Muscle Physiology

Question 1

Name the 4 steps of cross-bridge formation

Answer 1

1. rest
2. excitation
3. contraction
4. relaxation

Question 2

What occurs during the rest phase of cross-bridge formation?

Answer 2

• actin binding sites physically blocked by troponin-tropomyosin complex
• ATP is hydrolyzed = ADP Pi format on myosin head
• keeps myosin head released (“cocked”) from actin

Question 3

What happens during the excitation phase of cross-bridge formation?

Answer 3

• AP changes DHP & RyR receptors allowing Ca2+ release from SR
• Ca2+ binds to troponin, pulls away from binding sites on actin

Question 4

What happens during the contraction phase of cross-bridge formation?

Answer 4

• myosin head binds w/ actin
• myosin head power stroke pulls thick filament along thin
• can continue as long as AP is sustained (ATP binds to myosin head, detaches, repeats)

Question 5

What happens during the relaxation phase of cross-bridge formation?

Answer 5

• ATP binds to myosin head and detaches
• AP ends
• Ca2+ sequestered in SR
• troponin-tropomyosin complex blocks actin binding sites

Question 6

How does tetanus affect the cross-bridge cycle of sliding filament theory?

Answer 6

• stops inhibitory nn.
• excitatory nn. stay contracted

Question 7

How does rigor mortus occur in regards to the cross-bridge cycle of sliding filament theory?

Answer 7

• depleted ATP –> unable to release actin-myosin
• stays contracted

Question 8

The additive effect of several electrical impulses on a neuromuscular junction is called ____

Answer 8

summation

Question 9

The fusion of individual contractions or twitches to form a continuous contraction is called ____

Answer 9

tetanus

Question 10

Graded muscle contractions are built by ____

Answer 10

repeated contractions

Question 11

During contraction, the origin and insertion of a muscle ____

Answer 11

approximate

Question 12

Do calcium levels have a neurologic effect or muscular effect?

Answer 12

neurologic

Question 13

Tension produced during contraction is related to ____

Answer 13

sarcomere length

Question 14

At what sarcomere lengths are a muscle the weakest?

Answer 14

shortened (max. flexion) and lengthened (full extension)

Question 15

What is the “functional length” of a sarcomere?

Answer 15

length at which the most tension on the sarcomere occurs (~70-110 deg)

Question 16

What is the velocity of contraction dependent on?

Answer 16

number of sarcomeres in a cell and Force applied

Question 17

What is the relationship between force applied and muscle contraction velocity?

Answer 17

inverse (i.e., more weight/force = slower contraction)

Question 18

At what load/force is muscle shortening velocity maximized?

Answer 18

0

Question 19

As more load/force is applied to a muscle, slowing the shortening velocity, this produces an ____ contraction

Answer 19

isotonic

Question 20

As load increases, the contractile system yields, lengthening the muscle which produces an ____ contraction

Answer 20

eccentric

Question 21

When maximum force is developed, and velocity is 0, this produces an ____ contraction

Answer 21

isometric

Question 22

Most failure/injuries occur during ____ contraction

Answer 22

eccentric