Map #7

Front 1

Action potential propagation in a skeletal muscle fiber ceases when acetylcholine is removed from the synaptic cleft. Which of the following mechanisms ensures a rapid and efficient removal of acetylcholine?
a. Acetylcholine is transported back into the axon terminal by a reuptake mechanism.
b. Acetylcholine is transported into the postsynaptic neuron by receptor-mediated endocytosis.
c. Acetylcholine diffuses away from the cleft.
d. Acetylcholine is degraded by acetylcholinesterase.

Back 1

d. Acetylcholine is degraded by acetylcholinesterase.

Front 2

The neuromuscular junction is a well-studied example of a chemical synapse. Which of the following statements describes a critical event that occurs at the neuromuscular junction?
a. Acetylcholine is released and moves across the synaptic cleft bound to a transport protein.
b. When the action potential reaches the end of the axon terminal, voltage-gated sodium channels open and sodium ions diffuse into the terminal.
c. Acetylcholine binds to its receptor in the junctional folds of the sarcolemma. Its receptor is linked to a G protein.
d. Acetylcholine is released by axon terminals of the motor neuron.

Back 2

d. Acetylcholine is released by axon terminals of the motor neuron.

Front 3

Action potentials travel the length of the axons of motor neurons to the axon terminals. These motor neurons __________.

Back 3

extend from the brain or spinal cord to the sarcolemma of a skeletal muscle fiber

Front 4

Calcium entry into the axon terminal triggers what events?

Back 4

Synaptic vesicles fuse to the plasma membrane of the axon terminal and release acetylcholine.

Front 5

Acetylcholine binds to its receptor in the sarcolemma and triggers __________.

Back 5

the opening of ligand-gated cation channels

Front 6

Sodium and potassium ions do not diffuse in equal numbers through ligand-gated cation channels. Why?

Back 6

The inside surface of the sarcolemma is negatively charged compared to the outside surface. Sodium ions diffuse inward along favorable chemical and electrical gradients.

Front 7

Excitation-contraction coupling is a series of events that occur after the events of the neuromuscular junction have transpired. The term excitation refers to which step in the process?

Back 7

Excitation, in this case, refers to the propagation of action potentials along the sarcolemma.

Front 8

Excitation of the sarcolemma is coupled or linked to the contraction of a skeletal muscle fiber. What specific event initiates the contraction?

Back 8

Calcium release from the sarcoplasmic reticulum initiates the contraction.

Front 9

A triad is composed of a T-tubule and two adjacent terminal cisternae of the sarcoplasmic reticulum. How are these components connected?

Back 9

A series of proteins that control calcium release.

Front 10

What is name given to the regularly spaced infoldings of the sarcolemma?

Back 10

transverse or T tubules

Front 11

Which of the following is most directly responsible for the coupling of excitation to contraction of skeletal muscle fibers?

Back 11

Calcium ions

Front 12

The cross bridge cycle is a series of molecular events that occur after excitation of the sarcolemma. What is a cross bridge?

Back 12

A myosin head bound to actin

Front 13

What structure is the functional unit of contraction in a skeletal muscle fiber?

Back 13

The sarcomere

Front 14

Calcium ions couple excitation of a skeletal muscle fiber to contraction of the fiber. Where are calcium ions stored within the fiber?

Back 14

Calcium ions are stored in the sarcoplasmic reticulum.

Front 15

After a power stroke, the myosin head must detach from actin before another power stroke can occur. What causes cross bridge detachment?

Back 15

ATP binds to the myosin head

Front 16

How does the myosin head obtain the energy required for activation?

Back 16

The energy comes from the hydrolysis of ATP.

Front 17

What specific event triggers the uncovering of the myosin binding site on actin?

Back 17

Calcium ions bind to troponin and change its shape.

Front 18

When does cross bridge cycling end?

Back 18

Cross bridge cycling ends when sufficient calcium has been actively transported back into the sarcoplasmic reticulum to allow calcium to unbind from troponin.

Front 19

What causes the release of calcium from the terminal cisternae of the sarcoplasmic reticulum within a muscle cell?

Back 19

arrival of an action potential

Front 20

The binding of calcium to which molecule causes the myosin binding sites to be exposed?

Back 20

troponin

Front 21

A myosin head binds to which molecule to form a cross bridge?

Back 21

myosin

Front 22

What causes the myosin head to disconnect from actin?

Back 22

binding of ATP

Front 23

What energizes the power stroke?

Back 23

hydrolysis of ATP

Front 24

What is the role of calcium in the cross bridge cycle?

Back 24

Calcium binds to troponin, altering its shape.

Front 25

What role does tropomyosin play in the cross bridge cycle?

Back 25

The displacement of tropomyosin exposes the active sites of actin, allowing cross bridges to form.

Front 26

How does troponin facilitate cross bridge formation?

Back 26

Troponin controls the position of tropomyosin on the thin filament, enabling myosin heads to bind to the active sites on actin.

Front 27

What, specifically, is a cross bridge?

Back 27

myosin binding to actin

Front 28

What event causes cross bridge detachment?

Back 28

ATP binding to the myosin head

Front 29

Where in the cross bridge cycle does ATP hydrolysis occur?

Back 29

during the cocking of the myosin head

Front 30

How/when does the myosin head cock back to store energy for the next cycle?

Back 30

ATP hydrolysis is used to re-cock the myosin head.

Front 31

BMD (2,3-butanedione 2-monoximime) inhibits myosin, such that ATP can bind to myosin but myosin is unable to hydrolyze the bound ATP. What effect would BMD have on the cross bridge cycle?

Back 31

Myosin heads would remain detached, unable to cock.

Front 32

During contraction, what prevents actin myofilaments from sliding backward when a myosin head releases?

Back 32

There are always some myosin heads attached to the actin myofilament when other myosin heads are detaching.

Front 33

Which muscle fiber type is best suited for endurance activities?

Back 33

slow oxidative fibers

Front 34

Which of the following is not a usual result of resistance exercise?

a. increase in the number of myofibrils within the muscle cells

b. increase in the efficiency of the circulatory system

c. increase in the efficiency of the respiratory system

d. increase in the number of muscle cells

Back 34

d. increase in the number of muscle cells

Front 35

Myoglobin ________.

Back 35

stores oxygen in muscle cells

Front 36

Immediately following the arrival of the stimulus at a skeletal muscle cell there is a short period called the ________ period during which the events of excitation-contraction coupling occur.

Back 36

latent

Front 37

Creatine phosphate functions in the muscle cell by ________.

Back 37

storing energy that will be transferred to ADP to resynthesize ATP

Front 38

Rigor mortis occurs because _____.

Back 38

no ATP is available to release attached actin and myosin molecules

Front 39

During vigorous exercise, there may be insufficient oxygen available to completely break down pyruvic acid for energy. As a result, the pyruvic acid is converted to ________.

Back 39

lactic acid

Front 40

An anaerobic metabolic pathway that results in the production of two net ATPs per glucose plus two pyruvic acid molecules is ________.

Back 40

glycolysis

Front 41

After nervous stimulation stops, what prevents ACh in the synaptic cleft from continuing to stimulate contraction?

Back 41

acetylcholinesterase destroying the ACh

Front 42

Three discrete types of muscle fibers are identified on the basis of their size, speed, and endurance. Which of the following athletic endeavors best represents the use of red fibers?

Back 42

a long, relaxing swim

Front 43

Hypothetically, if a muscle were stretched to the point where thick and thin filaments no longer overlapped, ________.

Back 43

no muscle tension would be generated

Front 44

What part of the sarcolemma contains acetylcholine receptors?

Back 44

motor end plate

Front 45

True/False: Once a motor neuron has fired, all the muscle fibers in a muscle contract.

Back 45

False

Front 46

True/False: The force of muscle contraction is controlled by multiple motor unit summation or recruitment.

Back 46

True

Front 47

The H zone contains

Back 47

thick filaments

Front 48

The tension generated in a muscle fiber is directly proportional to the

Back 48

number of cross bridges formed

Front 49

Each myosin head has

Back 49

a binding site for an ATP molecule and for an actin molecule, and the ability to swivel when powered by ATP.

Front 50

The contraction cycle is triggered by the rise in __________ released from the SR.

Back 50

Ca2+

Front 51

Within a single fiber, the tension developed during a twitch depends on

Back 51

the length of the sarcomeres prior to contraction

Front 52

When comparing complete tetanus with unfused tetanus, which is true?

Back 52

In complete tetanus, no relaxation occurs between stimuli, maximum tension is developed, and the muscle fiber is stimulated at a higher frequency.

Front 53

A motor unit consists of

Back 53

one neuron and the muscle fibers it controls

Front 54

In muscles used for fine actions, such as controlling eye movement or use of the hand, a motor unit will have __________ muscle fibers when compared to a motor unit in muscles used for power and strength.

Back 54

very few

Front 55

Asynchronous recruitment

Back 55

helps avoid fatigue during sustained muscle contractions, refers to different motor units taking turns maintaining muscle tension, and makes an entire muscle seem to contract smoothly.

Front 56

The force generated by a single muscle fiber

Back 56

can be increased by increasing the frequency of action potentials and due to summation.

Front 57

A muscle fiber develops its maximum tension when it is in what position at the moment it is stimulated?

Back 57

at its typical resting length