Muscle Tissue and Mechanics

Question 1

Muscle Structure

Answer 1

Largest to Smallest:

Muscle- surrounded by epimysium
Fascicle- surrounded by perimysium
Fiber- surrounded by endomysium
Myofibrils
Myofilaments

Question 2

Greatest Force vs. Maximal Shortening Velocity

Answer 2

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

Question 3

Structure of Sarcomere

Answer 3

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

Question 4

Components of Sarcomere: Myosin, Actin, Troponin, Tropomyosin, Alpha Actinin, and Titin

Answer 4

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

Question 5

Titin, Nebulin, Obscurin

Answer 5

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

Question 6

Triad

Answer 6

1 T tubule + 2 terminal cisterna of SR

Question 7

Isotonic Contraction

Answer 7

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

Question 8

Isometric Contraction

Answer 8

Same length; keeping the muscle at the same length, but stimulate it in different ways and measure tension

muscle tension = load

Question 9

Passive Length Tension Curve

Answer 9

Passive L/T curve of resting muscle reflects the parallel elastic component:
Titin
Extracellular connective tissue (endomysium, perimysium)

Question 10

Active Length Tension Curve

Answer 10

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

Question 11

At Shorter Lengths, Force is Decreased By

Answer 11

1. Presence of thin filaments in wrong half of sarcomere
2. Collision between thick filament and Z-disc
3. Compression of titin
4. Compression of t-tubules, leading AP conduction failure

Question 12

Preloaded Muscle

Answer 12

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.

Question 13

Afterloaded Muscle

Answer 13

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.

Question 14

Length Tension Curve: Under and Above the Curve

Answer 14

Above = muscle lengthens/ cannot hold the load
Below = muscle shortens

Question 15

Force per Motor Unit: Concentric vs. Eccentric

Answer 15

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.

Question 16

DOMS

Answer 16

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.

Question 17

3 Energetic Systems

Answer 17

1. Phosphagen System: fast acting, but doesn’t provide energy for a long time; short duration
2. Glycogen-Lactic Acid System: relatively fast, but get acid production to cause fatigue
3. 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

Question 18

Substrate Utilization During Exercise

Answer 18

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

Question 19

Metabolite Levels and Fatigue

Answer 19

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

Question 20

McArdles Patients

Answer 20

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

Question 21

H+ and Fatigue

Answer 21

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.