Skeletal Muscle 1 Flashcards
What type of fibers are the lower motor neurons?
A alpha fibers
Big to small, what is the anatomical organization of skeletal muscle?
-whole muscle
-muscle fascicles
-muscle fibers
-myofibrils
-myofilaments arranged in sarcomeres
What is the functional unit of skeletal muscle?
sarcomere
What is the dark band in the sarcomere?
A band
What is the light band in the sarcomere?
I band
Which of the two bands shorted during contraction?
H zone and I band
What band stays the same length during muscle contraction?
A band
-only thick filament so does not move
What is the H zone?
the space between the two thin filaments next to each other
What is the A band?
entire length of thick filament
What is the I band?
only thin filament
What is the H zone?
only thick filaments
What is the Z line?
thin filaments anchored here
What is the M line?
link the central regions of the thick filament
What is the thin filament?
made of actin, tropomyosin, and troponin
What are the 3 subunits of troponin?
T- tropomyosin binds
C- calcium binds
I- actin binds
What is the thick filament?
myosin filament that has multiple cross-bridges where the heads can bind to the G actin molecules
What type of activity of myosin have?
ATPase activity
What does tropomyosin do during rest?
blocks the actin binding site
What is the dystrophin-glycoprotein complex?
-connects thin filament to glycoprotein in sarcolemma
-provides scaffolding for sarcomeres
What can happen if dystrophin is messed up?
the complex is not maintained in the membrane
-this does not provide the stability that the muscle cell needs
-the cell membrane breaks and muscles cells die
-leads to many different types of muscular dystrophies that have varying severities and modes of inheritances
What does the alpha motor neuron release into the synapse?
release Ach to bind to nicotinic receptors on the muscle fibers
What does botulinim toxin A cause?
inhibits the release of Ach into the neuromuscular junction
What are t-tubules?
invaginations of the skeletal muscle memrbane that increases the surface area that Ach can act on on the membrane
-allows the message to get into the inside of the muscle as well
Where does the Ca needed for muscle contraction come from?
sacroplasmic reticulum
What blocks the binding of myosin to actin in a resting state?
tropomyosin
When troponin binds to Ca, waht happens?
tropomyosin is pulled away from the myosin binding site and allows for the power stroke
What is the terminal cisternae?
portion of SR that contacts the T tubule
What are the steps that occur for Ca to be released from the SR?
-AP moves down the membrane
-down T tubules
-activate DHP receptors in plasma membrane
-open ryanodine receptors (calcium channels) on the SR
-Ca does into the sarcoplasm
What does ATP binding to the mysoin head do?
break the cross bridging
What does the energy from ATP hydrolysis do?
provide energy for cocking the myosin head back into resting position
How much ATP do muscle cells have?
enough for 8 twitches
What are the sources of ATP in muscle?
aerobic and anaerobic metabolism and phosphocreatine
What does CK presence help determine?
if damage to the muscle tissues has occurred
What happens to fatigued muscles?
-decreased tension generation
-take longer to contract
-relax more slowly and may not completed relax
What are theories for why muscles fatigue?
-changes in membrane potential
-decreased ACH
-blockage of blood flow
-central fatigue
-increased metabolic byproducts
-depleted glycogen
What is the rigor state of cross bridge cycling?
myosin and actin are tightly bound
When ATP binds myosin, what happens?
myosin affinity to bind with actin decreases and actin and myosin separate
When the myosin head moves toward the Z line, waht happens?
ATP is hydrolyzed
When ADP is released, waht happens?
actin and myosin resume the brief rigor state
How long does cross-bridge cycling occur?
until you run out of ATP or calcium E
What must happen for relaxation of skeletal muscle?
alpha motor neuron stop firing and cytosolic Ca must decrease
What are the steps of muscle relaxation?
-calcium ATPase on SR to remove calcium from cytosol
-tropomyosin moves, and covers actin’s myosin binding site
-actin slowly slides back to its original resting place and sacromere returns back to original length
Without the presense of ATP, what occurs?
the rigor state is maintained
-this is why rigor mortis occurs
-no more energy to break the cross bridge
Characteristics of Type I muscle fibers?
slow twitch
oxidative phosphorylation for ATP creation
high myoglobin
slow myosin ATPase activity
moderate calcium capacity
small
moderate glycolytic capacity
high oxidative capacity
slow to fatique
Characteristics of Type IIA muscle fibers?
fast twitch
-oxidative phosphorylation and glycolysis
high myoglobin
-fast myosin ATPase activity
-fast SR Ca ATPase activity
-moderate diameter
high glyocolytic activity
moderate oxidative capacity
fast resistant
Charactertistics of Type IIB muscle fibers?
fast twitch
glycolytic
white (low myoglobin)
fast myosin ATPase activity
fast SR Ca capacity
large diameter
high glycolytic activity
low oxidative capacity
fast and fatigable
What are the changes in size of skeletal muscles that can occur?
-hypertrophy (increase in size)
-atrophy (decrease in size)
-sarcopenia (decrease in size due to age)
What type of fibers are present in the jaw muscles?
usually a homogenous mixture of type I and II fibers
What can occur in the fibers in the muscles of the jaw?
-the fiber types can change with age
-type I fibers tend to decrease and type II fibers increase
What is unique about the type of fibers in the jaw?
the type II fibers are smaller than the type I fibers (typically, type II is bigger than type I)
What are isometric contractions?
force produced is less than the load
-there is no movement
-no shortening of the muscle occurs
What is isotonic contractions?
force produced is great enough to move the load
What is the usually progression of muscle contractions?
the isometric contractions will continue until enough force is built to create an isotonic contraction (isotonic contractions not always possible though)
What is an example of isometric exercise?
plank
What is an example of isotonic exercise?
bicep curl
Is the max force used in every isotonic contraction?
absolutely not
-the amount of force needed to move the object is used, no more
ex) something weighing 5 pounds will only use 5 pounds of force
What are ways to increase the total force of contraction?
-increase the number of muscle fibers contracting
-increasing the frequency of fiber activation
How are motor units recruited?
in order of size
-small recruited first because smaller motor units control fewer fibers
What happens when an increase in the number of motor units get activated?
the total tension created by the contraciton of the muscle increases
-spatial summation
What is asynchronous recruitment?
random motor units are activated in random manners
-alternates so the same motor units are not used every time
-try to resist fatigue
What are small motor units made of?
slow twitch oxidative fibers
-lowest threshold for firing and are recruited first
What are larger motor units made of?
fast twitch glycolytic gibers (IIB)
-highest threshold and are recruited last
What happens when the twitches are close together? q
the Ca from the first twitch is still present in the sacroplasm when the second twitch is activated
-not complete relaxation between stimuli
What happens when there is max tension?
the cross bridges are saturated
What alters tension in a single muscle twitch?
sarcomere lenght
What is the optimal length?
the best degree of overlap between the thick and thin filament
