Transcript Exam #4 Monday May 3 1 p.m. - Washington State University

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 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
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.
1
2
3
Muscle cell
types
schematic:
1) skeletal
2) cardiac
3) smooth
Skeletal muscle
Cardiac
muscle
http://www.youtube
.com/watch?v=Cdl8
Awn_lDY&feature=
related
http://www.youtube
.com/watch?v=b1W
D564sjWw&feature
=related
Smooth muscle