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Orthopaedic Biomechanics > Muscles > Flashcards

Muscles Flashcards

1
Q

What is the hierarchical structure of muscle

A

Sarcomeres –> Myofibril –> Fibres –> Fascicles –> Muscle

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2
Q

What does the endomysium surround

A

Inidividual muscle fibres

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3
Q

What does the perimysium surround

A

Fascicles

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4
Q

What does the epimysium surround

A

Entire muscle - continuous with the tendon

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5
Q

What does the z-line/disk demarcate in sarcomeres

A

The lateral borders of the sarcomeres

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6
Q

Is actin the thin or thick filament

A

thin

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7
Q

Structure of actin

A

Contains two twisted alpha helices

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8
Q

Special feature of actin filaments?

A

They exhibit polarity

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9
Q

What 2 proteins are associated with actin

A

Troponin & Tropomyosin

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10
Q

What is the function of Titin in the sarcomere

A

Anchors the myosin filaments to the Z-line

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11
Q

What is the function of CapZ in the sarcomere

A

Covers the positive end of actin filaments

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12
Q

Shape and function of troponin

A

Globular protein

Binding site for Calcium

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13
Q

Shape and function of tropomyosin

A

Rod-like filamentous protein
Spirals round actin to stabilise it
Seals myosin binding sites on actin

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14
Q

What do we learn from looking at the length-tension curve on a sarcomere scale

A

At resting length, there is maximum contact between filaments so maximum tension can be generated
• Any shorter, there is excessive overlap between actin filaments which reduces the contact area and minimal forces can be generated
• Any longer (due to stretch), there is no overlap so there is NO contact area & minimal forces can be generated

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15
Q

What are the 3 components to a length-tension curve on a whole muscle scale

A

Active tension
Passive tension
Total tension

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16
Q

What is the active tension component of the length-tension curve on a whole muscle scale

A

Tension generated by muscle contraction

17
Q

What is the passive tension component of the length-tension curve on a whole muscle scale

A

Increase in tension due to stretching of connective tissues (e.g. tendons, epimysium) when contracting a muscle that has been stretched past the ideal/resting length

18
Q

What is active insufficiency

A

Failure to produce significant/sufficient force when the muscles are too short

19
Q

What is passive insufficiency

A

Failure to produce significant/sufficient force when the muscles are too stretched

20
Q

Describe the Hill Muscle model

A

A contractile element is in series with an elastic element and in parallel with another elastic element

21
Q

Describe the Hill Muscle model

A

A contractile element is in series with an elastic element and they are both in parallel with another elastic element

22
Q

What does the elastic element in series represent in the Hill Muscle model

A

This represents the tendons and cross-bridges

23
Q

What does the elastic element in parallel represent in the Hill Muscle model

A

Connective tissue in the muscle (epimysium, endomysium and perimysium)

24
Q

What factors affect force production in muscles? (3)

A

Length of muscle
Velocity of shortening
Amount of stimulation

25
Q

What is concentric contraction and examples

A

Where movement is caused by shortening of the muscle
Extending the knee
Lifting a dumbbell close to the chest

26
Q

What is an isometric contraction and examples

A

When there is no change in muscle length and thus no movement
Holding a bicep at 90 degrees to the body

27
Q

What is the relationship between moment and joint angle in concentric contraction

A

The moment is in the same direction as joint angle change

28
Q

What is an eccentric contraction and examples

A

When a muscle increases in length to decelerate joint movement
Extension phase of a bicep curl

29
Q

What is the relationship between moment and joint angle in eccentric contraction

A

The moment is in the opposite direction as joint angle change

30
Q

Place the 3 types of contractions in descending order of force they are able to produce

A

Eccentric > Isometric > Concentric

31
Q

Why is eccentric able to produce the most force ? (4)

A

Greater cross bridging due to greater length
Contraction time (decreased rate of cross-bridge detachments)
Passive tension in elastic components
Elastic energy stored in the actin-myosin cross bridges

32
Q

How many times greater is the max eccentric tension than an isometric

A

1.25x greater

33
Q

How does velocity of ECCENTRIC contraction affect tension

A

Increasing velocity increases force up to a maximum

34
Q

How does velocity of CONCENTRIC contraction affect tension

A

Increases velocity decreases force to ZERO

a rapid concentric contraction will generate no/minimal force

Orthopaedic Biomechanics (15 decks)

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