MUSCLE TISSUE

Question 1

The fourth basic tissue type with epithelia, connective tissues, and nervous tissue, is composed of cells that optimize the universal cell property of ______.

Answer 1

contractility

Question 2

As in all cells, ______ and associated ______ generate the forces necessary for the muscle contraction, which drives movement within organ systems, of blood, and of the body as a whole.

Answer 2

actin microfilaments, proteins

Question 3

Essentially all muscle cells are of ______ origin and differentiate by a gradual process of cell lengthening with abundant synthesis of the myofibrillar proteins ______ and ______.

Answer 3

mesodermal, actin, myosin

Question 4

Three types of muscle tissue can be distinguished on the basis of ______ and ______ characteristics, with the structure of each adapted to its ______ role.

Answer 4

morphologic, functional, physiologic

Question 5

THREE TYPES OF MUSCLE TISSUE:

Answer 5

Skeletal muscle
Cardiac muscle
Smooth muscle

Question 6

THREE TYPES OF MUSCLE TISSUE:

______ contains bundles of very long, multi- nucleated cells with cross-striations.

Answer 6

Skeletal muscle

Question 7

THREE TYPES OF MUSCLE TISSUE:

______ - Their contraction is quick, forceful, and usually under voluntary control.

Answer 7

Skeletal muscle

Question 8

THREE TYPES OF MUSCLE TISSUE:

______ also has cross-striations and is composed of elongated, often branched cells bound to one another at structures called intercalated discs which are unique to cardiac muscle. Contraction is involuntary, vigorous, and rhythmic.

Answer 8

Cardiac muscle

Question 9

THREE TYPES OF MUSCLE TISSUE:

______ consists of collections of fusiform cells which lack striations and have slow, involuntary contractions.

Answer 9

Smooth muscle

Question 10

In all types of muscle, contraction is caused by the sliding interaction of thick ______ along thin ______.

Answer 10

myosin filaments, actin filaments

Question 11

The forces necessary for sliding are generated by other proteins affecting the weak interactions in the bridges between ______ and ______.

Answer 11

actin, myosin

Question 12

As with neurons, muscle specialists refer to certain muscle cell ______ with special names.

Answer 12

organelles

Question 13

The cytoplasm of muscle cells is often called ______, the smooth ER is the ______, and the muscle cell membrane and its external lamina are the ______.

Answer 13

sarcoplasm, sarcoplasmic reticulum, sarcolemma

Question 14

The variation in ______ of muscle fibers depends on factors such as the specific muscle, age, gender, nutritional status, and physical training of the individual.

Answer 14

diameter

Question 15

Exercise enlarges the skeletal musculature by stimulating formation of new ______ and growth in the diameter of individual ______.

This process, characterized by increased cell volume, is called ______.

Answer 15

myofibrils, muscle fibers, hypertrophy

Question 16

Tissue growth by an increase in the number of cells is termed ______, which takes place very readily in smooth muscle, whose cells have not lost the capacity to divide by mitosis.

Answer 16

hyperplasia

Question 17

______ consists of muscle fibers, which are long, cylindrical multinucleated cells with diameters of ______-______ μm.

Answer 17

Striated muscle, 10, 100

Question 18

During ______ muscle development, ______ fuse, forming ______ with many nuclei.

Answer 18

embryonic, mesenchymal myoblasts, myotubes

Question 19

______ then further differentiate to form striated muscle fibers.

Answer 19

Myotubes

Question 20

Elongated nuclei are found peripherally just under the ______, a characteristic nuclear location unique to ______ muscle fibers/cells.

Answer 20

sarcolemma, skeletal

Question 21

A small population of reserve progenitor cells called ______ remains adjacent to most fibers of differentiated skeletal muscle.

Answer 21

muscle satellite cells

Question 22

Thin layers of connective tissue surround and organize the contractile fibers in all three types of muscle, and these layers are seen particularly well in ______ muscle.

Answer 22

skeletal

Question 23

Thin layers of connective tissue surround and organize the contractile fibers in all three types of muscle, and these layers are seen particularly well in skeletal muscle.

The concentric organization given by these supportive layers resembles that in large peripheral nerves:

Answer 23

epimysium
perimysium
endomysium

Question 24

The concentric organization given by these supportive layers resembles that in large peripheral nerves:

The ______, an external sheath of dense irregular connective tissue, surrounds the entire muscle. Septa of this tissue extend inward, carrying the larger nerves, blood vessels, and lymphatics of the muscle.

Answer 24

epimysium

Question 25

The concentric organization given by these supportive layers resembles that in large peripheral nerves:

The ______ is a thin connective tissue layer that immediately surrounds each bundle of muscle fibers termed a ______. Each ______ of muscle fibers makes up a functional unit in which the fibers work together. Nerves, blood vessels, and lymphatics penetrate the perimysium to supply each fascicle.

Answer 25

perimysium, fascicle, fascicle

Question 26

The concentric organization given by these supportive layers resembles that in large peripheral nerves:

Within fascicles a very thin, delicate layer of reticular fibers and scattered fibroblasts, the ______, surrounds the external lamina of individual muscle fibers.

Answer 26

endomysium

Question 27

In addition to nerve fibers, capillaries form a rich network in the endomysium bringing ______ to the muscle fibers.

Answer 27

O2

Question 28

Collagens in these connective tissue layers of muscle serve to transmit the ______ forces generated by the contracting muscle cells/fibers; individual muscle fibers seldom extend from one end of a muscle to the other.

Answer 28

mechanical

Question 29

All three layers plus the dense irregular connective tissue of the deep fascia, which overlies the epimysium, are continuous with the tough connective tissue of a tendon at ______ which join the muscle to bone, skin, or another muscle.

Answer 29

myotendinous junctions

Question 30

Ultrastructural studies show that in these transitional regions, ______ fibers from the tendon insert themselves among muscle fibers and associate directly with complex infoldings of ______.

Answer 30

collagen, sarcolemma

Question 31

Longitudinally sectioned skeletal muscle fibers show striations of alternating ______ and ______ bands.

Answer 31

light, dark

Question 32

The sarcoplasm is highly organized, containing primarily long cylindrical filament bundles called ______ that run parallel to the long axis of the fiber.

Answer 32

myofibrils

Question 33

The dark bands on the myofibrils are called ______ (anisotropic or birefringent in polarized light microscopy); the light bands are called ______ (isotropic, do not alter polarized light). In the TEM, each I band is seen to be bisected by a dark transverse line, the ______.

Answer 33

A bands, I bands, Z disc

Question 34

The repetitive functional subunit of the contractile apparatus, the ______, extends from Z disc to Z disc and is about ______-μm long in resting muscle.

Answer 34

sarcomere, 2.5

Question 35

Mitochondria and sarcoplasmic reticulum are found between the ______, which typically have diameters of ______-______ μm. ______ consist of an end-to-end repetitive arrangement of sarcomeres; the lateral registration of sarcomeres in adjacent myofibrils causes the entire muscle fiber to exhibit a characteristic pattern of transverse striations.

Answer 35

myofibrils, 1, 2, Myofibrils

Question 36

The A and I banding pattern in sarcomeres is due mainly to the regular arrangement of thick and thin ______, composed of ______ and ______, respectively, organized within each myofibril in a symmetric pattern containing thousands of each filament type.

Answer 36

myofilaments, myosin, F-actin

Question 37

The thick myosin filaments are ______-μm long and ______-nm wide; they occupy the ______ at the middle region of the sarcomere.

Answer 37

1.6, 15, A band

Question 38

______ is a large complex (~500 kDa) with two iden- tical heavy chains and two pairs of light chains. ______ heavy chains are thin, rodlike motor proteins (150-nm long and 2-3 nm thick) twisted together as ______.

Answer 38

Myosin, Myosin, myosin tails

Question 39

______ containing the four myosin light chains form a head at one end of each heavy chain.

Answer 39

Globular projections

Question 40

The myosin heads bind both actin, forming transient crossbridges between the thick and thin filaments, and ATP, catalyzing energy release (______).

Answer 40

actomyosin ATPase activity

Question 41

Several hundred ______ molecules are arranged within each thick filament with overlapping rodlike portions and the globular heads directed toward either end.

Answer 41

myosin

Question 42

The thin, helical ______ are each ______-μm long and ______-nm wide and run between the thick filaments. Each ______ monomer contains a binding site for myosin.

Answer 42

actin filaments, 1.0, 8, G-actin

Question 43

The thin filaments have two tightly associated regulatory proteins:

Answer 43

Tropomyosin
Troponin

Question 44

The thin filaments have two tightly associated regulatory proteins:

______, a 40-nm-long coil of two polypeptide chains located in the groove between the two twisted actin strands

Answer 44

Tropomyosin

Question 45

The thin filaments have two tightly associated regulatory proteins:

______, a complex of three subunits: TnT, which attaches to tropomyosin; TnC, which binds Ca2+; and TnI, which regulates the actin-myosin interaction

Answer 45

Troponin

Question 46

______ complexes attach at specific sites regularly spaced along each tropomyosin molecule.

Answer 46

Troponin

Question 47

______ consist of the portions of the thin filaments which do not overlap the thick filaments in the A bands, which is why ______ stain more lightly than A bands.

Answer 47

I bands, I bands

Question 48

Actin filaments are anchored perpendicularly on the Z disc by the actin-binding protein ______ and exhibit opposite ______ on each side of this disc.

Answer 48

α-actinin, polarity

Question 49

An important accessory protein in I bands is ______ (3700 kDa), the largest protein in the body, with scaffolding and elastic properties, which supports the thick myofilaments and connects them to the Z disc.

Answer 49

titin

Question 50

Another large accessory protein, ______, binds each thin myofilament laterally, helps anchor them to α-actinin, and specifies the length of the actin polymers during myogenesis.

Answer 50

nebulin

Question 51

The ______ contain both the thick filaments and the overlapping portions of thin filaments. Close observation of the A band shows the presence of a lighter zone in its center, the ______, corresponding to a region with only the rodlike portions of the myosin molecule and no thin filaments. Bisecting the H zone is the ______, containing a myosin-binding protein ______ that holds the thick filaments in place, and ______. This enzyme catalyzes transfer of phosphate groups from ______, a storage form of high-energy phosphate groups, to ______, helping to supply ATP for muscle contraction.

Answer 51

A bands, H zone, M line, myomesin, creatine kinase, phosphocreatine, ADP

Question 52

Despite the many proteins present in sarcomeres, ______ and ______ together represent over half of the total protein in striated muscle. The overlapping arrangement of thin and thick filaments within sarcomeres produces in TEM cross sections hexagonal patterns of structures which were important in determining the functions of the filaments and other proteins in the myofibril.

Answer 52

myosin, actin

Question 53

In skeletal muscle fibers the membranous smooth ER, called here ______, contains pumps and other proteins for Ca2+ sequestration and surrounds the myofibrils.

Answer 53

sarcoplasmic reticulum

Question 54

Calcium release from cisternae of the sarcoplasmic reticulum through voltage-gated Ca2+ chanels is triggered by membrane ______ produced by a ______.

Answer 54

depolarization, motor nerve

Question 55

To trigger Ca2+ release from sarcoplasmic reticulum through- out the muscle fiber simultaneously and produce uniform contraction of all myofibrils, the sarcolemma has tubular infoldings called ______ or ______.

These long fingerlike invaginations of the cell membrane penetrate deeply into the sarcoplasm and encircle each myofibril near the aligned ______ and ______.

Answer 55

transverse, T-tubules, A-, I-band

Question 56

Adjacent to each T-tubule are expanded ______ of sarcoplasmic reticulum.

Answer 56

terminal cisternae

Question 57

In longitudinal TEM sections, this complex of a T-tubule with two terminal cisternae is called a ______.

Answer 57

triad

Question 58

The triad complex allows depolarization of the sarcolemma in a ______ to affect the sarcoplasmic reticulum and trigger release of ______ ions into cytoplasm around the thick and thin filaments, which initiates contraction of sarcomeres.

Answer 58

T-tubule, Ca2+

Question 59

______
- During this process neither the thick nor the thin filaments change their length.

Answer 59

MECHANISM OF CONTRACTION

Question 60

______ occurs as the overlapping thin and thick filaments of each sarcomere slide past one another.

Answer 60

Contraction

Question 61

Contraction is induced when an action potential arrives at a synapse, the ______, and is transmitted along the T-tubules to terminal cisternae of the sarcoplasmic reticulum to trigger Ca2+ release. In a resting muscle, the myosin heads cannot bind actin because the binding sites are blocked by the ______ complex on the ______ filaments.

Answer 61

neuromuscular junction (NMJ), troponin-tropomyosin, F-actin

Question 62

Calcium ions released upon neural stimulation bind ______, changing its shape and moving ______ on the F-actin to expose the myosin-binding active sites and allow crossbridges to form.

Answer 62

troponin, tropomyosin

Question 63

Binding actin produces a conformational change or pivot in the ______, which pulls the thin filaments farther into the ______, toward the ______.

Answer 63

myosins, A band, Z disc

Question 64

Energy for the myosin head pivot that pulls actin is provided by hydrolysis of ______ bound to the myosin heads, after which myosin binds another ATP and detaches from actin. In the continued presence of ______ and ______, these attach- pivot-detach events occur in a repeating cycle, each lasting about ______, which rapidly shorten the sarcomere and contract the muscle.

A single muscle contraction results from ______ of these cycles.

Answer 64

ATP, Ca2+, ATP, 50 milliseconds, hundreds

Question 65

When the neural impulse stops and levels of free ______ ions diminish, ______ again covers the myosin-binding sites on actin and the filaments passively slide back and sarcomeres return to their relaxed length.

Answer 65

Ca2+, tropomyosin

Question 66

In the absence of ATP, the actin-myosin crossbridges become stable, which accounts for the rigidity of skeletal muscles (______) that occurs as mitochondrial activity stops after death.

Answer 66

rigor mortis

Question 67

______ nerves branch out within the perimysium, where each nerve gives rise to several ______ that pass through endomysium and form synapses with individual muscle fibers.

Answer 67

Myelinated motor, unmyelinated terminal twigs

Question 68

______ enclose the small axon branches and cover their points of contact with the muscle cells.

Answer 68

Schwann cells

Question 69

The ______ of the Schwann cell fuses with that of the sarcolemma.

Answer 69

external lamina

Question 70

Each axonal branch forms a dilated termination situated within a trough on the muscle cell surface, which are part of the synapses termed the ______, or ______.

Answer 70

neuromuscular junctions, motor end plates (MEPs)

Question 71

As in all synapses the axon terminal contains mitochondria and numerous synaptic vesicles; here the vesicles contain the neurotransmitter ______.

Answer 71

acetylcholine

Question 72

Between the axon and the muscle is the ______.

Answer 72

synaptic cleft

Question 73

Adjacent to the synaptic cleft, the sarcolemma is thrown into numerous deep ______, which provide for greater postsynaptic surface area and more transmembrane acetylcholine receptors.

Answer 73

junctional folds

Question 74

When a ______ reaches the MEP, acetylcholine is liberated from the axon terminal, diffuses across the cleft, and binds to its receptors in the folded ______.

Answer 74

nerve action potential, sarcolemma

Question 75

The ______ contains a nonselective cation channel that opens upon neurotransmitter binding, allowing influx of cations, depolarizing the sarcolemma, and producing the ______.

Answer 75

acetylcholine receptor, muscle action potential

Question 76

Acetylcholine quickly dissociates from its receptors, and free neurotransmitter is removed from the synaptic cleft by the extracellular enzyme ______, preventing prolonged contact of the transmitter with its receptors.

Answer 76

acetylcholines- terase

Question 77

The muscle action potential moves along the ______ and along ______ which penetrate deeply into sarcoplasm.

Answer 77

sarcolemma, T-tubules

Question 78

At triads the depolarization signal triggers the release of ______ from terminal cisterns of the sarcoplasmic reticulum, initiating the ______.

Answer 78

Ca2+, contraction cycle

Question 79

An axon from a single motor neuron can form ______ with one or many muscle fibers.

Answer 79

MEPs

Question 80

Innervation of single muscle fibers by single motor neurons provides precise ______ of muscle activity and occurs, for example, in the ______ for eye movements.

Answer 80

control, extraocular muscles

Question 81

Larger muscles with coarser movements have motor axons that typically branch profusely and innervate ______ or more muscle fibers. In this case the single axon and all the muscle fibers in contact with its branches make up a ______.

Answer 81

100, motor unit

Question 82

Individual striated muscle fibers do not show ______—they contract either ______ or ______.

Answer 82

graded contraction, all the way, not at all

Question 83

To vary the force of contraction, the fibers within a muscle fascicle do not all ______ at the same time.

Answer 83

contract

Question 84

With large muscles composed of many motor units, the firing of a single motor axon will generate tension proportional to the number of ______ it innervates.

Answer 84

muscle fibers

Question 85

Thus, the number of motor units and their variable size control the ______ and ______ of a muscle contraction.

Answer 85

intensity, precision

Question 86

______
- is an autoimmune disorder that involves circulating antibodies against proteins of acetylcholine receptors. Antibody binding to the antigenic sites interferes with acetylcholine activation of their receptors, leading to intermittent periods of skeletal muscle weakness. As the body attempts to correct the condition, junctional folds
of sarcolemma with affected receptors are internalized, digested by lysosomes, and replaced by newly formed recep- tors. These receptors, however, are again made unresponsive to acetylcholine by similar antibodies, and the disease follows a progressive course. The extraocular muscles of the eyes are commonly the first affected.

Answer 86

MYASTHENIA GRAVIS

Question 87

______ and ______ contain sensory receptors acting as proprioceptors (L. proprius, one’s own + capio, to take), providing the central nervous system (CNS) with data from the musculoskeletal system.

Answer 87

Striated muscles, myotendinous junctions

Question 88

Among the muscle fascicles are stretch detectors known as ______, approximately 2-mm long and 0.1-mm wide.

Answer 88

muscle spindles

Question 89

A muscle spindle is encapsulated by modified perimysium, with concentric layers of flattened cells, containing interstitial fluid and a few thin muscle fibers filled with nuclei and called ______.

Answer 89

intrafusal fibers

Question 90

Several sensory nerve axons penetrate each muscle spindle and wrap around individual ______.

Answer 90

intrafusal fibers

Question 91

Changes in length (______) of the surrounding (______) muscle fibers caused by body movements are detected by the muscle spindles and the sensory nerves relay this information to the spinal cord.

Answer 91

distension, extrafusal

Question 92

Different types of ______ and ______ mediate reflexes of varying complexity to help maintain posture and to regulate the activity of opposing muscle groups involved in motor activi- ties such as walking.

Answer 92

sensory, intrafusal fibers

Question 93

A similar role is played by ______, much smaller encapsulated structures that enclose sensory axons penetrating among the collagen bundles at the myotendinous junction.

Answer 93

Golgi tendon organs

Question 94

Tendon organs detect changes in tension within tendons produced by muscle contraction and act to ______ motor nerve activity if tension becomes excessive.

Because both of these proprioceptors detect increases in tension, they help regulate the amount of effort required to perform movements that call for variable amounts of muscular force.

Answer 94

inhibit

Question 95

______ is a large actin-binding protein located just inside the sarcolemma of skeletal muscle fibers, which is involved in the functional organization of myofibrils.

Answer 95

Dystrophin

Question 96

Research on ______ revealed that mutations of the dystrophin gene can lead to defective link- ages between the cytoskeleton and the extracellular matrix (ECM). Muscle contractions can disrupt these weak linkages, causing the atrophy of muscle fibers typical of this disease.

Answer 96

Duchenne muscular dystrophy

Question 97

Skeletal muscles such as those that move the eyes and eyelids need to ______ rapidly, while others such as those for bodily posture must maintain ______ for longer periods while resisting fatigue.

These metabolic differences are possible because of varied expression in muscle fibers of contractile or regulatory protein isoforms and other factors affecting oxygen delivery and use.

Answer 97

contract, tension

Question 98

Different types of fibers can be identified on the basis of:

Answer 98

(1) their maximal rate of contraction (fast or slow fibers) and
(2) their major pathway for ATP synthesis (oxidative phosphorylation or glycolysis). Fast versus slow rates of fiber contraction are due largely to myosin isoforms with different maximal rates of ATP hydrolysis.

Question 99

Histochemical staining is used to identify fibers with differing amounts of “______” and “______” ATPases.

Answer 99

fast, slow

Question 100

Other histological features reflecting metabolic differences among muscle fibers include the density of surrounding ______, the number of ______, and levels of ______ and ______, a globular sarcoplasmic protein similar to hemoglobin which contains iron atoms and allows for O2 storage.

Answer 100

capillaries, mitochondria, glycogen, myoglobin

Question 101

Each of these features exists as a continuum in skeletal muscle fibers, but fiber diversity is divided into three major types:

Answer 101

Slow oxidative
Fast glycolytic
Fast oxidative-glycolytic

Question 102

Each of these features exists as a continuum in skeletal muscle fibers, but fiber diversity is divided into three major types:

______ muscle fibers are adapted for slow con- tractions over long periods without fatigue, having many mitochondria, many surrounding capillaries, and much myoglobin, all features that make fresh tissue rich in these fibers dark or red in color.

Answer 102

Slow oxidative

Question 103

Each of these features exists as a continuum in skeletal muscle fibers, but fiber diversity is divided into three major types:

______ fibers are specialized for rapid, short- term contraction, having few mitochondria or capillar- ies and depending largely on anaerobic metabolism of glucose derived from stored glycogen, features which make such fibers appear white. Rapid contractions lead to rapid fatigue as lactic acid produced by glycolysis accumulates.

Answer 103

Fast glycolytic

Question 104

Each of these features exists as a continuum in skeletal muscle fibers, but fiber diversity is divided into three major types:

______ fibers have physiological and histological features intermediate between those of the other two types.

Answer 104

Fast oxidative-glycolytic

Question 105

The metabolic type of each fiber is determined by the rate of ______ along its motor nerve supply, so that all fibers of a motor unit are similar.

Answer 105

impulse conduction

Question 106

Most skeletal muscles receive ______ input from multiple nerves and contain a mixture of fiber types.

Answer 106

motor

Question 107

Determining the fiber types in needle biopsies of skeletal muscle helps in the diagnosis of specific ______, motor neuron diseases, and other causes of muscle atrophy. Different fiber types also exist in cardiac muscle at various locations within the heart and in smooth muscle of dif- ferent organs.

Answer 107

myopathies

Question 108

During embryonic development ______ around the primitive heart tube align into chainlike arrays.

Answer 108

mesenchymal cells

Question 109

Rather than fusing into multinucleated cells/fibers as in developing skeletal muscle fibers, ______ cells form complex junctions between interdigitating processes.

Cells within one fiber often branch and join with cells in adjacent fibers.

Answer 109

cardiac muscle

Question 110

Consequently, the ______ consists of tightly knit bundles of cells, interwoven in spiraling layers that provide for a characteristic wave of contraction that resembles wringing out of the heart ventricles.

Answer 110

heart

Question 111

Mature cardiac muscle cells are ______-______ μm in diameter and ______-______ μm long, with a striated banding pattern comparable to that of skeletal muscle.

Answer 111

15, 30, 85, 120

Question 112

Unlike skeletal muscle, however, each cardiac muscle cell usually has only one ______ and is ______ located.

Answer 112

nucleus, centrally

Question 113

Surrounding the muscle cells is a delicate sheath of ______ with a rich capillary network.

Answer 113

endomysium

Question 114

A thicker ______ separates bundles and layers of muscle fibers and in specific areas forms larger masses of fibrous connective tissue comprising the “______.”

Answer 114

perimysium, cardiac skeleton

Question 115

A unique characteristic of cardiac muscle is the presence of ______ that cross the fibers at irregular intervals where the myocardial cells join.

These ______ represent the interfaces between adjacent cells and consist of many junctional complexes.

Answer 115

transverse lines, intercalated discs

Question 116

Transverse regions of these irregular, steplike discs are composed of many ______ and ______ junctions, which together provide strong intercellular adhesion during the cells’ constant contractile activity.

Answer 116

desmosomes, fascia adherens

Question 117

The less abundant, longitudinally oriented regions of each intercalated disc run parallel to the myofibrils and are filled with ______ which provide ionic continuity between the cells.

These regions serve as “______,” promoting rapid impulse conduction through many cardiac muscle cells simultaneously and contraction of many adjacent cells as a unit.

Answer 117

gap junctions, electrical synapses

Question 118

The structure and function of the contractile apparatus in cardiac muscle cells are essentially the same as in ______.

Answer 118

skeletal muscle

Question 119

Mitochondria occupy up to ______% of the cell volume, higher than in slow oxidative skeletal muscle fibers.

Answer 119

40

Question 120

______, the major fuel of the heart, are stored as ______ in small lipid droplets. ______ granules as well as perinuclear ______ pigment granules may also be present.

Answer 120

Fatty acids, triglycerides, Glycogen, lipofuscin

Question 121

Muscle of the heart ______ is much thicker than that of the atria, reflecting its role in pumping blood through the cardiovascular system.

Answer 121

ventricles

Question 122

______ in ventricular muscle fibers are well-developed, with large lumens and penetrate the sarco- plasm in the vicinity of the myofibrils’ Z discs.

Answer 122

T-tubules

Question 123

In atrial muscle T-tubules are much ______ or entirely ______.

Answer 123

smaller, absent

Question 124

______ is less well-organized in cardiac compared to skel- etal muscle fibers.

Answer 124

Sarcoplasmic reticulum

Question 125

CARDIAC MUSCLE

The junctions between its terminal cisterns and T-tubules typically involve only one structure of each type, forming profiles called ______ rather than triads in TEM sections.

Answer 125

dyads

Question 126

Components of this cardiac muscle ______ system have the same basic functions as their counterparts in skeletal muscle fibers.

Answer 126

transverse tubule

Question 127

Cardiac muscle fiber contraction is ______ and ______, as evidenced by the continued contraction of the cells in tissue culture. Impulses for the ______ (or ______) are initiated, regulated, and coordinated locally by nodes of unique myocardial fibers specialized for impulse generation and conduction.

Answer 127

intrinsic, spontaneous, rhythmic contraction, heartbeat

Question 128

CARDIAC MUSCLE

As with skeletal muscle fibers, contraction of individual myocardial fibers is ______. The rate of contraction is mod- ified by autonomic innervation at the nodes of conducting cells, with the ______ nerve supply accelerating and the ______ supply decreasing the frequency of the impulses.

Answer 128

all-or-none, sympathetic, parasympathetic

Question 129

______ about 0.2-0.3 μm in diameter are found near atrial muscle nuclei and are associated with small Golgi complexes.

Answer 129

Secretory granules

Question 130

Secretory Granules

These granules release the peptide hormone ______ which acts on target cells in the kidney to affect ______ and ______. The contractile cells of the heart’s atria thus also serve an endocrine function.

Answer 130

atrial natriuretic factor (ANF), Na+ excretion, water balance

Question 131

Most common injury sustained by cardiac muscle is that due to ______, or tissue damage due to lack of oxygen when coronary arteries are occluded by heart disease.

Answer 131

ischemia

Question 132

Lacking muscle satellite cells, adult mammalian cardiac muscle has little potential to ______ after injury.

Answer 132

regenerate

Question 133

However, certain fish and amphibians, as well as newborn mice, do form new muscle when the heart is partially removed, despite the lack of ______. Research on the possibility of mammalian heart muscle regeneration builds on work with the animal models, focusing primarily on the potential of mesenchymal stem cells to form new, site-specific muscle.

Answer 133

satellite cells

Question 134

______ is specialized for slow, steady contraction under the influence of autonomic nerves and various hormones.

Answer 134

Smooth muscle

Question 135

______
- This type of muscle is a major component of blood vessels and of the digestive, respiratory, urinary, and reproductive tracts and their associated organs.

Answer 135

SMOOTH MUSCLE

Question 136

Fibers of smooth muscle (also called ______) are elongated, tapering, and unstriated cells, each of which is enclosed by an ______ and a network of type ______ and type ______ collagen fibers comprising the endomysium.

Answer 136

visceral muscle, external lamina, I, III

Question 137

Smooth muscle cells range in length from ______ μm in small blood vessels to ______ μm in the pregnant uterus.

At each cell’s central, broadest part, where its diameter is ______-______ μm, is a single elongated ______.

Answer 137

20, 500, 5, 10, nucleus

Question 138

SMOOTH MUSCLE

The cells stain uniformly along their lengths, and close packing is achieved with the narrow ends of each cell adjacent to the broad parts of neighboring cells.

With this arrangement cross sections of smooth muscle show a range of cell diameters, with only the largest profiles containing a ______.

Answer 138

nucleus

Question 139

SMOOTH MUSCLE

All cells are linked by numerous ______. The borders of the cell become scalloped when smooth muscle contracts and the nucleus becomes distorted.

Answer 139

gap junctions

Question 140

SMOOTH MUSCLE

Concentrated near the nucleus are ______, ______, ______, and ______ of a Golgi apparatus.

Answer 140

mitochondria, polyribosomes, RER, vesicles

Question 141

At the smooth muscle cell surface are numerous small plasmalemma invaginations resembling ______, which in these cells compartmentalize various signaling components.

Answer 141

caveolae

Question 142

SMOOTH MUSCLE

The fibers have rudimentary ______, but lack ______; their function is unnecessary in these smaller, tapering cells with many gap junctions.

Answer 142

sarcoplasmic reticulum, T-tubules

Question 143

______ of smooth muscle cells contain the major ion channels that control Ca2+ release from sarcoplasmic cisternae at myofibrils that initiates contraction.

Answer 143

Caveolae

Question 144

The characteristic contractile activity of smooth muscle is generated by ______ of ______ and ______ organized somewhat differently from those of striated muscle.

Answer 144

myofibrillar arrays, actin, myosin

Question 145

In smooth muscle cells bundles of thin and thick myofilaments crisscross the sarcoplasm ______.

Answer 145

obliquely

Question 146

SMOOTH MUSCLE

The ______ have a less regular arrangement among the thin filaments and fewer crossbridges than in striated muscle.

Answer 146

myosin filaments

Question 147

Moreover smooth muscle actin filaments are not associated with troponin and tropomyosin, using instead ______ and Ca2+-sensitive ______ to produce contraction.

Answer 147

calmodulin, myosin light-chain kinase (MLCK)

Question 148

SMOOTH MUSCLE

The contraction mechanism, however, is basically similar to that in ______.

Answer 148

striated muscle

Question 149

SMOOTH MUSCLE

The actin myofilaments insert into anchoring cytoplasmic and plasmalemma- associated ______ which contain ______ and are functionally similar to the Z discs of striated and cardiac muscle.

Answer 149

dense bodies, α-actinin

Question 150

Smooth muscle cells also have an elaborate array of 10-nm intermediate filaments, composed of ______, which also attach to the dense bodies.

Answer 150

desmin

Question 151

The submembranous dense bodies include ______ of ______ linking adjacent smooth muscle cells.

Answer 151

cadherins, desmosomes

Question 152

Dense bodies in smooth muscle cells thus serve as points for transmitting the ______ force not only within the cells, but also between adjacent cells

Answer 152

contractile

Question 153

The ______ and other ______ layers help combine the force generated by the smooth muscle fibers into a concerted action, for example, peristalsis in the intestine.

Answer 153

endomysium, connective tissue

Question 154

______ muscle is not under voluntary motor control and its fibers typically lack well-defined neuromuscular junctions.

Answer 154

Smooth

Question 155

SMOOTH MUSCLE

Contraction is most commonly stimulated by ______ nerves, but in the gastrointestinal tract smooth muscle is also controlled by various paracrine secretions and in the uterus by oxytocin from the pituitary gland.

Answer 155

autonomic

Question 156

Axons of autonomic nerves passing through smooth muscle have periodic ______ or ______ that lie in close contact with muscle fibers.

Answer 156

swellings, varicosities

Question 157

SMOOTH MUSCLE

Synaptic vesicles in the varicosities release a neurotransmitter, usually ______ or ______, which diffuses and binds receptors in the sarcolemmae of numerous muscle cells.

There is little or no specialized structure to such junctions.

Answer 157

acetylcholine, norepinephrine

Question 158

As in cardiac muscle, stimulation is propagated to more ______ fibers via ______ that allow all the smooth muscle cells to contract synchronously or in a coordinated manner.

Answer 158

distant, gap junctions

Question 159

In addition to contractile activity, smooth muscle cells also supplement ______ activity, synthesizing ______, ______, and ______, with a major influence on the ECM in tissues where these contractile cells are abundant.

Answer 159

fibroblast, collagen, elastin, proteoglycans

Question 160

Active synthesis of ______ by the small cells/fibers of smooth muscle may reflect less specialization for strong contractions than in skeletal and cardiac muscle and is similar to this synthetic function in other contractile cells, such as ______ and ______.

Answer 160

ECM, myofibroblasts, pericytes

Question 161

Benign tumors called ______ commonly develop from smooth muscle fibers but are seldom problematic.

They most frequently occur in the wall of the uterus, where they are more commonly called ______ and where they can become sufficiently large to produce painful pressure and unexpected bleeding

Answer 161

leiomyomas, fibroids

Question 162

In skeletal muscle, although the multinucleated cells cannot undergo ______, the tissue can still display limited ______.

Answer 162

mitosis, regeneration

Question 163

The source of regenerating cells is the sparse population of mesenchymal ______ lying inside the external lamina of each muscle fiber.

Answer 163

satellite cells

Question 164

______ cells are inactive, reserve myoblasts which persist after muscle differentiation.

Answer 164

Satellite

Question 165

After injury the normally ______ cells become activated, proliferating, and fusing to form new skeletal muscle fibers.

Answer 165

quiescent satellite

Question 166

A similar activity of satellite cells has been implicated in muscle growth after extensive exercise, a process in which they fuse with existing fibers to increase muscle mass beyond that which occurs by ______.

Answer 166

cell hypertrophy

Question 167

Following major traumatic injuries, scarring and excessive connective tissue growth interferes with ______ muscle regeneration.

Answer 167

skeletal

Question 168

Cardiac muscle lacks ______ and shows very little ______ capacity beyond early childhood.

Answer 168

satellite cells, regenerative

Question 169

Defects or damage (eg, infarcts) to heart muscle are generally replaced by proliferating ______ and growth of ______, forming only ______.

Answer 169

fibroblasts, connective tissue, myocardial scars

Question 170

Smooth muscle, composed of simpler, smaller, mononucleated cells, is capable of a more active ______ response. After injury, viable smooth muscle cells undergo ______ and replace the damaged tissue.

Answer 170

regenerative, mitosis

Question 171

Contractile ______ from the walls of small blood vessels participate in the repair of vascular smooth muscle.

Answer 171

pericytes