Muscle Tissue and Mechanics Flashcards
Muscle Structure
Largest to Smallest:
Muscle- surrounded by epimysium Fascicle- surrounded by perimysium Fiber- surrounded by endomysium Myofibrils Myofilaments
Greatest Force vs. Maximal Shortening Velocity
Pennate muscles generate the greatest force because they have the most muscle fibers; muscle fiber length is less than muscle length
Fusiform would generate the greatest maximal shortening velocity because muscle fiber length equals muscle length
Structure of Sarcomere
A-bands – region of thick filaments; doesn’t change in length during contraction
I-bands – where there are no thick filaments, only thin filaments; disappears during contraction
Z-discs – bound the sarcomere and serves as attachment for thin filaments
M-line – binds thick filaments together to help prevent individual thick filament from sliding toward one or the other Z disc
H zone – middle of A band that is less dark and is bisected by M-line; absence of thin filaments; do not see actin filaments in resting muscle; once the contraction starts the H zone begins to shorten and disappear
Components of Sarcomere: Myosin, Actin, Troponin, Tropomyosin, Alpha Actinin, and Titin
Myosin anchored at M line and actin anchored at Z discs
Tropomyosin and troponin are connected to actin and allow myosin to bind or not
Alpha actinin: anchors actin filaments to Z line
Titin, Nebulin, Obscurin
Titin: largest protein in vertebrates, spring-like properties, center thick filament in sarcomere; primary cellular component responsible for passive force
Nebulin: runs from Z disk along actin thin filaments and supports actin filaments
Obscurin: concentrated at the peripheries of Z disks and M lines and binds titin and SR protein
Triad
1 T tubule + 2 terminal cisterna of SR
Isotonic Contraction
Same load; different lengths but weight does not change
If you have shortening that is called concentric, overcoming the load or tension > load, and eccentric is lengthening where load overcomes the force that is generated or load
Isometric Contraction
Same length; keeping the muscle at the same length, but stimulate it in different ways and measure tension
muscle tension = load
Passive Length Tension Curve
Passive L/T curve of resting muscle reflects the parallel elastic component:
Titin
Extracellular connective tissue (endomysium, perimysium)
Active Length Tension Curve
Active L/T curve of contracting muscle reflects the tension developed by a contracting muscle fiber.
Dependent on amount of thin and thick filament overlap
At Shorter Lengths, Force is Decreased By
- Presence of thin filaments in wrong half of sarcomere
- Collision between thick filament and Z-disc
- Compression of titin
- Compression of t-tubules, leading AP conduction failure
Preloaded Muscle
Muscle experiences the load PRIOR to stimulation
Determines resting muscle length (heavy loads stretch the resting muscle more than light loads)
When the muscle is stimulated it will lift the load.
Afterloaded Muscle
Muscle experiences the load AFTER it is stimulated
The muscle will undergo isometric contraction until it reaches the tension to match the load, and then will undergo concentric or eccentric contraction depending on the magnitude of the load.
Length Tension Curve: Under and Above the Curve
Above = muscle lengthens/ cannot hold the load Below = muscle shortens
Force per Motor Unit: Concentric vs. Eccentric
The force per active motor unit is greater during lengthening contractions than in the other contractions, because fewer motor units are bearing the load.
Because force per unit motor unit is greatest during lengthening, muscles are most often injured during lengthening contractions.
DOMS
Post-exercise muscle soreness (also called DOMS, for delayed-onset muscle soreness) represents a relatively mild, but very common, muscle injury.
It is delayed following the exercise because the inflammatory response takes time to develop. The injury causes immediate weakness, but delayed soreness and swelling.
3 Energetic Systems
- Phosphagen System: fast acting, but doesn’t provide energy for a long time; short duration
- Glycogen-Lactic Acid System: relatively fast, but get acid production to cause fatigue
- Aerobic Respiration System: use O2, and powers the cell the longest (indefinite supply of ATP), but last to turn on and requires O2; must have complex organelles to maintain the event
Substrate Utilization During Exercise
ATP store depletes quickly, then creatine phosphate replenishes for a few seconds, then glycogen stores lasts minutes and hours, but the one that lasts the longest and comes in later is the use of fat for ATP
Metabolite Levels and Fatigue
Stimulate muscle and when you increase stimulation, the ATP seems to stay consistent and haven’t declined that much
Phosophocreatine declines but increase in inorganic phosphate
Summary: ATP doesn’t change that much, phosphocreatine declines, and inorganic phosphate increases with increasing stimulation to muscles
McArdles Patients
Cannot breakdown glycogen to G1P (glucose 1 phosphate); need glycolysis to replenish ATP, but don’t have this step; if you let them rest and recover they get 2nd wind because using blood borne substrates to continue to exercise to allow more stores of ATP to kick in
H+ and Fatigue
In second graph, shows that temperature is the primary variable in determining fatigue and that acidic pH is not primary
Indirect Effect of Acidification:
Stimulate group III and IV afferents driving the perception of discomfort and having an inhibitory effect.