Muscle contraction

Question 1

Nerve impulses elicit a muscle action potential in the following way:

Answer 1

1. Release of acetylcholine
2. Activation of ACh receptors
3. Production of muscle action potential
4. Termination of ACh activity

Question 2

Contraction cycle consists of 4 steps:

Answer 2

1. ATP hydrolysis
2. Formation of cross-bridges
3. Power stroke
4. Detachment of myosin from actin

Question 3

Maximum amount of muscle tension achieved =

Answer 3

strength of stimulus increases and frequency of action potentials increase - more and more alpha neurons are activated

Question 4

Minimal stimulus =

Answer 4

minimal # of alpha motor neurons = small amount of muscle tension

Question 5

Production of ATP in muscle fibers:

Answer 5

• Huge amount of ATP is needed to:
• Power the contraction cycle
• Pump Ca++ into the SR

Question 6

sources of ATP in muscle

Answer 6

PCr: creatine phosphate (seconds) 10-15 seconds
glycolytic: anaerobic glycolysis (minutes)
Aerobic: oxidative phosphorylation (hours)

*uses gluclose!

Question 7

Creatine phosphate

Answer 7

• Excess ATP is used to synthesize creatine phosphate
  - Energy-rich molecule
• Creatine phosphate transfers its higher energy phosphate group to ADP regenerating new ATP
• Creatine phosphate and ATP provide enough energy for contraction for about 15 seconds

Question 8

Anaerobic respiration

Answer 8

• ATP producing reactions do not require oxygen
• Glucose is used to generate ATP when the supply of creatine phosphate is depleted

Question 9

Aerobic respiration

Answer 9

• Myoglobin and hemoglobin are oxygen binding proteins
• supplies ATP for prolonged activity
• Provides <90% of the needed ATP in activities lasting more than 10 minutes
• Muscle tissue has 2 source of O2: hemoglobin and myoglobin

Question 10

muscle fatigue

Answer 10

• Results in cramping due to complete loss of ATP molecules (break the bonds between actin and myosin)
• Buildup of lactic acid causes muscle soreness but lowers pH (increased H+). the pain of pH and pH changes affects “central fatigue” not in specific muscle
• 40% of energy released is use for work

Question 11

The _________ are an invagination in the muscle cell’s sarcolemma.
a. Sarcoplasmic reticulum
b. Transverse T tubules
c. Cisternae
d. Microtubules

Answer 11

transverse T tubules

Question 12

Which of the following best describes the action potential of skeletal muscle upon stimulation?

a. It spreads inward to all parts of the muscle via the T-tubules
b. Is has prolonged plateau phase
It causes immediate uptake of Ca2+ into the lateral sacs of SR
c. It is longer than the action potential of cardiac muscle
d. It is not essential for contraction

Answer 12

a. it spreads inward to all parts of the muscle via T-tubules

Question 13

Which of the following is the most durable source of energy during exercise?

a.Anaerobic respiration
b. Aerobic respiration
c. ADP and creatine phosphate in the cell

Answer 13

b. aerobic respiration

Question 14

Muscles get fatigued due to accumulation of

a. Lactic acid
b. ATP
c.CO2
d. glycogen

Answer 14

a. lactic acid

Question 15

cardiac muscle

Answer 15

• contracts when stimulated by its own autorhythmic muscle fibers
• Enables coordinated contraction

Question 16

smooth muscle

Answer 16

• Can be stimulated or inhibited by presynaptic neurotransmitters or independently stimulated to contract due to stretch receptors or externally by hormones
• DO NOT contain sarcomeres
• Relies on Ca++ with their sliding filaments but rely on different mechanism to provide Ca++