Lecture 2: Muscles and Biomechanics Flashcards

1
Q

What is torque

A

Tendency of a force to cause an object to roatate around a point = fulcrum or centr of rotation

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2
Q

Formula for torque

A

Force X perpendicular distance to the fulcrum (lever length)

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3
Q

What can generate the greatest torque

A

Maximize length fo lever = bigger
Needs to be perpendicular, better if no parallel vector

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4
Q

Describe muscles line of action

A

Must be at a certain anatomical distance to centre of rotation to generate torque

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5
Q

What do bones, joints and ligaments create

A

Create passive linked lever systems that cannot move on their own

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6
Q

What are muscles

A

Active component of msk lever system

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7
Q

Describe skeletal muscle

A

Hierarchically organized contractile tissue that can generate tensile forces on levers (bones) and torques at joints

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8
Q

Describe muscled torques

A

Internal = may oppose/overcome torques created by external forces = gravity or reaction forces to generate rotation of joint = movement

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9
Q

What is myofibril made up

A

Sacromeres= actin and myosin, attached to each other
Heads can that he and walk along it and generate tensile forces
Put sarcomeres end to end

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10
Q

Describe muscle hierarchy

A

Sarcomeres (basic contractile units, actin and myosin) —> myofibrils —> myofibers (msucle cell) —> Fascicles (bundled) —> Bundles/heads (multiple fascicles, bellies) —> Named msucle that has one or more heads

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11
Q

Describe muscles macroscopically

A

Striated striped appearance = reflects parallel arrange of fascicles
Indicates direction along which fibres shorten
= direction along which muscle can generate tensile forces

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12
Q

What is a tendon

A

Tough cord like
Fibrous ct
Connects all msucle to bone
Elastic, not contractile

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13
Q

What is function of tendon

A

Attaches msucle tissue to bone = interface between
Transmits force across joint and fills in space = allows diff muscle architectures

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14
Q

Descrive what connects bones to muscles

A

All msucles connects to Bone via tendon of variable length, some short, some many times longer than the msucle

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15
Q

What are sheaths

A

Ct around
myofibers = endomysium
Fascicles = perimysium
Bundles and whole muscle = epimysium

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16
Q

What is function of sheath

A

Bundle/align myofibers and facicles for proper force transmission = also for smooth gliding = improve gliding of fibres
Helps keep line of action parallel to direction of sarcomeres

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17
Q

What is epimysium

A

Wraps belly or whole msucle
Deep fascia
Invests msucles and muscle bellies/heads
Creating planes along which the head or whole muscle can be separated = by dissection

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18
Q

Define fascia

A

Sheet or band of fibrous ct that envelops, separates or binds together structures such as muscles, organs and other sof tissues

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19
Q

How many bones do muscles have attachments on

A

On at least 2

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20
Q

What is origin

A

Attchemnt on immobile bone = moves less when msucle contracts

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21
Q

What is insertion

A

Attachment on bone that moves when muscle contracts

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22
Q

Do we use origin —> insertion

A

No cause ambiguous =
Better to say bone they attach to or proximal/distal

23
Q

How many joints do muscles cross

A

At least one joint
May cross more than one
Have actions at all joints it crosses

24
Q

Describe biceps = attachments and joints

A

2 proximal attachments on scapula (coracoid process short head and supraglenoid tubercle long head)
1 distal attachment on radius (insertion on radial tuberosity)
Crosses 2 joints = shoulder and elbow = has flexion at both

Has 2 functions = one main and one accessory function, primary = flex elbow, accessory = flex shoulder

25
Q

How do muscles produce force

A

By contacting and generating tension = cannot push, only pull

26
Q

What are msk lever systems

A

Composite = more or 2 muscles on opposite sides of joint generate opposite torques and rotations

27
Q

What is msucles action at a joint determined by

A

Its position relative to that joint and direction of its fibres = based on which side

28
Q

Describe biceps vs triceps

A

Biceps = attaches to ant side elbow joint = elbow flexion
Triceps = attaching on posterior aspect of elbow joint = generates extension

29
Q

Describe elbow flexion

A

Bicep shortens through contraction, triceps relaxes
= creates a Torque that causes forearm to move superiority relative to arm and allow angle to decrease = flexion

30
Q

Describe elbow extension

A

Biceps relaxes and triceps shortens through contraction = creates reverse torque that causes forearm to move inferiorly from its flexed position relative to arm = elbow angle increase = extension
A

31
Q

What does angular motion at a joint depend on

A

Balance of internal and external torques
Muscles can produce diff torques

32
Q

Name type of torques muscles can produce

A

Isometric = resist external torques
Concentric= overcome external torques
Eccentric = reduce effects of external torques, brake

33
Q

Describe isometric contraction

A

Internal muscle and external torques equal
No joint rotation movement
No change in muscle length = sarcomeres in locked position
Muscle is still contracting it resists external torque
Equilibrium tho = cancel each other out, all myosin heads attached to actin but not moving

34
Q

Describe concentric contraction

A

Internal greater than external torque
Joint rotates = movement
Muscle shortens
Muscle contraction overcomes external force to cause motion
Muscle doing what its supposed to do, abducts = shoulder movement

35
Q

Describe eccentric contraction

A

Internal less than external torque
Joint rotates = movement opposite to concentric contraction
Muscle lengthens in controlled manner
Muscle still contracting, produces controlled joint rotation = brakes, release torque gently
If deltoid paralyzed but slowly

36
Q

Describe set up of pint of Guinness

A

Objects to be moved = pint and arm
Joint of interest = elbow
External forces = weight of arm and pint
Internal force = biceps and brachialis

37
Q

Describe torques equal of pint of Guinness

A

No movement
Holding pint steady = isometric contraction of biceps brachii generates equal and opposite torque to resist torque created by weight of arm and pint but still costs energy

38
Q

Describe torques NOT EQUAL of pint of Guinness

A

Raising glass = bicep torque greater than arm/pint torque = elbow flexion through concentric contraction bicep
Putting glass down = arm/pint > biceps torque = elbow extension but controlled through eccentric contraction of biceps = not triceps bc want in controlled manner

39
Q

DESCRIBE MSUCLE architecture

A

Muscles come in all shapes and sizes
2 broad architectures can be recognized

40
Q

What are 2 broad architectures of msucles

A

Fusiform and pennate

41
Q

Describe fusiform msucle

A

Fibres largely parallel to muscles main direction = line of action, tendon= FUSIFORM, FLAT, STRAPLIKE

42
Q

Describe pennate msucle

A

Pennate muscles = fibres oriented at angle to main line of action (tendon) = UNI, BI, MULTI PENNATE

43
Q

Describe how much msucle fibres can contract

A

Can contract about 50% of their length

44
Q

What is a muscles capacity to generate torque depend on

A

To generate force and therefore torque = function of its cross sectional area = more myofibrils/cm^2 (more fibers = more force)

45
Q

Describe fusiform muscle contraction

A

Contract over long distances (fibers parallle to attachments) but have more limited power

46
Q

Describe pennate muscle contraction

A

Generate ore power = greater torques but over short distances (fibers at angle to attachments)

47
Q

Describe fusiform msucle contraction specifics

A

Fibers all mostly parallel to line of action = muscles best at generating greater shortening lengt = great range of motion
Small cross sectional area tho

48
Q

describe unipennate muscle contraction specifics

A

Much larger cross sectional area
Smaller actual contraction bc of angle
Shorten less but with much greater torque bc more crosss sectional area= more muscles

48
Q

Describe bipennate msucle contractions

A

Much larger, doubles it = increase torque but less range of motion
Comes at expense of ranges of motion

48
Q

What are some msucle lever systems boosted by

A

Bony protrusions that lengthen muscles lever arm= move line of action further away from centre of rotation =
Through processes, tubercles, sesamoids etc

48
Q

What does ability of muscle to generate torque also depend on

A

Cross sectional area but also how far line of action is form joint it moves
Increase torque by increase force or increase length lever arm

49
Q

Describe exs of boosting msk lever systems

A

Line of actions =
Gluteus medius = femoral neck increase lever arm also for gluteus minimus (hip abductors)
Quadriceps = patella boosts lever arm
Gastrocnemius = ankle, calcaneus allows gastrocnemius to insert a bit further away from ankle joint

49
Q

What are muscle actions dictated by

A

Direction of muscle fibers = along which they shorten
Location fo fibers/tendons relative to joints
Joint geometry

49
Q

Describe ex = teres major

A

Fibers run from inf scapula to ant humerus
Crosses inf to shoulder joint = glenohumeral joint
Pulling on both ends of the muscle that brings the humerus towards the scapula = shoulder adduction, reduces angle fo shoulder