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Physics > Bone Structure and Elastic Properties > Flashcards

Bone Structure and Elastic Properties Flashcards

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1
Q

6 functions of bones

A 
support
locomotions - joints allow motion
protection of organs
storage of chemicals e.g. calcium
nourishment - teeth break food
sound transmission - ossicles in middle ear
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2
Q

osteocytes

A

cells which keep the bone in a healthy condition

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3
Q

aseptic necrosis

A

If these cells die (perhaps due to a poor blood supply), the bone will die and lose strength

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4
Q

bone remodelling

A

a continuous process of destroying old bone and building new bone

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5
Q

cells involved in bone remodelling

A

osteoclasts

osteoblasts

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6
Q

osteoclast function

A

destroy bone containing about 0.5 grams of calcium per day.

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7
Q

osteoblast function

A

build new bone using about the same amount of calcium.

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8
Q

below 35-40 yrs old osteoblast and osteoclast ratio

A

Below the age of 35-40 years old, osteoblast activity dominates over osteoclast activity
Skeleton grows

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9
Q

osteoclast and osteoblast ratio after 40

A

more osteoclast than osteoblast activity

bone mass decreases gradually until death

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10
Q

collagen

A

Organic material. Constitutes 40% of the weight of bone and 60% of the volume.

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11
Q

bone material

A

Inorganic material. Constitutes 60% of the weight of the bone and 40% of the volume.

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12
Q

bone mineral crystals have what kind of shape

A

rod shaped

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13
Q

5 categories of bones by size

A 
flat
long
cylindrical
irregular 
others
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14
Q

trabecular bone location

A

at the end of long bones in the centre

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15
Q

compact bone location

A

around the edge/ around the centre of long bones

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16
Q

elastic properties of biological materials

A

all materials undergo deformation (change in shape) when stress is added

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17
Q

what does deformation depend on

A

the FORCE PER UNIT AREA, not on the total force

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18
Q

stress

A

in a material with cross-sectional area A subjected to a force F is given by
force /area (N/m^2)

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19
Q

how is the stress in an object resisted

A

The stress in any object is resisted by intermolecular forces within the object

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20
Q

3 types of stresses applied

A

compression
tension
shear stress

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21
Q

strain/ fractional change in length

A

when a material of length (L) is subjected to a compressional or tensional stress - a change of length (omegaL) occurs
=omegaL/L

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22
Q

how are stress and strain related

A

when low volumes of stress is added the strain is directly proportional - has a linear limit
after limit elastic limit - it is no longer linear stretch elastic permanently
after maximum stress before it breaks or deforms

23
Q

elastic deformation

A

from 0 to point B

24
Q

plastic deformation

A

point B to D

25
Q

youngs modulus

A

(E) is defined as the ratio of Stress to Strain, i.e.
stress/strain
E = s/e (N m^-2)

26
Q

youngs modulus is a measure of …

A

stiffness or rigidity

slope of stress/strain

27
Q

What does Young’s Modulus tell us?

A

lower slope is more elastic deforms easily

the smaller the value of young’s modulus the more elastic a material is

28
Q

Is Young’s Modulus the same for different types of Stress??

A

no

29
Q

anisotropy

A

if a stress applied in a particular direction will the bone act the same if that same stress is applied in a different direction

30
Q

materials can be

A

ductile - more elastic

brittle

31
Q

Bones and joints which are heavily used for prolonged periods may suffer from …

A

fatigue

32
Q

ultimate tensile strength

A

12 x 10^7 Nm^-2

33
Q

ultimate compressive strength

A

17x107 Nm-2

34
Q

bone tension

A

1.6 x 10^10 N m-2

35
Q

bone compression

A

0.9 x 1010 N m-2

36
Q

greenstick fracture results from

A

direct trauma

37
Q

why do greenstick fracture arises

A

fact that bone is more elastic and ‘stronger’ under compression than under tension (smaller Young’s modulus value, greater compressive strength).

38
Q

how do intermolecular forces try to restore its original shape under tension

A

is under tension and the intermolecular forces are trying to ‘pull’ the surface back into its original shape

39
Q

how do intermolecular forces try to restore its original shape under compression

A

under compression and the intermolecular forces are trying to ‘push’ the surface back into its original shape.

40
Q

neutral surface

A

a surface in between which undergoes NO change in length

41
Q

where does the greatest intermolecular resisting forces occur

A

occur at the surfaces which undergo greatest tension or compression

42
Q

further you from neutral surface

A

the bigger contribution you will get from restoring torque

43
Q

how do the resisting forces change the further they are from the neutral surface

A

Since the resisting forces increase the further they are from the neutral surface,

44
Q

neutral surface of long cylindrical bone

A

centre

45
Q

what kind of bone will have more resistance to bending a solid bone or hollow

A

hollow will have more resistance

46
Q

goal of bones in terms of physical properties

A

maximum resistance and minimum weight

47
Q

why do other connective tissue e.g. tendon, skin no display a linear behaviour at stress below their elastic limit

A

presence of collagen in these tissues

48
Q

what does the spine support

A

offering maximum load-bearing support.

49
Q

what does the spine support

A

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

50
Q

what type of stress can the vertebrae resist

A

compressional, tensional and torsional stresses associated with various movements.

51
Q

how come the vertebrae is able to resist certain stresses

A

is due to the orientation of the trabeculae within the vertebrae.

52
Q

when does crushing of vertebral disc occur

A

common when the disc receives excessive loading that the ‘intervertebral disc’ can bulge, causing a ‘squeeze’ on the spinal cord, or in severe cases rupture.

53
Q

what type of stress is vertical trabeculae resistant to

A

compressional load

54
Q

what type of stress is horizontal trabeculae resistant to

A

tensional tress

Physics (9 decks)

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