Muscle Mechanics

Question 1

describe the temporal relation between skeletal action potential, calcium and tension.

Answer 1

action potential comes first, followed by calcium increase and tension. there is a slight gap between each of the phases

Question 2

what is an isometric contraction?

Answer 2

when skeletal muscle contracts and stays the same length because it is attached to two immovable objects

Question 3

how much work is done in an isomeric contraction? how much power?

Answer 3

none of either because there was no distance moved

Question 4

in what instances are isometric contractions involved?

Answer 4

maintaining posture.

also used to experiment with muscle properties

Question 5

how does an isometric contraction occur with the shortening of contractile units?

Answer 5

the elastic element of the muscle (tendon) elongates by an equal distance to keep the length of the muscle fiber constant

Question 6

what is an isotonic contraction?

Answer 6

a contraction associated with a change in length

Question 7

what are most coordinated movements of the body involving?

Answer 7

isometric and isotonic combinations of contractions

isometric contractions maintain posture while isotonic contractions produce movement

Question 8

how is isotonic twitch measured?

Answer 8

by attaching the muscle to a movable load

Question 9

describe the force of an isotonic twitch.

what will create a different tension curve?

Answer 9

the force shows a plateau during which the force is constant
a different curve will occur with a change in load

Question 10

how does a greater load affect the tension curve of an isotonic twitch?

Answer 10

higher plateau and greater time lag between stimuli ad the start of muscle shortening

Question 11

what occurs when the load exceeds the amount of force that the isotonic muscle can generate?

Answer 11

an isometric twitch results

Question 12

what is the series elastic element?

Answer 12

a rubber band like tendon that includes all of the elasticity that is in the system

Question 13

at what point does the load begin to move in an isotonic twitch?

Answer 13

when the tension builds up to the point it equals or slightly exceeds the load

Question 14

what happens to the tension once the load begins to move?

Answer 14

the tension becomes constant

Question 15

what are the four stages of an isotonic twitch?

Answer 15

1) isometric tension development
2) isotonic shortening at constant tension
3) isotonic relaxation- return to initial length at constant tension
4) isometric relaxation

Question 16

what is the formula for work? what is the formula for power?

Answer 16

work=tension x distance shortened

power= work/time

Question 17

what is the initial velocity of shortening? what is the rate of development of tension?

Answer 17

the initial slope of the shortening curve

the slope of the tension vs time curve

Question 18

what is the rate of tension development a function of?

Answer 18

the active properties of the muscle and the passive properties of the tissue (like tendons)

Question 19

when is the velocity of shortening maximal?

Answer 19

at the beginning of shortening

Question 20

as the load increases for an isotonic twitch, what three aspects of muscle shortening change?

Answer 20

initial velocity of shortening decreases, the amount of shortening decreases and the duration of shortening increases

Question 21

at what point is the maximal amount of tension for the initial length?

Answer 21

when the muscle cannot lift the weight at all

Question 22

what is a measure of strength or health of a heart?

Answer 22

the maximal rate of tension development during isovolumic contraction

Question 23

what are some effects in the distance shortened vs time plot with increasing isotonically with increasing loads?

Answer 23

latent period increases, duration of shortening decreases and the velocity of shortening decreases

Question 24

at what condition is Vmax experienced for an isotonic contraction? what is Vmax a function of?

Answer 24

under zero load

a function of myosin ATP ase in varying muscle types

Question 25

what is Po?

Answer 25

the maximal isometric tension that can be generated at a given initial length and a state of contractility (when the muscle can not lift, the largest tension)

Question 26

what is Po a function of?

Answer 26

the number of cross bridges that can be formed

larger muscle have larger number of cross bridges

Question 27

how can Po for a skeletal muscle increase?

Answer 27

frequency modulation, recruitment of additional motor units and with initial lengths closer to the optimal initial length

Question 28

how can Po for cardiac muscle increase?

Answer 28

increased initial length, and by increased contractility (not by recruitment because all cells already contract)

Question 29

when do myofibers produce maximum work and power?

Answer 29

at intermediate loads

Question 30

why is velocity of shortening an important concept?

Answer 30

because different types of fibers differ in their velocity of shortening

Question 31

what are preload and afterload?

Answer 31

preload is the load required to stretch a muscle from its resting length
afterload is equivalent to the total tension

Question 32

at what length do muscles normally operate?

Answer 32

at 100-115% of resting length

Question 33

what comprises the total load of a muscle?

Answer 33

the preload and afterload

Question 34

how was the length tension diagram devised?

Answer 34

by measuring isometric twitches at varied lengths

Question 35

what are the characteristics of tension for an isometric skeletal muscle contraction?

Answer 35

tension develps at constant length to maximal tension for that particular initial length and then decreases to 0g at constant length

Question 36

how many newtons are in a kg of force?

Answer 36

9.8N