IPHY 3430 Exam 3 Questions with
Accurate/Complete Answers 2026
Updated.
Distinguish between myocardial contractile cells and myocardial autorhythmic cells in terms of
location, function, and relative quantity and diagram the mechanisms by which action
potentials are generated in each cell type (including ion species involved, channel types and
characteristics (i.e., why and when they open/close/inactivate), and direction of ion
movements)
a. Predict how a change in these mechanisms would influence the action potential. - Answer
Contractile Cells:
- 99% of all cardiac myocytes (cardiac muscle cells)
- Perform mechanical work (creating tension which causes effects in BP)
- Cannot produce their own action potential
- Resting membrane potential is around 90 mV
- Always has a suprathreshold
Cardiac Contractile Cell AP
1. action potential arrives at the cardiomyocyte from some other source
2. action potential produces a suprathreshold event which will open voltage-gated Na+ channels
3. The increase in Na+ permeability causes the initial depolarization (cell gets more positive)
4. At the peak the same Na+ Voltage-gated channels are going to close and become inactive
(Na+ permeability decreases)
5. Short plateau phase is caused by a decrease in K+ permeability and Ca2+ permeability is
increased. (opening of L-type Ca2+ voltage-gated channels)
6. After the plateau the Ca2+ channels close (Ca2+ permeability decreases) and slowly K+
channels open again increasing K+ permeability and the cell is at rest.
Autorhythemic:
- Pacemaker
- nodal cells
- do not contribute to the contractile force of the heart
- Specialized electrical current and potential
- Initiating, and transmitting action potentials without any outside stimulus
- spontaneously depolarize
- Unsable membrane potential (-60 mV)
, - Never truly rests
- IF channels = funny channels (permeable to both Na+ (influx) and K+ (efflux))
- opens as more negative membranes
- when IF channels close, depolarization can initiate
Action Potential:
1. IF channels = Funny (halfway to getting to the threshold): Permeable to both Na+ and K+,
When the funny channels are open, there will be an influx of Na+ and an efflux of K+. The
sodium influx is greater than the potassium efflux. IF channels open att. more negative
membrane potentials.
starts around -60mV and the threshold is around -40mV
2) depol
What are the similarities and differences between Cardiac and Skeletal muscles? - Answer
Differences:
- Muscle fibers are smaller
- Single nucleus
- Branching cells connected by Intercalated discs
Similarities:
- Both contain Gap junctions
- SR smaller than in skeletal muscle which suggests that outside Ca2+ is needed
Cell Adhesion molecules of Cardiac muscle - Answer Desmosomes:
- Create a strong attachment between cells
- allows for some flexibility
Gap Junctions:
- a pore that connects the cytosol of one cell to the cytosol of the next
- Important for the production of action potentials
- allows action potentials to diffuse very quickly between cells (the cells become stimulated at
the same time)
Explain the mechanical events of the cardiac cycle including:
Accurate/Complete Answers 2026
Updated.
Distinguish between myocardial contractile cells and myocardial autorhythmic cells in terms of
location, function, and relative quantity and diagram the mechanisms by which action
potentials are generated in each cell type (including ion species involved, channel types and
characteristics (i.e., why and when they open/close/inactivate), and direction of ion
movements)
a. Predict how a change in these mechanisms would influence the action potential. - Answer
Contractile Cells:
- 99% of all cardiac myocytes (cardiac muscle cells)
- Perform mechanical work (creating tension which causes effects in BP)
- Cannot produce their own action potential
- Resting membrane potential is around 90 mV
- Always has a suprathreshold
Cardiac Contractile Cell AP
1. action potential arrives at the cardiomyocyte from some other source
2. action potential produces a suprathreshold event which will open voltage-gated Na+ channels
3. The increase in Na+ permeability causes the initial depolarization (cell gets more positive)
4. At the peak the same Na+ Voltage-gated channels are going to close and become inactive
(Na+ permeability decreases)
5. Short plateau phase is caused by a decrease in K+ permeability and Ca2+ permeability is
increased. (opening of L-type Ca2+ voltage-gated channels)
6. After the plateau the Ca2+ channels close (Ca2+ permeability decreases) and slowly K+
channels open again increasing K+ permeability and the cell is at rest.
Autorhythemic:
- Pacemaker
- nodal cells
- do not contribute to the contractile force of the heart
- Specialized electrical current and potential
- Initiating, and transmitting action potentials without any outside stimulus
- spontaneously depolarize
- Unsable membrane potential (-60 mV)
, - Never truly rests
- IF channels = funny channels (permeable to both Na+ (influx) and K+ (efflux))
- opens as more negative membranes
- when IF channels close, depolarization can initiate
Action Potential:
1. IF channels = Funny (halfway to getting to the threshold): Permeable to both Na+ and K+,
When the funny channels are open, there will be an influx of Na+ and an efflux of K+. The
sodium influx is greater than the potassium efflux. IF channels open att. more negative
membrane potentials.
starts around -60mV and the threshold is around -40mV
2) depol
What are the similarities and differences between Cardiac and Skeletal muscles? - Answer
Differences:
- Muscle fibers are smaller
- Single nucleus
- Branching cells connected by Intercalated discs
Similarities:
- Both contain Gap junctions
- SR smaller than in skeletal muscle which suggests that outside Ca2+ is needed
Cell Adhesion molecules of Cardiac muscle - Answer Desmosomes:
- Create a strong attachment between cells
- allows for some flexibility
Gap Junctions:
- a pore that connects the cytosol of one cell to the cytosol of the next
- Important for the production of action potentials
- allows action potentials to diffuse very quickly between cells (the cells become stimulated at
the same time)
Explain the mechanical events of the cardiac cycle including:
