cardiac excitation (midterm 2) Flashcards

1
Q

what are other functions than contraction the heart does

A
  • generation of rhythmical electrical impulses to cause rhythmical contraction of heart muscle
  • conduction of ^ impulses rapidly through cardiac muscle
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2
Q

what are results of the rhythmical excitation of the heart

A

atria contraction before ventricular
spatial homogeneity of ventricular contraction

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3
Q

what does the sinus node do

A

it’s a strip of cardiac muscle that generates the normal rhythmical impulse

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4
Q

what do the internodal pathways do

A

conduct the impulse from the sinus node to the AV node

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5
Q

what does the AV bundle do

A

conducts impulses from the atria into the ventricles

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6
Q

what do the left and right branches of purkinje fibers do

A

conduct the cardiac impulse to all parts of the ventricles

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7
Q

where is the sinus node located and how big is it

A

located in the superior posterolateral wall of the right atrium
3 mm wide, 15 mm long, 1 mm thick

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8
Q

what happens because fibers connect directly with the atrial muscle fibers

A

any AP that begins in the sinus node spreads immediately into the atrial muscle wall

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9
Q

how is tissue self-excitatory

A

it doesn’t contract, but hits a threshold where AP fires on its own

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10
Q

how is the sinus node the pacemaker of the heart

A

the sinus node controls the heart rate of the entire heart - sinus fibers are self-excitatory

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11
Q

what is the resting membrane potential of the sinus nodal fiber between discharges

A

-55 to -60 mV

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12
Q

what causes the sinus nodal fiber to be less negative

A

cell membranes of the sinus fibers are naturally to Na+ and Ca++ channels,, which allows Na+ and Ca++ into the cell to eventually generate an AP via threshold value

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13
Q

when are channels active/inactive in sinus nodal fiber and what is the result of this

A
  • fast Na+ are inactivated
  • slow Na+-Ca++ channels can open and initiate an action potential
    atrial nodal AP is slower to develop than ventricular muscle AP
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14
Q

when does an AP of sinus nodal fibers occur

A

Na+ influx into cardiac muscle fiber that activates Na+-Ca++ channels

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15
Q

what are internodal pathways

A

where the ends of the sinus nodal fibers connect directly with surrounding atrial muscle fibers

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16
Q

what is the velocity of AP conduction in atrial muscle

A

0.3 m/sec or 1 m/sec for small bands of fibers

17
Q

how long does it take for an impulse to reach the AV node after traveling through the internodal pathways and what is the next delay

A

0.03 sec followed by a delay of 0.09 sec before impulse enters the penetrating portion of AV bundle, where it passes into ventricles

18
Q

what is the final delay of impulses in AV node

A

0.04 seconds occurring mainly in this penetrating AV bundle

19
Q

what is the total delay before the excitatory signal reaches the contracting muscle of the ventricles

A

0.16 seconds

20
Q

what is speed a function of

A

of gap junctions - less gap junctions = greater resistance to conduction of excitatory ions from one fibers to the next

21
Q

what does special purkinje fibers do

A

lead from the AV node through the AV bundle into the ventricles

22
Q

what is the velocity and size of special purkinje fibers

A

large - 6x of ventricular muscle, 150x of Av nodal fibers
velocity of 1.5-4 m/s

23
Q

why is there no retrograde transmission of AP in AV bundle

A

prevents passage of cardiac impulse between atrial and ventricular muscle

24
Q

what is the fastest rate of rhythmical dischage in sinus node

A

70-80/min = pacemaker
impulse is conducted into AV node and purkinje fibers, also discharging their excitable membranes

25
what is the rate of rhythmical discharge in unstimulated AV nodal fibers
40-60/min
26
what is the rate of rhythmical discharge in unstimulated purkinje fibers
15-40/min
27
what is parasympathetic (vagal) stimulation
causes acetylcholine release, decreasing rate of rhythm of the sinus node
28
what is sympathetic stimulation
increases rate of sinus nodal discharge and rate of conduction + force of contraction - increases overall activity of the heart