Assignment 10 (Chapter 9)

The connective tissue that covers the epimysium is continuous with which of the following? A. tendon B. sarcolemma C. endomysium D. ligament

What corresponds to a single fascicle? A. Epimysium B. Fascicle C. Muscle fiber D. myofibril

Myofilament with a knob-like head?

Myofilament stiffened and stabilized by tropomyosin?

The cytoplasm of a skeletal muscle fiber?

Bundle of skeletal muscle fibers enclosed by connective tissue called perimysium?

Membrane of muscle cell?

Blocks myosin-binding sites on actin?

Long cylindrical cells?

Contractile unit?

Made up of several sacromeres?

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 diffuses away from the cleft. B. Acetylcholine is transported back into the axon terminal by a reuptake mechanism. C. Acetylcholine is transported into the postsynaptic neuron by receptor-mediated endocytosis. D. Acetylcholine is degraded by acetylcholinesterase.

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. Acetylcholine is released by axon terminals of the motor neuron. C. Acetylcholine binds to its receptor in the junctional folds of the sarcolemma. Its receptor is linked to a G protein. D. When the action potential reaches the end of the axon terminal, voltage-gated sodium channels open and sodium ions diffuse into the terminal.

Action potentials travel the length of the axons of motor neurons to the axon terminals. These motor neurons __________. A. extend from the spinal cord to the sarcolemma of a skeletal muscle fiber B. arise in the epimysium of a skeletal muscle and extend to individual skeletal muscle fibers C. extend from the brain or spinal cord to the sarcolemma of a skeletal muscle fiber D. extend from the brain to the sarcolemma of a skeletal muscle fiber

Calcium entry into the axon terminal triggers which of the following events? A. Synaptic vesicles fuse to the plasma membrane of the axon terminal and release acetylcholine. B. Cation channels open and sodium ions enter the axon terminal while potassium ions exit the axon terminal. C. Acetylcholine is released into the cleft by active transporters in the plasma membrane of the axon terminal. D. Acetylcholine binds to its receptor.

Acetylcholine binds to its receptor in the sarcolemma and triggers __________. A. the opening of ligand-gated cation channels B. the opening of voltage-gated calcium channels C. the opening of ligand-gated anion channels D. the opening of calcium-release channels

Sodium and potassium ions do not diffuse in equal numbers through ligand-gated cation channels. Why? A. The inside surface of the sarcolemma is negatively charged compared to the outside surface. Sodium ions diffuse inward along favorable chemical and electrical gradients. B. The inside surface of the sarcolemma is negatively charged compared to the outside surface. Potassium ions diffuse inward along favorable chemical and electrical gradients. C. The outside surface of the sarcolemma is negatively charged compared to the inside surface. Sodium ions diffuse outward along favorable chemical and electrical gradients. D. The outside surface of the sarcolemma is negatively charged compared to the inside surface. Potassium ions diffuse outward along favorable chemical and electrical gradients.

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? A. Excitation, in this case, refers to the propagation of action potentials along the sarcolemma. B. Excitation refers to the shape change that occurs in voltage-sensitive proteins in the sarcolemma. C. Excitation refers to the propagation of action potentials along the axon of a motor neuron. D. Excitation refers to the release of calcium ions from the sarcoplasmic reticulum.

Excitation of the sarcolemma is coupled or linked to the contraction of a skeletal muscle fiber. What specific event initiates the contraction? A. Voltage-sensitive proteins change shape. B. Calcium release from the sarcoplasmic reticulum initiates the contraction. C. Sodium release from the sarcoplasmic reticulum initiates the contraction. D. Action potentials propagate into the interior of the skeletal muscle fiber.

A triad is composed of a T-tubule and two adjacent terminal cisternae of the sarcoplasmic reticulum. How are these components connected? A. Potassium leak channels. B. Voltage-gated sodium channels. C. A series of proteins that control calcium release. D. Myosin cross-bridge binding sites.

What is name given to the regularly spaced infoldings of the sarcolemma? A. sarcoplasmic reticulum B. transverse or T tubules C. terminal cisternae D. motor endplates

Which of the following is most directly responsible for the coupling of excitation to contraction of skeletal muscle fibers? A. Calcium ions. B. Acetylcholine. C. Action potentials. D. Sodium ions.

What is the relationship between the number of motor neurons recruited and the number of skeletal muscle fibers innervated? A. A motor neuron typically innervates only one skeletal muscle fiber. B. A skeletal muscle fiber is innervated by multiple motor neurons. C. Motor neurons always innervate thousands of skeletal muscle fibers. D. Typically, hundreds of skeletal muscle fibers are innervated by a single motor neuron.

The cross bridge cycle is a series of molecular events that occur after excitation of the sarcolemma. What is a cross bridge? A. ATP bound to a myosin head B. Troponin bound to tropomyosin C. Calcium bound to troponin D. A myosin head bound to actin

What structure is the functional unit of contraction in a skeletal muscle fiber? A. The triad B. The cross bridge C. The junctional folds of the sarcolemma D. The sarcomere

Calcium ions couple excitation of a skeletal muscle fiber to contraction of the fiber. Where are calcium ions stored within the fiber? A. Calcium ions are stored in the nuclei. B. Calcium ions are stored in the sarcoplasmic reticulum. C. Calcium ions are stored in the mitochondria. D. Calcium ions are stored in the transverse tubules.

After a power stroke, the myosin head must detach from actin before another power stroke can occur. What causes cross bridge detachment? A. Calcium ions bind to troponin. B. Acetylcholine binds to receptors in the junctional folds of the sarcolemma. C. ATP binds to the myosin head. D. ADP and inorganic phosphate are bound to the myosin head.

How does the myosin head obtain the energy required for activation? A. The energy comes from the direct phosphorylation of ADP by creatine phosphate. B. The energy comes from oxidative phophorylation. C. The energy comes from the hydrolysis of GTP. D. The energy comes from the hydrolysis of ATP.

What specific event triggers the uncovering of the myosin binding site on actin? A. Calcium release channels open in the sarcoplasmic reticulum, and calcium levels rise in the sarcoplasm. B. Calcium ions bind to troponin and change its shape. C. Calcium ions bind to tropomyosin and change its shape. D. Sodium ions bind to troponin and change its shape.

When does cross bridge cycling end? A. Cross bridge cycling ends when calcium release channels in the sarcoplasmic reticulum open. B. Cross bridge cycling ends when calcium ions are passively transported back into the sarcoplasmic reticulum. C. Cross bridge cycling ends when sufficient calcium has been actively transported back into the sarcoplasmic reticulum to allow calcium to unbind from troponin. D. Cross bridge cycling ends when ATP binds to the myosin head.

The development of tension in a muscle, in response to a single stimulus above threshold, is called A. a muscle twitch B. wave summation. C. tetanus. D. a contraction.

Which of the following is NOT associated with the latent phase of a muscle twitch? A. propagation of impulse along T tubules B. formation of first myosin-actin cross bridges C. release of calcium from SR D. sliding of myofilaments

If both of the neurons in the figure were activated, more muscle fibers would contract than if either neuron alone were active. This mechanism for control of the force of muscle contraction is known as ______. A. tetanus. B. wave summation. C. excitation-contraction coupling. D. recruitment.

Which of the following describes the motor neuron of a skeletal muscle? A. autonomic motor neurons B. somatic motor neurons C. sensory neurons

With rapid, multiple stimulations, the contractions fuse into a smooth, continuous contraction.What is this stage called? A. Recruitment B. Treppe C. Latent period D. Complete tetanus E. Temporal summation

Which of the following represents the first supply of high energy phosphate bonds available for ATP regeneration during muscle activity? A. Krebs cycle B. glycolysis C. creatine phosphate D. oxidative phosphorylation

In the body, recruitment of more muscle units within a muscle during a contraction is achieved by? A. increasing the frequency of stimulation of each muscle fiber. B. stimulation by an increasing number of motor units. C. increasing the strength of the action potentials delivered by each motor neuron.

Maximal contractile force is generated in a muscle under which of the following conditions?A. moderately stretched B. overstretched C. unstretched

The increasing contractile force of a muscle produced as the frequency of stimulation is increased can most directly be attributed to? A. increasing amounts of calcium released into the sarcoplasm of affected muscle fibers. B. increasing amounts of myosin and actin synthesized within affected muscle fibers. C. an increasing number of muscle fibers affected by the stimulatory events. D. generation of stronger action potentials along the sarcolemma of affected muscle fibers.

Which of these serves as a source of glucose utilized during muscle activity? A. myoglobin B. glycogen C. lactic acid D. ATP

Which of the following binds oxygen and therefore increase the amount of oxygen available to skeletal muscle tissues? A. glycogen B. tropomyosin C. ATP D. myosin E. myoglobin

White muscle fibers are also refered to as A. smooth muscle fibers B. slow-twitch fibers C. oxidative fibers D. glycolytic fibers

What is a cross bridge cycle? A. It is the cycle in which an energized myosin head binds to actin and performs a power stroke, then binds to ATP in order to detach and re-energize. B. It is the cycle in which motor units are recruited from small to large, in order to produce gradual increases in force. C. It is a cycle of repeated stimuli resulting in summation of muscle twitches. D. It is the cycle by which the sarcolemma is repeatedly depolarized and repolarized.

Which protein inhibits interaction between actin and myosin to prevent skeletal muscle contraction; and which ions remove the inhibition? A. actin; calcium ions B. myosin; sodium ions C. troponin; sodium ions D. tropomyosin; calcium ions

Which of the following is TRUE? A. Skeletal muscle cells have one nucleus, but smooth muscle cells are multinucleated. B. Skeletal muscle fibers contain sarcomeres; smooth muscle fibers do not. C. Skeletal muscle lacks the coarse connective tissue sheaths that are found in smooth muscle. D. Skeletal muscle fibers tend to be shorter than smooth muscle fibers.

Maximal contractile force is generated in a muscle under which of the following conditions? A. moderately stretched B. overstretched C. unstretched