Bio 436 Cardiac/Skeletal Review Questions and Correct Answers
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BIO 436
Two types of cardiac cells? 1) pacemaker/conducting/autorhymic cells 2) contracting cells/ cardiac myocytes
How are cardiac myocytes similar to skeletal muscle cells? 1) basic contractile unit is the sarcomere
Do cardiac cells stretch the length or width of the heart? Yes or no? Explain cardiac f...
how are cardiac myocytes similar to skeletal muscl
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Bio 436 Cardiac/Skeletal Review
Questions and Correct Answers
Two types of cardiac cells? ✅1) pacemaker/conducting/autorhymic cells
2) contracting cells/ cardiac myocytes
How are cardiac myocytes similar to skeletal muscle cells? ✅1) basic contractile unit is
the sarcomere
Do cardiac cells stretch the length or width of the heart? Yes or no? Explain ✅cardiac
fiber cells DON'T stretch the length or width of the heart b/c they are actually
individualized cells that are linked together throughout the heart
Where cardiac cell membranes interdigitate extensively is called what? ✅where
cardiac fibers/cells form/meet is called: Intercalated disks (in which the cell membranes
interdigitate extensively.)
What are the two things intercalated disks include? ✅1) Gap junctions- provide
channels for electrical continuity and propagation throughout the heart
2) Desmosomes- form tight connections so that cardiac cells don't fall apart
Cardiac myocytes are branched... What does that mean? ✅branched meaning; they
have a number of branch points to be able to interdigitate (or mix/bind) to adjacent cells
Describe desmosomes and why they are important ✅-they are made of great # of
proteins both inside and outside of the cell
-they help anchor proteins that extend through the plasma membrane, then they
intertwine to form a very tight junction
-desmosomes= "velcro"
- important do that when myocytes contract they don't pull apart
What specific proteins are gap junctions made of? ✅they made up of a channel protein
called CONNEXINS; connexins (allow) open & close, to allow small ions and small
amino acids to go down a concentration gradient from one cell to another
Ex: Na+ and Ca+ leak through, this can depolarize the adjacent cell and activate it
Which has more SR, cardiac cells or skeletal muscle cells? ✅skeletal muscle cells
have wayyy more SR than cardiac muscle cells b/c the t-tubules are physically linked to
terminal cisternae vs in cardiac muscle cells where the t tubules are not physically
linked to terminal cisternae
, Why are cardiac conducting cells(pacemaker cells) also called autorhythmic cells?
✅(both atrial & ventricular) which set the rhythm of the heart beat and cells (ex: nodal
and purkinjee) which conduct the action potential throughout the heart
What is the term used to describe autorhythmic cells linked together via gap junctions?
✅when cells are linked together via gap junctions is called SYNCYTIUM; this is
because when all cells are linked together they act as one big cell, which is b/c one cell
can spread its depolarization to all its adjacent cells, ends of being the entire heart
The heart muscle itself electrically resembles two large cells.. Two BLANK will be one
large cell and two BLANK is the second large cell ✅two ATRIA and two VENTRICLES
What links autorhymic cells to contracting cells? ✅gap junctions
Define myogenic ✅the atrial and ventricular cells are referred to myogenic because the
heartbeat originates from the heart itself,
-"The signal for a heartbeat is initiated by the heart muscle cells (cardiomyocytes) rather
than from brain signals"
-BUT THE ATRIAL CELLS ACT AS A UNIT SEPERATE FROM THE VENTRICULAR
CELLS
What is sets the heartbeat frequency? ✅-it is set by the SA nodal cells, these cells
SHOW THE FASTEST RATE OF of spontaneous depolarization
-these nodes ARE RESPONSIBLE FOR STARTING DEPOLARIZATION for the entire
heart
Describe the summary of the pathway in heart ✅start at SA node, it will concurrently
spread through the interatrial and internodal pathway, it will converge down on the AV
node-there is a pause here- then it foes down the bundle of His into both the right and
left bundle branches, and then out to the Purkinje fibers
What kind of channels do all pacemaker cells contain? And how the channel works ✅-
HCN channels (hyper-polarized activated cyclic-nucleotide channels)
- HCN channels allow Na+ to come into the cell for cell to go from hyperpolarized to
threshold for an action potential to occur
Describe full circle of pathway regarding HCN channels ✅HCN channels allow Na+ to
go into cell, allowing it to reach threshold--> then VG Ca+ channels open up,
depolarize--> then around +20mv VG Ca+ channels close--> then VG K+ channels
open to repolarize membrane--> then hyperpolarizes the membrane
Why does a pacemaker cell NEVER have a resting membrane potential? ✅because of
HCN channels; these channels do not allow a resting membrane potential because they
are constantly allowing Na+ to creep in to reach threshold , there is no constant
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