muscle contraction Flashcards by Milleth Jane CAPANGPANGAN

Muscle Contraction Occurs by a ________

Sliding
Filament Mechanism

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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

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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

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Calcium is supposed to be lower
intracellularly than extracellularly. But for _______its different and interesting

muscle

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Myosin Filaments are Composed of
Multiple ________

Myosin Molecules

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There are tails of myosin molecules bundle together to form the _______

body of the filament

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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

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Protruding arms + heads =

cross bridges

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An important feature of Myosin head functions as
an _________enzyme

adenosine triphosphatase

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the high energy currency of cells.

Adenosine triphosphate

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These myosin head function as ___________ which allows to cleave the adenosine
triphosphate and release energy to energized the
contraction process

adenosine
triphosphatase

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The other filament is the_____.

actin filament

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Actin Filaments are Composed of ______

Actin,
Tropomyosin
Troponin

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Remember the muscles particularly the actin, it is
supposed to interact with ______after.

myosin

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Each actin filament is about _______ long

1 micrometer

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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

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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

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The actin filament is inhibited by the __________ complex

troponin-tropomyosin

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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

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Inhibition by the troponin-tropomyosin complex –
prevents the ___________

actin myosin contraction

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Activation by _________ activate the
contraction

There is an inhibitory effect on the actin.

calcium ions

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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

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Calcium binds to Troponin C, pulls on the ____________, thereby allowing the binding
of your actin with your myosin.

tropomyosin

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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

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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

1. Most of the ATP is used to activate the walk-along mechanism of muscle contraction 2. Active transport of calcium ions back into the sarcoplasmic reticulum causes contraction to terminate. 3. 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:

1. Multiple motor unit summation is when multiple units are stimulated. 2. 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