BIOM - Musculoskeletal System
SE components - perimysium info
- Surrounds fascicle and provides a pathway for nerves and blood vessels to reach the muscle fibers.
Force-Velocity (CE) Relationship - concentric contraction info
- The tension the CE of muscle can generate decreases dramatically as the velocity of muscle shortening (concentric) increases under load
Combined Muscle Length & Moment Arm - as joint angles change - what happens
= Schematic examples of moment arm and length change with changing joint angles.
image of change in tendon with mm shortening
?
Contractile (CC or CE) componenets (3)
• Stimulation-activation • Force-length • Force-velocity
Musculotendon force and Joint Moments - Joint moments of force (torque):
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Muscle Organization, Micro Level - fascicle def
- A bundle of muscle fibers
Muscle Organization, Micro Level - muscle fiber
- A cylindrical, multinucleate cell composed of numerous myofibrils that contract when stimulated. = Up to 50microm wide and 10 cm long.
torque - velocity - power chart
- A muscle contracts faster when warm (dashed line), shifting the FxV curve to the right (> Vmax). - For increasing velocities, force is greater, therefore muscle power increases with its peak reached at a muscle shortening velocity.
Force-Length & Passive parallel elastic Element
- As muscle lengthens, passive elastic structures in parallel (PE) are stretched and contribute (Fp) force to CE forces (Fc) resulting a combined effect (Ft). **At rest length (lo) or less, PE is in a slack state and does not contribute.**
A.V. Hill model info
- Behaviour model that predicted the mechanical nature of muscle. - Insight into how muscles function, basis for computer muscle models
A.V. Hill 3 component model
- CE - PE - Series elastic
Anatomical Cross-Section Area - eqn
- CSA = muscle volume/muscle fiber length (in cm) - muscle volume (cm^3) = muscle mass/density **density always = 1.056g/cm^2)
Physiological cross-sectional area (PCSA) - info
- Considers cross-sectional area of tissue pulling through the tendon (ie the effective force). - sum of all cross sections of fibers perpendicular to the direction of fibers
Mechanical model musculo-tendon unit - 3 elements at play
- Contractile element (CE/CC) - Parallel elastic element (PE/PEC) - Series elastic element (SE/SEC)
SE components - epimysium info
- Covering on outside of muscle that helps transmit muscular tension generated by contraction to the tendon.
Muscle Organization, Micro Level - myofibrils (3 infos)
- Densely packed, thread like contractile elements - They make up most of the muscle volume - The arrangement of myofibrils within a fiber is such that a perfectly aligned repeating series of dark A bands and light I bands is evident
force - velocity - power chart
- Different synergist muscles have different F-V characteristics; therefore, they will have different muscle power profiles
Muscle 0rganization, macro level - penniform types info
- Fibers diagonal to central tendon of muscle, therefore change in fiber length is not equal to change in muscle-tendon length. - Generally these have a shorter range of motion but they are stronger due to greater PCSA (ie can fit more fasicles).
Force & Velocity of Contraction - note on the fact that the greater the x-sectional area the greater the force (pennate mm arch)
- Generally, more fibers packed in pennate muscle architecture. Advantage force, even though fiber force (Fm) through tendon (Fm,t) is less (Cos Θ • Fm)
Force & Velocity of Contraction: 3 points
- Greater muscle cross-sectional area (sarcomeres, fibers, fasicles in parallel) the greater the force (F = nF). - The longer the fibers of muscle (sarcomeres in series) the greater the ability of muscle to shorten (ΔL = n(Δl)) per unit time (velocity). - Muscle contraction time and maximum velocity of shortening is related to the biochemical properties of the muscle (fiber type).
Parallel elastic comps (PE or PEC) -
- Inactive muscle elastic response to stretch. - Associated mostly with fascia surrounding muscle.
How Muscle Fiber Length affects V_max - From Resting Length Lo, which is length of muscle where force production is maximal in an isometric contraction (long fiber vs short fiber)
- Long Fiber: each sarcomere moves away from Lo 0.125 μm. - Short Fiber: each sarcomere moves away from Lo 0.25 μm **Force generated by Long Fiber "higher" on the Force-Length curve than short fiber
Structure → (leads to what)
- Mechanical Model of Muscle
Peak Torque-Angle relation would be a combination of
- Optimal muscle length (top) and greatest moment arm (bottom)
stress strain curve - PE vs SE
- PE = parallel elastic comp (fascia) - SE = tendon
power def
- Power (F∙V) is the term used to express force and velocity's combined effect.
SE Components - endomysium
- Protective sheath for each muscle fiber that carries the capillaries and nerves for each muscle fiber.
Force-Length & Passive (SE) Element - under dynamic conditions ....
- SE tissue will influence the time course of muscle tension transferred to the bone.
what happens to the SEC and CE during an isometric contraction
- SEC increases (series elastic comp) - CE decreases (conrtacile elements) - and angle stays the same
Muscle Organization, Micro Level - sliding filament theory
- Simultaneous sliding of thousands of sarcomeres in series changes the length and force of the muscle - Sarcomere contracts as the myosin filament walks along the actin filament, forming cross-bridges between the head of the myosin - Force developed in muscle proportional to the number of crossbridges formed. **this is the accepted theory of mm fx**
Force Generation - pennate vs nonpennate - if the number of mm fibers where the exact same
F(t-penniform) = 0.707 F(t-fusiform) **ie penniform will produce more force with same #'s of fibers**
Force Generation - pennate vs nonpennate - if there were 2 times as many pennate fibers as there were fusiform fibers
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Muscle Organization, Micro Level - sarcomere image
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Force-Velocity (CE) Relationship - eccentric contraction info
- The tension the CE of muscle can generate increases dramatically as the velocity of muscle lengthening (eccentric) increases under load, to a point (180%) on curve shown.
series elastic components
- Transfers forces to bone (mostly tendon)
Muscles with different architecture = PCSA & Fiber Length Effects (graphs)
- Two muscles of equal PCSA but different fiber lengths generate equal peak muscle force but have different working range, optimal length and maximum contraction (shortening) velocity. - Two muscles of equal fiber lengths but different PCSA have the same working range, optimal length and maximum contraction (shortening) velocity but generate different peak force.
Contractile (CE) Mechanics - pennate mm info
- a muscle with fascicles that attach obliquely (in a slanting position) to its tendon. - allow higher force production but smaller range of motion - when a muscle contracts and shortens, the pennation angle increases
Gross Structure of Muscle - fascia 3 infos
- a sheet of fibrous tissue - conpartmentilizes groups of mm - mm in the same compartment are innervated by the same nerve
Musculotendon unit - extensibility info (2)
- ability to be stretched or extended beyond resting length - also used as a Protective mechanism - shock or energy absorption/transfer (lengthening contraction)
Musculotendon unit - elasticity def
- ability to recoil (stored elastic energy, connective tissue)
Contractile (CE) Mechanics - ASCA/PSCA
- anatomical cross-sectional area (green) - physiological cross-sectional area (blue)
CE force vs length and force-velocity curves
- bottom
Force-Length (CE) Relationship - force is dependent on what (actin wise)
- dependent on the number of actin-myosin binding sites **graph proof**
Musculotendon unit - 4 definers
- exceitability/irritability - contractility - extensibility - elasticity
Contractile (CE) Mechanics - parts of the structural mm fiber
- fasicile - fiber - myofibril - sarcomere (fx unit) - controllable unit (ie MU) - mm mechanics
at high Concentric velocities, Length does not play a very large role in ....
- force modulation as very little force is generated with this high a shortening velocity.
at low Concentric velocities Length plays a large role as a
- force modulator
Contractile (CE) Mechanics - mm mechanics includes (4)
- force-length, force-velocity, direction of contraction, recruitment
Muscle 0rganization, macro level - fusiform types info
- fusiform - eg = biceps mm - Fascicles & therefore force and length changes parallel to long axis of muscletendon complex. **Generally you get a greater range of shortening and movement velocity with this type**
relation of mm architecture with force production
- fusiform = parallel so creates more force than a angled pennate fiber BUT - by angling the fibers you are able to get more fibers into a same surface area
Force-Length & Passive (SE) Element - under static conditions ....
- if unaccounted for, SE compliance will influence the F-L relationship for muscle tissue (bottom figure).
at very low Eccentric contraction velocities, length does play a role in
- in force modulation.
types of contractions - image
- isometric = muscle length stays the same - concentric = muscle shortens - eccentric = muscle lengthens
as velocity increases what happens to force get
- it decreases - peak power occurs at 30% (F*V)
Force-Length (CE) Relationship - the magnitude of force (CE) produced depends on what
- its length - taking the cross-bridge theory into play - - > the interaction of actin and myosin filaments generates force and length change
Anatomical Cross-Section Area - info
- looks at the mm perpendicular to the long axis
Contractile (CE) Mechanics - 3 elements
- macrolevel - ie muscle architecture - microlevel - ie structural unit (mm fiber) - mechanical model, musculotendon unit
Force-Length & Force-Velocity Curves Combined - at high eccentric contraction velocity, length does not ...
- modulate force much as muscle has to undergo huge force production regardless
The combined force length curve for CE and PE are usually shown for maximal activation conditions. At submax activation PE tension contributes in the same way (predominately) independent of activation. CE is under active control, PE is function of _______________ only.
- muscle length change only!
CE force is dependent on (3)
- muscle length, velocity of contraction, and type of contraction (concentric or eccentric).
Individual Muscle Organization - excitable vs non-excitable (basic statement)
- muscle tissue is excitable - CT and fascia is NOT excitable
Musculotendon force and Joint Moments - 3
- muscle-tendon force - contracile muscle dynamic - joint moments of force (ie torque)
Combined Muscle Length & Moment Arm - optimal joint moment-angle relationship does not coincide with
- optimal length or moment arm but is somewhere between.
Contractile (CE) Mechanics - muscle architecture aspects (3)
- penniation - fiber types - ACSA/PCSA
Individual Muscle Organization - SE components include what
- series elastic components are : - tendons, bones and fascia (fasica = epimysium, perimysium, and endomysium)
How Muscle Fiber Length affects V_max - sarcomere length and speed of contraction
- single sarcomere undergoes a 0.5 μm shortening in 1 sec - so the more sarcomeres you have (ie the longer the mm) the faster it contracts
Force-Length & Passive (SE) Element - Under isometric conditions...
- the CE of muscle will shorten at the expense of SE elements lengthening. Hence, an isometric contraction at a fixed joint angle can result in muscle (CE) shortening, and therefore, the CE force as a function of muscle length will have changed without a change in joint angle.
CE force produced for a given velocity depends on where the movement is on what
- the force-velocity curve
Musculotendon unit - excitibility/irritability def
- the units ability ti receive and respond to stim
Musculotendon unit - contractility def
- the units ability to shorten forcibly (50-70%) when it receives sufficient stimulation (force & length)
Cross-bridge theory suggests force decreases at faster shortening velocities because .. and is this theory true
- there is less time for actin-myosin bonding to take place. - This theory doesn't hold for eccetric conditions. Still under investigation, two theories are: 1) with lengthening, actin-myosin bonds are broken rather than formed so this requires more force; 2) there is rotation of the actinmyosin bonding heads and stretching of elastic elements that contribute, thereby increasing force.
muscles usually act how with each other
- they typically act in unison NOT individually
Muscle Fiber Action Potential - what is coupled
- this is excitation contraction coupling