Chapter 14 (Part 1)

Question 1

when i say “cardiac muscle contraction uses the same players as skeletal muscle,” what do i mean really? (3)

Answer 1

• T tubules– T tubules direct APs to the interior of each cardiac muscle fiber
• sarcomere– basic contractile unit is the sarcomere
• myosin– myosin binds to actin for crossbridge cycling and is regulated by troponin and tropomyosin

Question 2

how do heart valves operate?

Answer 2

by pressure

Question 3

what ensures the heart contracts in a coordinated fashio?

Answer 3

conduction system

Question 4

AP spreads through both atria via… (2)

Answer 4

• 3 internodal tracts
• gap junction

Question 5

AP spreads through both atria via… (2)

Answer 5

• 3 internodal tracts
• gap junctions

Question 6

AP firing rate _____ along the conduction system

Answer 6

varies

Question 7

AP from the SA node is sent via _____ to the AV node?

Answer 7

internodal tract

Question 8

internodal tract sends what to what?

Answer 8

AP from the SA node to the AV node

Question 9

AV node delays in relaying AP to the what?

Answer 9

ventricles

Question 10

why does the AV node have a delay of 0.1 sec before going on to the ventricles? be honest.

Answer 10

to ensure the atria complete their contraction before the ventricles contract to ensure the ventricles fill properly

Question 11

the heart contracts from the bottom up. why is that important?

Answer 11

to make sure all the blood is pumped out in one direction. similar to squeezing toothpaste out of a bottle, if you start at the bottom you can get it all out.

Question 12

what are the two specialized types of cardiac cells in the heart?

Answer 12

• autorhythmic cells
• contractile cells

Question 13

describe autorhythmic cells. what is their makeup/composition? what is their role ?

Answer 13

• contain very few myofibrils
• therefore, very few sarcomeres for contraction
• specialized for initiating and conducting APs

Question 14

describe contractile cells

Answer 14

• make up 99% of cardiac muscle cells
• do the mechanical work of pumping

Question 15

what is the main job of autorhythmic cells?

Answer 15

initiate and conduct APs

Question 16

what is the main job of contractile cells?

Answer 16

do the mechanical work of pumping

Question 17

autorhythmic cells are the _____ cells of the heart.

Answer 17

pacemaker

Question 18

autorhythmic cells are the pacemaker cells of the heart. why do we say that?

Answer 18

• an autorhythmic cell SPONTANEOUSLY depolarizes and fires Aps
• no rest phase in between APs

Question 19

an autorhythmic cell spontaneously depolarizes and fires APs, and there’s no rest phase between APs. in other words,…

Answer 19

autorhythmic cells go immediately from being depolarized to being hyperpolarized and repeat…

Question 20

how are autorhythmic APs different from neuron action potentials

Answer 20

• no voltage-gated Na+ channels
• depolarization is spontaneously initiated by: 1) funny channels 2) voltage-gated K+ channels

Question 21

depolarization of autorhythmic APs is spontaneously initiated by… (2)

Answer 21

• funny channels
• voltage-gated K+ channels

Question 22

describe “funny” channels

Answer 22

Na+ leak channels that are very leaky at (-)Vm and not very leaky at (+)Vm

Question 23

describe voltage-gated K+ channels in depolarization of autorhythmic APs

Answer 23

close at peak (-)Vm (hyperpolarization) to trap K+ inside the cell

Question 24

what might we call peak (-)Vm in autorhythmic Aps?

Answer 24

hyperpolarization