Ch 10: Muscular Tissue

Question 1

There are three major types of muscle:

Answer 1

(1) skeletal or striated muscle, (2) cardiac muscle, and (3) smooth or visceral muscle.

Question 2

Skeletal muscle cells

Answer 2

very long, multinucleated fibers, cylindrically shaped and with diameters up to 100 μm.

The sarcolemma of each fiber is surrounded by an external lamina and thin connective tissue, endomysium, containing capillaries.

Question 3

Groups of fibers called fascicles are surrounded by

Answer 3

perimysium; all fascicles are enclosed within a dense connective tissue epimysium.

Question 4

Internally each muscle fiber has:

Answer 4

is filled with myofibrils, composed of thousands of thick myosin filaments and thin actin filaments, highly organized into contractile units called sarcomeres.

Question 5

Within sarcomeres

Answer 5

thick and thin filaments interdigitate; globular myosin heads project from the thick filaments toward the F-actin filaments, which are associated with tropomyosin and troponin.

Question 6

Sarcomeres are separated

Answer 6

by Z discs that bisect the light-staining I bands that contain mainly the thin filaments attached to α-actinin in the Z disc

Question 7

Between the two I bands of a sarcomere

Answer 7

is the dark-staining A band with the thick myosin filaments; alternating light and dark bands appear as microscopic striations along the fibers.

Question 8

In the sarcoplasm between parallel myofibrils are mitochondria and cisternae of smooth ER, called

Answer 8

the sarcoplasmic reticulum(SR) specialized for Ca2+ sequestration and release.

Question 9

At each sarcomere, two terminal cisterns of SR contact a deep invagination of the sarcolemma called a transverse or T-tubule

what does this cause?

Answer 9

a forming a triad that triggers Ca2+ release when the sarcolemma is depolarized.

Question 10

Ca2+ binding to troponin causes tropomyosin to change shape and

Answer 10

allow the myosin heads to bind the actin subunits, forming crossbridges between thick and thin filaments.

The myosin heads then pivot with ATP hydrolysis, which pulls the thin filaments along the thick filaments.

Question 11

With Ca2+ and ATP present, a contraction cycle ensues in which:

Answer 11

myosin heads repeatedly attach, pivot, detach, and return, causing the filaments to slide past one another, shortening the sarcomere.

Question 12

When the membrane depolarization ends, Ca2+ is again sequestered, this causes….

Answer 12

the ending contraction and allowing the sarcomeres to lengthen again as the muscle relaxes.

Question 13

Synapses of motor axons with skeletal muscle are called:

Answer 13

motor end plates (MEPs), neuromuscular junctions (NMJs), or myoneural junctions; the neurotransmitter used is acetylcholine.

Question 14

A motor axon may form many terminal branches, each ending on an MEP of a muscle fiber, but….

Answer 14

all fibers innervated by branches of that axon comprise a motor unit.

Question 15

Muscle Spindles & Tendon Organs

Answer 15

These are both sensory proprioceptors in which sensory axons wrap around intrafusal fibers in small specialized fascicles or around myotendinous collagen bundles, respectively.

Question 16

Muscle Fiber Types

Skeletal muscles contain fibers that can be physiologically classified as the three main types:

Answer 16

1) slow, oxidative (type I);
(2) fast, intermediate oxidative-glycolytic (type IIa);
(3) fast, glycolytic (type IIb).

Question 17

Cardiac Muscle

Cardiac muscle fibers are also striated, but they consist of individual cylindrical cells, each containing one (or two) central nuclei

Answer 17

and linked by adherent and gap junctions at prominent intercalated discs.

Sarcomeres of cardiac muscle are organized and function similarly to those of skeletal muscle.

Question 18

Cardiac Muscle

Contraction of cardiac muscle is intrinsic at

Answer 18

at nodes of impulse-generating pacemaker muscle fibers; autonomic nerves regulate the rate of contraction.

Question 19

Smooth Muscle

Smooth muscle fibers are individual small, fusiform (tapering) cells,

they are linked by…..

Answer 19

numerous gap junctions.

Thin and thick filaments in smooth muscle fibers do not form sarcomeres, and no striations are present.

Question 20

Smooth Muscle

Thin actin filaments attach to α-actinin located in dense bodies that are located ….

Answer 20

throughout the sarcoplasm and near the sarcolemma; contraction causes cells to shorten individually.

Question 21

Smooth Muscle

Sarcoplasmic reticulum is less well-organized in ….

Answer 21

smooth muscle fibers, and there is no transverse tubule system.

Question 22

Smooth Muscle

Troponin is lacking in smooth muscle; proteins controlling the sliding filaments here include….

Answer 22

myosin light-chain kinase (MLCK) and the Ca2+-binding protein calmodulin.

Question 23

Regeneration of Muscle Tissue

Repair and regeneration can occur in….

Answer 23

skeletal muscle because of a population of reserve muscle satellite cells that can proliferate, fuse, and form new muscle fibers.

Question 24

Regeneration of Muscle Tissue

Cardiac muscle lacks

Answer 24

satellite cells and has little capacity for regeneration.

Question 25

Regeneration of Muscle Tissue

egeneration is rapid in smooth muscle because ….

Answer 25

the cells/fibers are small and relatively less differentiated, which allow renewed mitotic activity after injury.

Question 26

The basal lamina of a muscle fiber is part of which structure?

Answer 26

a. Perimysium

 b. Epimysium

 c. Fascia

 d. Endomysium

 e. Sarcoplasmic reticulum

Question 27

With the transmission electron microscope skeletal muscle fibers can be seen to contain structures called triads. What do the two lateral components of a triad represent?

Answer 27

a. Attachment sites for thick myofilaments

 b. Sites for calcium sequestration and release

 c. Sites for impulse conduction into the fiber

 d. Sites for ATP production

 e. Sites for synthesis of proteins to be secreted outside the cell

Question 28

Which characteristic is unique to cardiac muscle?

Answer 28

 a. Contain centrally located nuclei

 b. Striated

 c. Often branched

 d. Multinucleated

 e. Lack T-tubules

Question 29

In smooth muscle calcium released by the smooth ER initiates contraction by binding to what protein?

Answer 29

a. Actin

 b. Calmodulin

 c. Desmin

 d. Myosin light chain kinase

 e. Tropomyosin

Question 30

Which feature typifies T-tubules?

Answer 30

a. Evaginations of the sarcoplasmic reticulum

 b. Sequester calcium during muscle relaxation, releasing it during contraction

 c. Carry depolarization to the muscle fiber interior

 d. Overlie the A-I junction in cardiac muscle cells

 e. Rich supply of acetylcholine receptors

Question 31

Which characteristic is unique to smooth muscle?

Answer 31

a. T-tubules lie across Z lines

 b. Each thick filament is surrounded by six thin filaments

 c. Thin filaments attach to dense bodies

 d. Cells are multinucleated

 e. Cells have centrally located nuclei

Question 32

In one type of muscle, numerous gap junctions, desmosomes, and adherens junctions are specifically localized in which structures?

Answer 32

a. Myofilaments

 b. Dense bodies

 c. Sarcomeres

 d. Neuromuscular spindles

 e. Intercalated discs

Question 33

A 66-year-old man who lives alone has a severe myocardial infarction and dies during the night. The medical examiner’s office is called the following morning and describes the man’s body as being in rigor mortis. This state of rigor mortis is due to which one of the following?

Answer 33

a. Inhibition of Ca2+ leakage from the extracellular fluid and sarcoplasmic reticulum

 b. Enhanced retrieval of Ca2+ by the sarcoplasmic reticulum

 c. Failure to disengage tropomyosin and troponin from the myosin active sites

 d. Absence of ATP preventing detachment of the myosin heads from actin

 e. Increased lactic acid production

Question 34

A 5-year-old boy sustains a small tear in his gastrocnemius muscle when he is involved in a bicycle accident. Regeneration of the muscle will occur through which of the following mechanisms?

Answer 34

 a. Dedifferentiation of muscle cells into myoblasts

 b. Differentiation of muscle satellite cells

 c. Fusion of damaged myofibers to form new myotubes

 d. Hyperplasia of existing muscle fibers

 e. Differentiation of fibroblasts to form myoblasts

Question 35

A healthy 32-year-old man lifts weights regularly as part of his workout. In one of his biceps muscle fibers at rest, the length of the I band is 1.0 μm and the A band is 1.5 μm. Contraction of that muscle fiber results in a 10% shortening of the length of the sarcomere. What is the length of the A band after the shortening produced by muscle contraction?

Answer 35

 a. 1.50 μm

 b. 1.35 μm

 c. 1.00 μm

 d. 1.90 μm

 e. 0.45 μm