Biology Lecture Week 6 - Biological Materials

Question 1

Bone contains the following …

Answer 1

• 25-30% water
• Collagen (30% dry weight). Gives resistance to tensile loading, ductility (flexibility) and toughness (resistance to shock loading
• Minerals (about 70% of dry weight). Mainly calcium phosphate/carbonate. These resist compression, and provide rigidity

Question 2

Bone is capable of withstanding loads …

Answer 2

Six times those experienced in normal life

Question 3

Define what Osteocytes are …

Answer 3

A specialised form of connective tissue which are light, in a collagen matrix and packed with minerals

Question 4

What are the two types of bone ?

Answer 4

1. Cortical
2. Trabecular

The combined strength to weight ratio is greater when combined than in the individual parts

Question 5

Compressive and tensile forces act on bone, which type of bone is better at resisting these forces ?

Answer 5

Cortical bone as trabecular bone is much weaker in resisting either type of force

Question 6

What are the different types of [fracture patterns] and their {load type} ?

Answer 6

1: [Diaphyseal impaction] - {Axial Compression}
2: [Transverse] - {Bending}
3: [Spiral] - {Torsion}
4: [Oblique transverse and butterfly] - {Axial compression and bending}
5: [Oblique] - {Axial Compression, bending, torsion}

Question 7

Define a transverse fracture …

Answer 7

• Bending Load
• Cortical bone weaker in tension than compression so bone under tension fails first
• Failure mechanism is break propagation perpendicular to bone’s long axis, from surface layer inwards

Question 8

Describe what Cartilage is …

Answer 8

• Cells are widely separated within a fibrous, organic matrix which may:
• • appear (but isn’t) structureless as in rigid hyaline cartilage
• • contain more connective tissue fibres in the matrix (eg. fibrocartilage)

Question 9

What does Cartilage consist of (genetic make-up)

Answer 9

• Cells (chondrocytes) account for less than 10% of tissue volume
• the organic matrix consists of collagen fibrils (10-30% net weight) within a proteoglycans solution (3-10%) net weight
• Remainder of tissue (60-87% is made up of water, inorganic salts and small quantities of matrix proteins, glycoproteins and lipids
• its mechanical properties are dependant on the direction of loading (anisotropic)

Question 10

what are Cartilage’s Biomechanical Properties

Answer 10

• Cartilage shows typical viscoelastic behaviour:
• • loading leads to rapid initial deformation followed by more gradual increase
• • returns to initial shape on load removal (hysteresis)
• • prolonged standing causes creep of intervertebral discs (hence shortening of the body’s overall height

Question 11

What leads to Articular Cartilage Injuries …

Answer 11

• Articular cartilage is capable of deformation; decreases stress on the joints by increasing load-bearing area
• Avascular and tends to have few nerve endings, meaning it shows little external symptoms and repairs poorly
• Overuse injuries cause cartilage to wear away, leading to osteoarthritis
• High impact loads lead to swelling of cartilage; if sever enough may fracture

Question 12

What are Tendons ?

Answer 12

Tough cords of closely packed collagen fibres

Question 13

What are Aponeuroses ?

Answer 13

Sheet like tendons

Attach muscles to bones and transmit tensile loads so that movement can occur

Question 14

What are Deep facia ?

Answer 14

Occur between muscles, enveloping individual muscles and binding them in groups

Question 15

What is Intermuscular Septa ?

Answer 15

Separates muscle groups passing from the deep fascia to the bone

Question 16

What are Ligaments ?

Answer 16

Like tendons but contain some elastic fibre (elastin)

Question 17

What are Ligamentous joint capsules ?

Answer 17

connect bone to bone, guide joint motion, enhance mechanical stability and prevent excessive motion

Question 18

What is the ultimate failure strain of tendons ?

Answer 18

between 8-10% (Herzog and Loitz, 1994)

Question 19

Tendons have limited viscoelastic behaviour with only __ to __ hysteresis ? (Herzog and Loitz, 1994)

Answer 19

2.5 to 20%

Question 20

Tendons are considered the main site for …

Answer 20

High energy return during elastic recoil in the muscle-tendon unit (alexander, 2002)

Question 21

The achilles tendon …

Answer 21

is an important site for energy storage before jumping in athletes. Basket ballers and high jumpers tend to have short, powerful calf muscles and long Achilles tendons

Question 22

Facts about ligaments …

Answer 22

1. designed to best cope with tensile forces
2. most everyday activities occur in the high deformation/ low force to region of the stress strain curve allowing easy movement
3. stiffness increases with force applied preventing bones from pulling apart
4. ligaments have mechanoreceptors which may initiate tension in nearby muscles in order to assist in maintaining joint stability eg rapid knee extension

Question 23

How do ligament sprains occur ?

Answer 23

excessive joint motion, most not severe

Question 24

Direct blows to ligaments can cause ?

Answer 24

stretching and permanent deformation

Question 25

“failure often due to bending and torsional loads applied to distal limb, as in tackle, and depends on load rate” what 3 other ligament injuries occur due to load rates ?

Answer 25

1 - mid substance tear at fast load rates
2 - bony avulsion at low load rates, mostly in young athletes
3 - separation of bone-ligament interface - rare because of its strength

Question 26

What are the effects of tears in the ligaments ?

Answer 26

• loss of stability, joint misalignment, abnormal contact pressure, loss of proprioception

Question 27

Muscle stiffness is related to …

Answer 27

the force produced un relation to its length

Question 28

Maximal muscle stiffness is encountered during …

Answer 28

eccentric contraction, up to 200 times that in concentric and is probably under reflex control

Question 29

Muscle and tendon should be considered a …

Answer 29

single unit where neither connective tissue acts independently of the other