BIO 360 - Exam 2 - Chapter 12 Review Questions

Question 1

The three types of muscle tissue found in the human body are ______, ______, and______.Which type is attached to the bones, enabling it to control body movement?

Answer 1

smooth, cardiac, skeletal. Skeletal are attached to bones.

Question 2

Which two muscle types are striated?

Answer 2

cardiac and skeletal muscle

Question 3

Which type of muscle tissue is controlled only by somatic motor neurons?

Answer 3

skeletal muscle

Question 4

Arrange the following skeletal muscle components in order, from outermost to innermost: sarcolemma, connective tissue sheath, thick and thin filaments, myofibrils.

Answer 4

connective tissue, sarcolemma, myofibrils, thick and thin filaments

Question 5

The modified endoplasmic reticulum of skeletal muscle is called the ______.Its role is to sequester ______ ions.

Answer 5

sarcoplasmic reticulum; Ca2+ ions

Question 6

Which of the following statement(s) is (are) true about skeletal muscles?
(a) They constitute about 60% of a person’s total body weight.
(b) They position and move the skeleton.
(c) The insertion of the muscle is more distal or mobile than the origin.
(d) They are often paired into antagonistic muscle groups called flexors and extensors.

Answer 6

(a) false, (b) true, (c) true, (d) true

Question 7

T-tubules allow ______ ______ to move to the interior of the muscle fiber.

Answer 7

action potentials

Question 8

List six proteins that make up the myofibrils. Which protein creates the power stroke for contraction?

Answer 8

Actin, myosin, troponin, tropomyosin, titin, and nebulin. Myosin produces the power stroke.

Question 9

List the letters used to label the elements of a sarcomere. Which band has a Z disk in the middle? Which is the darkest band? Why? Which element forms the boundaries of a sarcomere? Name the line that divides the A band in half. What is the function of this line?
Briefly explain the functions of titin and nebulin.

Answer 9

Z disk—ends of a sarcomere. I band—Z disk in the middle. A band (thick filaments)—darkest; H zone—lighter region of A band. M line divides A band in half; thick filaments link to each other.

Question 10

Briefly explain the functions of titin and nebulin.

Answer 10

They keep actin and myosin in alignment. Titin helps stretched muscles return to resting length.

Question 11

During contraction, the ______ band remains a constant length. This band is composed primarily of ______ molecules. Which components of the sarcomere approach each other during contraction?

Answer 11

A band; myosin. Z disks approach each other.

Question 12

Explain the sliding filament theory of contraction.

Answer 12

Contraction occurs when thin and thick filaments slide past each other as myosin binds to actin, swivels, and pulls actin toward the center of the sarcomere.

Question 13

Explain the roles of troponin, tropomyosin, and Ca2+
in skeletal muscle contraction.

Answer 13

Ca2+ binds to troponin, which repositions tropomyosin, uncovering actin’s myosin-binding sites.

Question 14

Which neurotransmitter is released by somatic motor neurons?

Answer 14

Acetylcholine

Question 15

What is the motor end plate, and what kinds of receptors are found there? Explain how neurotransmitter binding to these receptors creates an action potential.

Answer 15

The region of a muscle fiber where the synapse occurs. Contains ACh receptors. Influx of Na+ through ACh receptor-channels depolarizes muscle.

Question 16

Match the following characteristics with the appropriate type(s) of muscle.

(a) has the largest diameter
(b) uses anaerobic metabolism, thus fatigues quickly
(c) has the most blood vessels
(d) has some myoglobin
(e) is used for quick, fine movements
(f) is also called red muscle
(g) uses a combination of oxidative and glycolytic metabolism
(h) has the most mitochondria

Question 17

A single contraction-relaxation cycle in a skeletal muscle fiber is known as a(n) ______.

Answer 17

twitch

Question 18

List the steps of skeletal muscle contraction that require ATP.

Answer 18

ATP binding—myosin dissociates from actin. ATP hydrolysis—myosin head swings and binds to a new actin. Release of Pi initiates the power stroke.

Question 19

The basic unit of contraction in an intact skeletal muscle is the ______.The force of contraction within a skeletal muscle is increased by ______ additional motor units.

Answer 19

motor unit, recruitment

Question 20

The two functional types of smooth muscle are ______ and ______.

Answer 20

single-unit (visceral) and multi-unit

Question 21

Make a map of muscle fiber structure using the following terms. Add terms if you like.
actin
Ca2+
cell
cell membrane
contractile protein
crossbridges
cytoplasm
elastic protein
glycogen
mitochondria
muscle fiber
myosin
nucleus
regulatory protein
sarcolemma
sarcoplasm
sarcoplasmic
titin
tropomyosin
troponin
t-tubul

Answer 21

Use Figs. 12.3 to 12.6.

Question 22

How does an action potential in a muscle fiber trigger a Ca2+
signal inside the fiber?

Answer 22

Action potential activates DHP receptors that open SR Ca2+ channels.

Question 23

Muscle fibers depend on a continuous supply of ATP. How do the fibers in the different types of muscle generate ATP?

Answer 23

Generate ATP by energy transfer from phosphocreatine. Oxidative fibers use oxygen to make ATP from glucose and fatty acids; glycolytic fibers get ATP primarily from anaerobic glycolysis.

Question 24

Define muscle fatigue. Summarize factors that could play a role in its development. How can muscle fibers adapt to resist fatigue?

Answer 24

Fatigue—a reversible state in which a muscle can no longer generate or sustain the expected force. May involve changes in ion concentrations, depletion of nutrients, or excitation-contraction coupling. Increase size and number of mitochondria or increase blood supply.

Question 25

Explain how you vary the strength and effort made by your muscles in picking up a pencil versus picking up a full gallon container of milk.

Answer 25

The body uses different types of motor units and recruits different numbers of motor units. Small movements use motor units with fewer muscle fibers; gross movements use motor units with more fibers.

Question 26

Compare and contrast the following in skeletal and smooth muscle: (a) cellular anatomy (b) neural and chemical control of contraction

Answer 26

See Tbl. 12.3.

Question 27

Arrange the following terms to create a map of skeletal muscle excitation, contraction, and relaxation. Terms may be used more than once. Add terms if you like. acetylcholine ACh receptor actin action potential ADP ATP axon terminal Ca2+ myosin Na+ neuromuscular junction Pi power stroke relaxation rigor state Ca2+-ATPase calcium-release channels contraction crossbridge DHP receptor end-plate potential exocytosis motor end plate sarcoplasmic reticulum somatic motor neuron tropomyosin troponin t-tubules voltage-gated Ca2+ channels

Answer 27

Use Figs. 12.8 to 12.10.

Question 28

What is the role of the sarcoplasmic reticulum in muscular contraction? How can smooth muscle contract when it has so little sarcoplasmic reticulum?

Answer 28

Stores and releases Ca2+ on command. Smooth muscle uses Ca2+ from the ECF.

Question 29

Compare and contrast: (a) fast-twitch oxidative-glycolytic, fast-twitch glycolytic, and slow-twitch muscle fibers (b) a twitch and tetanus (c) action potentials in motor neurons and action potentials in skeletal muscles (d) temporal summation in motor neurons and summation in skeletal muscles (e) isotonic contraction and isometric contraction (f) slow-wave and pacemaker potentials (g) the source and role of Ca2+ in skeletal and smooth muscle contraction.

Answer 29

(a) Fast-twitch oxidative-glycolytic—smaller, some myoglobin, use both oxidative and glycolytic metabolism, more fatigue-resistant. Fast-twitch glycolytic fibers—largest, rely primarily on anaerobic glycolysis, least fatigue-resistant. Slow-twitch—develop tension more slowly, maintain tension longer, the most fatigue-resistant, depend primarily on oxidative phosphorylation, more mitochondria, greater vascularity, large amounts of myoglobin, smallest in diameter. (b) Twitch—a single contraction-relaxation cycle. Tetanus—contraction with little to no relaxation. (c) Both result from inward Na+ current and outward K+ current through voltage-gated channels. Motor neuron action potential triggers ACh release. Muscle action potential triggers Ca2+ release from the sarcoplasmic reticulum. (d) Motor neuron temporal summation determines whether or not the neuron fires an action potential. Muscle cell summation increases force of contraction. (e) Isotonic contraction moves a load. Isometric contraction creates tension without moving a load. (f) Slow-wave potentials—cycles of depolarization and repolarization in smooth muscle cells. Pacemaker potentials—repetitive depolarizations to threshold in some smooth muscle and cardiac muscle. (g) Skeletal muscle—sarcoplasmic reticulum. Smooth muscle—ECF and sarcoplasmic reticulum.

Question 30

Explain the different factors that influence Ca2+ entry and release in smooth muscle fibers.

Answer 30

Ca2+ release from smooth muscle SR uses RyR and IP3-activated channels. Influx from ECF uses mechanically, chemically, or voltage-gated channels.

Question 31

One way that scientists study muscles is to put them into a state of rigor by removing ATP. In this condition, actin and myosin are strongly linked but unable to move. On the basis of what you know about muscle contraction, predict what would happen to these muscles in a state of rigor if you (a) added ATP but no free calcium ions; (b) added ATP with a substantial concentration of calcium ions.

Answer 31

(a) Adding ATP allows crossbridges to detach. If insufficient Ca2+ is available, the muscle will relax. (b) With ATP and Ca2+, the muscle will continue in the contraction cycle until it is completely contracted.

Question 32

When curare, a South American Indian arrow poison, is placed on a nerve-muscle preparation, the muscle does not contract when the nerve is stimulated, even though neurotransmitter is still being released from the nerve. Provide every possible explanation you can think of for the action of curare.

Answer 32

Curare must interfere with a process that follows ACh release: diffusion of ACh across the synaptic cleft, ACh binding to receptors, and opening of the receptor-channel. Curare binds to the ACh receptor and stops the channel from opening.