Walk Along Theory & Muscle Strength

Question 1

What are the steps to the “Walk Along Theory” of muscle contraction?

Answer 1

1. Ca binds to troponin and the active site on actin is exposed.
2. Myosin head forms cross-bridge with actin.
3. “power stroke” = myosin head bends toward center of sarcomere and actin toward M line. ADP & P are released
4. New molecule of ATP attaches to myosin head = cross bridge detaches (low energy configuration).
5. ATP hydrolyzes to ADP & P = myosin in high energy “cocked” position.

Question 2

What are the 2 ways muscles change its strength of contraction?

Answer 2

1. Change # of motor units
2. Change frequency of stimulation

Question 3

What is the ‘latent period’?

Answer 3

Time between a stimulus to the motor neuron & the subsequent contraction of the innervated muscle.

Question 4

What are the 3 ways the strength of a skeletal muscle contraction are separated into?

Answer 4

Twitch, summation, tetanus.

Question 5

Describe ‘twitch’.

Answer 5

A single contraction (depol) & relaxation (repol) cycle by an AP within a muscle fiber.

Question 6

Describe ‘summation’.

Answer 6

Another AP comes before the complete relaxation of a muscle twitch, the next twitch will sum onto the previous one.

Question 7

What are the 2 types of summation?

Answer 7

Multiple fiber and frequency summation.

Question 8

Describe multiple fiber summation.

Answer 8

Increase in # of motor units and size results in a stronger contraction = ‘size principle’

Question 9

Describe frequency summation.

Answer 9

Increasing # of frequency of contraction increases the strength.
critical level = tetanization

Question 10

Describe tetanus.

Answer 10

The critical level frequency where the contractions are so rapid they fuse together into a smooth & continuous contraction = ‘tetanization’
MAX STRENGTH

Question 11

Describe the length-tension relationship.

Answer 11

-Amount of tension depends on # of cross bridge interactions and the degree of overlap between thin & thick filaments.
-Operate with the most strength at resting length = ideal length.
-If muscle is stretched (extended) or shortened (flexed), the strength of contraction is diminished.
-Muscle fibers contract forcefully when stimulated over narrow range of resting lengths.

Question 12

Describe the 3 lengths in the length-tension relationship?

Answer 12

1. Decreased length (flex) = sarcomere is overly contracted with a high degree of overlap between filaments. Muscle contraction can’t progress & tension decreases.
2. Optimal resting length = sarcomere at resting length, optimal # of cross bridges formed, contraction is optimal, & maxed tension.
3. Increased length (extend) = sarcomere pulled away, little or no interaction between filaments/none.

Question 13

List the sources of energy for muscle contraction.

Answer 13

Phosphocreatine/creatine phosphate, glycolysis, oxidative metabolism.

Question 14

Describe phosphocreatine/creatine phosphate.

Answer 14

-creatine made from liver.
-phosphorylated in muscle by enzyme ‘creatine phosphokinase’ (CPK) to make phosphocreatine.
-cleavage of phosphocreatine releases energy to bind a new P ion to ADP to make ATP.

Question 15

Describe glycolysis.

Answer 15

-enzymatic breakdown of carbohydrates = glucose + glycogen.
-release of energy makes ‘pyruvic acid’ & ‘lactic acid’.
-energy used to make ATP & phosphocreatine.
can be done w/o O2
-rate of ATP formation 2.5x faster than oxidative metabolism
-end products like lactate made

Question 16

Describe oxidative metabolism.

Answer 16

-makes 95% of energy for contraction
-combines O2 w/ end products of glycolysis & proteins, lipids, carbohydrates to make ATP (36)
-short periods = carbohydrates
-long periods = fatty acids

Question 17

What muscle tissues needs ATP?

Answer 17

1. Walk along mechanism
2. Ca pump in SR (active transport)
3. Na K pump in sarcolemma (active transport)