Skeletal Muscle Flashcards
Skeletal muscles contain ______
muscle fibers
multinucleate
The muscle fiber is surrounded by a cell
membrane called a ________
sarcolemma
he sarcolemma is attached to strands of
connective tissue called the ________
endomysium
Bundles of muscle fibers are grouped
together by a connective tissue sheath
called the _____
perimysium
The muscle fiber bundles that form the
muscle are contained within an outer
sheath of connective tissue called the
________
epimysium
The connective tissues are connected to
______ and to the tendons that attach
the muscle to the bones
each other
Skeletal muscle fibers are divided into
__________
myofibrils
The myofibrils are separated from each
other by longitudinal vesicles called the
__________
sarcoplasmic reticulum.
The ____________ contains the calcium that is used to initiate the contractile
process
sarcoplasmic reticulum
The myofibrils are divided into ________, which are the functional units responsible for muscle contraction
sarcomeres
Sarcomeres are composed of thick and thin
filaments and are bounded by a band of protein called the ____________
Z line
The thin filaments contain two helical chains of ____________.
actin
Thin filament have a long filamentous protein called _______ that lies in the groove
formed by the two intertwined actin
chains.
tropomyosin
what binds to tropomyosin?
troponin
A globular portion of the myosin molecule, called the __________, projects out of the thick filament.
cross bridge
The thick filaments are held together by transversely organized proteins called
______. These proteins are responsible for the formation of the M line
myomesin
A large elastic protein called ______ connects the M line to the Z line. Titin not only stabilizes the structure, it creates the elasticity that opposes passive stretching of the muscle and allows the muscle to spring back to its original length after being stretched
titin
what is exitation-contraciton EC coupling?
Generation of the muscle action
potential and depolarization of the T-tubule (initiation of muscle contraction)
Skeletal muscle fibers are activated by what kind of motor neuron?
α-motoneurons
how many α-motoneurons innervate a single muscle fiber?
one
what is a motor unit?
the motor neuron and all the fibers it innervates
when the motor neuron fires what happens to the muscle fibers?
all muscle fibers it innervates are activated
what are the first two steps of EC coupling?
- Generation of the muscle action potential and depolarization of the T- tubule
- The release of calcium from the sarcoplasmic reticulum
what are the third and froth step of EC?
- The binding of calcium to troponin
and the initiation of the cross bridge cycle - The re-accumulation of calcium within the SR
how is Ca released from the sarcoplasmic reticulum?
-depolarized membrane causes Ca release from SR
what are the Ca channels on SR called?
ryanodine receptors
what do DHP receptors do?
coupled to ryanodine receptor and bocks Ca release when membrane is polarized
what happens when t tube depolarize?
Depolarization of the T-tubule causes the
charged protein to move towards the DHP
receptor, unblocking the Ca2+ release channel
within the ryanodine receptor
Troponin C (TnC), which contains binding
sites for ______.
calcium
Troponin T (TnT), which binds the troponin
complex to _____ and______
tropomyosin and actin
Troponin I (TnI), which keeps the troponin
complex tied to actin and inhibits the
interaction between the _____ and _____
myosin cross bridge and actin
what initiates the cross bridge cycle?
Ca bind to trop C
The binding of calcium to troponin C causes
__________________
troponin I to separate from tropomyosin and actin
The movement of TnI allows tropomyosin ________________
to move away from the myosin binding sites on actin.
what is the first two steps of the sliding filament theory?
- The enzyme catalyzing the hydrolysis of
ATP, actin-myosin ATPase, is contained
within the cross bridge and is activated
when the myosin molecule binds to actin. - The ATP is bound to myosin as a high-
energy complex referred to as myosin
ADPPi
what is the third and forth step of the sliding filament theory?
- When the cross bridge bends, ADP and
Pi are released from myosin. - The thin filament detaches from myosin
when a new molecule of ATP binds to the
myosin molecule.
When skeletal muscle contracts, _____ sides over the _______ filaments.
the thin filaments slide over the thick
(The movement of the thin filaments over
the thick filaments is produced by the cross
bridge cycle)
how is Ca removed from the cross bridge?
Ca pumps (SERCA)
The removal of calcium from the cytoplasm
causes calcium to ________
dissociate from TnC
(TnI separates from TnC and rebinds to
tropomyosin.
- Tropomyosin returns to its position covering the myosin binding sites on actin.
- Cross bridge cycling stops)
what occurs in the atent period of the twitch contraction?
This is the period of time from the action
potential to the onset of contraction. The
time delay is due to the excitation-
contraction coupling
what occurs during the contraction phase of twitch contraction?
This is the time that tension is
developing due to the cross-bridge
cycling
what occurs during the relaxation phase of the twitch contraction?
This is the time that the tension is
decreasing (i.e., relaxing) and is longer
than the contraction phase. This is due
to the amount of time it takes to get all
the Ca2+ sequestered.
what is an isometric contraction?
total length of muscle does not change
what is preload?
initial length of the muscle prior to contraction
what factors impact the force produced by an isometric contraction?
- The preload (i.e., the overlap
between thick and thin filaments). - The number of muscle fibers
activated. - The frequency of action potentials
generated by the muscle.
what is an isotonic contraction?
muscle develops force and shortens
what is afterload?
load lifted by the muscle when it
shortens
what are the phases of isotonic contraction?
- It contracts isometrically until the force
developed is equal to the afterload. - It shortens isotonically at a constant
velocity until it shortens as much as it is
capable of shortening. - It contracts isometrically until it begins
to relax.
how is the velocity of shortening during an
isotonic contraction related to the afterload
inversely proportional to
how is The amount of shortening that occurs
during an isotonic contraction related to the afterload
is inversely proportional
The force produced during an isometric contraction depends on _________
the length of the fibers
The force produced by a muscle depends on the number of __________________
myosin cross bridges that bind to actin during the contraction
The relationship between the preload and the force of contraction is called the ____________
length-tension relationship
The maximum number of cross bridges can bind to the thin filament when the
initial sarcomere length is between ____ and ___
2.0 um and 2.2 um
The resistance to stretch depends on what?
the elastic properties of titin and other proteins in parallel with the thick and thin filaments.
how does the CNS vary the amount of force generated by a muscle?
varying the number of a motor neurons that are active
what is a twitch contraction?
the contractile force generated my one action potential
why can AP summate?
Because the duration of a twitch is greater than the duration of an action potential, the
contractions produced by successive action potentials can summate
is Ca present during contraction?
no, Although the calcium released by a single action potential activates all of the contractile
protein, the calcium is removed from the myoplasm before the contractile force reaches
its full potential
when does tetanus occur?
occurs when the frequency of action potentials is high enough to prevent any relaxation of contraction between action potentials and the force
how are contractie proteins connected to the bones?
elastic structures series called elastic component
what are the phases of isotonic contraction?
- It contracts isometrically until the force developed is equal to the afterload.
- It shortens isotonically at a constant velocity until it shortens as much as it is capable of shortening.
- It contracts isometrically until it begins to relax.
what happens if you increase afterload?
- Increases the latency + force between muscle and shortening.
- Decreases the velocity/amount of shortening.
The characteristics of an isotonic twitch depend upon ____________
the magnitude of the load being lifted
the heavier the load what changes occur?
(1) the latent period is longer,
(2) the velocity of shortening (distance shortened per unit of time) is slower,
(3) the duration of the twitch is shorter, and
(4) the distance shortened is less
(good graph on slide)
