Download - Motor mechanisms II
Motor mechanisms II
Review questions
Binding of ATP to myosin head causes:• a) actin filament to slide• b) Myosin head to detatch from actin
filament• C) Myosin head to cock
What will happen when ADP and Pi dissociate from myosin head?
• A) head will detatch from actin filament• B) head will retract and pull actin filament• C) head will bind ADP again
Ca++ induces muscle contraction by:• A) Causing actin monomers to assemble
into a filament• B) making ATP available to bind to myosin
head• C) allowing myosin head to bind to actin
filament
Muscle fiber types are the result of different types (isoforms) of
myosin• Type I - slow fibers (aerobic)• Type II - fast fibers (anaerobic)
– Type IIx - very fast– Type IIa - intermediate between II x and I– Types present in other vertebrates, not humans
e.g., IIb in rats and other small mammals
TYPE I - SLOW TWITCH Tonic muscles (darker: red) - Leg muscles
TYPE II - (IIa & IIx) FAST TWITCH Tetanic muscles (paler: white) - Pectoral muscles
slower contraction times (100-110 msec) faster contraction times (50 msec)contain myoglobin (red) no myoglobin (white)continuous use muscles - prolonged performance
for endurance performance ( marathoners)one time use muscles - brief performances
for power & speed (sprinters) marathoner: 80% type I & 20% type II sprinter: 20% type I & 80% type II
best in long slow sustained contractions best in rapid (short) contractions not easily fatigued easily fatiguedmore capillary beds, greater VO2 max less capillary bedssmaller in size larger in sizelower glycogen content higher glycogen content
poor anaerobic glycolysis * predominantly anaerobic glycolysis easily converts glycogen to lactate w/o O2
* predominant aerobic enzymes & metabolism some aerobic capacityhigher fat content lower fat content more mitochondria - Beta Oxidation high fewer mitochondria- Beta Oxidation lowpoorly formed sarcoplasmic reticulum well formed sacroplasmic reticulumslower release of Ca = slower contractions quick release of Ca = rapid contractions tropinin has lower affinity for Ca troponin - higher affinity for Ca
Changes between fiber types
• In response to weigh training and anaerobic exercise– IIx ---> IIa– I --> Iia
• Can IIa --> I?• Can increase cross sectional area of fast
fiber types by weigh training
Weight Training and Different Myosin Types sedentary people have higher amounts of IIx active people have more IIa fibers heavy weight-load repetitions..... decreases Fast IIx fibers and converts them to Fast IIa fibers nuclei stop expressing IIx gene and express IIa genes after 1 month all IIx --> IIa (muscle also become more massive) Can we recruit slow ---> fast ? maybe... but no good evidence to date for slow to fast recruitments.
Characteristics of other muscle types:
• Cardiac muscle - found only in the heart, striated, gap junctions allow direct electrical signaling between cells
• Smooth muscle - involuntary muscle, meshwork of actin and myosin, can contract more (greater shortening), but with less tension.
Muscle cell types
schematic:1) skeletal2) cardiac3) smooth
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2
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Skeletal muscle
Cardiacmuscle
http://www.youtube.com/watch?v=Cdl8Awn_lDY&feature=relatedhttp://www.youtube.com/watch?v=b1WD564sjWw&feature=related
Smooth muscle