muscle contraction Flashcards
Muscle Contraction Occurs by a ________
Sliding
Filament Mechanism
Mechanical forces generated by interactions
between actin and myosin filaments causes the ACTIN
filaments to slide _________among the myosin
filaments. And under resting conditions, these
forces are inhibited
inward
When an action potential travels over the muscle
fiber membrane, the sarcoplasmic reticulum
releases large quantities of ____________, which
activate the forces between myosin and actin
filaments, causing contraction to begin
calcium ions
Calcium is supposed to be lower
intracellularly than extracellularly. But for _______its different and interesting
muscle
Myosin Filaments are Composed of
Multiple ________
Myosin Molecules
There are tails of myosin molecules bundle together to form the _______
body of the filament
Myosin heads and part of each myosin molecule hang outward to the sides of the body, providing an
arm that extends the head ______.
outward from the body
Protruding arms + heads =
cross bridges
An important feature of Myosin head functions as
an _________enzyme
adenosine triphosphatase
the high energy currency of cells.
Adenosine triphosphate
These myosin head function as ___________ which allows to cleave the adenosine
triphosphate and release energy to energized the
contraction process
adenosine
triphosphatase
The other filament is the_____.
actin filament
Actin Filaments are Composed of ______
Actin,
Tropomyosin
Troponin
Remember the muscles particularly the actin, it is
supposed to interact with ______after.
myosin
Each actin filament is about _______ long
1 micrometer
The bases of the actin filaments are inserted strongly into the ___________,
whereas the other ends protrude in both directions into the adjacent
sarcomeres where they lie in the spaces between the
myosin molecules.
Z disks
There is a little bit already of adjacent positioning of actin and myosin and what it
does wait for is for the activation of ________ to start the contraction.
ATP and Calcium
The actin filament is inhibited by the __________ complex
troponin-tropomyosin
It mediates the inhibition of contraction. The active sites on the normal actin filament of the relax
muscles are inhibited by the physically covered
__________complex
troponin- tropomyosin
Inhibition by the troponin-tropomyosin complex –
prevents the ___________
actin myosin contraction
Activation by _________ activate the
contraction
There is an inhibitory effect on the actin.
calcium ions
Calcium ions can combine with ___________,
causing the troponin complex to tug on the tropomyosin molecule.
Allow the myosin to attach and allows the contraction.
Troponin C
Calcium binds to Troponin C, pulls on the ____________, thereby allowing the binding
of your actin with your myosin.
tropomyosin
When a myosin head attaches to an _________, the
head tilts (power stroke) automatically toward the arm that is dragging along the actin filament.
active site
tilting of the head
Power stroke
Immediately after tilting, the head automatically
_______away from the active site.
The head then returns to its normal
perpendicular direction.
breaks
it combines with a new active site
farther along the actin filament. Thus, the head of cross-bridging bend back and forth to allow the step
by step _______ to happen.
Resulting in
pulling of the ends of actin filaments towards the
center of the myosin filament.
walk - along theory
Once the contraction starts, eventually this Power stroke is going to drag along the actin, to further
allowing the binding of the ______ to _____
active site to the myosin
A muscle cannot develop tension at very long, nonphysiological sarcomere lengths because there is no
OVERLAP between _________
actin and myosin
As the sarcomere shortens and actin and myosin
filaments begin to _______,
the tension increases
progressively
overlap
Whole tension is maintained at the sarcomere at ________.
This is due to the actin filaments
overlapping all the cross-bridges of the myosin
filament
2 micrometers
- Cross-bridges can be found in _______
Myosin filaments
- Active sites can be found in ______
Actin filaments
Upon further shortening, the ends of the two filaments begin to overlap (in addition to
overlapping the myosin filaments), causing muscle
tension to ______
decrease
If the sarcomere is further shortened to 1/65 micrometers, the 2 z-discs of the sarcomere will
about the ___________, decreasing
the strength of contraction greatly
ends of the myosin filaments
are where the actin filaments are
attached to.
z-discs
Muscle Contraction Requires ATP to perform Three Main Functions
- Most of the ATP is used to activate the walk-along mechanism of muscle contraction
- Active transport of calcium ions back into the sarcoplasmic reticulum causes contraction to
terminate. - Active transport of sodium and potassium ions
through the muscle fiber membrane maintains an
appropriate ionic environment for the propagation
of action potentials.
After the action potential, Calcium is
released from the sarcoplasmic reticulum to
the cytoplasm.
To terminate it, Calcium is actively ____________, stopping the contraction.
pumped back into the sarcoplasmic
reticulum
Active transport of sodium and potassium ions
through the muscle fiber membrane maintains an
appropriate _________ for the propagation
of action potentials.
ionic environment
The concentration of ATP in the muscle fiber is sufficient to maintain full contraction for only _________
1 to 2 seconds
There are several sources of energy for this rephosphorylation:
Phosphocreatine
The breakdown of glycogen
Oxidative metabolism
It carried high energy bonds similar to ATP, but have more free energy.
The released energy bonds inorganic
phosphate to ADP, reconstituting
ATP.
Phosphocreatine
Its combination with ATP is enough
for 5-8 seconds of maximal contraction.
Phosphocreatine
is broken into pyruvic acid
and lactic acid, which liberates
energy that is used to convert ADP
to ATP.
Glycogen
The Glycolytic reaction can happen
without oxygen, which makes it ____
faster
2.5x
It can sustain maximal contraction
for about 1 minute
The breakdown of glycogen
Occurs when oxygen reacts with foodstuffs (carbohydrates, fats,
proteins), liberating more ATP
Oxidative metabolism
95% of the energy for sustained
muscle contraction is derived from
here, hence our body’s high oxygen
need
Oxidative metabolism
Isometric Contractions Do Not Shorten Muscle,
whereas Isotonic Contractions
____
Shorten Muscle at a Constant Tension
occurs when the muscle does not shorten during contraction.
True ___________ cannot be generated in the intact body
because the so-called series elastic components
Isometric contraction
are the tendons,
sarcolemmal ends of muscle fibers, and
hinge arms of the myosin cross bridges
elastic components
occurs when the muscle shortens and the tension on the muscle remains
constant
Isotonic contraction
The characteristics of the isotonic
contraction depend on the ______against which the
muscle contracts, as well as on the ________
load
inertia of the load
Fast Fibers are Adapted for _______
Powerful Muscle Contractions
Slow Fibers
are Adapted for _______
Prolonged Muscle Activity
Skeletal muscles are composed of 2 fibers:
Some of the fibers in the
muscle can be between the 2 extremes.
Fast fibers
slow fibers
are smaller muscle fibers
- have high capillarity and large numbers of
mitochondria to support high levels of oxidative metabolism
Slow fibers (Type I, red muscle)
contain large amounts of myoglobin, which gives the slow muscle a reddish appearance
Slow fibers (Type I, red muscle)
The deficit of red
myoglobin in fast muscle provides the name
“white muscle”
are larger for greater strength of contraction.
- have extensive sarcoplasmic reticulum for
rapid release of calcium ions.
Fast fibers (Type II, white muscle)
have large amounts of glycolytic enzymes for
rapid release of energy.
- have lower capillarity and fewer
mitochondria because oxidative metabolism
is of secondary importance
Fast fibers (Type II, white muscle)
Mechanisms of Skeletal Muscle
Contraction Force Summation is the
Adding Together of ____________ to Increase the Intensity of
Overall Muscle Contraction
Individual Twitch
Contractions
Summation occurs in two ways:
- Multiple motor unit summation is when multiple units are stimulated.
- Frequency summation and tetanization.
is when
multiple units are stimulated.
Multiple motor unit summation
When the central
nervous system sends a WEAK SIGNAL to contract a muscle, the motor units in the muscle that contain the ____________
are stimulated in preference to the larger motor
units.
smallest and fewest muscle fibers
As the
frequency of muscle contraction increases,
there comes a point at which each new
contraction occurs before the preceding one has
ended.
Frequency summation and tetanization.
second contraction is added partially to the first one so that the total strength of contraction would rise progressively with _________
increasing frequency
When the frequency reaches the critical
level, _________ are going to fuse and action would tend to appear completely smooth
successive contractions
as a result of summation you will no longer see the small contractions as it will appear as ______
tetanization
is an Increase in the Total Mass of a Muscle;
in the presence of
activity
Muscle Hypertrophy
is a Decrease in the Mass
in the absence of activity or
stimulation
Muscle Atrophy
results from an increase in the
number of actin and myosin filaments in each muscle fiber.
When the number of contractile
proteins increases sufficiently, the myofibrils split
within each muscle fiber to form new myofibrils.
Muscle hypertrophy
- Enlargement of the muscle is dependent on protein synthesis.
- Great increase in number of additional
myofibrils causes muscle fibers to undergo hypertrophy
Muscle Hypertrophy
under very intensive trainings (eg.
endurance training) the total number of muscle
fibers also
increased
Skeletal muscles do not undergo cell division anymore (is partially correct),
however, these muscles contain a little bit of _________ within them but the regenerative capacity of it
is actually low similar to that of the brain as well as
the cardiac muscles.
stem cells
on the other hand, which lines the hollow organs can undergo cell division.
Smooth muscles
When a muscle remains unused
for a long period, the rate of decay of the contractile
proteins occurs more rapidly than the rate of
replacement
Muscle atrophy
Atrophy of the muscle begins almost immediately when the muscle loses its
nerve supply
nerves have charged
axon potentials which causes the
muscle tone
losing the nerve, the muscle does not receive a contractile signal anymore
that are required to maintain the normal
_____
muscle size
Each _______contains several hundred
to several thousand myofibrils
composed of about 1500 adjacent
myosin filaments and 3000 actin filaments
muscle fiber
contain only actin filaments
and are called I bands because they are isotropic to polarized light.
light bands
contain myosin filaments, as
well as the ends of the actin filaments where they overlap
the myosin,
they are
anisotropic to polarized light.
dark bands
small projections from the sides of the myosin filaments
cross-bridges
the ends of the actin filaments are attached to a
composed of filamentous proteins different from the actin and myosin
filaments, passes crosswise across the myofibril and also
crosswise from myofibril to myofibril, attaching the myofibrils to one another all the way across the muscle fiber
Z disk
The portion of the myofibril (or of the whole muscle
fiber) that lies between two successive Z disks is
sarcomere
The side-by-side relationship
between the myosin and actin filaments is maintained by
a large number of filamentous molecules of a protein
called _____
titin
molecular weight of about 3 million, which makes it one of the largest protein molecules in the body filamentous, it is very springy.
titin
The spaces
between the myofibrils are filled with intracellular fluid
called __________, containing large quantities of potassium, magnesium, and phosphate, plus multiple protein
enzymes.
sarcoplasm
is composed of 6 polypeptide chains—two heavy chains, each with a
molecular weight of about 200,000, and four light chains with molecular weights of about 20,000 each
myosin molecule
The two heavy chains wrap spirally around each other to form a double helix, which is called the ___________of the myosin molecule.
tail
One end of each of these chains is folded bilaterally
into a globular polypeptide structure called a
myosin head
Attached
intermittently along the sides of the tropomyosin molecules are additional protein molecules called
troponin
has a strong affinity for actin
troponin I
has a strong affinity for tropomyosin
troponin T
has a strong affinity for calcium ions
(troponin C)
When a muscle contracts, work is performed and energy is required.
Large amounts of ATP are cleaved to form ADP
during the contraction process, and the greater the
amount of work performed by the muscle, the greater the amount of ATP that is cleaved;
Fenn effect
is important because it allows the gradations of muscle
force during weak contraction to occur in small steps,
whereas the steps become progressively greater when
large amounts of force are required
size principle
When a
muscle begins to contract after a long period of rest, its initial strength of contraction may be as little as one half its strength 10 to 50 muscle twitches later.
That is, the strength of contraction increases to a plateau, a phenomenon called the
staircase effect, or treppe
Prolonged and strong contraction of a
muscle leads to the well-known state of
muscle fatigue
The study of different types of muscles,
lever systems, and their movements is called
kinesiology
This increase in fiber number is called fiber
hyperplasia
