Muscle

Question 1

What is the organization of skeletal muscles?

Answer 1

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

Question 2

What do the CT coverings of skeletal muscle do?

Answer 2

Supply blood vessels, nerves, muscle spindles, and provide a means by which contractile forces are transmitted to other tissues

Question 3

What are the CT coverings of skeletal muscle called?

Answer 3

Endomysium, perimysium and epimysium

Question 4

What is the structure of the skeletal muscle?

Answer 4

10-110 micrometers in diameter
Up to 50 cm in length
Periphery nuclei
Many myofilaments that create light and dark bands
Striations

Question 5

What is the functional unit of a skeletal muscle?

Answer 5

Sarcomere

Question 6

Structure of the sarcomere

Answer 6

0.5- 1.00 micrometers in diameter
2.00 micrometers long
With I band, A band, H band, M line and Z line
Z line to Z line

Question 7

I band

Answer 7

Only thin (actin) filaments
White thick line next to A bands

Question 8

A band

Answer 8

Thick (myosin) and thin (actin) filaments
Thick dark line

Question 9

H band

Answer 9

Pale area in the center of the A band

Question 10

M line

Answer 10

Runs down the center of the H band
Results from attachment of adjacent myosin filaments

Question 11

Z line

Answer 11

Dark band in the center of the I band

Question 12

Skeletal muscle triad

Answer 12

T tubule in the center and SER cisterna on each side
In mammals, each sarcomere exhibits 2 triads one at each A-I band interface

Question 13

What is the role of SER in the T tubule?

Answer 13

Stores calcium that is released during contraction

Question 14

What are the 2 types of skeletal muscle fibers?

Answer 14

Red (type 1) and white (type 2) and intermediate (shares both)

Question 15

Red (type 1) skeletal muscle fiber?

Answer 15

Large amount of myoglobin, numerous mitochondria, energy from oxidative pathway, contract and fatigue slowly
Slow-twitch fibers

Question 16

White (type II) skeletal muscle fibers

Answer 16

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

Question 17

Regeneration of the skeletal muscle

Answer 17

Limited
Satellite (stem) cells present
Most injured muscle cells are replaced by CT

Question 18

Motor Unit

Answer 18

A nerve fiber and the muscle cell it innervates

Question 19

Motor End Plate

Answer 19

Point of attachment of a nerve with a skeletal muscle fiber

Question 20

What are the motor end plate modifications at the distal end of axon?

Answer 20

loss of myelin sheath, presence of mitochondria and acetylcholine vesicles, dilation of axon

Question 21

What are the motor end plate modifications at the muscle fiber?

Answer 21

Folding of cell membranes enclosing sub-neural clefts
Aggregation of mitochondria
Loss of striations

Question 22

Events of Impulse Conduction

Answer 22

1. Depolarization of axolemma
2. Release of Ach
3. Binding of Ach with Ach receptors present on sarcolemma
4. Depolarization of sarcolemma
5. Extension of depolarization wave to the T tubule and SER cisternae
6. Release of calcium
7. Contraction of myofilaments
8. Inactivation of Ach by cholinesterase enzyme present in sub–neural clefts
9. Active transport of calcium back to the SER
10. Relaxation of myofilaments

Question 23

What are the results of contraction?

Answer 23

I band and sarcomere reduces in length
H band disappears

Question 24

Huxley’s Sliding Filament Theory

Answer 24

Thick and thin filaments maintain the same length but slide past each other during muscle contraction

Question 25

Organophosphorus Toxicity

Answer 25

Cholinesterase enzyme is phosphorylated Results in initial stimulation followed by depression

Question 26

Botulism

Answer 26

Caused by toxins secreted by Clostridium botulinum Blocks the release of Ach Results in Flaccid tetraparesis

Question 27

Myasthenia Gravis

Answer 27

Caused by deficiency of Ach and/ or antibodies against Ach receptors Results in weakness in muscles

Question 28

Structure of the cardiac muscle

Answer 28

10-15 micrometers in diameter 100 micrometers long 1 or 2 nuclei per cell, centrally located Fibers branch Striated No regeneration

Question 29

What does the point of anastomosis show? (Cardiac)

Answer 29

Intercalated discs At EM levels consist of gap junctions, desmosomes and fascia

Question 30

What happens are events of contraction in a cardiac muscle?

Answer 30

Similar to skeletal muscle except T tubules are located at the Z line and take the form of dyads rather than triads

Question 31

Purkinje Fibers

Answer 31

Impulse conducting modified cardiac fibers

Question 32

Where are purkinje fibers located?

Answer 32

Interventricular septum and beneath the endocardium

Question 33

Purkinje fibers structure compared to cardiac muscle cells

Answer 33

Occur in groups 50 micrometers Contain fewer peripherally located myofibrils Less developed striations More glycogen

Question 34

Smooth muscle structure

Answer 34

Spindle-shaped Single centrally located nucleus 5-20 micrometers in diameter 20 micrometers to 1 mm or more in length contains actin myosin filaments Actively divides and regenerates

Question 35

What surrounds the smooth muscle?

Answer 35

Surrounded by external lamina except at sites of gap junctions

Question 36

What is present in the striated muscle?

Answer 36

Striations and troponin protein

Question 37

Myofilaments in the smooth muscle

Answer 37

Attached to dense bodies which are analogous to Z lines of striated muscle

Question 38

How do smooth muscles communicate?

Answer 38

Via gap junctions

Question 39

How does contraction in the smooth muscle differ from the skeletal muscle?

Answer 39

Occurs more slowly and lasts longer

Question 40

Steps of muscle contraction in smooth muscles

Answer 40

1. Increase in cytosolic calcium, 2. binding of calcium with calmodulin protein, 3. activation of myosin kinase 4. Phosphorylation of myosin 5. interaction of phosphorylated myosin and actin 6. contraction

Question 41

What leads to relaxation in the smooth muscle?

Answer 41

Desphosphorylization of myosin preventing myosin-actin interaction

Question 42

Urinary smooth muscle contraction

Answer 42

Triggered by stretching of the muscle, Spreads from cell to cell gap junctions Generates low level of rhythmic contraction Increased or decreased autonomic nervous system rather than actually initiating the contraction Ex; viscera of GI tract

Question 43

Multi-unit smooth muscle

Answer 43

Triggered by nerve impulses Precise contractions due to autonomic innervation of each muscle cell Lack gap junctions ex: constrictor and dilator muscles of the iris