exam 2: diversity of skeletal muscles Flashcards
diversity of skeletal muscle fibers 3 types:
slow twitch: type I
fast twitch:
oxidative-glycolytic: type IIA
glycolytic: type IIB
type I is slow and ____, which means it has a very rich blood supply
oxidative
color (myoglobin/capillaries for:
type I
type IIa
type IIb
I=red
IIA=red
IIB=white
myosin ATPase activity:
I=
II=
III=
I= slow
II=fast
III=fast
diameter
I=
II=
III=
I=small
II=moderate
III=large
oxidative capacity
I=
II=
III=
I= high
II= moderate
III=low
fatigue
I=
II=
III=
I=slow
II=fast resistance
III= fast fatigable
what type takes longer to reach peak tension?
which takes least amount to reach peak tension?
longer= slow twitch Type I
least amount= Type IIB
certain characteristic of skeletal muscle fibers can change in response to
- changes in size
- changes in fiber types (proportion of fiber types changes)
changes in size of skeletal muscle fibers:
1
2
3
- hypertrophy (increase in cell size)
- atrophy (decrease in size of muscle cell)
- sarcopenia (decrease in muscle cell from aging/loss of muscle tissue)
the amount of load and the force the muscle generates determines the type of
contraction
force produced is LESS than the load= no movement
generating tension but the muscle is not shortening
isometric contraction
in isometric contraction, the muscle length has not shortened but :
has happened which allows muscle length to remain the same
sarcomeres have shortened and elastic elements have stretched
force produced is great enough to move a load
isotonic contraction
sarcomeres shorten even more with even more overlap and because elastic elements are already stretched, the entire muscle must
shorten
the force of contraction increases until the isometric contraction becomes an
isotonic contraction
-not always possible!
muscle can only contract up to 17 grams. so with 20 grams what will happen?
muscle will not reach isotonic contraction bc the muscle will not be able to SHORTEN to move the LOAD. so it will stay as isometric contraction(generate tension but NO movement)
contraction of a whole skeletal muscle is
graded
increase of crossbridges= increase of
force
increase total force by:
1
2
- increasing the number of muscle fibers contracting (motor unit recruitment)
- increasing the frequency of fiber activation
a motor unit is the _______ and the muscle fibers it innervates
alpha motor neuron (LMN) or by releasing ACh
two ways nervous system can cause a greater muscle tension production aka increase total force:
increasing the number of muscle fibers contracting (motor unit recruitment)
and
increasing frequency of fiber activation
motor units are recruited in order of size.
_____ motor units are recruited first.
smallest motor units control ______
small
control fewer fibers
an increase in the number of motor units activated increases the TOTAL TENSION produced by a contraction of a muscle=
(asynchronous recruitment)- alternate what is active and when
spatial summation
increasing the frequency of activation increases:
action potential frequency (tetanus)
are composed of slow-twitch oxidative fibers. they have the lowest threshold for firing and are recruited first
small motor units
what has the lowest threshold for firing
slow-twitch oxidative fibers
composed of fast-twitch glycolytic fibers. have the highest threshold and are recruited last
large motor units
highest threshold and recruited last
fast twitch (type IIB)
an increase in the frequency of an alpha motor neuron stimulation will increase the amount of what produced
amount of tension
the tension produced in response to each action potential will sum if the muscle:
has not yet completely relaxed
can come to a point where you have such high AP frequency that you get fuzed tentaus where what happens:
absolutely no relaxation period
every actional potential causes ___ to be released
calcium
twitches are close enough together that ____ from the first twitch is still present in the sarcoplasm when the second twitch is activated.
this means there is not enough:
calcium
not enough relaxation between the stimuli
- increase ca, increase # cross-bridges=
- AP’s have already stretched that series elastic elements=
- increase in force
- why much stronger force production
for a single muscle twitch (one muscle fiber), the tension developed is altered by
sarcomere length
where there is best degree of overlap between the thick and thin filaments
optical length
at the optical length the greater number of actin/myosin cross-bridges can form, which results to maximal
tension produced
tension is reduced if
the muscle is not stretched enough or if it is stretched too much
if we increase the muscle length,
we decrease the amount of thick and thin overlap
if we decrease the muscle length, we
increase the overlap
the velocity of contraction(distance moved/time) depends on the
load a fiber is contracting again (fast with less weight compared to something heavier)
decrease in velocity:
increase in load
load isnt the only factor that dictates the speed of contraction. _____ also dictates it
fiber type
Type I fibers have an isoform of myosin with ______ ATPase activity
while Type II fibers have a _____ myosin ATPase
type I- slower
type II- faster myosin atpase
