75. The origin and conduction of the heart Flashcards
What is the heart
electrically controlled muscular pump
what is autorhythmicity
the fact that the heart can beat rhythmically in the absence of external stimuli
where in the heart does the excitation normally originate to initiate the heart beat
In Pacemaker cells in the Sino-Atrial Node
where is the Sino-Atrial Node located
Upper Right Atrium (close to where the superior vena cava enters the right atrium)
A heart CONTROLLED by the Sino-Atrial node is said to be in …. …..
sinus rhythum
The cells in the SA NODE have ……. resting membrane potential
no stable
The cells in the SA node generate
regular spontaneous pacemaker potentials
The spontaneous pacemaker potentials takes the membrane to what
the threshold
when the threshold is reached, what is generated
Action potential - This results in the generation of REGULAR SPONTANOUS ACTION POTENTIALS in the SA nodal cells
what is the threshold for Intracellular Recording from SA Node Cell
-40mV (from an initial -60mV)
what is the pacemaker potential
the slow depolarization of membrane potential to the threshold aka -40mV (from an initial -60mV)
what causes the pacemaker potential
- The funny current - slow Na+ influx through HCN channels which are open when the cell is hyperpolarized (more negative)
- Decrease K+ efflux at the end of hyperpolarization period, less K+ leaves the cell which helps the inside of the cell to become less negative
- Ca2+ Influx also start to enter the cell, contributing to the gradual depolarization. (less negative)
once the threshold is reached it causes what
action potential (ie depolarization)
The RISING PHASE OF ACTION POTENTIAL (i.e. DEPOLARISATION) is caused…. HINT - what channels and what influx
by opening of long lasting (L-TYPE) voltage-gated Ca++ CHANNELS
Resulting in Ca++ INFLUX
what is the falling phase of action potentials called
repolarization
what is repolarization caused by
- inactivation of L type Ca2+ channels
- activation of K+ channels resulting in K+ efflux
cardiac excitement spreads from the Sino Atrial node to….?
Atrio-Ventricular Node
how does excitement spread cell-to-cell
Via Gap Junctions (and maybe Desmosomes but i will check!)
what is the AV node
a small bundle of specialized cardiac cells
where is the AV node located
base of the right atrium
what are the properties of the AV node cells
small in diameter, slow conduction velocity
spread of excitation: From SA node to AV node: mainly cell-to-cell conduction via gap junctions; but there is also some
Internodal Pathways
conduction is delayed where?
Av Node
what does delay in conduction at the AV node allow
atrial systole (contraction) to proceed ventricle systole
The Bundle of …..and its branches and the network of ……… allow rapid spread of action potential to the ventricles
His, Purkinje fibers
Is the action potential in contractile cardiac muscle cells different to the action potential in pacemaker cells
YES
the resting membrane potential remains at …………….mV until the cell is excited (cardiac muscle cell)
-90mV
The rising phase (depoalrisation) is caused by what in cardiac muscle cells
fast Na+ influx
The rising phase (depoalrisation) in cardiac muscle cells reverses the membrane potential to ……mV
+20 mV
what is phase 0 of Contractile Myocytes Action Potential
Fast Na+ influx
what is phase 1 of Contractile Myocytes Action Potential
closure of Na+ channels and transient (brief) K+ efflux
what is phase 2 of Contractile Myocytes Action Potential
mainly Ca2+ influx (through L type Ca2+ channels)
what is phase 3 of Contractile Myocytes Action Potential
closure of Ca2+ channels and K+ efflux
what is phase 4 of Contractile Myocytes Action Potential
resting membrane potential
which phase of Contractile Myocytes Action Potential is the Plateau phase
2
what is the plateau phase of Contractile Myocytes Action Potential
the membrane potential is maintained near the peak of action potential for a few hundred milliseconds
Plateau phase is unique to Contractile Myocytes Action Potential or Pacemaker cells
Contractile Myocytes Action Potential
the falling phase is which stage of the contractile myocyte potentials
3
It is possible to record the spread of electrical activity through the heart from the skin surface. What is this test?
Electrocardiogram (ECG)
how does an ECG work
the wave of depolarisation and repolarisation moves across the heart and sets up electrical currents which can be detected by surface electrodes
what are the standard ECG limb leads
Lead 1 - Right arm and left arm
Lead 2 - right arm and left leg
Lead 3 - Left arm and Left leg
what is the P wave
atrial depolarization
what is the QRS complex
Ventricular depolarisation
what is the T wave
ventricular repolarisation
what is PR interval
largley AV node delay
what is the ST segment
Ventricular systole occurs here
What is TP interval
diastole occurs here
whats the order of ECG waves and intervals
P, PR Interval, QRS complex, ST segments, TP interval
which nerve is the parasympathetic supply to the heart
Vagus
what does the vagus nerve do on normal resting conditions
slows intrinsic heart rate from 100bpm to a normal resting heart rate of 70bpm
finish the sentence. Vagus nerve supplies the ……….. and ……….. And what does the Vagus Nerve do when stimulated
SA Node and AV Node. Slows rate of firing from SA Node and increases AV Node delay
when the vagus is stimulated the slope of pacemaker potential ………… and takes less/more time to reach threshold
decreases. More.
cardiac sympathetic nerves supply what
SA Node, AV Node and Myocardium
sympathetic stimulation does what?
increases the rate of firing from SA Node and decrease AV Node delay and increases force of contraction
what neurotransmitter is acting on which receptors for sympathetic stimulation
Noradrenaline acting on beta 1 adrenoreceptors
pacemaker potential reaches threshold slower/quicker.
Frequency of action potentials increase/decrease
quicker
increase
whats the main difference between cardiac myocytes and pacemaker cells
Cardiac Myocytes:
Contraction and force
Respond to electrical impulses
Stable resting membrane potential with a plateau phase in their action potential.
Pacemaker Cells:
Heart rhythm
Spontaneous depolarization
Without a stable resting membrane potential.
