Motor Unit and acute modulation Flashcards
what is key for muscle contraction?
Calcium ions “on and off switch”
when the muscle is resting or relaxed, myosin is attached to
actin in a “weak binding state”
where is calcium stored?
Sarcoplasmic reticulum
action potential is generated in a
motor nerve
(muscle turning on) Acetylcholine opens what gate?
chemical gated Na+ channel
(muscle turning on) T-tubules spread impulses along the?
triads
triads?
the structure formed by a T tubule with a sarcoplasmic reticulum (SR) known as the terminal cisterna on either side.
(muscle turning on) Depolarazation causes calcium gates to?
to open in the sarcoplasmic reticulum
(muscle turning on)calcium empties out of the
Sarcoplasmic reticulum into the cytoplasm and binds Tn-C
(muscle turning on)Once calcium is bound to the Tn-C, what occurs?
myosin can attach in the strong binding state
Muscle contraction is turned off by
removing calcium
(muscle turning off) calcium is pumped out of the cytoplasm into
the sarcoplasmic reticulum via Calcium-pumps
(muscle turning off) calcium pumps require energy in form of
ATP
to respond immediately to calcium
(muscle turning off) The rate and amount of calcium removal is tied to
the number of calcium pumps
(muscle turning off) when calcium is pumped out what occurs?
myosin goes back into the weak binding state and the muscle becomes relaxed
After the myosin goes back into the weak binding state, the muscle is also
repolarizing and can not turn on again unti its repolarized
myosin immediately hydrolyzes the ATP into
ADP+Pi
Calcium binding to TnC starts a
shape change and allows myosin to bind action in the strong binding state
once in a strong binding state myosin can?
exert force upon the actin
in a strong binding state, force occurs when the cross bridge?
changes from a 90 to 45 orientation
The 90 to 45 occur when
the Pi is released from the myosin. if its not released no force is produced
After the Pi is released, the cross bridge cycle will not continue until
the actin and myosin bond is broken
The actin and myosin bond is broken by
ATP attachment
Before the ATP can break the actin-myosin bond
ADP must be released from the myosin. The cycle is in a holding pattern until its released.
If ADP is released but there is no ATP available, the cycle enters a ?
state of rigor
rigor?
the actin-myosin are strongly stuck to each other (stiffness)
Once ADP is released?
ATP binds myosin, breaks the actin-myosin bond and the whole cycle starts again. As long as there is neural stimulation
muscle action is intiated by
nerve impulse
The nerve releases ACH, which allows
sodium to enter and depolarize the cell
If the cell is sufficiently depolarized,
an action potential occurs which releases stored calcium ions
Calcium ions intiate a series of events leading to
muscle cell contraction (Z line move towads each other)
Once myosin binds to actin,
the myosin head tilts and pulls the actin filament so they slide across each other
Muscle action end when
calcium is pumped out of the sarcoplasm to the sarcoplasmic reticulum for storage
Energy for muscle acton is provided when the myosin head binds to
ATP
ATPase on the myosin head splits the?
ATP into a usable energy source
Biochemical properties of muscle fiber types
- oxidative capacity
- type of ATPase and myosin heavy chain
Contractile properties of muscle fiber types
- maximal force production
- speed of contraction (Vmax)
- muscle fiber efficiency
Slow twitch fibers properties
- high aerobic (oxidative) capacity and fatigue resistance
- Low anaerobic (glycolytic) capacity and motor unit strength
- slow contractile speed
Fast twitch type IIa properties
- moderate/high aerobic (oxidative) capacity and fatigue resistance
- High anaerobic (glycolytic) capacity and motor unit strength
- fast contractile speed
Fast twitch type IIx
- Low aerobic (oxidative) capacity and fatigue resistance
- high anaerobic (glycolytic) capacity and motor unit strength
All or none response
for a motor unit to be recruited into activity the motor nerve impulse must meet or exceed the threshold
hypertrophy
increase of muscle size
hyperplasia
increase of muscle cell number
equation of power
power=force x velocity
force is determined by
Pi release
Velocity is determined by
ADP release
more sarcomeres in parallel
favor force production
more sarcomeres in series
favor velocity
force magnitude is equal to
the number of attached cross bridges going from 90 to 45
contraction velocity is related to
the cross bridge cycling rate or the rate of ADP release strongly related to the myosin ATPase type
2 people can generate the same power by different means. Power production can be changed by
changing force, velocity or both
both hypertrophy and hyperplasia are controlled by
satellite cells
