Chapter 10 muscle tissue

Question 1

6 functions of skeletal muscles

Answer 1

Produce skeletal movement 
Maintain posture and body position
Support soft tissues
Guard body entrances and exits
Maintain body temperature
Store nutrients

Question 2

Organization of the skeletal muscle

Answer 2

Muscle fiber (cell)
Muscle Fascicle ( bundle of fibers)
Skeletal muscle (organ)

Question 3

3 layers of connective tissue in muscles

Answer 3

Epimysium: dense layer of colligen fibers that surrounds the entire muscle
Perimysium:divides muscle into bundles of fibers called fascicles.
Endomysium: delicate, flexible and elastic connective tissue that surrounds each individual cell.

Question 4

Each endomysium contains (3)

Answer 4

1. capillary network that supply blood to the muscle
2. myosatillite stem cells that help repair damaged muscle
3. nerve fibers that control the muscle

Question 5

Features of skeletal muscle fibers

Answer 5

Enormous
Multinucleated
Striated: contain thin (actin) and thick (myosin) filaments
A muscle cell is formed by myocytes that fuse together as a fetus.

Question 6

Sarcolemma

Answer 6

Plasma membrane of a muscle fiber

Has membrane potential due to more negative cytoplasmic side and more positive extracellular side

Question 7

Sarcoplasm

Answer 7

Cytoplasm of a muscle fiber

Question 8

Transverse (T) tubules

Answer 8

Narrow tubes whose surfaces are continuous with the sacroplasm and extend deep into the sarcoplasm. Electrical impulses called action potentials travel along the T tubules and trigger the muscle fiber to contract

Question 9

Myofibrils

Answer 9

Cylindrical fiber within the muscle fiber that contains actin, myocin and titin–elastic myofilaments associated with the thick filaments.

Question 10

Sarcoplasmic reticulum (SR)

Answer 10

tubular network around each myofibril that is similar to a smooth ER.

Question 11

Terminal cisternae

Answer 11

Expanded chambers of the SR that form on either side of the T tubules. Contains 40,000 times the Ca+ as cytosol. .
Muscle contraction begins when the Ca+ is released into the cytosol

Question 12

Triad

Answer 12

A combination of 2 terminal cisternae with a t tubule in the center

Question 13

Sarcomeres contain (4):

Answer 13

The smallest functional units of the muscle fiber and contain:
1. thick filaments
2. thin filaments
3. proteins that stabilize the position of thick and thin filaments
4. proteins that regulate the interactions between thick and thin filaments
Each sarcomeres have dark A bands and light I bands

Question 14

A bands

Answer 14

Contain regions of overlapping thick (myosin) and thin (actin) filaments. Within the A band is:

1. The M line-in the center of the A band, help stabilize the position of the thick filaments
2. The H band- the light region on each side of the M line, contains thick filaments but no thin
3. The zone of overlap- 3 thick surround each thin and 6 thin surround each thick. Triads are located in this zone

Question 15

I bands

Answer 15

Region of the sarcomere that contains thin but no thick

Z lines bisect each I band and mark the boundary between each sarcomere

Question 16

Titin

Answer 16

Extend from the tips of the thick filaments and attach to the Z line.

1. Helps keep thick and thin filaments in proper allignment
2. Aids restoring sarcomere length after contraction

Question 17

Thin filaments

Answer 17

Contain 4 proteins: F-actin, nebulin, tropomyosin and troponin
F-actin in a double helix held together by a central nebulin
G- actin are the molecules that contain the active site for myocin to bind
Troponin-tropomyosin complex prevents myocin from binding

Question 18

Tropomyocin

Answer 18

Covers the active sites on G-actin and prevents actin-myocin interaction

Question 19

Troponin

Answer 19

Molecule that consists of 3 globular sub-units that bind to tropomyosin and G actin and a third binds to two Ca+ ions. When Ca+ binds to troponin it releases tropomyocin complex which exposed the active site for myocin.

Question 20

5 levels of organization in skeletal muscle

Answer 20

Sarcomere 
Myofibril
Muscle fiber
Muscle fascicle 
Skeletal muscle

Question 21

Thick filaments

Answer 21

Contains about 300 myocin molecules that are composed of a myosin tail and a double head on a hinge. The tails are twisted together and the head faces the nearest thin filament.

Question 22

Cross- bridges

Answer 22

When the myosin heads interact with the thin filaments during contraction

Question 23

What happens when the skeletal muscle contracts (4 steps)

Answer 23

1. H bands and I bands of the sarcomere narrow
2. The zones of overlap widen
3. Z lines move closer together
4. The width of the A bands remains constant

Question 24

Events at the neuromuscular junction (5)

Answer 24

1. ACh is released in the from the axon terminal into the synaptic cleft
2. ACh stimulates an action potential that travels along the length of the axon
3. Action potrntial reached the axon terminal and releases ACh by exocytosis
4. ACh binds o the motor end plate of the muscle and alters the cells permeability to Na+
5. Influx of Na+ creates action potential in sacrolemma then

Question 25

Excitable membranes

Answer 25

Permit rapid communication between different parts of the cell Cells on the inner surface are slightly negative compared to cells in the outer surface This creates typical resting membrane potentials of -70 mV and -85 mV Contain voltage gated channels that are activated and inactivated by changes in membrane potential.

Question 26

Excitation contraction coupling (6 steps)

Answer 26

The generation of action potential in the sarcolemma and the start of a muscle contraction: 1. Neural Control 2. Excitation 3. Release of Calcium ions 4. Contraction Cycle Begins 5. Sarcomere Shortening 6. Generation of Muscle Tension

Question 27

^ steps of the contraction cycle and cross bridge formation

Answer 27

1. Contraction cycle begins 2. Active site exposure 3. Cross bridge formation 4. Myosin head pivoting 5. Cross bridge detachment 6. Myosin reactivation

Question 28

2 factors that affect muscle tension produced

Answer 28

1. the fibers resting length at the time of stimulation, which determines the degree of overlap 2. the frequency of stimulation, which affects the internal concentration of Ca+ and the amount of bound troponin

Question 29

3 phases of a twitch

Answer 29

1. latent: 2. contraction phase 3. relaxation phase

Question 30

The amount of tension produced in a whole muscle is determined by (2 things)

Answer 30

1. The tension produced by a single muscle fiber | 2. The total number of muscle fibers stimulated

Question 31

Motor unit

Answer 31

All the muscle fibers controlled by a single motor neuron

Question 32

Isotonic Contractions

Answer 32

Tension increases and muscle length changes: Concentric: The muscle tension exceeds the load and the muscle shortens Eccentric contraction: the peak tension developed is less than the load and the muscle elongates due to contraction of another muscle or gravity

Question 33

Isometric Contractions

Answer 33

Muscle as a whole does not change length and the tension produced never exceeds the load

Question 34

Cardiac muscle characteristics

Answer 34

Relatively small Single centrally placed nucleus Typically branched No triads SR lack terminal cisternae More sensitive to changes in extracellular Ca+ Each cardiac muscle cell contacts other cells by intercalated discs

Question 35

Intercalated discs

Answer 35

Gap junctions and desmosomes

Question 36

Cardiac muscle functional differences

Answer 36

1. Automaticity 2. Nervous system can alter the rate 3. Contractions last 10x longer 4. Cannot produce tetanic contractions

Question 37

Smooth muscle characteristics

Answer 37

Forms sheets, bundles and sheaths around other tissues Non striated Involuntary Long and slender Spindle shaped No T tubules Thick filaments are scattered throughout More myosin heads per thick filament Thin filaments are attached to dense bodies

Question 38

Smooth muscle functional differences

Answer 38

1. Free calcium in cytoplasm triggers contraction 2. Tension and resting length are not related (plasticity is the ability to function over a wide range) 3. Multiunit smooth muscle cells and visceral smooth muscle which is not connected to a motor unit 4. Smooth muscle tone can be controlled by both multiunit and visceral smooth muscle as well as hormonal or chemical factors