10.3-muscles- skeletal muscle fibers

Question 1

Skeletal muscle fibers develop by fusion of

Answer 1

embryonic cells called myoblasts

Question 2

what is the sacrolemma

Answer 2

Plasma membrane of a muscle fiber
– Surrounds the sarcoplasm (cytoplasm of a muscle
fiber)

Question 3

what is the transverse tubules

Answer 3

tubes that extend from surface of muscle fiber deep nto sarcoplasm
– Transmit action potentials from sarcolemma into cell
interior
▪ Action potentials trigger contraction

Question 4

describe the sarcoplasmic reticulum

Answer 4

– A tubular network surrounding each myofibril
– Similar to smooth endoplasmic reticulum
– Forms chambers (terminal cisternae) that attach to T tubules
▪ Two terminal cisternae plus a T tubule forms a triad
– Specialized for storage and release of calcium ions
▪ Ions are actively transported from cytosol into
terminal cisternae

Question 5

describe the myofibrils

Answer 5

Responsible for muscle contraction
– Made of bundles of protein filaments (myofilaments)
– Two types of myofilaments
▪ Thin filaments
– Composed primarily of actin
▪ Thick filaments
– Composed primarily of myosin

Question 6

Describe the sacromeres

Answer 6

Interactions between filaments produce contraction
– Arrangement of filaments accounts for striated pattern
of myofibrils
▪ Dark bands (A bands)
▪ Light bands (I bands)

Question 7

What are the parts of the A band

Answer 7

– M line
▪ In center of A band
▪ Proteins stabilize positions of thick filaments
– H band
▪ On either side of M line
▪ Has thick filaments but no thin filaments
– Zone of overlap
▪ Dark region
▪ Where thick and thin filaments overlap

Question 8

What are the parts of the I band

Answer 8

The I band
– Contains thin filaments but no thick filaments
– Z lines
▪ Bisect I bands
▪ Mark boundaries between adjacent sarcomeres
– Titin
▪ Elastic protein
▪ Extends from tips of thick filaments to the Z line
▪ Keeps filaments in proper alignment
▪ Aids in restoring resting sarcomere length

Question 9

What are the levels of functional organization in a skeletal muscle

Answer 9

the sarcomere makes up the myofibril which makes up them muscle fiber. These muscle fiber come together and form the muscle fascicle which makes up the skeletal muscle

Question 10

Describe the thin filaments

Answer 10

The thin filaments have filamentous actin which are twisted strands composed of two rows of globular G- action molecules. The G-actin has active sites that bind to myosin in the thick filament. Nebulin is used to hold f-actin together. Similarly, the tropomyosin covers the active sites on G -actin thus preventing actin-myosin interaction. In the same breath troponin binds tropomyosin, G-actin and Ca

Question 11

Describe the Thick filaments

Answer 11

The thick filaments consist of myosin molecules. Each myosin molecule consists of a tail that binds to other myosin molecules and a head that projects toward the nearest thin filament.

Question 12

What is the core of thick muscle made of

Answer 12

titin

Question 13

Explain the sliding-filament theory during contraction

Answer 13

During contraction, the H band and I band become narrow while the sones of overlap widen. The Z lines move closer together and the width of the A band remains constant. Thus the thin filaments slide toward the center of sacromere.