Session 12

Question 1

What is the definition of the Refractory Period?

Answer 1

A phase starting when sodium channels close.

Question 2

What are the three types of Refractory Periods?

Answer 2

• Absolute Refractory Period
• Relative Refractory Period
• Supernormal Refractory Period

Question 3

What occurs during the Absolute Refractory Period?

Answer 3

No impulses can depolarize the cell.

Question 4

What occurs during the Relative Refractory Period?

Answer 4

A stronger than normal impulse can depolarize the cell.

Question 5

What occurs during the Supernormal Refractory Period?

Answer 5

A slight impulse can depolarize the cell.

Question 6

What are Afterdepolarizations?

Answer 6

Abnormal depolarization of cardiac myocyte.

Question 7

During which phases can Afterdepolarizations occur?

Answer 7

• Phase 2
• Phase 3
• Phase 4

Question 8

What are the causes of Afterdepolarizations?

Answer 8

• Alteration in K+ channel function
• Overloading of Ca++

Question 9

What risks are associated with Afterdepolarizations?

Answer 9

Can cause lethal arrhythmias.

Question 10

What are Early Afterdepolarizations (EAD)?

Answer 10

Occur when membrane potential is ~ -20mV.

Question 11

What are Delayed Afterdepolarizations (DAD)?

Answer 11

Occur during the resting phase.

Question 12

What are the key contractile proteins?

Answer 12

• Actin
• Myosin
• Troponin
• Tropomyosin

Question 13

What is the structure of Actin?

Answer 13

Thin myofilament, double strand string of beads.

Question 14

What is the structure of Myosin?

Answer 14

Thick filament, long helical tail with two globular heads.

Question 15

What role does Myosin play in muscle contraction?

Answer 15

Crosses with actin to cause contraction.

Question 16

What are the subunits of Troponin?

Answer 16

• TnC
• TnI
• TnT

Question 17

What is the function of Tropomyosin?

Answer 17

Binds to actin to cover myosin binding sites.

Question 18

What is the process of Excitation-Contraction Coupling?

Answer 18

Converts electrical cell activation to muscle contraction.

Question 19

What happens during the contraction mechanism?

Answer 19

• Sarcolemma depolarizes
• T-tubules depolarize
• Terminal cisternae release Ca++
• Sarcoplasmic reticulum releases more Ca++

Question 20

What is calcium-induced calcium release?

Answer 20

Calcium released from terminal cisternae induces more calcium release from sarcoplasmic reticulum.

Question 21

What does Ca++ bind to during muscle contraction?

Answer 21

Binds to TnC to move tropomyosin away from binding sites of actin.

Question 22

What is the role of Myosin heads in muscle contraction?

Answer 22

Pull actin filaments toward the center of the sarcomere.

Question 23

What happens during the relaxation mechanism?

Answer 23

• Ca++ detaches from TnC
• Ca++ is pumped back into the sarcoplasmic reticulum
• Tropomyosin repositions over myosin binding site

Question 24

True or False: Stronger than normal impulses can depolarize the cell during the Relative Refractory Period.

Answer 24

True

Question 25

What is the thick myofilament protein?

Answer 25

Myosin

Question 26

What is the contraction mechanism?

Answer 26

Myosin heads pull actin toward the center of sarcomere to shorten I-bands.