Deck 21: Contractile Mechanisms in Skeletal Muscle

Question 1

Heterogeneity of muscle speed in different muscle fibers depends in part on the

A) Len gth o f its thick filam ents
B) Len gth o f its thin filam ents
C) M yos in iso form exp ress ed by th e m us cle fiber
D) Ac tin is of or m ex pr es se d b y the m us cle
E) Speed of nerve action potential conduction

Answer 1

C

Question 2

The velocity of muscle contraction at maximum recruitment depends on

A) Its afterload
B) Its velocity of action potential propagation
C) The turnover number of the myosin ATPase
D) The num ber of active cross bridges in each fiber
E) Both A and C are correct

Answer 2

A

Question 3

Myofibrils are

A) Single filament systems that can interact to produce force
B) Eq uiv ale nt o f m us cle ce lls w ith a ce ll m em br an e th at s ur ro un ds the m yof ibr ils
C) Ch ain of m itocho ndria betw een the c ontra ctile elem ents
D) Bundles of myofilaments w ithin the muscle fiber
E) C ytos ke leta l m atr ix th at jo ins the co ntr ac tile e lem en ts to the ex tra ce llula r m atr ix

Answer 3

D

Question 4

The thick filament is 1.6 µ m lon g and the thin filament is 1.0 µm. At a sarcomere length of 2.2 µm, wha t frac tion of the p art of th e thick filam ent c onta ining m yosin h ead s is co vere d by a th in filam ent?

A) 100%
B) 90%
C) 80%
D) 70%
E) 60%

Question 5

The A band contains all of the follow ing EXCEPT

A) M yos in
B) Ac tin
C) Actin in
D) TnC
E) T itin

Question 6

The plate au a t the top of the length -tens ion cu rve is d ue to

A) The "bare zone" in the middle of the thick filament that lacks myosin heads
B) Interference of thin filaments from adjacent half-sarcomeres
C) Interference of the thick filaments with the Z line proteins
D) The series-elastic elements limiting force transfer
E) Heterogeneity of sarcomere lengths along the muscle fiber

Question 7

The thick filament is 1.6 µm long and the thin filament is 1.0 µm . At a sarcom ere length of 2.2 µm, how m uch of the thin filam ent is c ove red b y the thick filam ent?

A) 90%
B) 80%
C) 70%
D) 60%
E) 50%

Question 8

Isometric active force developed by skeletal muscle at long lengths (greater than the rest length)

A) Is dire ctly prop ortion al to the ove rlap o f thin an d thick filam ents
B) Depends on the number of cross-bridges
C) Depends linearly on the distance
D) Is a m ajo r ev ide nc e fo r th e s lidin g fila m en t hyp oth es is
E) All of the above

Question 9

During a concentric contraction of m us cle

A) The A band shortens
B) The I and H zone shorten while the A band stays constant
C) The I band shortens while the H and A band stay constant
D) A, I and H bands all shorten
E) The A band shortens while the I band stays constant

Question 10

"Striations" are

A) Strip es th at ru n ac ros s th e m us cle fib er at rig ht a ng les to its lon g ax is
B) The long appearan ce of nuclei in mu scle fibers
C) Longitudinal stripes running parallel to the long axis of a muscle fiber
D) Str ipe s r un nin g p ar alle l to th e m yof ibr ils
E) Stripes caused by the orientation of m itochondria in mus cle fibers

Question 11

The thick filament is 1.6 µm lon g a nd the thin filam en t is 1.0 µm . At a s arc om ere le ngth of 2.2 µm, how wide is the H band?

A) 0.3 µm
B) 0.2 µ m
C) 0.6 µm
D) 0.4 µm
E) It cannot be determined

Question 12

The I ba nd do es no t co nta in

A) Ac tin
B) T ro po m yos in
C) TnT
D) M yos in
E) TnC

Question 13

ATP hydrolysis associated with force development is carried out by

A) The m yosin heads of the thin filament
B) Ac tin
C) M yos in
D) T ro po m yos in
E) T itin

Question 14

The "turnover number" refers to the

A) Number of completed reactions per second
B) R ate of r ep lac em en t of a p ro tein
C) Rate of replacement of cell nuclei
D) Num ber of contractions per second
E) Rate of oxygen consumption

Question 15

The thin filament contains all of the following proteins EXCEPT

A) T ro po m yos in
B) Ca lseq ue strin
C) Ac tin
D) N eb ulin
E) Troponin I

Question 16

The pro tein of t he thic k f ilam en t tha t ex ten ds to th e Z line is

A) N eb ulin
B) Ac tin
C) Ac tinin
D) Titin
E) T ro po m yos in

Question 17

The pro tein m ain ly res po ns ible for an ch or ing the thin filam en ts a t the Z d isc is

A) T ro po m yos in
B) TnC
C) TnI
D) TnT
E) Actin in

Question 18

The sarcomere is defined as

A) Everything in the A band
B) Everything from M-line to the adjacent Z-disc
C) Everything from M-line to the adjacent M-line
D) Everything in the I band
E) Everything from Z disc to the adjacent Z disc

Question 19

Fo rc e d ev elo pe d b y m us cle

A) De rives from com pres sion of ela stic ele m ents
B) Is ca use d by the thin filam ents
C) Is ca use d by the thick filam ents
D) Derives from a n interaction of the thick an d thin filame nts
E) Is linea r with len gth

Question 20

Proteins involved in the lateral transmisson of m us cle for ce to th e o uts ide of th e m us cle fiber include

A) D ystr op hin
B) Surface integrins
C) Syn tro ph in
D) Dystroglycan
E) All of the above

Question 21

The structures thought to be involved in the lateral transmission of force are the

A) Ryanodine rece ptors
B) T ro po m od ulin
C) N eb ulin
D) Costameres
E) C als eq ue str in