Chap 11 Muscle Tissue Part 2

Front 1

length-tension relationship

Back 1

-a principle that describes muscle action
-the force of contraction of a muscle (i.e., the amt. of tension or “pull” it can generate) depends on how stretched or contracted it was before it was stimulated.

Front 2

if muscle is overly contracted when at rest (too short)

Back 2

-when stimulated, muscle can’t contract much more
-result: contraction is weak

Front 3

-if muscle is overly stretched when at rest:

Back 3

-little overlap btwn thick & thin filaments
-myosin heads have little to grab on to
-result: contraction is weak
-example: go up steps two at a time; thigh muscles over-stretch before you step up; less efficient way of going up steps

Front 4

if muscle is at optimum contraction when at rest

Back 4

-there is a “best” resting length
-allows muscle to give greatest contraction
-muscle tone maintains resting muscles at optimum length
-keeps them “ready for action”

Front 5

lab set-up (Frog)

Back 5

-frog gastrocnemius muscle & attached sciatic nerve
-when stimulated w/electrodes, contraction measured as graph (myogram)

Front 6

threshold

Back 6

-smallest voltage needed to produce an action potential and a contraction
-a pulse of Ca+2 is released into the cytosol filaments slide

Front 7

the strength of a twitch can vary, depending on

Back 7

1-Stimulation Frequency

2-Conc. of Ca+2 in the sarcoplasma

3-how stretched muscle is at rest

4-temperature

5-the strength of a twitch can vary, depending on

Front 8

stimulation frequency

Back 8

-the closer together stimuli occur, the stronger the twitch

Front 9

conc. of Ca+2 in the sarcoplasm

Back 9

-more Ca+2 causes stronger twitch
-varied by stimulation frequency

Front 10

how stretched muscle is at rest

Back 10

-length-tension relationship

Front 11

temperature

Back 11

-warm muscle contracts stronger because enzymes controlling myosin heads work faster

Front 12

twitch strength can vary

Back 12

the strength of a twitch can vary, depending on (“fatigue” as lactic acid builds in a working muscle)

Front 13

variable strength of twitches needed

Back 13

lift light or heavy object

Front 14

apply low voltage (below threshold)

Back 14

no contraction

Front 15

apply threshold voltage

Back 15

small twitch

Front 16

apply increasing voltage

Back 16

larger contraction
-height of graph goes up

Front 17

this occurs because of recruitment

Back 17

-more motor units are recruited
-motor unit = one motor axon & all muscle fibers it touches
-as stimulus increases, more muscle fibers contract

Front 18

low freq. of stimuli

Back 18

muscle relaxes completely btwn. stimuli, each twitch is at same level of contraction

Front 19

moderate freq. of stimuli

Back 19

treppe is seen (staircase)

-muscle relaxes btwn. twitches, but each twitch is stronger
-caused by increased level of Ca+2 in sarcoplasm
-doesn’t have time to return to SR btwn. twitches

Front 20

incomplete tetanus

Back 20

higher freq. of stimulation

-muscle does not relax completely btwn. twitches
-each twitch is stronger than the last
-also called summation

Front 21

complete tetanus is seen...

Back 21

even higher freq.

-maximum sustained contraction
-do not confuse with bacterial toxin that causes condition of same name

Front 22

normal muscle function

Back 22

-tetanus is normal, but a whole muscle is not in complete tetanus
-motor units in a muscle alternate contracting & relaxing
-allows smooth movement & control of muscles