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KNPE 254 > Midterm 2 > Flashcards

Midterm 2 Flashcards

1
Q

tensile stress (Pa)

A

axial stress that tends to pull apart the molecules at the analysis plane
- object elongates

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2
Q

compressive stress (Pa)

A

axial stress that tends to push or squash the molecules together at the analysis plane
- object shortens

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3
Q

shear stress (Pa)

A

transverse stress that acts parallel to the analysis plane
- molecules slide past one another
- one force pushes down the other pushes up

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4
Q

simple (uniaxial) loads

A

one type of stress produced, uniform across plane

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5
Q

complex mechanical loads

A

multiple types of stress produced, stress varies across the plane

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6
Q

bending (Pa)

A

counteracting tensile and compressive stress
- object with greater depth and larger CSA can withstand greater bending

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7
Q

torsion (Pa)

A

twisting forces - shear force
- creates an internal torque
- object with greater diameter (area) can withstand greater torsion

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8
Q

combined loads

A

combination of loads
1. muscles, tendons & ligaments: carry one type of load (uniaxial tension)
2. bones and cartilage: carry multiple loads (more complex)

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8
Q

linear strain

A

change in length/deformation as a result of tensile or compressive stress

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9
Q

shear strain

A

change in orientation of adjacent molecules as a result of molecules slipping past each other due to shear stress

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10
Q

elastic modulus

A

ratio of stress to strain

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11
Q

elastic behaviour

A

occurs when an object stretches under tensile load, but return back to original shape when the load is removed (rubber band)

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12
Q

material strength

A

maximum stress/strain a material is able to withstand before failure

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12
Q

plastic behaviour

A

when a permanent deformation of the object occurs under a load

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13
Q

yield point

A

point on stress-strain curve where further stress will cause permanent deformation

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14
Q

yield strength

A

stress at the elastic limit of a materials stress-strain curve

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15
Q

ultimate strength

A

maximum stress the material is capable of withstanding

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16
Q

failure strength

A

stress where failure actually occurs (endpoint, breakage)

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17
Q

ductile vs brittle materials

A

ductile: can withstand lots of plastic deformation before failure = high failure strain
brittle: require little plastic deformation before failure = small failure strains

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18
Q

hard vs soft material

A

hard: stiff = large failure stress
soft: pliant = small failure stress

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19
Q

toughness

A

ability to absorb energy - area under stress-strain curve
- tougher = the more energy requires to reach failure

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20
Q

viscoelastic materials

A

both viscous and elastic behaviours
(liquid and solid)
ex. bone, tendon, ligament, cartilage, muscle

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21
Q

properties of viscoelastic materials

A
  1. strain-rate dependency
  2. stress-relaxation
  3. creep
  4. hysteresis
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22
Q

strain-rate dependency

A

rate at which you deform/strain a tissue will effect the stress it feels
- faster loading = more stress

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23
Q

stress-relaxation

A

Decrease in stress under constant strain
(length held constant)

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24
Q

creep

A

Increase in plastic strain under constant stress
(load held constant)

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25
Q

hysteresis

A

the amount of energy absorbed during loading and unloading

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26
Q

active element

A

muscle tissue

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27
Q

passive element

A

connective tissue

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28
Q

collagen

A

stiff, brittle, high tensile strength, unable to resist compression

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29
Q

elastin

A

pliant (soft), extensible, ductile, high failure strain

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30
Q

isotropic

A

same mechanical properties in every direction

31
Q

ansiotropic

A

have different mechanical properties depending on direction of the load
ex. tendon is stronger if tensile load is aligned with tendon fibres rather than transverse

32
Q

two primary factors affecting mechanical properties of tissues

A
  1. activity
  2. age
33
Q

activity

A
  1. strength of CT increases with use
  2. stiffness may also increase
    ***inactivity = decrease in strength of tissues
34
Q

age

A
  1. CT increases in stranght with age until 30 years old, then strength decreases
  2. bone become brittle and less tough with increasing age
  3. tendons and ligaments become less stiff
35
Q

bones

A
  1. strongest in compression, weakest in shear
  2. high tensile strength
  3. strongest and stiffest material
  4. ansiotropic
36
Q

cortical (compact) bone

A

found in dense and hard outer layers of bone

37
Q

cancellous (spongy/trabecular) bone

A

less dense, porous bone that is spongy in appearance and found deep to cortical bone

38
Q

cartilage

A

able to withstand compressive, tensile, and shear loads

39
Q

hyaline cartilage

A

covers the end of long bones at joints
1. no blood supply, thin to allow diffusion of nutrients
2. made of water and water is not compressible so under compressive load, collagen is under tension

40
Q

fibrous cartilage

A

found within some joint cavities

41
Q

elastic cartilage

A

found in external ear and in several other organs that are not part musculoskeletal system

42
Q

tendons and ligaments

A

major difference is arrangement of their collagen fibres

43
Q

tendons

A

collagen fibres are bound together in parallel
- parallel arrangement produces a structure that is very stiff and high in tensile strength
- little resistance to compression or shear

44
Q

ligaments

A

collagen fibres are bound together nearly parallel
- have slightly larger elastin component making them less stiff and slightly weaker than tendons

45
Q

muscle fibres

A

encased in endomysium

46
Q

fascicles

A

bundles of muscle fibres
- encased in perimysium

47
Q

whole muscle

A

bundles or muscles fascicles
- epimysium

48
Q

tendon

A

woven CT that connects muscle to bone allowing for movement

49
Q

sarcomeres

A

basic contractile unit of a muscle
- contain overlapping filaments of myosin (thick) and actin (thin)

50
Q

resting state

A

tropomyosin prevents myosin from bonding to actin

51
Q

z-line

A

band that anchors actin to each other, boundary of one sarcomere

52
Q

I-band

A

area that contains only actin

53
Q

A-band

A

area that contains myosin, overlapping with actin

54
Q

H-zone

A

area that contains only myosin

55
Q

M-line

A

band that anchors myosin to one another

56
Q

factors affecting force development

A
  1. length
  2. velocity
  3. physiological cross-sectional area
  4. muscle geometry
  5. activation
57
Q

resting length

A

greatest active tension - optimal length

58
Q

contractile element

A

represents force development by sarcomeres

59
Q

force-velocity relationship

A

the greater the shortening velocity, the smaller the force produced
- slower the contraction velocity = more force produced (more time for cross-bridges to form and exert force)

60
Q

concentric

A

muscle shortens while generation force (lifting weights)
1. muscle contraction or flexion - muscle is moving body part closer to center body
2. muscle tension exceeds the external load
AS VELOCITY INCREASES, FORCE DECREASES

61
Q

eccentric

A

muscle lengthens while generating force (lowering weight or body)
1. lengthening or extension - muscle is moving body part away
2. external load exceeds muscle tension = muscle lengthens
AS VELOCITY INCREASES, FORCE INCREASES

62
Q

physiological cross-sectional area

A

adding sarcomeres in parallel makes a muscle stronger

63
Q

activation of muscle fibres

A

force produced by a muscle is directly proportional to number of fibres that contract at any given time
- more fibres contracting = more force produced

64
Q

fine/precise control

A

smaller number of muscle fibres per motor neuron

65
Q

coarse control

A

larger number of muscle fibres per motor neuron

66
Q

hennemans size principle

A

motor units are recruited from smallest (slow-twitch) to largest (fast-twitch)
- beneficial for fatigue prevention + fine + coarse control

67
Q

sarcomere arrangement

A

length-wise= strong muscle
height-wise= fast muscle
***longer the muscle length, the easier the ability to create tension

68
Q

shorter moment arm

A

more force required with same torque

69
Q

larger joint angle

A

faster the muscle

70
Q

longer moment arm

A

less force required with same torque

71
Q

smaller joint angle

A

slower the muscle

72
Q

series element

A

muscle fibres aligned end-to-end so the forces are additive
1. greater ROM
2. greater force production
3. limited strength
***typically longitudinal muscle

73
Q

parallel element

A

muscle fibres aligned side-by-side, running parallel to each other
1. greater strength (not faster)
2. limited ROM

74
Q

force-length relationship - optimal length

A

generate highest force due to best overlap of myosin and actin to form cross-bridges

75
Q

force-length relationship - too short

A

force production is reduced cause there is limited overlap between myosin and actin thereby reducing cross-bridge formation

76
Q

force-length relationship - too stretched

A

force production is reduced cause myosin and actin are pulled too far apart, limiting cross-bridge formation

77
Q

passive tension

A

as a muscle length increases (overstretch), active force is decreasing and passive force component comes into play and increases total force production of the muscle

KNPE 254 (1 decks)

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