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A & P MASTERING: CHAPTER 9
Terms in this set (23)
Based on what you know of the relationship between the thick and the thin filaments, what would happen if a disorder existed that caused a person to produce no tropomyosin?
A) The muscle tissues would never be able to relax.
B) Actin will spontaneously fall apart.
C) The muscle would never contract.
D) The muscle would be weaker than normal.
The tropomyosin covers the myosin binding site on actin. Without tropomyosin, the myosin would constantly have access to those binding sites.
Which organelle can chemically regulate the shortening of the muscle?
A) the sarcolemma
B) the sarcoplasmic reticulum
C) the myofibril
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 degraded by acetylcholinesterase.
B) Acetylcholine is transported into the postsynaptic neuron by receptor-mediated endocytosis.
C) Acetylcholine diffuses away from the cleft.
D) Acetylcholine is transported back into the axon terminal by a reuptake mechanism.
Yes! Acetylcholinesterase is an enzyme that degrades acetylcholine. This degradation results in a rapid cessation of the acetylcholine signal and a swift removal from the cleft.
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) When the action potential reaches the end of the axon terminal, voltage-gated sodium channels open and sodium ions diffuse into the terminal.
D) Acetylcholine binds to its receptor in the junctional folds of the sarcolemma. Its receptor is linked to a G protein.
Yes! Acetylcholine is released into the synaptic cleft via exocytosis.
Action potentials travel the length of the axons of motor neurons to the axon terminals. These motor neurons __________.
A) extend from the brain or spinal cord to the sarcolemma of a skeletal muscle fiber
B) extend from the brain to the sarcolemma of a skeletal muscle fiber
C) extend from the spinal cord to the sarcolemma of a skeletal muscle fiber
D) arise in the epimysium of a skeletal muscle and extend to individual skeletal muscle fibers
Yes! The cell bodies of motor neurons to muscles in the head and neck are located in the brain. The cell bodies of motor neurons to the rest of our muscles are located in the spinal cord.
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) Acetylcholine is released into the cleft by active transporters in the plasma membrane of the axon terminal.
C) Cation channels open and sodium ions enter the axon terminal while potassium ions exit the axon terminal.
D) Acetylcholine binds to its receptor.
Yes! When synaptic vesicles fuse to the plasma membrane, acetylcholine is released via exocytosis.
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 calcium-release channels
D) the opening of ligand-gated anion channels
Yes! These channels permit sodium ions to diffuse inward and potassium ions to diffuse outward.
Sodium and potassium ions do not diffuse in equal numbers through ligand-gated cation channels. Why?
A) The outside surface of the sarcolemma is negatively charged compared to the inside surface. Sodium ions diffuse outward 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. Potassium ions diffuse outward along favorable chemical and electrical gradients.
D) The inside surface of the sarcolemma is negatively charged compared to the outside surface. Sodium ions diffuse inward along favorable chemical and electrical gradients.
Yes! The resting membrane potential of all cells is negative (inside compared to outside). Therefore, given the direction of the chemical and electrical gradients, more sodium ions diffuse inward than potassium ions diffuse outward.
The cross bridge cycle is a series of molecular events that occur after excitation of the sarcolemma. What is a cross bridge?
A) A myosin head bound to actin
B) Troponin bound to tropomyosin
C) Calcium bound to troponin
D) ATP bound to a myosin head
Yes! As soon as the activated myosin head forms a cross bridge with actin, the power stroke begins.
What structure is the functional unit of contraction in a skeletal muscle fiber?
A) The triad
B) The cross bridge
C) The sarcomere
D) The junctional folds of the sarcolemma
Yes! A sarcomere is a regular arrangement of thin and thick myofilaments that extends from one Z disc to the next. A myofibril consists of a series of sarcomeres.
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 transverse tubules.
D) Calcium ions are stored in the mitochondria.
Yes! Sarcoplasmic reticulum is the specific name given to the smooth endoplasmic reticulum in muscle fibers. The sarcoplasmic reticulum is very elaborate in skeletal muscle fibers, allowing for significant storage of calcium ions.
After a power stroke, the myosin head must detach from actin before another power stroke can occur. What causes cross bridge detachment?
A) Acetylcholine binds to receptors in the junctional folds of the sarcolemma.
B) ADP and inorganic phosphate are bound to the myosin head.
C) Calcium ions bind to troponin.
D) ATP binds to the myosin head.
Yes! The binding of ATP to the myosin head weakens the bond between myosin and actin, forcing the myosin head to detach. ATP also provides the energy for the next power stroke.
How does the myosin head obtain the energy required for activation?
A) The energy comes from oxidative phophorylation.
B) The energy comes from the hydrolysis of GTP.
C) The energy comes from the hydrolysis of ATP.
D) The energy comes from the direct phosphorylation of ADP by creatine phosphate.
Yes! Myosin is a large, complex protein with a binding site for actin. It also contains an ATPase. The energy released during the hydrolysis of ATP activates the myosin head.
What specific event triggers the uncovering of the myosin binding site on actin?
A) Calcium ions bind to troponin and change its shape.
B) Calcium release channels open in the sarcoplasmic reticulum, and calcium levels rise in the sarcoplasm.
C) Sodium ions bind to troponin and change its shape.
D) Calcium ions bind to tropomyosin and change its shape
Yes! The shape change caused by the binding of calcium to troponin shifts tropomyosin away from the myosin binding sites on actin.
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 ATP binds to the myosin head.
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 calcium ions are passively transported back into the sarcoplasmic reticulum.
Yes! The sarcoplasmic reticulum contains Ca2+-ATPases that actively transport Ca2+ into the SR. Without Ca2+, troponin returns to its resting shape, and tropomyosin glides over and covers the myosin binding sites on actin.
The interaction between which protein and ion initiates contraction of skeletal muscle?
A) troponin; calcium ions
B) myosin; sodium ions
C) tropomyosin; calcium ions
D) troponin; sodium ions
When calcium ions bind to troponin, troponin changes shape and moves tropomyosin away from its inhibitory position. As a result, the energized myosin heads can bind to the actin molecules and begin the cross bridge cycle, which shortens the muscle fiber.
Each neuron shown in this figure innervates a group of muscle fibers. What is the term for a group of muscle fibers innervated by a single neuron?
A) neuromuscular junction
D) motor unit
A group of muscle fibers innervated by a single neuron is called a motor unit.
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) wave summation
C) excitation-contraction coupling
Recruitment refers to the increased force generated by the activation of increasing numbers of motor units.
One action potential in a motor neuron causes the full reaction in skeletal muscle, which is called a twitch. One twitch can generate max tension in a muscle. Are these statements true or false?
A) The first statement is false; the second statement is true.
B) The first statement is true; the second statement is false.
C) Both of these statements are false.
D) Both statements are true.
One action potential causes a single muscle twitch. However, a single twitch would not generate any meaningful tension in a skeletal muscle.
Which muscle-fiber type is best suited for endurance activities, such as long-distance jogging?
A) slow glycolytic fibers
B) fast oxidative fibers
C) fast glycolytic fibers
D) slow oxidative fibers
Slow oxidative fibers are best suited for endurance activities because they produce ATP aerobically and are fatigue-resistant.
What feature of smooth muscle allows it to stretch without immediately resulting in a strong contraction?
A) slow, prolonged contractile activity
B) smooth muscle tone
C) low energy requirements
D) stress-relaxation response
Stretching of smooth muscle provokes contraction; however, the increased tension persists only briefly, and soon the muscle adapts to its new length and relaxes, while still retaining the ability to contract on demand. The stress-relaxation response of smooth muscle allows a hollow organ to fill or expand slowly to accommodate a greater volume without promoting strong contractions that would expel its contents.
Which of the following is true?
A) Smooth muscle lacks the thin and thick filaments characteristic of skeletal muscle.
B) Skeletal muscle lacks the coarse connective tissue sheaths that are found in smooth muscle.
C) Skeletal muscle fibers tend to be shorter than smooth muscle fibers.
D) Skeletal muscle fibers contain sarcomeres; smooth muscle fibers do not.
Skeletal muscle fibers contain sarcomeres (and are thus striated); smooth muscle fibers do not (and are thus nonstriated).
The mechanism of contraction in smooth muscle is different from skeletal muscle in that ________.
A) ATP energizes the sliding process
B) the site of calcium regulation differs
C) the trigger for contraction is a rise in intracellular calcium
D) actin and myosin interact by the sliding filament mechanism
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