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121 Cards in this Set

  • Front
  • Back

How much of the body is skeletal muscle?


How much of the body is smooth/cardiac muscle?


What is a bundle of muscle fibers called?

Muscle fasciculus ("little bundle")

What are the contractile subunits spanning the length of a muscle fiber called?


How much of the length of a muscle do the fibers typically span?

The whole thing

What is the thin membrane enclosing a skeletal muscle fiber?

The sarcolemma

What are the two layers of the sarcolemma?

The true cell membrane (plasma membrane)

Outer polysaccharide coat with collagen fibrils

How much actin and myosin are in each myofibril?

1500 myosin filaments

3000 actin filaments

(Just remember 2x as much actin)

What are the bands that contain only actin called?

I bands (are light)

What is found in I bands?

Actin only

What bands contain myosin filaments (with or without actin)?

A bands (are dArk)

What do A bands contain?

Myosin and likely some actin

What are the projections from the sides of myosin fibers called?


Contractions results from the interaction between what two structures in the skeletal muscle cells?

Myosin cross-bridges

Actin filaments

What are the ends of the actin filaments attached to?

The Z disc

What is the portion of the myofibril between Z discs?


How long is the sarcomere when the muscle is contracted?

2 micrometers

What protein keeps myosin and actin side by side?


Relatively speaking, how large are titin molecules?

Huge - one of the largest proteins in the body

What do the two ends of the titin attach to?

One end attaches to the Z disc

Other end attaches to the myosin thick filament

How does the titin molecule act during contraction?

Like a spring holding onto the myosin, changes length

What is the fluid in the space between the myofibrils?


What three ions are in abundance in the sarcoplasm?




What cellular component is found in abundance among the myofibrils?


What specialized organelle is found only in skeletal muscle, surrounding the myofibrils?

Sarcoplasmic reticulum

What neurotransmitter acts on the muscle fiber membrane?


What kind of gating do the muscle fiber membrane sodium channels have?


What happens to the action potential energy that flows into the center of the muscle fiber?

It causes the sarcoplasmic reticulum to release large quantities of Ca2+ ions

What ion is stored in the sarcoplasmic reticulum?


What role does the Ca2+ released by the sarcoplasmic reticulum have in muscle contraction?

Initiates the attractive forces between actin and myosin

How does the muscle fiber cell clear the Ca2+ that initiated contraction?

Ca2+ membrane pump returns it to the sarcoplasmic reticulum

What are the components of the myosin molecule?

Two heavy chains and four light chains

What do the two heavy chains of the myosin molecule create?

The tail

What do the two heavy chains and four light chains of the myosin come together to create?

The two heads

What forms the body of the myosin filament?

The tails of the myosin molecules

What creates the myosin filament cross-bridges?

The heads of the myosin molecules hanging out on their 'arms'

Where are the two hinges of the myosin cross-bridge?

1. Where the arm leaves the body of the myosin filament

2. Where the head attaches to the arm

How long is each myosin filament?

1.6 micrometers

How are the myosin cross-bridges arranged on the filament?

Twisted so each successive pair of bridges is 120 degrees from the last

What enzymatic activity does the myosin head display?

Functions as an ATPase enzyme

What molecule is the backbone of the actin filament?

A double-stranded helical F-actin protein molecule

What molecule serves as the active site on the actin filament?

ADP molecule attached to F-actin helix

Where is tropomyosin found?

Wrapped spirally around the F-actin helix, laying atop the active sites of the actin strand during rest

Where are troponin molecules found?

Attached to tropomyosin molecules

What is the structure of troponin and what do its subunits have affinities for?

Three loosely bound protein subunits

I subunit: affinity for actin

T subunit: affinity for tropomyosin

C subunit: affinity for calcium

Barring the influence of tropomyosin, what two molecules will cause instant binding between actin and myosin?

Magnesium and ATP

What is the function of tropomyosin?

Blocks the active sites on the actin strand

What role do calcium ions play in actin-myosin interaction?

They inhibit the tropomyosin's inhibitory behavior (i.e. they move it out of the way so the two can bind)

What is the theory behind how calcium inhibits tropomyosin?

Ca2+ binding with troponin C creates a conformational change that moves the tropomyosin out of the way

What is the prevailing theory for how actin and myosin strands cause muscle contraction? What is it called and what is its basic premise?

The "walk-along" theory; binding of actin and myosin causes changes in intramolecular forces between head and arm of crossbridge, which makes it tilt and drag the actin filament then break away and return to its original angle, where it finds a new active site to repeat the process.

What part of the myosin strand cleaves ATP?

The head

What initially happens to the ATP cleaved by the myosin head?

The ADP and phosphate stay bound to the head

What is the term for the conformational change in the myosin head that pulls on the actin strand?

Power stroke

What supplies energy for the power stroke stage of muscle contraction?

Stored energy from the cleaved ATP at the myosin head

At what point does the myosin head release the ADP and phosphate bound to it and what is the effect of this?

After the head of the cross-bridge tilts during the power stroke; this allows a new ATP to bind and the head to release from the actin

Where are the actin and myosin in relation to one another at the point of least tension on a muscle fiber?

Not overlapped at all

Where are the actin and myosin in relation to one another at the point of maximum tension on a muscle fiber?

When the actin has overlapped all of the myosin cross-bridges but hasn't yet reached center of myosin filament

When the actin and myosin are fully overlapped, what is the relative amount of tension on the muscle?

Not full tension, but not zero; diminished from peak

Explain this graph, briefly:

Explain this graph, briefly:

Muscles have fibers of different lengths, and sarcomeres in different parts of muscle do not always contract the same amount.

Sarcomeres at their normal resting length (2 micrometers) contract with maxiumum force.

Longer fibers have more tension at rest and do not increase tension as much during contraction.

How does the load on a muscle affect speed of contraction?

Increased load means decreased speed of contraction

Where does most of the ATP required for muscle contraction get used?

In the walk-along mechanism of the cross-bridges and the actin

What two ways does ATP assist in ion movement during muscle contraction?

1. Pumping calcium from sarcoplasm into sarcoplasmic reticulum

2. Pumping Na+/K+ through muscle fiber membrane to maintain ionic environment

What 3 ways does the muscle rephosphorylate ADP in order to sustain a contraction?

1. Phosphocreatinine (relatively little energy; 5-8 seconds' contraction worth)

2. Glycolysis of glycogen to pyruvic & lactic acid (about 1 minute of contraction time before end product buildup)

3. Oxidative metabolism (long-term)

What is the best-case efficiency of skeletal muscle?


What % velocity of maximum is generally the most efficient?


What is isometric contraction?

When muscle does not shorten during contraction

What is isotonic contraction?

When muscle shortens but tension remains constant

How fast, relatively speaking, are ocular muscles?


How fast, relatively speaking, are the soleus muscles?


What are two other names for slow fibers?

Type 1

Red muscle

What makes slow fibers red?

Myoglobin, which supports oxidative metabolism in the mitochondria

What are two other names for fast fibers?

Type II

White muscle

Slow or fast fibers: Smaller fibers


Slow or fast fibers: Innervated by smaller nerves


Slow or fast fibers: More extensive blood vessel system/capillaries


Slow or fast fibers: Greater numbers of mitochondria


Slow or fast fibers: Large amounts of myoglobin


Slow or fast fibers: Large fibers


Slow or fast fibers: Extensive sarcoplasmic reticulum


Slow or fast fibers: Large amounts of glycolytic enzymes


Slow or fast fibers: Less extensive blood supply


Slow or fast fibers: Fewer mitochondria


What do you call all of the muscle fibers innervated by a single nerve fiber?

Motor unit

What are characteristics of muscles with a low ratio of muscle fibers to muscle unit (i.e. high amount of innervating nerve fibers)?

Precise, detailed, fine motor skills, rapid reactions, etc.

What type of summation is an increase in the number of motor units contracting simultaneously?

Multiple fiber summation

What type of summation is an increase in the frequency of contraction?

Frequency summation

What is the size principle of multiple fiber summation?

Smaller, weaker motor units are stimulated first (by the smaller, more excitable nerve fibers) then as the signal increases, larger and stronger motor units are excited as well

What is tetanization?

When contractions become continuous and rapid enough that they 'fuse' together and the muscle contraction appears smooth/continuous

What causes tetanization?

Enough calcium ions are maintained in the sarcoplasm between action potentials that the contractile state is sustained

What is the maximum strength of tetanic contraction of a muscle at normal length?

50 pounds per square inch!

What is the staircase effect?

When a muscle contracts after rest, it may take 10-50 twitches to reach full strength

What causes the staircase effect?

Each twitch increases the calcium ion concentration in the cytosol due to lack of complete recapture by the sarcoplasm

What is the term for the amount of muscle tautness at rest?

Muscle tone

What causes skeletal muscle tone?

Low rate of nerve impulses coming from the spinal cord

What do we call the pairings of muscles that control every movement of the body?

Agonist and antagonist

How long does it take for a muscle to remodel to adjust to new requirements?

Often within a few weeks

What is an increase or decrease in muscle mass called?

Muscle hypertrophy or atrophy

Where is the extra mass coming from in muscle hypertrophy?

Increased actin and myosin fibers (fiber hypertrophy)

How does a muscle remodel to add length?

New sarcomeres are added to the end of the muscle fibers

How soon after muscle denervation does atrophy begin?


After how long will muscles not return to function even if nerve supply grows back?

1 to 2 years

How long does a nerve have to regrow if full muscle function is to be maintained?

Within 3 months

What happens in the final stage of denervation atrophy?

Muscle fibers are destroyed and replaced with fibrous and fatty tissue

What is the term describing when denervated muscle fibers are replaced with fibrous tissues that continue to shorten over many months?


What happens in rigor mortis?

Loss of ATP supply in death means cross-bridges cannot separate from actin until muscle proteins denature 15-25 hours later

How long can you use creatine-P for an energy source?

About 10 seconds

Why is creatine-P advantageous for energy source in the muscles?

It's a smaller molecule and moves faster to rephosphorylate in the mitochondria

What is creatinine?

Physiologically unused, nonenzymatic form of creatine-P (about 1.3% daily gets converted)

In what population would you expect higher creatinine levels?

Muscular, athletes, bodybuilders, etc

What does creatine kinase in the blood indicate?

Cellular damage

What are the three creatine kinases?

MM - skeletal muscle

MB - heart

BB - brain

What does elevated CK-MB indicate?

Damage to the cardiomyocytes

What causes the burning feeling during a workout?

Localized acidosis (the lactate actually buffers this and becomes lactic acid)

What causes soreness the day after heavier-than-usual muscle use?

Damage to nerve fibers

How many nuclei do muscle fibers have?

Many, around the edge of the cell

Why do muscle fibers have multiple nuclei?

Each one is responsible for a set volume to ensure protein synthesis is available

Is the gastrocnemius a fast or slow muscle?


Is the soleus a fast or slow muscle?

Slow - keeps us upright and stable when standing

What muscle motor units are recruited first/frequently - slow or fast twitch?

Slow (they better be fatigue resistant, they're always being used)

What has happened to the muscle fibers indicated?

What has happened to the muscle fibers indicated?


What has happened to the muscle fibers indicated by 1?

What has happened to the muscle fibers indicated by 1?

Denervated and reinnervated by a nerve that also innervates muscle fibers of the opposite type (slow vs fast) so they have "converted"