Characteristics of Cardiac Muscle Cells

Question 1

Cardiac muscle APs differ from skeletal APs and promote rhythmic excitation of the heart that has 3 characteristics.

Answer 1

Self-generating
Conducted directly from cell to cell
Long duration (long refractory period)

Question 2

Potassium has what equilibrium potential

Answer 2

-90mv

Question 3

Activation Gates: Responds to

Answer 3

membrane depolarization QUICKLY by opening.

Question 4

Inactivation Gates: Responds to

Answer 4

membrane depolarization SLOWLY by closing. Limits the time a channel can remain open, despite continued stimulation. Not in all channels.

Question 5

What are the main differences in AP between the contractile and the pacemaker cells in the phases?

Answer 5

Phase 0: Mediated by Na+ in contractile cells, Ca2+ in pacemaker cells
Phase 1 & 2: Absent in pacemaker cells
Phase 3: No difference
Phase 4: Resting vs Pacemaker Potential

Question 6

Intercalated Disks:

Answer 6

specialized adherens junction structure that connects ends of two adjacent cells.

Question 7

Three types of adhering junctions make up intercalated discs:

Answer 7

Fascia Adherens
Macula Adherens (aka Desmosomes)
Gap Junctions

Question 8

Fascia Adherens:

Answer 8

anchoring sites for actin, connect to the closest sarcomere

Question 9

Macula Adherens (aka Desmosomes):

Answer 9

join cells together by binding intermediate filaments

Question 10

Gap Junctions:

Answer 10

channels formed of proteins called connexin permit passage of ions between cells, thus allowing the spread of action potentials

Question 11

Fascia adherens and macula adherens (desmosomes)

ENSURE THE TRANSMITTION OF

Answer 11

FORCE FROM ONE MUSCLE CELL TO THE NEXT

Question 12

The speed at which AP travels between cells is largely determined by the

Answer 12

# of gap junctions in the intercalated discs
Fewer gap junctions = slower

Question 13

AV node has_________ gap junctions than the SA node and atrial myocardium

Answer 13

AV node has fewer gap junctions than the SA node and atrial myocardium

Question 14

P wave is the

Answer 14

atrial depolarization

Question 15

PR interval

Answer 15

is the conduction time through atria & AV node

Question 16

R wave

Answer 16

is the ventricular depolarization

is larger due to the larger amount of tissue depolarizing

Question 17

QT interval

Answer 17

is the total duration of ventricular systole

Question 18

ST segment

Answer 18

plateau phase of ventricular APs

Question 19

T wave

Answer 19

Ventricular repolarization

Question 20

Cardiac Parasympathetic Fibers:

Answer 20

work via vagus nerves
Release acetylcholine
Increases permeability of resting membrane to K+
Decreases diastolic funny current through HCN channels

Question 21

Cardiac Sympathetic Fibers:

Answer 21

Release norepinephrine

Increase diastolic inward currents (if) through HCN channels

Question 22

Reversal Potential for Ca

Answer 22

123

Question 23

Reversal Potential for Na

Answer 23

67

Question 24

Reversal Potential for K

Answer 24

-92

Question 25

Fascia adherens and macula adherens (desmosomes): ensure what happens?

Answer 25

ENSURE THE TRANSMITION OF FORCE FROM ONE MUSCLE CELL TO THE NEXT

Question 26

Cardiac Parasympathetic Fibers via vagus nerves (LEFT)

Answer 26

Release acetylcholine – slows the rate of firing of AP in the SA node –> slows heart rate
Increases permeability of resting membrane to K+
Decreases diastolic if current through HCN channels

Question 27

Cardiac Sympathetic Fibers: (RIGHT)

Answer 27

Release norepinephrine – speeds up heart rate, SHORTENS time to depolarization
Increase diastolic inward currents (if) through HCN channels (increases permeability)

Question 28

Preload:

Answer 28

passive/resting tension placed on cardiac muscle cells before contraction
A function of the volume and pressure at the end of diastole
Increased in hypervolemia, regurgitation of cardiac valves, heart failure

Question 29

Afterload:

Answer 29

the active tension placed on cardiac muscle cells during contraction
A function of the resistance the left ventricle must overcome to circulate blood
Increased in hypertension, vasoconstriction

Question 30

Isometric Contraction:

Answer 30

“fixed length”
Activation of muscle whose ends are held rigidly means it can develop tension, but cannot shorten
Active tension developed during isometric contraction depends on the muscle length at which contraction
There is an optimal muscle fiber length in which to achieve maximum contraction

Question 31

Isotonic Contraction:

Answer 31

“fixed tension”
occurs (which is linked to the resting tension)
Activation of unrestrained muscle causes it to shorten without force development because it has nothing to develop force against
Total load is the summation of preload and afterload

Question 32

Inotrope: what is it

Answer 32

Can be positive or negative
Influences the amount of tension the muscle can develop
Influences the amount of shortening the muscle can achieve

Question 33

Norepinephrine and cardiac function

Answer 33

= positive inotrope
Increases afterloaded shortening
Increases isometric tension – muscle fiber is able to shorten beyond what it normally could have

Question 34

The Law of Laplace

Answer 34

The total ventricular wall tension (T) depends on both intraventricular pressure (P) & the internal ventricular radius (r)
T = P × r
easier for muscle cells to produce adequate internal pressure at end of ejection (small radius) than beginning of ejection (large radius)

Clinical relevance for cardiac dilation and hypertrophy

Question 35

Bachmann’s bundle

Answer 35

Carries depolarization from SA node (in the right atrium) to the left atrium.

Question 36

Bundles off of the Bundle of His

Answer 36

Left and right bundles
Left splits into Left Posterior Fascicle and Left Anterior Fascicle
Right bundle does not split into sub bundles
All 3 bundles end up spreading out and that is called the purkinje fibers

Question 37

Negative Chronotropic Effect means what

Answer 37

prolongs time to depolarization

ex: parasympathetic effect on heart

Question 38

Positive Chronotropic Effect means what

Answer 38

shortens time to depolarization

ex. sympathetic effect on the heart

Question 39

Activation of muscle whose ends are held rigidly means it can develop

Answer 39

tension, but cannot shorten

Question 40

Active tension developed during isometric contraction depends on the

Answer 40

muscle length at which contraction occurs (which is linked to the resting tension)

Question 41

Inotrope:

Answer 41

Influences the amount of tension the muscle can develop

Influences the amount of shortening the muscle can achieve

Question 42

Norepinephrine:

Answer 42

Positive Inotrope
Increases afterloaded shortening
Increases isometric tension