Lecture 2: Muscles and Biomechanics Flashcards
What is torque
Tendency of a force to cause an object to roatate around a point = fulcrum or centr of rotation
Formula for torque
Force X perpendicular distance to the fulcrum (lever length)
What can generate the greatest torque
Maximize length fo lever = bigger
Needs to be perpendicular, better if no parallel vector
Describe muscles line of action
Must be at a certain anatomical distance to centre of rotation to generate torque
What do bones, joints and ligaments create
Create passive linked lever systems that cannot move on their own
What are muscles
Active component of msk lever system
Describe skeletal muscle
Hierarchically organized contractile tissue that can generate tensile forces on levers (bones) and torques at joints
Describe muscled torques
Internal = may oppose/overcome torques created by external forces = gravity or reaction forces to generate rotation of joint = movement
What is myofibril made up
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
Describe muscle hierarchy
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
Describe muscles macroscopically
Striated striped appearance = reflects parallel arrange of fascicles
Indicates direction along which fibres shorten
= direction along which muscle can generate tensile forces
What is a tendon
Tough cord like
Fibrous ct
Connects all msucle to bone
Elastic, not contractile
What is function of tendon
Attaches msucle tissue to bone = interface between
Transmits force across joint and fills in space = allows diff muscle architectures
Descrive what connects bones to muscles
All msucles connects to Bone via tendon of variable length, some short, some many times longer than the msucle
What are sheaths
Ct around
myofibers = endomysium
Fascicles = perimysium
Bundles and whole muscle = epimysium
What is function of sheath
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
What is epimysium
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
Define fascia
Sheet or band of fibrous ct that envelops, separates or binds together structures such as muscles, organs and other sof tissues
How many bones do muscles have attachments on
On at least 2
What is origin
Attchemnt on immobile bone = moves less when msucle contracts
What is insertion
Attachment on bone that moves when muscle contracts
Do we use origin —> insertion
No cause ambiguous =
Better to say bone they attach to or proximal/distal
How many joints do muscles cross
At least one joint
May cross more than one
Have actions at all joints it crosses
Describe biceps = attachments and joints
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
How do muscles produce force
By contacting and generating tension = cannot push, only pull
What are msk lever systems
Composite = more or 2 muscles on opposite sides of joint generate opposite torques and rotations
What is msucles action at a joint determined by
Its position relative to that joint and direction of its fibres = based on which side
Describe biceps vs triceps
Biceps = attaches to ant side elbow joint = elbow flexion
Triceps = attaching on posterior aspect of elbow joint = generates extension
Describe elbow flexion
Bicep shortens through contraction, triceps relaxes
= creates a Torque that causes forearm to move superiority relative to arm and allow angle to decrease = flexion
Describe elbow extension
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
What does angular motion at a joint depend on
Balance of internal and external torques
Muscles can produce diff torques
Name type of torques muscles can produce
Isometric = resist external torques
Concentric= overcome external torques
Eccentric = reduce effects of external torques, brake
Describe isometric contraction
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
Describe concentric contraction
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
Describe eccentric contraction
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
Describe set up of pint of Guinness
Objects to be moved = pint and arm
Joint of interest = elbow
External forces = weight of arm and pint
Internal force = biceps and brachialis
Describe torques equal of pint of Guinness
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
Describe torques NOT EQUAL of pint of Guinness
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
DESCRIBE MSUCLE architecture
Muscles come in all shapes and sizes
2 broad architectures can be recognized
What are 2 broad architectures of msucles
Fusiform and pennate
Describe fusiform msucle
Fibres largely parallel to muscles main direction = line of action, tendon= FUSIFORM, FLAT, STRAPLIKE
Describe pennate msucle
Pennate muscles = fibres oriented at angle to main line of action (tendon) = UNI, BI, MULTI PENNATE
Describe how much msucle fibres can contract
Can contract about 50% of their length
What is a muscles capacity to generate torque depend on
To generate force and therefore torque = function of its cross sectional area = more myofibrils/cm^2 (more fibers = more force)
Describe fusiform muscle contraction
Contract over long distances (fibers parallle to attachments) but have more limited power
Describe pennate muscle contraction
Generate ore power = greater torques but over short distances (fibers at angle to attachments)
Describe fusiform msucle contraction specifics
Fibers all mostly parallel to line of action = muscles best at generating greater shortening lengt = great range of motion
Small cross sectional area tho
describe unipennate muscle contraction specifics
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
Describe bipennate msucle contractions
Much larger, doubles it = increase torque but less range of motion
Comes at expense of ranges of motion
What are some msucle lever systems boosted by
Bony protrusions that lengthen muscles lever arm= move line of action further away from centre of rotation =
Through processes, tubercles, sesamoids etc
What does ability of muscle to generate torque also depend on
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
Describe exs of boosting msk lever systems
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
What are muscle actions dictated by
Direction of muscle fibers = along which they shorten
Location fo fibers/tendons relative to joints
Joint geometry
Describe ex = teres major
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