L5: Skeletal muscle contraction Flashcards Preview

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Flashcards in L5: Skeletal muscle contraction Deck (35):

What is the epimysium?

CT surrounding entire muscle


What are muscles made up of?



What is the perimysium?

CT surrounding fascicles


What is a fascicle?

a bundle of myofibers


what is endomysium?

CT around each myofiber


What is the sarcolemma?

the cell membrane of the muscle fiber


What is a myofiber?

individual multinucleated muscle cell


what is a myofibril?

a chain of sarcomeres


what is a myofilament?

actin and myosin filaments that make up sarcomere


Sarcomeres are the functional component of the _____.



Describe the structural and molecular components of the sarcomere.

Sarcolemma = plasmalemma

T tubules - two per sarcomere, lie close to sarcoplasmic reticulum

Sarcoplasmic reticulum - equivalent to the endoplasmic reticulum

Z discs - anchor actin filament, at the end of each sarcomere

I bands - composed of actin, width changes during contraction

A bands- composed of actin and myosin, width does not change during contraction

H bands - composed of myosin, width changes during contraction


Which bands do and don't change in length during contraction?

I and H bands shorten
A band does not change


List sequence of event that occur between myosin and actin filaments during the contraction of a sarcomere.

Once calcium is bound to troponin
Tropomyosin uncover myosin binding sites on actin
ATPase heads of myosin molecule split ATP and bind to actin.
Stored energy in myosin head causes deformation that the thick and thin filaments slide past one another
A second ATP binds to myosin a causes it to release actin


why ATP is required in the contraction of a sarcomere?

contraction stops when ATP-dependent calcium pumps sequester calcium ion back into the SR


Describe the role of the t-tubules.

DHP channels on t-tubules interact with RyrR
Opening of RyR - release calcium
increases calcium concentration in cytosol


Describe role of calcium in muscle contraction.

Calcium travels through channels located in the t tubules
Causes increase in calcium ion conc. in the cytosol
Activation of sliding filament mechanism
Calcium binds to troponin
Contraction stops when calcium in sequestered back into the SR


Describe the function of SERCA and calsquestrian in controlling calcium concentration.

SERCA uses ATP to pump calcium back into the SR

Calsequestrin in the SR maintains an optium calcium concentration gradients to facilitate return of calcium to SR


Explain the function of DHP and ryanodine channels.

DHP is a voltage sensitive L type calcium channels
interacts with the ryanodine receptor
allow calcium to leave the SR


What is preload?

load on a muscle in the relaxed state (before it contracts)

Stretches the muscle which stretches the sarcomere
Generates passive tension in the muscle
The muscle resists the tension applied to it
The force of the resistance is measured as passive tension

The greater the preload, the greater the passive tension in muscle


What is after load?

load the muscle works against

If muscle generates MORE force than the afterload, an ISOTONIC contraction occurs
If muscle generates LESS force than the afterload, an ISOMETRIC contraction occurs


Differentiate between active and passive tension.

Passive: produced by the preload
Active: produced by cross-bridge cycling
Total: sum of active and passive tension


what is meant by cross-bridge cycling?

Contraction is the continuous cycling attaching and detaching.


Describe where ATP is required during muscle contraction.

Most used for sliding filament mechanism

Pumping calcium ions from sarcoplasm back into SR

Pumping sodium & potassium ions through the sarcolemma to reestablish resting potential


List the sources for rephosphorylation during muscle contraction.

Phosphocreatine release energy rapidly and reconstitutes ATP

ATP + phosphocreatine provides enough energy for 5-8 seconds of contraction


What is an isometric contraction?

contraction occurs when there is an increase in tension but not in length


what is an isotonic contraction?

muscle length changes in an isotonic contraction

Eccentric-contraction occurs when the muscle lengthens
Concentric-contraction occurs when the muscle shortens


characteristics of fast fibers

white fibers
Fast twitch fibers contract rapidly but have less endurance
Fewer mitochondria
Primarily use anaerobic respiration resulting in a buildup of pyruvic and lactic acid
Little myoglobin
Larger concentration of ATPase


characteristics of slow fibers.

red fibers
Slow twitch fibers contract more slowly but have more endurance
More mitochondria
Primarily use aerobic respiration
Smaller concentration of ATPase


Define motor unit.

a single nerve cell (neuron) may innervate from a few to several hundred myofibers


What is summation?

An additional spike can occur before the previous calcium ions have been returned to the SR
This increases the total amount of calcium ion in the cytosol and increase the rate of cycling between the myosin and actin cross bridges
This increases muscle tension
Each additional spike adds to the effects of the previous spikes


what is tetany?

If the frequency of spikes is fast enough, there is no time for relaxation between spikes
The muscle remains at maximal contraction


What are the three types of lever systems?

first class: fulcrum is in middle
second class: resistance (out-force) is in the middle
third class: effort (in-force) is in the middle


example of first class lever system.

raising chin using sternocleidomastoids
in force and out force move in opposite directions


example of second class lever system.

rising the body on the ball of the foot
both in and out force are on the same side of fulcrum


example of third class lever system.

lifting a weight in a the palm of your hand
both in and out force are on the same side of fulcrum and move in same direction