muscle physiology : Mechanism of Force Generation

Question 1

ATP used by muscles for:

Answer 1

1. CROSSBRIDGE CYCLE

2. active transport of calcium back into sarcoplasmic reticulum (relaxation)

Question 2

Muscle Metabolism

the 3 metabolic pathways

Answer 2

1. Creatine Phosphate
2. Glycolysis
3. Oxidative Phosphorylation

Question 3

1. Creatine Phosphate (and ATP) system

formula

Answer 3

……………………………………….creatine kinase……………………………
Creatine Phosphate + ADP <———–>. creatine + ATP

…………………. ATPase…………………………………………..
ATP + H20. <———>. ADH + Pi+ H+. + energy

Question 4

1.Creatine Phosphate (and ATP) system

features

Answer 4

creatine phosphate = first source of ATP
can provide 4-5 times the amount of ATP in cell at rest

one step process, very rapid
very limited amount, used up rapidly

Question 5

2. Anaerobic or Non-Oxidative Glycolysis

used when

Answer 5

-when oxygen supply to muscle is limited (during intense excersize) …
Anaerobic Glycolysis=primary source of ATP

high intensity excersize : 20-120 seconds

this is the breakdown of glucose ,02 absent

Question 6

2. Anaerobic or Non-Oxidative Glycolysis
   formula
   source of ATP

Answer 6

Glucose——–> 2 lactic acid + 2 ATP

rapid source of ATP:
Only two ATP/glucose
Limited glucose availability
Build up lactic acid (burning sensation)

Question 7

3. Oxidative Phosphorylation
   energy source…
   oxygen supply
   occurs in

Answer 7

//Primary energy source for Light / Moderate exercise (> 2 minutes)
• Muscle stores limited amount of glucose as glycogen
‒ Substrate of oxidative phosphorylation up to 30 mins
• Glucose and fatty acids delivered to muscle by blood
‒ Dominant after 30 mins

//adequate

// mitochondria

Question 8

The Mechanics of Contraction:

twitch contraction

Answer 8

a single action potential from a motor nueron will produce a single isolated contraction in a muscle fiber

this single isolated contraction is known as a twitch

Question 9

Phases of a Muscle Twitch

Answer 9

1. latent period
2. contraction phase
3. relaxation phase

Question 10

Latent period

Answer 10

Time from action potential in muscle cell to onset of contraction (few msec)

Excitation-contraction coupling

Question 11

2. Contraction phase

Answer 11

Tension is increasing (10–100 msec)

Crossbridge cycles take place repeatedly

Question 12

3. Relaxation phase

Answer 12

Tension is decreasing back to zero (longer than contraction phase)
Calcium reuptake

Question 13

isotonic vs isometric contraction

Answer 13

isotonic = load remains constant as muscle changes length

isometric= muscle is prevented from shortening so tension develops at constant muscle length

Question 14

Isometric Twitch Contraction

Answer 14

• length constant
• contractile elements generating tension
• Stretches series elastic elements
• muscle doesn’t shorten, load not lifted

Question 15

Isotonic Twitch Contraction

Answer 15

• constant tension

- load is lifted as muscle shortens

Question 16

Normal Muscle Activity:

purely isometric contractions occur…
purely isotonic contractions occur…

Answer 16

• in some daily situations

- rare

Question 17

Normal Muscle Activity:

Even load is constant..

Answer 17

isometric precedes isotonic phase of contraction

as tension ↑ the isometric contraction continues until tension exceeds than load

THEN isotonic contraction begins

tension remains constant as muscle shortens

Question 18

Graded Muscle Contractions:

The level of force generated by muscle depends on:

Answer 18

(Factors affecting the force or tension generated by individual muscle fibers )

• -frequency of stimulations
• -fiber diameter
• -changes in fiber length
• -extent of fatigue

(Regulation of the force/tension generated by whole muscle)
-number of fibers contracting

Question 19

Graded Muscle Contraction: Frequency of Stimulation

Answer 19

⇧frequency of action potentials in muscle fibers….⇧ tension

in 2 ways:
– Treppe
– Summation and tetanus

Question 20

what is a twitch

Answer 20

the. period of contraction and relaxation of a muscle after a single action potential

Question 21

what is summation
what
what happens

Answer 21

When multiple electrical stimuli are applied to a muscle at a high frequency,

twitches merge into higher force contractions.

Question 22

Twitch summation or treppe
what
results

Answer 22

addition of a second twitch, resulting in greater tension,

it results from stimulating the muscle before it has a chance to relax completely.

Question 23

Tetanus
what
results from

Answer 23

prolonged contraction without relaxation

results from repeating stimulation before the muscle has a chance to relax at all.