Introduction to Muscle Contraction

Question 1

A complex consisting of a T tubule and usually two small cisternae of sarcoplasmic reticulum is known as a _______________

Answer 1

Triad

Question 2

At the __________, depolarization of the sarcolemma-derived T tubules is transmitted to the sarcoplasmic reticulum membrane

Answer 2

Triad

Question 3

Muscle contraction depends on the availability of _____________ and its relaxation is related to the absence of ____________

Answer 3

Calcium ions

Calcium ions

Question 4

The sarcoplasmic reticulum specifically regulates ___________ flow, which is necessary for rapid contraction and relaxation cycles

Answer 4

Calcium

Question 5

What neutransmitter stiumlates a nerve impluse?

Answer 5

Acetylcholine

Question 6

There are three overall steps to muscle contraction:

1. Neurally mediated depolarization of the __________________
2. ______________ are passively released into the vicinity of overlapping thick and thin filaments
3. ______________ binds to ________________, allowing actin and myosin to bridge together

Answer 6

Sarcoplasmic reticulum

Calcium

Calcium

Troponin

Question 7

Initiation of the nerve impulse:

A nerve impulse triggers release of ___________________ from the synaptic knob inAto the synaptic cleft. This neurotransmitter then binds to its receptors in the ____________________ of the neuromuscular junction, initiating a muscle impulse in the __________________ of the muscle fiber

As the muscle impulse spreads quickly from the ___________________ along ___________________, _____________________ ions are released from terminal cisternae into the sarcoplasm

Answer 7

Acetylcholine

Motor end plate

Sarcolemma

Sarcolemma

T-tubules

Calcium

Question 8

Muscle contraction:

________________ ions bind to ___________________, which changes shape and moves ____________________ onto actin. This exposes active sites on actin molecules so that __________________ heads of thick filaments can attach to the exposed active sites, forming ______________________

As __________________ heads pivot, the thin filaments move toward the __________________ center. _________ binds myosin heads and is broken down into ______________ at which point the myosin heads detach from the filaments and return to their pre-pivot position

Answer 8

Calcium

Troponin

Tropomyosin

Myosin

Crossbridges

Myosin

Sarcomere

ATP

ADP and P

Question 9

The power stroke: __________ is released from the sarcoplasmic reticulum where it binds to ________________, which changes conformation and pulls _____________ away so as to expose _____________-binding sites on the actin filament. __________ ____________ bind to actin, which releases its _______. In the __________________, the myosin head changes conformation and the thick and thin filaments slide past each other. _______ binds to myosin, casuing myosin to release actin.

If calcium is returned to the sarcoplasmic reticiulum, the muscle relaxes; if calcium remains available, the cycle repeats

Answer 9

Calcium

Troponin

Tropomyosin

Myosin-binding sites

Myosin heads

ADP

Power stroke

ATP

Question 10

___________________ sarcomeres consist of partially overlapping thick and thin filaments

Answer 10

Resting

Question 11

_______________ sarcomeres consist of increased overlap between thick and thin filaments

Answer 11

Contracting

Question 12

During muscle contraction, do thick or thin filaments change their lengths?

Answer 12

No; contraction is the result of an increase in the amount of overlap between the filaments caused by the sliding of thin and thick filaments past one another

Question 13

Contraction is induced by an _________________ produced at a ___________________, the neuromuscular junction, between the muscle fiber and terminus of a motor axon

Answer 13

Action potential

Synpase

Question 14

What visible changes result when a muscle becomes contracted?

Answer 14

The I band decreases in size

the H zone becomes significantly contracted and can be used to identify quickly whether a sarcomere is relaxed or contracted

Question 15

During contraction the ____________ decreases in size as thin filaments penetrate the _____________

Answer 15

I band
A band

Question 16

During contraction, the ___________, part of the _________ with only thick filaments, diminishes in width as the thin filament completely overlap the thick filaments

Answer 16

H band

A band

Question 17

The net result of contraction is that each sarcomere and subsequent muscle cell (fiber) is greatly ___________________

Answer 17

Shortened

Question 18

Where does the neural signal for contraction come from?

Answer 18

Neuromuscular junction or the motor end-plate

Question 19

At the synaptic cleft, the sacrolemma has numerous deep folds to increase the _______________ available to receive chemical transmitting signals

Answer 19

Surface area

Question 20

Muscle Tissue Innervation Steps #1 - 4:

1. The action potential reaches the _______________
2. ______________ is released from the axon terminal
3. This neurotransmitter diffuses across the synaptic celft and binds its receptors in the folded _____________
4. Binding of the neurotransmitter opens _______ changes in the sacrolema and produces membrane depolarization

Answer 20

Motor end plate

Acetylcholine

Sarcolemma

Na+

Question 21

Muscle Tissue Innervation Steps #5 - 7

5. Depolarization initated at the motor end-plate is _____________ along the surface
6. The signal is passed to the ___________________ a, which releases ______________ that initate the contraction cycle
7. When depolarization ceases, the _____________ is actively transported back into the sarcoplasmic reticulum cisternae and the muscle relaxes

Answer 21

Propagated

Sarcoplasmic reticulum

Calcium ions

Calcium ions

Question 22

A single nerve fiber or ____________ can innervate one muscle fiber or branch and innervate hundred of fibers

Answer 22

Axon

Question 23

A single nerve fiber and all of the muscle fibers it innervates is called a _____________________

Answer 23

Motor unit

Question 24

Do individual striated muscle fivers should graded contraction?

Answer 24

No, they contract either all the way or not at all

Question 25

What do we mean by varied force?

Answer 25

Fibers within a muscle bundle do not all contract at the same time; since muscles are composed of many motor units, the firing of a single motor axon will generate tension proportional to the number of muscle fibers innervated by that axon