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Test 2 Flashcards

1
Q

Mechanical stress

A

The internal force divided by the cross-sectional area of the surface on which the internal force acts
Ability of an object to develop a resistance to internal loading forces and to resist deformation caused by those forces

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2
Q

Tensile stress

A

Axial stress as a result of a force or load that tends to pull apart the molecules bonding the object together at the analysis plane

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3
Q

Compressive stress

A

Axial stress as a result of a force or load that tends to push or squash the molecules bonding the object together at the analysis plane

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4
Q

Shear stress

A

Transverse stress that acts parallel to the analysis plane as result of forces acting parallel to this plane
Internally resists sliding movement of one parallel layer of a material relative to the other

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5
Q

Uniaxial mechanical loads

A

Tensile
Compressive
Shear

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6
Q

Complex mechanical loads

A

Bending
Torsion
Combined loads

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7
Q

Bending

A

Counteracting tensile and compressive loads

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8
Q

Torsion

A

Torques acting about the long axis of the object at each end causing an internal torque created by the shear force btwn the molecules

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9
Q

Combined loads

A

Combination of loading configurations (uniaxial, complex)

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10
Q

Mechanical strain

A

Quantification of the deformation of a material from stress

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11
Q

Stress vs strain

A

stress measures the deforming force per unit area of the object, whereas strain measures the relative change in length caused by a deforming force

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12
Q

Linear strain

A

change in length as a result of tensile or compressive stress

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13
Q

Shear strain

A

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

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14
Q

Stress-strain relationship (elastic or young’s modulus)

A

Ratio of stress to strain (rise over run)

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15
Q

Elastic behaviour

A

occurs if an object stretches under a tensile load but returns to its original shape when the load is removed

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16
Q

Linear elastic behaviour

A

As stress increases, strain increases by a proportional amount
ex rubber band

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17
Q

Plastic behaviour

A

When a permanent deformation of an object occurs under a load
ex paper clip

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18
Q

Material strength

A

Max stress/strain a material is able to withstand before failure (breakage)

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19
Q

Yield point

A

Point of stress-strain curve where further stress will cause permanent deformation
Elastic region before, plastic region after

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20
Q

Yield strength

A

stress at the elastic limit of a material’s stress-strain curve

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21
Q

Ultimate strength

A

max stress material is capable of withstanding

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22
Q

Failure strength

A

stress where failure actually occurs

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23
Q

Ductile materials

A

large failure strains

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24
Q

Brittle materials

A

small failure strains

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25
Hard materials
large failure stresses
26
Soft materials
small failure stresses
27
Toughness
Ability to absorb energy; area under stress-strain curve Tougher= more energy required to break/reach failure
28
Viscoelastic materials
any material that exhibits both viscous and elastic characteristics (behaves as a liquid and a solid) - bone, tendon, ligament, cartilage, muscle
29
Viscoelastic properties
Strain rate dependency Stress relaxation Creep Hysteresis
30
Strain rate dependency
The rate at which you deform/strain a tissue will effect the stress it feels Faster loading rate = more stress created
31
Stress relaxation
Decrease in stress under constant strain (length held constant)
32
Creep
Increase in plastic strain under constant stress (load held constant)
33
Hysteresis
the amount of energy dissipated as a result of internal friction during mechanical loading and unloading Ex tendon hysteresis is imp for efficiency of locomotion
34
Active element of musculoskeletal system
Muscle tissue
35
Passive elements of musculoskeletal system
Connective tissue (bone, cartilage, ligament, tendon)
36
Anisotropic
having diff mechanical properties depending on the direction of load
37
Isotropic
having the same mechanical properties in every direction
38
Stiffness
measure of the resistance of elastic materials to deformation caused by stress how much load a tissue can take before it deforms slope of stress-strain curve
39
Two factors affecting mechanical properties of tissues
1. Activity: strength of connective tissues increases w regular use 2. Age: Connective tissues increase in ultimate strength w age until the third decade of life where strength decreases, bones become more brittle, tendons and ligaments become less stiff
40
Connective tissue
Composed of living cells and extracellular components (collagen, elastin, ground substance, minerals, water)
41
Collagen
stiff (brittle) high tensile strength (hard) unable to resist compression
42
Bone
Strongest and stiffest - strongest in compression, then tensile, weakest in shear -30-35% collagen (high tensile strength) - 45% minerals (high compressive strength)
43
Cortical bone
dense and hard outer layer can handle high stress, low strain
44
Elastin
pliant (soft) very extensible (ductile)
45
Cancellous/trabecular/spongey bone
Less dense, porous inner portion can handle low stress, high strain
46
Cartilage
can withstand compressive, tensile and shear loads 1. Hyaline: 10-30% collagen, 60-80% water 2. Fibrous: joint cavities, intervertebral discs 3. Elastic: external ear, organs
47
Tendons/ligaments
Stiff, high tensile strength, little resistance to compression or shear - 70% water, 25% collagen, 5% ground substance and elastin Ligaments have a larger elastic component and their collagen fibres are arranged only near parallel compared to tendons being parallel making them less stiff and weaker than tendons Ligaments can carry non uniaxial loads
48
Muscle fibres
single muscle cells; encased in ct sheath (endomysium)
49
Fascicles
bundles of muscle fibres; encased in ct sheath (perimysium)
50
Whole muscles
bundles of fascicles; encased in ct sheath (epimysium)
51
Tendons and aponeurosis
connect muscle to bone
52
Myofibrils
thread like structures lying parallel to each other within muscle fibre; light and dark bands
53
Sarcomere
contractile unit of a muscle; repeating unit of myofibril btwn the stripes (z-bands)
54
Myofilaments
Thin: actin, troponin C, tropomyosin Thick: myosin
55
I- band
contains actin and z-line; light band
56
A-band
contains actin and myosin; dark band
57
H-zone
region of A-band containing only myosin and M-line
58
M-line
transverse band that anchors myosin to each other
59
Z-line
transverse band anchoring actin to each other; mark beginning and end of sarcomere
60
Factors affecting muscle force production
1. Length 2. Velocity 3. Physiological cross-sectional area 4. Muscle geometry 5. Activation
61
Muscle force-length relationship
Optimal sarcomere length for force generation= 120% resting length (plateau) Sarcomere shorter than optimal length = opposing actin filaments begin to overlap and myosin cant attach= less force (ascending) Sarcomere contracts even shorter = actin and myosin jammed against opposite Z-band= no force produced Sarcomere stretches longer than optimal length= thick and thin filaments spread too far apart and cant slide over each other= less force (descending)
62
Passive tension
Developed in sarcomere and within whole muscle by stretching of connective tissues As muscle fibre length increases and active force is decreasing, passive force component comes into play and increases total force production of muscle
63
Stretching theory
Stretching you muscle enhances your force generating capcity by adding the passive component to the active component
64
Muscle force-velocity relationship
the greater the shortening velocity of a muscle= the smaller the force produced more cross bridges in release step of contraction cycle and each cross bridge spends a large proportion of the contraction time in release step so less tension is developed ex barbell bench press
65
Muscle contraction
As the muscle shortens during a contraction, the cross bridges attach to the actin myofilament, pull it toward them, release it, and then reattach to it farther along its length Cross bridge formation: Attach, pull, release and then contract
66
Essentric
Lengthening of muscle fibres Can produce more force than a muscle contracting concentrically (along w isometric)
67
Concentric
Shortening of muscle fibres
68
Physiological cross sectional area
Adding sarcomeres in parallel by increasing number of myofibrils will increase muscle diameter and cross- sectional area = STRONGER Adding sarcomeres in series (end to end) increases length of myofibril and longer muscles can stretch and shorten over greater lengths
69
Muscle geometry
Longitudinal vs pennate Pennate have large cross sectional area due to the angle of their fibres and therefore can produce more force But they have shorter fibres which limits the distance over which they can shorten
70
Activation
Number of muscle fibres that are stimulated to contract at any given time
71
Fine/precise control
smaller number of motor fibres per motor neuron better for muscles
72
Coarse control
larger number of muscle fibres per motor neuron
73
Motor unit
a single motor neuron and all the muscle fibres w which it synapses
74
How to increase activation
1. Increase firing frequency of a given motor unit - leads to a repeated series of twitches which cause a tetanic response from a single fibre (sustained contraction w plateaued tension) 2. Recruit more motor units
75
Henneman's size principle
motor units are recruited from smallest (slow twitch) to largest (fast twitch)
76
Benefits of henneman's size principle
Fatigue prevention: save fast twitch fibres for when needed Fine and coarse control: allow us to apply smaller, finer forces then higher forces when needed
77
Stiffness
measure of the resistance of elastic materials to deformation caused by stress how much load a tissue can take before it deforms slope of stress-strain curve
78
Depth
An object with greater depth (and more cross- sectional area farther from its neutral axis) is able to withstand greater bending loads. The counteracting tensile and compressive stresses are lower, because they have a larger moment arm. Under similar bending loads, the stresses in such an object will be smaller.
79
Moment arm, forces and stress
Ex pencil moment arm is small, so the internal forces (and stresses) must be large to create a large enough countering torque An object with a larger diameter is able to withstand greater torsional loads since the shear stresses are smaller as a result of the larger diameter and large moment arm

KNPE254 (1 decks)

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