Lecture 2: Muscles and Biomechanics

Question 1

What is torque

Answer 1

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

Question 2

Formula for torque

Answer 2

Force X perpendicular distance to the fulcrum (lever length)

Question 3

What can generate the greatest torque

Answer 3

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

Question 4

Describe muscles line of action

Answer 4

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

Question 5

What do bones, joints and ligaments create

Answer 5

Create passive linked lever systems that cannot move on their own

Question 6

What are muscles

Answer 6

Active component of msk lever system

Question 7

Describe skeletal muscle

Answer 7

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

Question 8

Describe muscled torques

Answer 8

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

Question 9

What is myofibril made up

Answer 9

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

Question 10

Describe muscle hierarchy

Answer 10

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

Question 11

Describe muscles macroscopically

Answer 11

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

Question 12

What is a tendon

Answer 12

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

Question 13

What is function of tendon

Answer 13

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

Question 14

Descrive what connects bones to muscles

Answer 14

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

Question 15

What are sheaths

Answer 15

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

Question 16

What is function of sheath

Answer 16

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

Question 17

What is epimysium

Answer 17

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

Question 18

Define fascia

Answer 18

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

Question 19

How many bones do muscles have attachments on

Answer 19

On at least 2

Question 20

What is origin

Answer 20

Attchemnt on immobile bone = moves less when msucle contracts

Question 21

What is insertion

Answer 21

Attachment on bone that moves when muscle contracts

Question 22

Do we use origin —> insertion

Answer 22

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

Question 23

How many joints do muscles cross

Answer 23

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

Question 24

Describe biceps = attachments and joints

Answer 24

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

Question 25

How do muscles produce force

Answer 25

By contacting and generating tension = cannot push, only pull

Question 26

What are msk lever systems

Answer 26

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

Question 27

What is msucles action at a joint determined by

Answer 27

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

Question 28

Describe biceps vs triceps

Answer 28

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

Question 29

Describe elbow flexion

Answer 29

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

Question 30

Describe elbow extension

Answer 30

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

Question 31

What does angular motion at a joint depend on

Answer 31

Balance of internal and external torques Muscles can produce diff torques

Question 32

Name type of torques muscles can produce

Answer 32

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

Question 33

Describe isometric contraction

Answer 33

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

Question 34

Describe concentric contraction

Answer 34

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

Question 35

Describe eccentric contraction

Answer 35

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

Question 36

Describe set up of pint of Guinness

Answer 36

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

Question 37

Describe torques equal of pint of Guinness

Answer 37

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

Question 38

Describe torques NOT EQUAL of pint of Guinness

Answer 38

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

Question 39

DESCRIBE MSUCLE architecture

Answer 39

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

Question 40

What are 2 broad architectures of msucles

Answer 40

Fusiform and pennate

Question 41

Describe fusiform msucle

Answer 41

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

Question 42

Describe pennate msucle

Answer 42

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

Question 43

Describe how much msucle fibres can contract

Answer 43

Can contract about 50% of their length

Question 44

What is a muscles capacity to generate torque depend on

Answer 44

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

Question 45

Describe fusiform muscle contraction

Answer 45

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

Question 46

Describe pennate muscle contraction

Answer 46

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

Question 47

Describe fusiform msucle contraction specifics

Answer 47

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

Question 48

describe unipennate muscle contraction specifics

Answer 48

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

Question 48

Describe bipennate msucle contractions

Answer 48

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

Question 48

What are some msucle lever systems boosted by

Answer 48

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

Question 48

What does ability of muscle to generate torque also depend on

Answer 48

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

Question 49

Describe exs of boosting msk lever systems

Answer 49

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

Question 49

What are muscle actions dictated by

Answer 49

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

Question 49

Describe ex = teres major

Answer 49

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