CHAPTER 6

Question 1

The sarcolemma consists of a
true cell membrane, called the

Answer 1

plasma membrane

Question 2

In turn collect into bundles to form the muscle tendons that then insert into the bones

Answer 2

tendon fibers

Question 2

Each myofibril (Figure 6-1D and E) is
composed of about

Answer 2

about 1500 adjacent myosin filaments and 3000 actin filaments

Question 2

which are large polymerized protein molecules that are responsible for the actual muscle contraction.

Answer 2

actin filaments

Question 3

The thick filaments in the diagrams are

Answer 3

myosin

Question 4

and the thin
filaments are a

Answer 4

actin

Question 4

The portion of the myofibril (or of the whole muscle fiber) that lies between two successive Z discs is called

Answer 4

sarcomere

Question 5

The side-by-side relationship between the myosin and actin filaments is difficult to maintain. This is achieved by a large number of filamentous molecules of a protein called

Answer 5

titin

Question 6

The light bands contain only actin filaments and are called

Answer 6

I bands

Question 6

called I bands because they are

Answer 6

Isotropic’ to polarized light.

Question 7

The dark bands contain myosin filaments, as well as the ends of the actin filaments where they overlap the myosin, and are called

Answer 7

A bands

Question 7

Note also the small projections from the sides of the myosin filaments these are

Answer 7

cross -ridge

Question 7

called A bands because they are

Answer 7

“anisotropic” to polarized light.

Question 8

also shows that the ends of the actin filaments are attached to a so-called

Answer 8

Z disc

Question 9

act as a framework that holds the myosin and actin filaments in place so that the contractile machinery of the sarcomere will work

Answer 9

springy titin molecules

Question 9

The spaces between the myofibrils are filled with intracellular fluid called

Answer 9

sarcoplasm

Question 10

Also in the sarcoplasm surrounding the myofibrils of each muscle fiber is an extensive reticulum called the

Answer 10

Sarcoplasmic reticulum

Question 10

sarcoplasm, containing large quantities of

Answer 10

potassium
magnesium
phosphate, plus multiple protein
enzymes

Question 10

acts on a local area of the muscle
fiber membrane to open multiple “acetylcholine-gated” cation channels through protein molecules floating in the membrane

Answer 10

Acetylcholine

Question 10

At each ending, the nerve secretes a small amount of the neurotransmitter substance

Answer 10

acetylcholine

Question 11

Also, the Z discs have been pulled by
the actin filaments up to the ends of the myosin filaments. Thus, muscle contraction occurs by a

Answer 11

sliding filament mechanism

Question 12

But what causes the actin filaments to slide inward among the myosin filaments?

Answer 12

This is caused by forces generated by interaction of the cross-bridges from the myosin filaments with the actin filaments.

Question 13

The two heavy chains wrap spirally around each other to form a double helix called

Answer 13

“tail” of the myosin molecule

Question 14

The myosin molecule (see Figure 6-6A) is composed of six polypeptide chains

Answer 14

Two heavy chains
Four light chains

Question 15

One end of each of these chains is folded bilaterally into a globular polypeptide structure called a

Answer 15

myosin head

Question 16

The protruding arms and heads together are called

Answer 16

cross-bridges

Question 17

Each cross-bridge is flexible at two points called

Answer 17

hinges

Question 18

Another feature of the myosin head that is essential for muscle contraction is that it functions as an A

Answer 18

ATPase enzyme

Question 19

The backbone of the actin filament is a double-stranded

Answer 19

F-actin protein molecule

Question 20

Each strand of the double F-actin helix is composed of polymerized

Answer 20

of the double F-actin helix is composed of polymerized G-actin

Question 21

Although the precise manner by which this interaction between the cross-bridges and the actin causes contraction is still partly theoretical, one hypothesis for which considerable evidence exists is the

Answer 21

“walk-along” theory (or “ratchet” theory) of contraction.

Question 21

The actin filament also contains another protein

Answer 21

tropomyosin

Question 22

Attached intermittently along the sides of the tropomyosin molecules are still other protein molecules called

Answer 22

troponin

Question 23

This tilt of the head is called the

Answer 23

power stroke

Question 24

Large amounts of ATP are cleaved to form ADP during the contraction process; the greater the amount of work performed by the muscle, the greater the amount of ATP that is cleaved, which is called the

Answer 24

Fenn effect

Question 25

which carries a high-energy phosphate bond similar to the bonds of ATP

Answer 25

phosphocreatine

Question 26

of glycogen previously stored in the muscle cells.

Answer 26

“glycolysis”

Question 27

The third and final source of energy is o This means combining oxygen with the end products of glycolysis and with various other cellular foodstuffs to liberate ATP

Answer 27

oxidative metabolism

Question 28

The efficiency of an engine or a motor is calculated as the percentage of energy input that is converted into work instead of heat.

Question 29

Maximum efficiency can be realized only when the muscle contracts at a moderate velocity. If the muscle contracts slowly or without any movement, small amounts of

Answer 29

maintenance heat

Question 30

Many features of muscle contraction can be demonstrated by eliciting single

Answer 30

muscle twitches

Question 31

Muscle contraction is said to be ---- when the muscle does not shorten during contraction

Answer 31

isometric

Question 32

when it does shorten but the tension on the muscle remains constant throughout the contraction.

Answer 32

Isotonic

Question 33

Slow Fibers (Type 1, Red Muscle).

Answer 33

(1) Smaller fibers. (2) Also innervated by smaller nerve fibers. (3) More extensive blood vessel system and capillaries to supply extra amounts of oxygen. (4) Greatly increased numbers of mitochondria, also to support high levels of oxidative metabolism. (5) Fibers contain large amounts of myoglobin, an iron-containing protein similar to hemoglobin in red blood cells.

Question 34

Myoglobin combines with oxygen and stores it until needed; this also greatly speeds oxygen transport to the mitochondria. The myoglobin gives the slow muscle a reddish appearance and the name

Answer 34

red muscle

Question 35

Fast Fibers (Type II, White Muscle). (

Answer 35

(1) Large fibers for great strength of contraction. (2) Extensive sarcoplasmic reticulum for rapid release of calcium ions to initiate contraction. (3) Large amounts of glycolytic enzymes for rapid release of energy by the glycolytic process. (4) Less extensive blood supply because oxidative metabolism is of secondary importance. (5) Fewer mitochondria

Question 36

A deficit of red myoglobin in fast muscle gives it the name

Answer 36

white muscle

Question 36

All the muscle fibers innervated by a single nerve fiber are called a

Answer 36

motor unit

Question 37

means the adding together of individual twitch contractions to increase the intensity of overall muscle contraction.

Answer 37

Summation

Question 37

Summation occurs in two ways:

Answer 37

(1) by increasing the number of motor units contracting simultaneously, which is called multiple fiber summation, and (2) by increasing the frequency of contraction, which is called frequency summation and can lead to tetanization.

Question 38

by increasing the number of motor units contracting simultaneously, which is called

Answer 38

multiple fiber summation

Question 38

By increasing the frequency of contraction, which is called

Answer 38

Frequency summation

Question 39

with the largest motor units often having as much as 50 times the contractile force of the smallest units. This is called the

Answer 39

size principle.

Question 40

Even when muscles are at rest, a certain amount of tautness usually remains. This is called

Answer 40

muscle tone

Question 40

When the frequency reaches a critical level, the successive contractions eventually become so rapid that they fuse together and the whole muscle contraction appears to be completely smooth and continuous, This is called

Answer 40

tetanization

Question 41

That is, the strength of contraction increases to a plateau, a phenomenon called the

Answer 41

staircase effect, or treppe

Question 42

an analysis of the lever systems of the body depends on knowledge of

Answer 42

(1) the point of muscle insertion (2) its distance from the fulcrum of the lever (3) the length of the lever arm, and (4) the position of the lever.

Question 43

The study of different types of muscles, lever systems, and their movements is called

Answer 43

kinesiology

Question 43

When the total mass of a muscle increases, this is called

Answer 43

muscle hypertrophy

Question 43

When it decreases, the process is called

Answer 43

muscle atrophy.

Question 44

Virtually all muscle hypertrophy results from an increase in the number of actin and myosin filaments in each muscle fiber, causing enlargement of the individual muscle fibers; this is called simply

Answer 44

Fiber hypertrophy

Question 45

The pathway that appears to account for much of the protein degradation in a muscle undergoing atrophy is the

Answer 45

ATP-dependent ubiquitin-proteasome pathway

Question 46

is a regulatory protein that basically labels which cells will be targeted for proteasomal degradation.

Answer 46

Ubiquitin

Question 46

Proteasomes are large protein complexes that degrade damaged or unneeded proteins by

Answer 46

Proteolysis

Question 46

This increase in fiber number is called f

Answer 46

fiber hyperplasia

Question 47

The fibrous tissue that replaces the muscle fibers during denervation atrophy also has a tendency to continue shortening for many months, which is called

Answer 47

contracture

Question 48

When some but not all nerve fibers to a muscle are destroyed, as commonly occurs in

Answer 48

poliomyelitis

Question 48

the remaining nerve fibers branch off to form new axons that then innervate many of the paralyzed muscle fibers. This causes large motor units called

Answer 48

macromotor units

Question 49

Several hours after death, all the muscles of the body go into a state of contracture called

Answer 49

“rigor mortis”