Question 1

Removal of external Ca2+ to levels below about 0.2 mM result in no discernible force from the heart. This is because

Accepted Answer

A)  There is no cardiac action potential without extracellular Ca2+ 
B)  There is no calcium-induced-calcium release without extracellular Ca2+ 
C)  Ca2+ cannot enter over the NCX to activate the myofilaments 
D)  Ca2+ is pumped out of the cell by the PMCA 
E)  TnC is insensitive to Ca2+ when the heart is relaxed 
A)  There is no cardiac action potential without extracellular Ca2+ 
B)  There is no calcium-induced-calcium release without extracellular Ca2+ 
C)  Ca2+ cannot enter over the NCX to activate the myofilaments 
D)  Ca2+ is pumped out of the cell by the PMCA 
E)  TnC is insensitive to Ca2+ when the heart is relaxed B

Question 2

Stretch increases the force of cardiac contraction mainly by

Accepted Answer

A)  Increasing the size of the Ca2+ transient 
B)  Increasing the sensitivity of the myofilaments for Ca2+ 
C)  Increasing the turnover number of activated acto-myosin cross bridges 
D)  Decreasing the jamming of the myofilaments at short lengths 
E)  Increasing stretch of passive elements 
A)  Increasing the size of the Ca2+ transient 
B)  Increasing the sensitivity of the myofilaments for Ca2+ 
C)  Increasing the turnover number of activated acto-myosin cross bridges 
D)  Decreasing the jamming of the myofilaments at short lengths 
E)  Increasing stretch of passive elements B

Question 3

Ca2+ enters the cardiomyocytes every heart beat through

Accepted Answer

A)  L-type Ca2+ channels 
B)  Na-K-ATPase 
C)  PMCA 
D)  RyR2 
E)  SERCA2a 
A)  L-type Ca2+ channels 
B)  Na-K-ATPase 
C)  PMCA 
D)  RyR2 
E)  SERCA2a A

Question 4

W hich of the following is NOT one of the ways in which cardiomyocytes differ from skeletal muscle fibers?

Accepted Answer

A)  Cardiom yocytes have a greater volume of mitochondria than skeletal muscle fibers 
B)  There is on average one T-tubule per sarcomere in cardiomyocytes, two in skeletal muscle 
C)  Most cardiomyocytes have 1-2 nuclei; skeletal muscle fibers have many 
D)  Cardiomyocytes make electrical connections between adjacent cells, skeletal muscle fibers do not 
E)  Cardiomyocytes do not require external stimulation whereas skeletal muscle fibers do 
A)  Cardiom yocytes have a greater volume of mitochondria than skeletal muscle fibers 
B)  There is on average one T-tubule per sarcomere in cardiomyocytes, two in skeletal muscle 
C)  Most cardiomyocytes have 1-2 nuclei; skeletal muscle fibers have many 
D)  Cardiomyocytes make electrical connections between adjacent cells, skeletal muscle fibers do not 
E)  Cardiomyocytes do not require external stimulation whereas skeletal muscle fibers do

Question 5

Sympathetic stimulation increases all of the following EXCEPT

Accepted Answer

A)  Ca2+ entry over the L-type Ca2+ channel 
B)  Phospholamban phosphorylation 
C)  Ca2+ release through RyR2 
D)  Rate of Ca2+ dissociation from TnC 
E)  Ca2+ exit over the PMCA 
A)  Ca2+ entry over the L-type Ca2+ channel 
B)  Phospholamban phosphorylation 
C)  Ca2+ release through RyR2 
D)  Rate of Ca2+ dissociation from TnC 
E)  Ca2+ exit over the PMCA

Question 6

Cardiac muscle can increase its strength of contraction by all of the following EXCEPT

Accepted Answer

A)  Stretch, by increasing the sensitivity of the myofilaments to Ca2+ 
B)  Increasing the size of the Ca2+ transients by phosphorylation of phospholamban 
C)  Increasing recruitment of cardiomyocytes 
D)  Increasing the size of the Ca2+ transients by phosphorylation of DHPR 
E)  Increasing the size of the Ca2+ transients by phosphorylation of RyR2 
A)  Stretch, by increasing the sensitivity of the myofilaments to Ca2+ 
B)  Increasing the size of the Ca2+ transients by phosphorylation of phospholamban 
C)  Increasing recruitment of cardiomyocytes 
D)  Increasing the size of the Ca2+ transients by phosphorylation of DHPR 
E)  Increasing the size of the Ca2+ transients by phosphorylation of RyR2

Question 7

The space between myofibrils in cardiomyocytes is occupied mainly (in terms of volume) by

Accepted Answer

A)  glycogen granules 
B)  sarcoplasmic reticulum 
C)  Mitochondria 
D)  Nuclei 
E)  T-tubules 
A)  glycogen granules 
B)  sarcoplasmic reticulum 
C)  Mitochondria 
D)  Nuclei 
E)  T-tubules

Question 8

The force-frequency relation in the heart (the relation between frequency of stimulation and strength of the heart) is caused principally by

Accepted Answer

A)  Stretch of the cardiac muscle with Increasing frequency of stimulation 
B)  Increased in the sensit ivity of the myofilaments to Ca2+ 
C)  Phosphorylation of TnC 
D)  Increased [Ca2+] in the mitochondria 
E)  Increased [Ca2+] transients due to loading of the SR 
A)  Stretch of the cardiac muscle with Increasing frequency of stimulation 
B)  Increased in the sensit ivity of the myofilaments to Ca2+ 
C)  Phosphorylation of TnC 
D)  Increased [Ca2+] in the mitochondria 
E)  Increased [Ca2+] transients due to loading of the SR

Question 9

Cardiomyocytes form a functional syncytium by being electrically coupled to one another at the

Accepted Answer

A)  T-tubules 
B)  Sarcolemm a 
C)  Sarcoplasmic reticulum 
D)  Intercalated disks 
E)  Z disks 
A)  T-tubules 
B)  Sarcolemm a 
C)  Sarcoplasmic reticulum 
D)  Intercalated disks 
E)  Z disks

Question 10

Relaxation of the cardiomyocytes is caused mainly by

Accepted Answer

A)  Pumping Ca2+ out of the cytosol by the PMCA 
B)  Pumping Ca2+ of the cytosol by NCX 
C)  Removal Ca2+ out of the cytosol by SERCA2a 
D)  Rem oving ATP from the rigor com plex of myosin 
E)  Removing Ca2+ from the cytosol by the L-type Ca2+ channel 
A)  Pumping Ca2+ out of the cytosol by the PMCA 
B)  Pumping Ca2+ of the cytosol by NCX 
C)  Removal Ca2+ out of the cytosol by SERCA2a 
D)  Rem oving ATP from the rigor com plex of myosin 
E)  Removing Ca2+ from the cytosol by the L-type Ca2+ channel

Question 11

Cardiac m uscle cannot increase its strength of contraction by repetitive stimulation (wave summation) because

Accepted Answer

A)  The action potential lasts hundreds of milliseconds, as long as the cardiac cycle 
B)  The SR empties its Ca2+ with every heart beat 
C)  The SA node fires too frequently for the cardiomyocytes to follow 
D)  The absolute refractory period is longer than the action potential 
E)  The bundle of His has no reserve capacity 
A)  The action potential lasts hundreds of milliseconds, as long as the cardiac cycle 
B)  The SR empties its Ca2+ with every heart beat 
C)  The SA node fires too frequently for the cardiomyocytes to follow 
D)  The absolute refractory period is longer than the action potential 
E)  The bundle of His has no reserve capacity

Question 12

Cardiac muscle cannot increase its strength by recruitment because

Accepted Answer

A)  The functional syncytium prevents activation of adjacent cells 
B)  Cells are coupled electrically through gap junctions, so all are activated every
contraction 
C)  The cardiac action potential lasts as long as the contraction 
D)  The [Ca2+] transient does not saturate cardiac TnC during most contractions 
E)  The bundle of His has no reserve capacity 
A)  The functional syncytium prevents activation of adjacent cells 
B)  Cells are coupled electrically through gap junctions, so all are activated every
contraction 
C)  The cardiac action potential lasts as long as the contraction 
D)  The [Ca2+] transient does not saturate cardiac TnC during most contractions 
E)  The bundle of His has no reserve capacity

Question 13

Which of the following are NOT found in the I band?

Accepted Answer

A)  Nebulin 
B)  Titin 
C)  Actin 
D)  Actinin 
E)  Myomesin 
A)  Nebulin 
B)  Titin 
C)  Actin 
D)  Actinin 
E)  Myomesin

Question 14

Modestly increasing the frequency of the heart beat from 70 min-1 to 120 min-1 will

Accepted Answer

A)  Increase the strength of contraction by increasing the size of the Ca2+ transient 
B)  Decrease the strength of contraction due to fatigue 
C)  Increase the strength of contraction by initiating contraction before the heart has completely relaxed 
D)  Increase the strength of contraction by stretching the m yofilaments 
E)  Increase the strength of contraction by inhibiting NCX 
A)  Increase the strength of contraction by increasing the size of the Ca2+ transient 
B)  Decrease the strength of contraction due to fatigue 
C)  Increase the strength of contraction by initiating contraction before the heart has completely relaxed 
D)  Increase the strength of contraction by stretching the m yofilaments 
E)  Increase the strength of contraction by inhibiting NCX

Question 15

“Calcium-induced calcium release” refers to

Accepted Answer

A)  Increased Ica upon beta adrenergic stimulation 
B)  Release of Ca from the cardiac SR by Ca that enters the cell across the T-tubule 
C)  Relaxation of cardiac muscle when Ca is removed by the SR SERCA2a pump 
D)  Increased Ca uptake by SR following contraction 
E)  Both A and C are correct 
A)  Increased Ica upon beta adrenergic stimulation 
B)  Release of Ca from the cardiac SR by Ca that enters the cell across the T-tubule 
C)  Relaxation of cardiac muscle when Ca is removed by the SR SERCA2a pump 
D)  Increased Ca uptake by SR following contraction 
E)  Both A and C are correct

Question 16

The inotropic effect of sym pathetic stim ulation is due mainly to

Accepted Answer

A)  Decreased duration of the action potential 
B)  Increased size of the Ca2+ transient 
C)  Increased affinity of TnC for Ca2+ 
D)  Increased rate of relaxation 
E)  Increased amplitude of the action potential 
A)  Decreased duration of the action potential 
B)  Increased size of the Ca2+ transient 
C)  Increased affinity of TnC for Ca2+ 
D)  Increased rate of relaxation 
E)  Increased amplitude of the action potential

Question 17

In cardiac muscle, the T-tubules are located

Accepted Answer

A)  along the Z disk 
B)  In the center of the I band 
C)  In the center of the A band 
D)  At the junction of the I band and the A band 
E)  In the center of the H zone or H band 
A)  along the Z disk 
B)  In the center of the I band 
C)  In the center of the A band 
D)  At the junction of the I band and the A band 
E)  In the center of the H zone or H band

Exam 38: Cellular Basis of Cardiac Contractility

Removal of external Ca2+ to levels below about 0.2 mM result in no discernible force from the heart. This is because

Stretch increases the force of cardiac contraction mainly by

Ca2+ enters the cardiomyocytes every heart beat through

W hich of the following is NOT one of the ways in which cardiomyocytes differ from skeletal muscle fibers?

Sympathetic stimulation increases all of the following EXCEPT

Cardiac muscle can increase its strength of contraction by all of the following EXCEPT

The space between myofibrils in cardiomyocytes is occupied mainly (in terms of volume) by

The force-frequency relation in the heart (the relation between frequency of stimulation and strength of the heart) is caused principally by

Cardiomyocytes form a functional syncytium by being electrically coupled to one another at the

Relaxation of the cardiomyocytes is caused mainly by

Cardiac m uscle cannot increase its strength of contraction by repetitive stimulation (wave summation) because

Cardiac muscle cannot increase its strength by recruitment because

Which of the following are NOT found in the I band?

Modestly increasing the frequency of the heart beat from 70 min-1 to 120 min-1 will

“Calcium-induced calcium release” refers to

The inotropic effect of sym pathetic stim ulation is due mainly to

In cardiac muscle, the T-tubules are located

Physical Foundations Ii: Electrical Force Potential Capacitance and Current

Chemical Foundations I: Chemical Energy and Intermolecular Forces

Chemical Foundations Ii: Concentration and Kinetics

Diffusion

Electrochemical Potential and Free Energy

Cell Structure

Dna and Protein Synthesis

Protein Structure

Biological Membranes

Passive Transport and Facilitated Diffusion

Active Transport: Pumps and Exchangers

Osmosis and Osmotic Pressure

Cell Signaling

ATP Production I: Glycolysis

Atp Production Ii: Tca Cycle and Oxidative Phosphorylation

Atp Production Iii: Fatty Acid Oxidation and Amino Acid Oxidation

Origin of the Membrane Potential

The Action Potential

Propagation of the Action Potential

Skeletal Muscle Mechanics

Contractile Mechanisms in Skeletal Muscle

Neuromuscular Junction and Ec Coupling

Muscle Energetics Fatigue and Training

Smooth Muscle

Organization of the Nervous System

Cells Synapses and Neurotransmitters

Cutaneous Sensory Systems

Spinal Reflexes

Balance and Control of Movement

the Chemical Senses

Hearing

Vision

Autonomic Nervous System

Overview of the Cv System and Blood

Plasma and Red Blood Cells

White Blood Cells and Inflammation

The Heart As a Pump

the Cardiac Function Curve

Vascular Function: Hemodynamics

Microcirculation and Solute Exchange

Regulation of Perfusion

Integration of Cardiac Output and Venous Return

Regulation of Arterial Pressure

Mechanics of Breathing

Lung Volumes and Airway Resistance

Gas Exchange in the Lung

Oxygen and Carbon Dioxide Transport

Acid Base Physiology I Bicarbonate Buffers and Respiratory Compensation

Control of Ventilation

Anatomy and Renal Overview

Glomerular Filtration

Tubular Reabsorption and Secretion

Concentration and Dilution of Urine

Mouth and Esophagus

The Stomach

Intestinal and Colonic Motility

Pancreatic and Biliary Secretion

Digestion and Absorption of the Macronutrients

Energy Balance and Regulation of Food Intake

General Principles of Endocrinology

Hypothalamus and Pituitary Gland

The Thyroid Gland

Removal of external Ca²⁺ to levels below about 0.2 mM result in no discernible force from the heart. This is because

Ca²⁺ enters the cardiomyocytes every heart beat through

Modestly increasing the frequency of the heart beat from 70 min^-1 to 120 min^-1 will