exam 2: skeletal muscle Flashcards
the dark band
a-band
thick and thin
light band
I-band
only thin
functional unit of cardiac and skeletal muscle
sarcomere
when the sarcomere shortens, what moves and what stays
I-band shrinks during contractions (H-zone)
and
A-band remains the same
alternating A-bands and I-bands create the _________ appearance in skeletal and cardiac muscle
striated appearance
entire length of thick filament
a-band (dark)
includes only the thin filament
I-band (light)
only thick filament
H-zone
thin filaments anchored here
z-line
link the central regions of thick filaments
m-line
during contraction what decreases:
H-zone and I-band
why doesnt a-band change in size
because its the same length as the thick filament
thin filaments are composed of____
, ______, and _____
actin, tropomyosin, and troponin
(with G-actin molecules, the active site which bind myosin)
actin
(which binds actin, tropomyosin and calcium)
troponin
covers up myosin binding site of actin
tropomyosin
troponin has 3 globular proteins:
T, C and I
_____(thick) filaments has multiple cross-bridges where the “heads” can bind to the
myosin
g-actin molecule
myosin also functions as the
ATPase enzyme
this connects thin filaments to glycoproteins in sarcolemma
dystrophin protein
provides scaffolding for sarcomeres
dysotrophin protein
muscular dystrophies:
- duchenne (x-linked)
- beckers (milder phenotype)
- myotonic
- oculopharyngeal
- limb girdle
what is muscular dystrophy
not enough dystrophin
excitation/contraction coupling.
the alpha motor neuron (LMN) releases _____ which binds to a nicotinic ACh receptor on the muscle fiber
this is happening at the motor end plate or aka
ACh
aka neuromuscular junction
this inhibits the release of ACh at the neuromuscular junction. it can be used in dentistry
botulinism toxin A
muscle twitch has 3 phases in order:
- latent period= muscle Action potential (really fast)
- contraction= muscle increase
- relaxation= of muscle
what ap is first and what is right after that is second
- AP of alpha motor neuron is first
- ap of muscle is right after
(Na and K out)
for contraction to happen, the intracellular _____ in the muscle fiber must increase
calcium
in resting muscle, _______ prevents a strong bond between the myosin head and g-actin molecules
tropomyosin
when troponin binds to cytosolic Ca2+, tropomyosin is:
pulled away from myosin binding site and allows for the power stroke
(myosin heads can then attach to actin)
calcium is released from
the sarcoplasmic reticulum
modified ER that sequesters(hide away) Ca2+
sarcoplasmic reticulum (SR)
invaginations of sarcolemma
transverse (T)-tubules
portion of SR that contact t-tubules
terminal cisternae
the action potential travels down the membrane, down T-tubules and activates:
which are on the t-tubules
sensitive dihydropyridine (DHP) receptors
DHP in turn open_____ on the SR. calicum goes from SR to the sarcoplasm
calcium channels (ryanodine receptors)
the intracellular structure of_________ ensures spread of action potential (and calcium) throughout the cell
myocytes
what is necessary for contraction?
atp
ATP binding to the myosin head:
breaks the cross-bridge (connection between actin and myosin)
energy released from ATP hydrolysis by the myosin head provides:
ATP-> ADP + Pi+energy
energy for cocking the myosin head (myosin is now in the high energy form)
release of what from the myosin head provides energy for the POWER STROKE? which leads to
inorganic phosphate
(myosin head pulling actin towards the center of the sarcomere)
leads to sarcomere shortening
muscle cells only have enough ATP for ~ _____ twitches
8 twitches
cross-bridge cycling will stop only when
you run out of atp or ca2+
both ___ and ___ produce ATP for muscle fibers
aerobic and anaerobic metabolism
both aerobic and anaerobic metabolism produce ATP for muscle fibers. however, the contribution of each in a specific muscle fiber depends on:
1.
2.
- the metabolic enzymes are present in the cell (glycolytic vs. oxidative fibers)
- the intensity of the exercise
when muscles are resting, they build up a bunch of:
which can use by adding ADP and CK to for ATP
phosphocreatine
measurements of this in the blood is down to determine if damage to muscle tissue (skeletal and cardiac) has occurred
creatine kinase (CK)
what happens if atp runs out
fatigue
fatigue muscles:
- have decreased tension generation
- take longer to contract
- relax more slowly and may not completely relax
theories for fatigue:
- change in membrane potential
- decreased ACH
- blockage of blood flow
- central fatigue
- increased metabolic byproducts (lactic acid or high K+ in ECF)
- depleted glycogen
what 2 things must be present for cross-bridge cycling
both Ca and ATP
cross-bridge cycling.
prior to atp binding, when myosin and actin are tightly bound
rigor state
cross-bridge cycling.
step two, atp binds to ____, decreases its affinity for actin and the two separate
atp binds to myosin head
cross-bridge cycling.
step 3, myosin head moves in the direction of the ______, ATP is_____
direction of the z-line
atp is hydrolyzed
cross-bridge cycling.
step 4
myosin binds the next actin (one closer to z-line) and _____ occurs (pulls actin towards M-line
power stroke
cross-bridge cycling.
step 5._____ is released and the actin and myosin resume to the rigor state
ADP
to get relaxation of skeletal muscle, ______ must stop firing
and
____ must decrease
but ____ must be present to remove myosin from actin
alpha motor neuron stop firing and cytosolic (intracellular) calcium concen. decrease
atp must be present
relaxation of skeletal muscle.
what removes calcium from cystol on SR
calcium ATPase
what happens when atp is lost and myosin is stuck to actin
rigor mortis
relaxation of skeletal muscle.
____ moves and covers actin’s myosin-binding site
tropomyosin
relaxation of skeletal muscle.
actin slowly slides back to its original resting place and the ____ returns to its original length
sarcomere
where is DHP?
where is ryanodine?
dhp= muscle membrane
ryanodine= SR
botox works by
blocking ACH release
what provides energy for power stroke
release of phosphate
