Cardiac Physiology

Question 0

describe the location of the pacemaker of the heart

Answer 0

SA node is medial to the opening of the superior vena cava

Question 1

name the five parts of the conducting system of the heart

Answer 1

Sinoatrial Node (SA)
atrioventricular node (AV)
AV bundle
right and left bundle branches
purkinje fibers

Question 2

what are the differences between cardiac muscle cells and the cardiac muscle cells that make up the SA node

Answer 2

they spontaneously generate AP at a greater frequency than that of other cardiac muscle cells
smaller diameter cardiac muscle cells
form a knot or lump
have fewer myofibrils

Question 3

where do the APs from the SA node travel fastes?

Answer 3

the AV node

Question 4

what cardiac muscle cells do the SA node affect?

Answer 4

atrial muscle cells and AV node

Question 5

explain the location of the AV node

Answer 5

medial to the right atrioventricular valve

Question 6

where within the heart do the cmc’s propogate APs slowest?

Answer 6

AV node

Question 7

where do the APs travel after the AV node?

Answer 7

AV bundle&raquo_space; right and left bundle branches&raquo_space; purkinje fibers

Question 8

what specialized conducting cells penetrate the myocardium of the ventricles?

Answer 8

purkinje fibers

Question 9

how do the specialized conducting fibers of the ventricles receive the AP to cntx?

Answer 9

AV node

Question 10

to what ions are the CMCs permeable to create the resting membrane potential?

Answer 10

low permeability to Na+ and Ca++ and higher permeability to K+

Question 11

what phase of CMCs makes APs so much slower?

Answer 11

plateau phases

Question 12

what happens during the plateau phase of CMCs APs

Answer 12

slow repolarization

Question 13

_________ passes through a hole in the cardiac skeleton to reach ______________

Answer 13

AV bundle – interventricular septum

Question 14

right and left bundle branches extend …

Answer 14

beneath endocardium to apices of right and left ventricle

Question 15

how do purkinje fibers differ from other CMCs

Answer 15

large diameter
few myofibrils
many gap junctions
longer
fewer intercalated disks

Question 16

how does the length and amount of intercalated disks affect the efficacy of the Purkinje fibers?

Answer 16

longer fibers causes less of a delay bc fewer intercalated disks means AP can travel easier path–just down length of sarcolemma

Question 17

compare and contrast CMCs and SMFs

Answer 17

• Cardiac APs are conducted from cell to cell via gap junctions at the intercalated disk. Skeletal APs travel along the length of a single fiber.
• gap junctions and small diameter fibers cause the rate of AP propagation to be slower in CMCs. Skeletal fibers are larger in diameter and propagation only has to travel the length of a single cell.
• Ca++ induced Ca++ release is unique to CMCs. Ca++ moves through sarcolemma and stimulates release of Ca++ from the sarcoplasmic reticulum

Question 18

what causes repolarization and plateau phase to move so slowly in APs of CMCs

Answer 18

movement of K+ out of the cell (to begin repolarization) is counteracted by mvmt of Ca++ (and some Na+) through the voltage gated Ca++ channels that are slow to close.

Question 19

eventually Ca++ channels close and many more voltage gated K+ channels open causing

Answer 19

final repolarization of CMCs

Question 20

what develops spontaneously in the SA node and what is it?

Answer 20

pacemaker potential: a local action potential that reaches threshold and generates AP in the SA node

Question 21

what causes the pacemaker potential?

Answer 21

changes in ion movement into and out of the pacemaker cells

Question 22

what ions cause depolarization in the pacemaker by moving into the cells through a specialized nongated channel?

Answer 22

Na+

Question 23

mvmt of _____ into the cells and decreased permeability to allowing ___ out of the cells begins depolarization and opens voltage-gated ____

Answer 23

Na+ K+ Ca++

Question 24

depolarization causes many more ____ to open

Answer 24

voltage-gated Ca+ channels

Question 25

what is different about the ions that cause depolarization in the pacemaker cells from other CMCs?

Answer 25

pacemaker cells primarily rely on Ca++ movement to cause depolarization and other CMCs rely primarily on Na+

Question 26

repolarization occurs when voltage-gated ______ channels close and voltage-gated _____ open

Answer 26

Ca++ – K+

Question 27

how do epinephrin increase heart rate and force of cntx?

Answer 27

by opening voltage gated Ca++ channels

Question 28

name some calcium channel blockers

Answer 28

nifedipie and verapamil

Question 29

how would nifedipine or verapmil affect heart rate?

Answer 29

they are Ca++ channel blockers so they slow the pacemaker’s ability to develop an action potential

Question 30

what are the parasympathetic nerve fibers that connect to the heart?

Answer 30

vagus nerve

Question 31

where are the terminal ganglia of the parasympathetic vagus nerves?

Answer 31

within the wall of the heart

Question 32

where do post ganglionic fibers of the parasympathetic nerves innervate the heart?

Answer 32

SA node
AV node
coronary blood vessels
atrial myocardium

Question 33

_______ is produced by postganglionic parasympathetic neurons and binds to ______________ that cause sarcolemma of the CMC to become _____ permeable to ______, thus ________ the membrane, and ______heart rate

Answer 33

Ach
ligand-gated channels
more
K+
hyperpolarizing
decreasing

Question 34

sympathetic nerve fibers synapse with post______ at the _______

Answer 34

ganglionic

ganglia

Question 35

which part of the nervous system projects into the heart as cardiac nerves?

Answer 35

sympathetic

Question 36

How would cutting the paravagus nerve affect the heart rate? What if it was stimulated?

Answer 36

The inhibitory effect of the vagus nerve Ach release would be stopped, hr would increase. If stimulated. Ach release would resume