Muscle Physiology

Question 1

What is the structure of skeletal muscle?

Answer 1

whole muscle< fascicles< muscle cells/fibres< myofibrils< myofilaments

Question 2

What are the two types of myofilaments?

Answer 2

thin and thick

Question 3

What is the structure of skeletal muscle?

Answer 3

diagram page 148

Question 4

What is the sarcolemma?

Answer 4

surrounds the cell membrane

Question 5

What do the transverse tubules do?

Answer 5

• continuation of the sarcolemma that travels down into the muscle cell and wrap around each myofibrils
• allow the AP to travel from the surface of the sarcolemma into the muscle cell where the contractile proteins are located

Question 6

What do the sarcoplasmic reticulum do? (SR)

Answer 6

wrap around myofibrils

• Ca is stored
• the portion of the SR that comes in contact with the T-tubule is called the lateral sac

Question 7

What is the structure of a thin myofilament?

Answer 7

diagram page 150

Question 8

What are the 3 contractile proteins in thin myofilaments?

Answer 8

1. G- Actin: contains myosin binding sites
2. tropomyosin: partially covers myosin binding sites
3. troponin: positions tropomyosin over binding sites until Ca++ arrives and rips it off

Question 9

What is the structure of a thick myofilament?

Answer 9

diagram page 151

Question 10

What is the actin/myosin relationship?

Answer 10

diagram page 152

Question 11

What is the smallest functional unit of the muscle cell?

Answer 11

sarcromere

Question 12

When does a cross bridge form?

Answer 12

when a myosin head attaches to an actin molecule, when this occurs a power stroke is initiated and a contraction will occur

Question 13

What events happen during the sliding filament theory?

Answer 13

• when myosin head binds to an actin a cross-bridge is formed
• myosin then changes shape and a peer stroke occurs
• actin slides past myosin

Question 14

What is the sliding filament theory?

Answer 14

the only structure that changes length in the muscle during a contraction is the sarcomere, not the thin or thick myofilaments

Question 15

What happens during neuromuscular transmission?

Answer 15

1 AP in the motor nerve will always produce 1 AP on the muscle cell membrane (sarcolemma)
steps and diagram page 155-156

Question 16

What is excitation- contraction coupling?

Answer 16

process by which an AP in the sarcolemma leads to the release of Ca++ from the SR, cross bridge activity and contraction
-the AP triggers the release of Ca++ from the lateral sac of the SR

Question 17

What are the events that occur during excitation- contraction coupling?

Answer 17

diagram and steps page 158

Question 18

What are the steps in the actin-myosin ATP cycle?

Answer 18

diagram page 159

Question 19

What is rigor mortis?

Answer 19

stiffening of muscles after death

-begins 3-4 hours after death and is complete about 12 hrs after death

Question 20

What is the cause of rigor mortis?

Answer 20

No O2-> no ATP
no ATP-> no Ca++ being pumped back into the SR
no ATP-> actin and myosin can’t dissociate, muscle is permanently fused into muscle starts decomposing

Question 21

What are the 2ways that the muscle can alter the force of contraction?

Answer 21

1. summation of twitch contraction- when you increase the frequency of AP, each muscle twitch has less time to relax causing a sustained contraction
2. recruitment of motor units- as you increase the amount of motor units firing the contractile forces increase giving you a larger muscle twitch

Question 22

What is a single muscle twitch?

Answer 22

muscle contraction in réponse to 1 AP on the motor neuron