electrophysiology of the cv system Flashcards
define atria
receiving chambers of the heart
define ventricle
discharging chambers of the heart
Where is the tricuspid valve located ?
between right atrium and ventricle
where is the bicuspid valve located ?
between left atrium and ventricle
key word : membrane potential means
The difference in charge between the
inside and outside of the cell
key word : polar means
Having ‘poles’
Positive (+) and negative (-) sides
key word : depolarisation means
Membrane potential going from more
negative to less negative (or positive)
The difference in charge across the
membrane, i.e. the poles, getting smaller
key word : repolarisation means
becoming polarised again
positive and negative sides become more different
key word :ion channels means
Proteins which act as openings to let
specific ions move through
May be ‘gated’ – Open in response to
certain stimuli
where are autorhythmic cells in the heart located ?
sinoatrial node [ SA node ]
Atrioventricular node [ AV node ]
Describe electrical conduction to the AV node
- Internodal pathways connect SA & AV
nodes - Electrical activity spreads rapidly
to AV node via internodal
pathways - Depolarization spreads more
slowly across atrial muscle - Conduction slows within AV node
why does electrical conduction to AV node occur ?
- Action potentials pass into Bundle of His
(Wall of the septum between the
ventricles) - Bundle divides into left & right bundle
branches - Fibres continue downward and divide into
many small Purkinje fibres that spread
outward among the contractile cells
what is p wave in ECG ?
atrial depolarisation
what is QRS complex in ECG ?
Ventricular depolarisation
what is t wave in ECG ?
Indicates ventricular repolarization
what is the PR interval in ECG ?
indicates delay in AV node
electrical activity of the atria
what is the QT interval in ECG ?
electrical activity of the ventricles
what are the three mechanism the cardiovascular system is regulated by ?
humoral- response to changing levels of ions or nutrients in the blood
neural - stimulation by nerves
hormonal - stimulation received from other hormones
what does the motor neurons in the autonomic nervous system do ?
innervate smooth muscle , cardiac muscle , internal organs and skin
makes adjustments to ensure optimal support for body activities
operates via subconscious control
what does the sympatheic fibres in the autonomic nervous system do ?
increase heart rate , respiratory rate and inhibits digestion and elimination
what does the parasympathetic fibres do in the autonomic nervous system do ?
decrease heart and respiratory rate , allow for digestion and discarding of waste
what neurotransmitter is involved in the sympathetic fibres ?
catecholamines
what neurotransmitter is involved in the parasympathetic fibres ?
acetylcholine
what happens at phase 0 [ depolarisation ] of the heart cardiac myocytes action potential ?
action potential from SA node opens fast Na+ channels
large but transient increase in Na+ permeability
Na+ enters
accompanied by dramatic reduction in K+
conductance
prevents K+ efflux and repolarization
what happens at phase 1 [ repolarisation ] of the heart cardiac myocytes action potential ?
fast Na+ channels close
membrane potential begins to fall
reflects partial repolarization
what happens at phase 2 [ plateau ] of the heart cardiac myocytes action potential ?
- Despite closure of fast Na+ channels,
potential remains positive or near 0
for ~300 msec - Largely due to opening of voltage-
gated slow Ca2+ channels - Ca2+ entry is involved in
excitation-contraction coupling - Plateau because:
- Na+ influx from slow Na+ channel
- Slow leakage of K+ out of cell
keeps potential from rising
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what happens at phase 3 [ reolarization ] of the heart cardiac myocytes action potential ?
- Intracellular K+ moves down
concentration gradient - leaves cell
causing it to repolarize - Repolarization facilitated by closure
of Ca2+ and slow Na+ channels
what happens at phase 4 [ resting membrane potential ] of the heart cardiac myocytes action potential ?
- Cell repolarized and ready for the
next stimulus
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how does the AP spread between the cells ?
- gap junctions [ direct transfer of ionic current from one cells to the next ]
- cells connected by gap junctions are said to be electrically coupled
- flow of ions from cytoplasm to cytoplasm
- very fast , fail-safe transmission
- almost simultaneous AP generation
does skeletal system depend on action potential for neural activity ?
yes
does cardiac system depend on action potential for neural activity ?
no
what is the resting membrane potential for skeletal system ?
- 85mv
what is the resting membrane potential for cardiac system ?
-90mv
what is the duration of the action potential of the skeletal system ?
2.5 m sec
what is the duration of the action potential of the cardiac system ?
300m sec
