LS 7C Week 4.2 Launchpad

Muscle fibers generate maximum force: A. when the overlap between actin and myosin is minimal. B. at intermediate lengths. C. when pulled to long lengths before contraction. D. when the myosin filaments contact the Z discs. E. when contracting at short lengths.

B. at intermediate lengths.

ATP hydrolysis allows for what component of skeletal muscle contraction? A. the myosin head to bind to actin B. cocking of the myosin head to its high-energy position C. the reorientation of tropomyosin and troponin D. the actin head to bind to tropomyosin E. calcium levels in the cytoplasm to rise

B. cocking of the myosin head to its high-energy position

Muscle contractions have _____ force at slower shortening contraction velocities compared to higher shortening contraction velocities. A. less stable B. increased C. equal D. decreased

B. increased

A single motor neuron and the population of muscle fibers that it innervates is called a(n): A. excitation-contraction coupling. B. motor unit. C. motor endplate. D. twitch fiber. E. neuromuscular junction.

B. motor unit.

Tetanus is a(n): A. contraction where the muscle does not change length. B. muscle contraction of sustained force resulting from repeated action potentials. C. contraction that slowly increases in force. D. contraction caused by a single action potential. E. abnormal muscle contraction.

B. muscle contraction of sustained force resulting from repeated action potentials.

The power stroke corresponds to which event in muscle contraction? A. cocking of the myosin head B. sliding of actin relative to myosin filaments C. detachment of myosin from actin D. binding of the myosin head to actin

B. sliding of actin relative to myosin filaments

A researcher is comparing the size of sarcomeres in mice to those in elephants. What will he find? A. Sarcomere size is inversely proportional to animal size; sarcomeres in mice will be much larger than sarcomeres in elephants. B. It is impossible to determine sarcomere size in elephants and mice, given that sarcomeres are dynamic and are constantly changing in length and diameter. C. Sarcomere size is relatively constant in vertebrates. As a result, mouse and elephant sarcomeres will likely be equal in size. D. Sarcomere size is proportional to the size of the animal; sarcomeres of elephants will be much larger than sarcomeres in mice.

C. Sarcomere size is relatively constant in vertebrates. As a result, mouse and elephant sarcomeres will likely be equal in size.

What is a muscle fiber? A. a group of muscle cells that make up the same muscle group B. the connective tissue outer covering of a muscle C. a single cell of a muscle D. the myosin that makes up the contractile unit of a muscle cell

C. a single cell of a muscle

Vertebrate smooth muscle cells are activated when Ca+ binds to: A. myosin. B. myosin kinase. C. calmodulin. D. troponin. E. tropomyosin.

C. calmodulin.

Muscles produce higher forces when lengthening than when shortening. A. True B. False

A. True

When skeletal muscles contract such that bone segments move closer together, this action is known as: A. flexion. B. lengthening contraction C. tetanus. D. extension.

A. flexion.

What is the basic contracting unit of a skeletal muscle? A. sarcomere B. actin filament C. myofibril D. myosin

A. sarcomere

Skeletal muscle appears striated with light and dark regions. Which of the following is found in the dark regions? Choice A., actin and myosin Choice B., myosin and the Z disc Choice C., actin and the Z disc Choice D., thick filaments, but not the thin filaments

Choice A., actin and myosin

What is required to separate actin and myosin during sarcomere contraction? Choice A., ADP and Pi Choice B., ATP Choice C., Actin and myosin do not separate during sarcomere contraction.

Choice B., ATP

Which of the following is referred to as the power stroke? Choice A., the sliding of bundles of myosin along actin filaments Choice B., a conformational change in myosin , Choice C., the hydrolysis by myosin of ATD to ADP Choice D., the hydrolysis by actin of ATP to ADP

Choice B., a conformational change in myosin ,

The force generated by a long muscle varies as it contracts through its range of movement. At which point is the greatest force generated? Choice A., at the beginning of the contraction when the muscle is at its greatest length Choice B., in the middle of the contraction when the muscle is at an intermediate length. Choice C., near the end of the contraction when the degree of actin and myosin filament overlap is greatest, and the muscle is at its shortest length

Choice B., in the middle of the contraction when the muscle is at an intermediate length.

The cells that make up skeletal muscles are called: Choice A., muscle bundles. Choice B., muscle fibers. Choice C., myofibrils. Choice D., sarcomeres.

Choice B., muscle fibers.

Place the following events in muscle contraction in the correct sequence from first to last. 1. ATP binds to myosin head. 2. Myosin head interacts with actin. 3. ATP is converted to ADP and Pi. 4. Myosin head is cocked back. 5. Myosin head pivots in the power stroke. 6. ADP and Pi are released from myosin. Choice A., 1, 2, 3, 4, 5, 6 Choice B., 1, 2, 4, 3, 6, 5 Choice C., 1, 3, 6, 2, 4, 5 Choice D., 1, 3, 4, 2, 6, 5

Choice D., 1, 3, 4, 2, 6, 5

Which of the following is not true of muscle fibers? Choice A., Muscle fibers have more than one nucleus. Choice B., Actin and myosin filaments are arranged in parallel along the longitudinal axis on the myofibril. Choice C., Movement is generated by muscles when actin filaments interact with myosin filaments. Choice D., Many muscle fibers are packaged into a muscle fibril.

Choice D., Many muscle fibers are packaged into a muscle fibril.

Thick filaments are made of ______ and thin filaments are made of _____. Choice A., actin; myosin Choice B., actin; myostatin Choice C., myosin; myostatin Choice D., myosin; actin

Choice D., myosin; actin

The functional unit of skeletal muscles are called: Choice A., muscle bundles. Choice B., muscle fibers. Choice C., myofibrils. Choice D., sarcomeres.

Choice D., sarcomeres

The force generated by a muscle depends on: Choice A., the number of sarcomeres contracting. Choice B., the degree of overlap between actin and myosin in the sarcomeres. Choice C., the number of cross bridges between actin and myosin in the sarcomeres. Choice D., the amount of ATP available. Choice E., All of these responses are required for force generation.

Choice E., All of these responses are required for force generation.

Why is calcium necessary for muscle contraction? A. Calcium is needed to detach the myosin from the actin. B. Calcium is needed to allow the muscle fiber to become depolarized. C. Calcium is needed to cock the myosin head so that it can form a cross-bridge with actin. D. Calcium is needed to activate troponin so that tropomyosin can be moved to expose the myosin-binding sites on the actin filament. E. Calcium functions as a neurotransmitter and is released from the motor neuron.

D. Calcium is needed to activate troponin so that tropomyosin can be moved to expose the myosin-binding sites on the actin filament.

What stimulates a skeletal muscle cell to contract? A. auto-depolarizing cells in the membrane of muscle cells B. an impulse from a sensory neuron C. hormones D. an impulse from a motor neuron

D. an impulse from a motor neuron

During _____ bone segments rotate closer, whereas during _____ bone segments move further apart. A. rotation; flexion B. contraction; flexion C. contraction; extension D. flexion; extension E. extension; flexion

D. flexion; extension

Calcium is necessary to initiate muscle contraction. Which of the following molecules binds calcium? A. actin B. myosin C. tropomyosin D. troponin

D. troponin

You take a human smooth muscle cell and block the release of calcium from the sarcoplasmic reticulum. What effect does that have on contraction of that smooth muscle cell, and why? A. Contraction is completely blocked because calcium binding to troponin is required for contraction. B. Contraction still occurs because Ca2+ can enter the cell directly through Ca2+ channels in the plasma membrane and bind to troponin. C. Contraction is completely blocked because calcium binding to calmodulin is required for contraction. D. Contraction still occurs because contraction in smooth muscle is completely independent of Ca2+ levels. E. Contraction still occurs because Ca2+ can enter the cell directly through Ca2+ channels in the plasma membrane and bind to calmodulin.

E. Contraction still occurs because Ca2+ can enter the cell directly through Ca2+ channels in the plasma membrane and bind to calmodulin.