BIO 431 Exam 2 Questions With New
Update Solutions + Pass
Location of the heart - CORRECT ANSWER--Inside the pericardial sac in the
mediastinum
>Mediastinum is seperated into the superior mediastinum and the pericardial
cavity
-Pericardial sac surrounds the heart. It contains fluid to decrease friction so it can
beat in a frictionless environment.
Two types of cardiac muscle cells - CORRECT ANSWER-CONTRACTILE
CELLS
-Most cells
-Contractile cells receive their stimulation from these pacemaker cells
AUTORHYTHMIC CELLS (PACEMAKERS)
-Few, smaller, noncontractile
,-Spontaneously depolarize - no neural stimulation required for the heart muscle to
contract
-No movement
-Strategically located to help in the initiation and spread of electricity from one
cardiac muscle cell to another
An action potential is initiated in pacemaker cells and spreads VIA GAP
JUNCTIONS from one contractile cell to the next.
Action Potentials in Pacemaker Cells - CORRECT ANSWER--Spontaneously
depolarize (known as the pacemaker potential stage)
>Pacemaker potential: -60 mV to -40 mV (threshold)
>-40 mV is where voltage gated channels open
>Na+ influx exceeds K+ efflux
-At threshold: AP initiated
>Ca+ channels (voltage-gated) open → rapid depolarization of pacemaker cells.
This causes repolarization.
-Repolarization
© 2026 Copyright. All Rights Reserved. This document is
protected by copyright law
,>Ca+ channels close
>K+ channels open: K+ efflux
*Frequency of spontaneous depolarization of these cells establishes heart rate (the
frequency of contraction of the heart)
*NO RESTING MEMBRANE POTENTIAL EVER. No flat line.
Autonomic Influence on Heart Rate (Sympathetic) - CORRECT ANSWER--
Increases HR
-Catecholamines: NE (neurons + adrenal medulla) + EPI (adrenal medulla)
released from chromaffin cells
-Catecholamines bind to β1-adrenergic receptors on pacemaker cells
>cAMP 2nd messenger system changes ion channels
>Increased membrane permeability to both Na+ and Ca2+
-More rapid depolarization to threshold to increase rate of action potentials
produced from pacemaker cells
-On the graph: Reach threshold (-40 mV) a lot faster so more APs produced over a
certain period of time
Exact Steps of Action Potentials in Pacemaker Cells - CORRECT ANSWER-1.
Pacemaker potential: This slow
, depolarization is due to both opening of Na+
channels and closing of K+ channels. Notice
that the membrane potential is never a flat line.
NO RMP!
2. Depolarization: The action potential
begins when the pacemaker potential reaches
threshold. Depolarization is due to Ca2+ influx
through Ca2+ channels.
3. Repolarization is due to Ca2+ channels
inactivating and K+ channels opening. This
allows K+ efflux, which brings the membrane
potential back to its most negative voltage
Autonomic Influence on Heart Rate (Parasympathetic) - CORRECT ANSWER--
Decreases HR
-Release ACh to bind to muscarinic receptors
>cAMP 2nd messenger system changes ion channels
© 2026 Copyright. All Rights Reserved. This document is
protected by copyright law
Update Solutions + Pass
Location of the heart - CORRECT ANSWER--Inside the pericardial sac in the
mediastinum
>Mediastinum is seperated into the superior mediastinum and the pericardial
cavity
-Pericardial sac surrounds the heart. It contains fluid to decrease friction so it can
beat in a frictionless environment.
Two types of cardiac muscle cells - CORRECT ANSWER-CONTRACTILE
CELLS
-Most cells
-Contractile cells receive their stimulation from these pacemaker cells
AUTORHYTHMIC CELLS (PACEMAKERS)
-Few, smaller, noncontractile
,-Spontaneously depolarize - no neural stimulation required for the heart muscle to
contract
-No movement
-Strategically located to help in the initiation and spread of electricity from one
cardiac muscle cell to another
An action potential is initiated in pacemaker cells and spreads VIA GAP
JUNCTIONS from one contractile cell to the next.
Action Potentials in Pacemaker Cells - CORRECT ANSWER--Spontaneously
depolarize (known as the pacemaker potential stage)
>Pacemaker potential: -60 mV to -40 mV (threshold)
>-40 mV is where voltage gated channels open
>Na+ influx exceeds K+ efflux
-At threshold: AP initiated
>Ca+ channels (voltage-gated) open → rapid depolarization of pacemaker cells.
This causes repolarization.
-Repolarization
© 2026 Copyright. All Rights Reserved. This document is
protected by copyright law
,>Ca+ channels close
>K+ channels open: K+ efflux
*Frequency of spontaneous depolarization of these cells establishes heart rate (the
frequency of contraction of the heart)
*NO RESTING MEMBRANE POTENTIAL EVER. No flat line.
Autonomic Influence on Heart Rate (Sympathetic) - CORRECT ANSWER--
Increases HR
-Catecholamines: NE (neurons + adrenal medulla) + EPI (adrenal medulla)
released from chromaffin cells
-Catecholamines bind to β1-adrenergic receptors on pacemaker cells
>cAMP 2nd messenger system changes ion channels
>Increased membrane permeability to both Na+ and Ca2+
-More rapid depolarization to threshold to increase rate of action potentials
produced from pacemaker cells
-On the graph: Reach threshold (-40 mV) a lot faster so more APs produced over a
certain period of time
Exact Steps of Action Potentials in Pacemaker Cells - CORRECT ANSWER-1.
Pacemaker potential: This slow
, depolarization is due to both opening of Na+
channels and closing of K+ channels. Notice
that the membrane potential is never a flat line.
NO RMP!
2. Depolarization: The action potential
begins when the pacemaker potential reaches
threshold. Depolarization is due to Ca2+ influx
through Ca2+ channels.
3. Repolarization is due to Ca2+ channels
inactivating and K+ channels opening. This
allows K+ efflux, which brings the membrane
potential back to its most negative voltage
Autonomic Influence on Heart Rate (Parasympathetic) - CORRECT ANSWER--
Decreases HR
-Release ACh to bind to muscarinic receptors
>cAMP 2nd messenger system changes ion channels
© 2026 Copyright. All Rights Reserved. This document is
protected by copyright law
