - hyaline/elastic/fibrocartilage
Synovial membrane

Question 12

What are the functions of tendons?

Answer 12

Tendons connect muscle to bone.

Their role is force-transmission from the contracting the muscle to the bone to which they are attached.

Question 13

Through what are tendons anchored to bone?

Answer 13

Sharpey’s fibres

Question 14

Why do tendons heal slowly?

Answer 14

Relatively poor blood supply

Low water content - limits diffusion of nutrients

Question 15

Why don’t tendons stretch too much when pulled?

Answer 15

Contain lots of collagen but little elastin - minimal waste of energy transfer

Question 16

What are the functions of ligaments?

Answer 16

Ligaments connect bone to bone.

They support joints and prevent an excessive range of movement

Question 17

Why is ligament healing compromised?

Answer 17

Relatively poor blood supply

Question 18

What are ligaments composed of?

Answer 18

Dense regular bundles of connective tissue protected by dense irregular connective tissue sheaths

Question 19

What do peri-articular (capsular) ligaments comprise of and what do they do? Give an example

Answer 19

Comprise of thickening of the capsule that surrounds synovial joints

Act as mechanical reinforcements

E.g. anterior and posterior cruciate ligaments of the knee

Question 20

What is fascia and what is its function?

Answer 20

Fascia is sheets of connective tissue. One of the major functions of fascia is to envelop groups of muscles and divide body parts (e.g. the arm) into anatomical compartments. Some sheets of fascia are very tough (e.g. fascia lata in the thigh) and therefore also serve a protective function for the underlying structures.

Question 21

What is superficial fascia?

Answer 21

loose connective tissue and fat underlying the skin - subcutaneous fatty layer

Also surrounds organs and glands and neurovascular bundles

Question 22

What is the purpose of superficial fascia?

Answer 22

• storage of fat and water
• passageway for lymphatics, nerves and blood vessels
• protective padding for organs

Question 23

What is deep fascia?

Answer 23

• Deep fascia is a layer of dense connective tissue that can surround individual muscles and groups of muscles to separate into fascial compartments.
• This fibrous connective tissue interpenetrates and surrounds the muscles, bones, nerves, and blood vessels of the body.
• Comprises of collagen bundles and elastin fibres orientated in a wavy pattern parallel to the direction of pull
• Flexible and able to resist great unidirectional forces

Question 24

What is the purpose of articular/hyaline cartilage?

Answer 24

• the cartilage found on the ends of bones contributing to joints. It is very smooth and helps to create almost
frictionless motion at the joint
• shock-ansorber

Question 25

What is the purpose of fibrocartilage?

Answer 25

• Fibrocartilage has a higher collagen content than hyaline cartilage. • involved in shock absorption • increase bony congruity at joints (congruity = creating a complementary shape of bony surfaces to improve stability). • The menisci of the knee are made of fibrocartilage

Question 26

What is the purpose of the synovial membrane and where is it found?

Answer 26

* This tissue is found within joints, bursae and tendon sheaths. * It produces synovial fluid which lubricates the joints. * act as a shock absorber * transport nutrients to (and remove waste from) the articular cartilage of the joint as articular cartilage is avascular and synovial joints are surrounded by a plexus of arteries so have a rich blood supply

Question 27

What does synovial fluid contain?

Answer 27

hyaluronic acid and lubricin, proteinases and collagenases

Question 28

What is the nature of synovial fluid?

Answer 28

Clear/pale yellow, viscous, slightly alkaline at rest

Question 29

What are bursae?

Answer 29

* A bursa is a small sac lined by synovial membrane and containing a thin layer of synovial fluid. * It provides a cushion between bones and tendons and/or muscles around a joint. * This helps to reduce friction between the bones and allows free movement. * They can either be communicating or non communicating with the joint cavity.

Question 30

What are tendon sheaths?

Answer 30

Tendon sheaths are elongated bursae that wrap around a tendon and reduce the friction associated with movement of the tendon.

Question 31

What is the major component that differentiates bone from other connective tissue?

Answer 31

The presence of calcium phosphate (CaPO4)/ hydroxyapatite which mineralises the extracellular matrix conferring rigidity into the bone

Question 32

What are the two divisions of bone?

Answer 32

Bone is divided into cellular and non-cellular components

Question 33

What are the cellular components of bone?

Answer 33

The cellular components of bone are predominantly osteocytes, osteoblasts and osteoclasts. There are also fibroblasts, macrophages, mast cells and adipocytes within bone.

Question 34

What does the ECM of the bone contain?

Answer 34

Fibres: collagen(mainly) and elastic(small amounts) Ground substance: water, GAGs, PGs

Question 35

What are the 2 major components that give bone its mechanical properties?

Answer 35

The two major components giving bone its mechanical properties are collagen and calcium phosphate. The calcium phosphate confers great compressive strength and the collagen confers great tensile strength to the bone.

Question 36

Why are bones calcified?

Answer 36

Makes them more rigid and gives it strength under compression

Question 37

How many bones in adult skeleton? Where are they found?

Answer 37

206 total 26 vertebrae 64 upper limbs (32 each side) 62 lower limbs

Question 38

What are the 2 divisions of the skeleton

Answer 38

The axial (longitudinal axis of the body) and the appendicular (compromises the bones of the upper and lower limbs)

Question 39

What is the function of osteoblasts?

Answer 39

Osteoblasts are responsible for synthesising new bone. They migrate over the matrix and synthesise and deposit osteoid, the matrix protein of bone.The osteoblasts then deposit calcium phosphate into the osteoid to make bone

Question 40

What does osteoid contain?

Answer 40

Osteoid contains collagen as its major protein and specialised proteins in smaller quantities, including osteocalcin and osteopontin

Question 41

What are osteoclasts and what is their function?

Answer 41

Osteoclasts are multinucleate cells formed by fusion of progenitor cells of thev monocyte/macrophage lineage. Role in resorbing bone -bone breakdown and mineral uptake

Question 42

How is resorption carried out by osteoclasts?

Answer 42

• They migrate over the surface of the bone matrix and secrete acidic chemicals to dissolve it, forming a pit on the surface of the cortical bone • As an osteoclast becomes active, the surface that is in contact with the bone becomes ruffled. • This increases the surface area for absorption of minerals such as calcium and phosphate. • The minerals in their ionic form are absorbed into the osteoclast, which later releases them into the extracellular fluid, from where they enter the blood.

Question 43

What are osteocytes and what is their job?

Answer 43

* Osteoblasts can become trapped within the bone matrix where they transform into osteocytes (figure 1.4). * They are trapped inside lacunae and become involved in signalling processes inside the bone. * Important for detecting strain/ stress on bone and sending information to osteoblasts/clasts for remodelling - maintains bone

Question 44

Explain the 2 types of bone

Answer 44

COMPACT BONE: dense outer layer of bone | CANELLOUS/SPONGEY: interior of bone, mesh like trabeculae, filled with bone marrow

Question 45

What are the classifications of bone?

Answer 45

```  Long  Flat  Short  Irregular  Sesamoid ```

Question 46

What is the function of long bones?

Answer 46

They are longer than they are wide. These bones act as rigid levers and are positioned in space by the action of the muscles.

Question 47

Where are long bones found?

Answer 47

They are mostly found in the appendicular skeleton. | E.g. the femur and humerus

Question 48

What is the diaphysis?

Answer 48

shaft of a long bone

Question 49

Where does the metaphysis and epiphysis lie?

Answer 49

The diaphysis flares out at each end into the metaphysis, which lies adjacent to the growth plate. On the other side of the growth plate is the epiphysis. ``` structure: Proximal epiphyses metaphyses diaphyses metaphyses distal epiphyses ```

Question 50

What is the medullary cavity of bone lined with?

Answer 50

Endosteum

Question 51

What does the medullary cavity contain in children?

Answer 51

Red marrow - which is actively involved in haematopoiesis

Question 52

What does the medullary cavity contain in adults?

Answer 52

High fat content and yellow marrow

Question 53

How is blood supplied to bones?

Answer 53

Epiphyseal arteries Major nutrient artery Periosteal arteries When development is finished, the growth plates fuse and the epiphyseal vessels shrivel and become insignificant Some bones have metaphysical arteries which enter at the site of attachment of the capsule. In a child these don't cross the growth plate so the secondary ossification centre is dependent on the epiphyseal artery. In adulthood, when the epiphysis fuses, an anastomosis is formed between the epiphyseal and metaphyseal arteries

Question 54

How is blood supplied to long bones?

Answer 54

The nutrient artery supplies the marrow and enters the bone through a nutrient foramen, usually near the middle of the diaphysis

Question 55

Describe short bones, including their function and location

Answer 55

* approximately as long as they are wide. * short bones provide stability and, when working together, they facilitate a great range of movement (e.g. at the wrist). * The carpal bones in the wrist and the tarsal bones in the ankles are examples of short bones

Question 56

Describe flat bones, including their function and location

Answer 56

• in the skull, the thoracic cage (sternum and ribs), and the pelvis (ilium, ischium, and pubis). • The function of flat bones is to protect the internal organs such as the brain, heart, and pelvic organs. • Flat bones can also provide large areas of attachment for muscles.

Question 57

Describe irregular bones, including their function and location

Answer 57

• vary in shape and structure and therefore do not fit into any other category (flat, short, long, or sesamoid). • They often have a complex shape, which helps protect internal organs. • For example, the vertebrae protect the spinal cord.

Question 58

Describe sesamoid bones, including their function and location

Answer 58

* bones embedded in tendons. * main function is to protect the tendons from stress and wear, but they also provide mechanical advantage by acting as a fulcrum for a muscle crossing a joint with a wide range of movement. * commonly found in the tendons of the hands, knees, and feet. The patella (kneecap), is an example of a sesamoid bone; it is found within the quadriceps tendon and provides mechanical advantage to the quadriceps muscles.

Question 59

how are Short, flat, sesamoid and irregular bones different from long bones?

Answer 59

* Short, flat, sesamoid and irregular bones consist of two layers of compact bone with a layer of spongy bone between them. * These bones have no growth plate or epiphysis.

Question 60

What are processes (in relation to bones)? What are they divided into?

Answer 60

Prominent projections of a bone. | Divided into articulating and non-articulating.

Question 61

Which are the articulating processes?

Answer 61

* Head * Condyle * Facet

Question 62

What is an articular head?

Answer 62

Rounded articular projection supported by a neck (e.g.head of humerus)

Question 63

What is a condyle?

Answer 63

Large, knuckle-like, articular projection (e.g. medial condyle of the femur)

Question 64

What is a Facet?

Answer 64

Smooth flat surface (superior and inferior articulating facets of the vertebrae)

Question 65

What results in non articulating processes?

Answer 65

These are usually the result of traction on the developing bone by muscles, ligaments etc. The stronger the force exerted on the bone, the larger the bony prominence that develops.

Question 66

Which are the non-articulating processes?

Answer 66

* epicondyle * trochanter * tubercle * tuberosity * crest * line * spine

Question 67

What is an epicondyle?

Answer 67

Smaller projection above the condyle (usually attachment site for muscles and ligaments e.g. medial epicondyle of femur)

Question 68

What is a trochanter?

Answer 68

``` Blunt projection (only on femur; greater and lesser trochanters of femur) ```

Question 69

What is a tubercle?

Answer 69

Small knob-like rounded process (e.g. greater tubercle of humerus)

Question 70

What is tuberosity?

Answer 70

Large, usually roughened, process (usually an attachment site e.g. tibial tuberosity)

Question 71

What is a crest?

Answer 71

Prominent border or ridge (e.g. iliac crest)

Question 72

What is a line?

Answer 72

Less prominent ridge than a crest (e.g. linea aspera)

Question 73

What is a spine?

Answer 73

Sharp slender process (e.g. spinous process of a vertebra)

Question 74

What are depressions on bone?

Answer 74

Depressions on the surface of bones provide for the passage of blood vessels and other soft tissues

Question 75

What are examples of depression on bone?

Answer 75

* fovea * sulcus / groove * fossa * cavity * notch

Question 76

What is a fovea?

Answer 76

Pit-like depression (e.g. fovea capitis of femur)

Question 77

what is a sulcus / groove?

Answer 77

Furrow that accommodates soft tissue such as blood vessels, nerves or tendons (e.g. intertubercular sulcus of the humerus through which the tendon of the long head of biceps brachii passes)

Question 78

what is a fossa?

Answer 78

Basin-like depression (e.g. glenoid fossa at the shoulder)

Question 79

what is a cavity?

Answer 79

Spacious open area (e.g. acetabulum of pelvis)

Question 80

what is a notch?

Answer 80

a C- or U-shaped depression (e.g. femoral notch at the | knee)

Question 81

What are openings?

Answer 81

Openings occur primarily where blood vessels and nerves pass into or through the bone: • fissure - Narrow slit-like opening between adjacent parts of bones through which blood vessels or nerves pass (e.g. superior orbital fissure of sphenoid bone in the skull) • foramen - Hole or window in the bone (e.g. foramen magnum at the base of the skull, for passage of the spinal cord) • canal - Tube-like passageway (e.g. optic canal in the skull, forpassage of the optic nerve)`

Question 82

Which are the 3 arteries that supply blood to bones? Where are they found?

Answer 82

Nutrient artery - enters diaphysis. Supplies marrow + cortex. Periosteal arteries - within periosteum and supply the periosteum and the outer third of the cortex of the bone Metaphysical arteries - in some bones eg femur. Enter at site of attachment of capsule

Question 83

How do metaphysical arteries differ in adults and children?

Answer 83

Children = metaphyseal arteries do not cross the growth plate so the secondary ossification centre in the epiphysis is completely dependent on the epiphyseal artery. Adults = epiphysis fuses, an anastomosis is formed between the epiphyseal and metaphyseal arteries.

Question 84

What is anastomosis?

Answer 84

No capillary intermediate. Artery to artery communication.

Question 85

What is avascular necrosis?

Answer 85

death of bone tissue due to lack of blood supply

Question 86

What are causes of avascular necrosis?

Answer 86

The most common cause is a fracture, but other risk factors include alcoholism, excessive steroid use, other trauma (non-fracture), radiation, thrombosis (blood clot), hypertension (high blood pressure) and decompression sickness (after deep sea diving). Radiation exposure can lead to obliteration of small arteries. In decompression sickness, small bubbles of nitrogen form which can impede the blood supply to the bone

Question 87

When does bone remodeling occur?

Answer 87

- in response to environmental factors e.g sustained application of a load due to a change in the balance in activity between osteoblasts and osteoclasts E.g. humerus in dominant arm of cricketer is thicker