Lecture 3

Question 1

What are the 5 functions of bones?

Answer 1

• Support
• Leverage
• Protection of organs
• Storage of minerals and lipids (calcium)
• Blood cell production (red and white cells are produced in the red marrow)

Question 2

Flat bones?

Answer 2

Scapula, sternum, cranium

Question 3

Long bones?

Answer 3

Femur, humerus, tibia

Question 4

Short bones?

Answer 4

Carpals, tarsals

Question 5

Irregular bones?

Answer 5

Vertebrae, mandible

Question 6

Sesamoid bones?

Answer 6

Patella

Question 7

Sutural bones?

Answer 7

Small, flat irregular bones of the skull

Question 8

Trabecular, cancellous or spongy bone?

Answer 8

• Network of trabecular struts

- Commonly found at the end (epiphyses) of long bones

Question 9

Compact or cortical bone?

Answer 9

• Solid bone

- Forms the solid outer shell and shaft (diaphysis) of long bones

Question 10

What are the two main components/phases of bone?

Answer 10

Organic phase:
- Type 1 collagen. Very pliable (easily bent

Inorganic phase:
- Calcium Hydroxyapatite crystals. Offer compressive strength to the bone

Question 11

What is the composition of a bone?

Answer 11

• Bone material (inorganic)
• Collagen (organic)
• Water and ground substance
• Bone is a living tissue which has a blood supply and nerves

Question 12

Osteoporosis?

Answer 12

A disease which compromises the matrix structure of bone, significantly reducing its mechanical strength.

Question 13

Are vertebrae able to resist compression, tension and torsion associated with various movements?

Answer 13

They are able to resist compression, tension and torsion associated with various movements. This is in part due to the orientation of the trabeculae within the vertebrae.

Question 14

What does the spine offer support for?

Answer 14

For the head, upper limbs and thoracic cage during movement and weight bearing activities

Question 15

Femur?

Answer 15

The femur is a long, slightly curved, hollow (essentially) cylindrical shaped bone with compact bone around the centre of the shaft and trabecular bone at the ends.

Question 16

What is the function/purpose of mechanosensing cells (osteocytes) in the body?

Answer 16

These cells detect changes in their physical and chemical surroundings and release chemicals in response causing bone to be removed or formed

Question 17

Deformation?

Answer 17

Change fo shape

Question 18

What does deformation depend on?

Answer 18

Depends not only on the size of the force but also the area over which the force is applied,
Force per Unit Area (N/m2

Question 19

What are the three common types of stress applied to the bones and tissue within the human body

Answer 19

• unstressed object
• compression
• tension
• shear stress

Question 20

Stress (action)?

Answer 20

The stress (σ) in a material with cross-sectional area (A) subjected to a force (F) is given by:

𝜎=𝐹/𝐴

Question 21

Stress (reaction)?

Answer 21

• When a material of length (L) is subjected to a compressional or tensional stress, a change of length (ΔL) occurs. The resulting strain (Ɛ) is defined as the fractional change in length of the material (therefore Ɛ has no units).
• Measures the change un shape as a result of an action

𝜀=Δ𝐿/𝐿

Question 22

Young’s modulus equation?

Answer 22

• Young’s Modulus (E) is the ratio (slope of graph) of Stress to Strain (Nm-2)

𝐸=𝜎/𝜀

Question 23

Elastic region vs. Plastic deformation?

Answer 23

Elastic - bone will go back to original shape

Plastic - bone is permanently deformed

Question 24

Tension?

Answer 24

In tension, bone undergoes less strain before reaching the yield point.

Question 25

Compression?

Answer 25

Bone is stronger under compression

can withstand higher stress

Question 26

Anisotropic material?

Answer 26

• What bone is

- Having a physical property which has a different value when measured in different directions

Question 27

What does Young’s Modulus measure?

Answer 27

• Measure of stiffness or rigidity

High Young’s Modulus = Stiff material

Question 28

When can you not measure Young’s Modulus?

Answer 28

On a curved line, bc it has to be linear

Question 29

Bone bending?

Answer 29

• Hydrogen and covalent bonds hold bones together

- When bending a bone, you stretch and stress all of these bonds

Question 30

When bending bone, where is the greatest change in length?

Answer 30

Along the surface, therefore the greatest resistance forces occur at the surface (Newton’s Third Law)

Question 31

Neutral surface?

Answer 31

• When a bone is bending, the resistance forces decrease as you move towards the centre
• As you move from the outside of the bone (experiencing the most resistance/change in length) towards the inside of the bone, the change in length decreases, thus the resistance decreases until eventually there is no change of length/resistance…the neutral surface

Question 32

Will there be more or less resistance to bending in a hollow or solid structure?

Answer 32

There will be more resistance to bending in a hallow structure, bc there isn’t any material in the centre (no bonds holding material together), therefore there is no change in length and no stress happening in the middle, so you’re only getting really big resistance forces and changes of length at the surface

Question 33

When will resisting forces be the greatest?

Answer 33

When the material is distributed as far as possible from the neutral surface (hollow surfaces), but there must be a compromise, bc if the available material is spread too far from the neutral surface, the walls will become too thin, and there is a danger that the structure will buckle under compression

Question 34

What bone structures in the human body have an optimal biomechanical design due to their hollow nature with regards to bending?

Answer 34

• Femur

- Vertebrae