1. Motor mechanisms II

2. Review questions

3. 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

4. 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

6. 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

7. 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

8. 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 ( 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 fatigued
more capillary beds, greater VO2 max 
less capillary beds
smaller in size
larger in size
lower 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 capacity
higher fat content
lower fat content 
more mitochondria - Beta Oxidation high
fewer mitochondria- Beta Oxidation low
poorly formed sarcoplasmic reticulum
well formed sacroplasmic reticulum
slower release of Ca = slower contractions
quick release of Ca = rapid contractions 
tropinin has lower affinity for Ca
troponin - higher affinity for Ca

10. 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

11.   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.

14. 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.

15. Muscle cell types schematic: 1) skeletal 2) cardiac 3) smooth

16. Skeletal muscle

17. Cardiac muscle

18. Smooth muscle