lecture 17 muscle 1.2

Question 1

muscle tension

Answer 1

forced exerted on an object by contracting a muscle

Question 2

load

Answer 2

force exerted on the muscle by an object

Question 3

if muscle tension is larger than load what happens

Answer 3

muscle fiber shortens and will move load

Question 4

isometric contraction

Answer 4

constant length

Question 5

isotonic contraction

Answer 5

• constant tension
• 2 types : concentric (up) and eccentric (down)

Question 6

concentric contraction
cross bridge cycle link

Answer 6

• shortening
• go through power stroke = shortening of the sarcomeres

-brings I bands and Z lines closer together (sarcomere shorten)

Question 7

isometric contraction

Answer 7

• constant
• rotation during power stroke is absorbed by elastic elements within the sarcomere and muscle (TITIN?)

Question 8

eccentric contraction

Answer 8

• *-lengthening**
• pulls cross-bridges backwards toward the Z lines while they are still bound to actin and exerting a force

-I bands and X lines move farther apart

Question 9

twitch contractions

Answer 9

• *twitch** : mechanical response of a muscle to a single AP (muscle contraction)
• *Latent period and contraction time**

Question 10

latent period

Answer 10

after an ap is initiated but before muscle contracts

-processes associated with excitation contraction coupling are occuring

Question 11

contraction time

Answer 11

time interval from the beginning of tension development at the end of the latent period to the peak tension

Question 12

fast twitch fibers

Answer 12

contraction time as short as 10 msec

• greater activity in fast twitch fibres
• Ca ATPase activty in SR is increased for Fast twitch contraction

Question 13

slow twitch fibers

Answer 13

• contraction time of 100 msec or longer
• contraction time depends on cytosolic Ca2+ levels
• contraction time also dependant on cross bridges time to complete a cycle and detach after the removal of Ca

Question 14

contraction time

Answer 14

not all muscle fibers have the same contraction time

depends on cytosolic Ca2+ levels → less calcium less powerstroke

Ca2+ ATP activity → pump calcium back into SR

• has greater activity in fast twitch fibers
• Ca decrease= decreased power stroke

Question 15

latent period longer

Answer 15

longer in isotonic vs isometric twitch contraction

isometric : includes excitation contraction coupling

isotonic : includes excitation contraction coupling and a brief period of isometric contraction

→ duration of the mechanical event is more brief

Question 16

isotonic twitch depend on

Answer 16

magnitude of the load

Question 17

at heavier loads

Answer 17

latent period is longer, velocity of shortening is slower, and the distance shortened is less

Question 18

at lighter loads

Answer 18

latent period is shorter, velocity of shortening is faster, distance shortened is greater

Question 19

load-velocity relation

Answer 19

• how fast can it shorten
• determined by rate at which individual cross-bridge undergo their cyclical activity

→ function of maximum intrinsic rate of myosin ATPase enzyme

Question 20

increasing load on a cross bridge

Answer 20

slow movement during power stroke. Reduces overall rate of ATP hydrolysis and thus decrease velocity of shortening

Question 21

when line crosses maximum isometric tension (zero velocity)

Answer 21

muscle lengthens instead of shortens

Question 22

frequency-tension relation

and summation

Answer 22

the effects of additional added cross-bridges

-summation : increase in muscle tension from successive AP occuring during the phase of mechanical activity

Question 23

frequency-tension relation

Answer 23

tetanus : maintained contraction in response to repetitive stimulation

unfused tetanus : tension may oscillate as the muscle fiber partially relaxes between stimuli at low stimulation frequencies

Question 24

fused tetanus

Answer 24

with no oscillations, is produced at higher stimulation frequencies

Question 25

tetanic tension is greater than twitch tension

Answer 25

tetanic tension> twitch tension

Question 26

length tension relation

Question 27

Lo

Answer 27

• optimal length, length at which the fiber develops the greatest isometric active tension
• anything after will have a decrease in tension

Question 28

titin

Answer 28

• spring like properties, attached to the z line at one end and thick filaments at other,
• responsible for most of the passive elastic properties of relaxed muscle fibers

Question 29

active tension

Answer 29

can be altered by changing the length of the fiber

Question 30

isometric tension generation in skeletal muscle is

Answer 30

a function of the overlap between actin and myosin filaments

Question 31

limited/ no force production if

Answer 31

too much overlap or no overlap/cross bridges

Question 32

towards Lo

Answer 32

fibers shorten, more filaments overlap, and tension develops and increases with increased cross bridges

Question 33

shortening doesnt begin until

Answer 33

enough cross bridges have attached and the muscle tension exceeds the load on the fiber