Muscular System

Question 1

Skeletal Muscle

Answer 1

Large, elongated, multinucleated fibers; voluntary; neuromuscular junction.

10-100 um in diameter

Activity:
Strong, quick discontinuous voluntary contraction

Question 2

Cardiac Muscle

Answer 2

Large, fibers branch, one or two nuclei, involuntary, intercalated discs with gap junctions so that all fibers of the atrium or ventricle contract simultaneously.

10-100 um in diameter

Activity:
Strong, quick, continuous involuntary contraction

Question 3

Smooth Muscle

Answer 3

Small, fusiform fibers with tapering ends, nucleus in the center, involuntary, gap junctions between cells so that all muscles during peristalsis can contract in a unison.

4-5 um in diameter

Activity:
Weak, slow involuntary contraction

Question 4

Organization of Skeletal Muscle

Answer 4

Fasciculus, fibers, myofibrils, myofilaments (actin, myosin).

Question 5

Connective Tissue Coverings

Answer 5

Epimysium: surrounding the whole muscle

Perimysium: surrounding each fasciculus

Endomysium, surrounding each fiber.

Question 6

Function of Connective Tissue

Answer 6

Brings blood vessels and nerves closer to fibers and transmit force of muscle contraction to the tendon and, in turn, to the bone, consequently leading to the flexion or extension of the joint.

Question 7

Striated Skeletal Muscle in longitudinal section

Answer 7

Striations can be seen nuclei in the periphery

Question 8

Striated Skeletal Muscle in Transverse( cross) section

Answer 8

Nuclei located in the periphery of each fiber; striations cannot be clearly observed

Nuclei in the periphery are arranged in a row (can be confused with fibroblasts present in the endomysium).

Question 9

Striations under a microscope

Answer 9

Forms dark and light bands are clearly visible.

Question 10

A bands

Answer 10

The dark stained bands

contains both thick and thin filaments

(actin and myosin filaments overlapping)

each myosin filaments has 6 actin filaments surrounding it

center of A band only has myosin

Question 11

I band

Answer 11

the light-stained band

contains only thin filaments;

(only actin filament),

Question 12

Z line

Answer 12

Thin dark stained

border for the sarcomere

Question 13

H band

Answer 13

contains only thick filament (middle of A band)

Only myosin filaments

Question 14

M line

Answer 14

Present in the middle of H band and results from attachment of adjacent myosin filaments

Question 15

Triad

Answer 15

Each triad consists of a T tubule in the center (cell membrane invagination, extracellular) ) and a SER cisterna on each side (intracellular)

Question 16

Triads in amphibians

Answer 16

Triads in amphibian muscle are aligned with the Z line in each sarcomere.

Question 17

Triads In Mammalian Muscle

Answer 17

In mammalian muscle, each sarcomere exhibits 2 triads, one at each A–I band interface.

Question 18

Sarcomere

Answer 18

Is called a sarcomere, a structural and functional unit of the skeletal muscle. Hence, each muscle fiber contains thousands of sarcomeres along the length (depending upon the length) and hundreds of sarcomeres along the width. Giemsa stain.

Sarcomere is from one Z line to the adjacent one
- the structural and functional unit of the skeletal muscle

Question 19

SER Cisterna

Answer 19

due to depolarization, Calcium is released which is vital for muscle contraction

The depolarization wave extends along the length of the T tubule and is transmitted to the adjacent SER, from where calcium is released, resulting in muscle contraction

Question 20

Types of skeletal muscle fibers identified by staining mitochondria with succinate dehydrogenase enzyme. ( can also use atpase)

Answer 20

Red (Type I, aerobic)

White (Type II, anaerobic)

Intermediate

Question 21

White skeletal muscle fibers (Type II, anaerobic)

Answer 21

Larger, fewer mitochondria, more extensive SER, energy from anaerobic glycolysis, contract and fatigue more rapidly, fast-twitch fibers.

• has more glycogen

Question 22

Red skeletal muscle fibers (Type I, aerobic):

Answer 22

large amount of myoglobin, numerous mitochondria, energy from oxidative pathway, contract and fatigue slowly, slow-twitch fibers.

posture muscles tend to be red fibers

Question 23

Intermediate skeletal muscle fibers

Answer 23

Share characteristics of both fibers.

Question 24

Where are white fibers found

Question 25

Where are red fibers found

Question 26

Neuromuscular junction (Motor end plate)

Answer 26

Each branch terminates as a motor end plate on a different muscle fiber.

Hence, all muscle fibers innervated by one axon (one neuron) constitute a motor unit.

Question 27

Importance of size of a motor unit

Answer 27

The larger the size of the motor unit the cruder the muscle movement (for example, hip muscle, one neuron may innervate hundreds of fibers).

Conversely, the smaller the motor unit, the finer the movement (for example, eye muscles, one neuron may innervate 5-10 muscle fibers).

muscles can be trained to be less crude and more finer

Question 28

Changes at the distal end of the axon

Answer 28

Dilation of the axon, myelin sheath loss, and aggregation of mitochondria and vesicles containing acetylcholine (Ach).

Question 29

Changes at the Muscle Fiber

Answer 29

Folding of cell membrane (sarcolemma) enclosing sub-neural clefts, aggregation of mitochondria, and loss of striations.

Question 30

Events of Impulse Conduction:

Answer 30

1) Depolarization of axolemma

2) release of Ach

3) binding of Ach with Ach receptors on sarcolemma

4) depolarization of sarcolemma

5) extension of depolarization wave to the T tubule and SER cisternae (triad)

6) release of Ca++

7) contraction of myofilaments

8) inactivation of Ach by cholinesterase enzyme present in sub-neural clefts

9) active transport of Ca++ back into SER

10) relaxation of myofilaments

Question 31

Results of Contraction

Answer 31

1) I band reduces in length

2) sarcomere reduces in length

3) H band disappears

4) and no change in the length of the A band or of actin and myosin filaments.

Question 32

Huxley’s Sliding Filament Theory of Muscle Contraction

Answer 32

Thick and thin filaments maintain the same length but slide past each other.

Question 33

What are the three main proteins present in actin filaments

Answer 33

actin, tropomyosin, and troponin.

Question 34

Actin

Answer 34

Is a globular protein and is polymerized to form a structure resembling double helix;

Question 35

Each tropomyosin molecule location?

Answer 35

Lies in the double helix groove;

Question 36

Each troponin (Tn) molecule has

Answer 36

three binding sites: TnC: binds calcium,
TnT: binds tropomyosin, TnI: inhibits actin myosin interaction.