Cardio Physiology 1 (Topic 14) Flashcards
describe cardiac physiology
- the heart is a dual pump that contains valves
- cardiac muscle fibres are connected to one another thru gap junctions
- the heartbeat originates in the conduction system
where does the heartbeat originates from?
the conduction system
the conduction system contains what type of cells?
Non Contractile cardiac muscle cells
what are Non contractile cardiac muscle cells?
they are cardiac muscle cells that have been modified and are no longer able to contract
how do the Non contractile muscle cells able to produce electrical activity like an action potential
its able to make an Action potentials without any outside stimulus. It can do it involuntarily.
what are the parts of the conduction system
- SA node - Sinoatrial node
- AV node - Atrioventricular node
- Bundle of HIS (AV BUNDLE BRANCHES) + right and left bundle branches
- Purkinje fibres
where is the SA node of the conduction system located
at the top of the Right atrium
what is the natural pacemaker of the heart?
SA node - Sinoatrial node
describe how the SA node is the Natural pacemaker of the heart
- it makes the FASTEST Action Potentials:
- 100 AP/minute but slowed down to 75 AP/minute by the PSNS
how can the SA Node stimulates the contraction of of the heart?
it stimulates the contraction of the Atrial contractile myocardium thru INTERATRIAL pathway
the AV Node is located where in the heart
bottom of the Right Atrium
how many Action Potentials does the AV node makes?
50 AP
Explain how the AV node gets the electrical stimulation from the SA node
-AV node receives electrical stimulation from the SA node thru the internodal pathway
Explain the “DELAY” that occur in the AV node
- At the AV node the AP slows down due to the small fober size which delays the arrival of the stimulation from the SA Node
- this gives enough time for the atrium to empty their blood into the ventricles which gives enough time for the ventricles to fill up with blood before the next round of ventricular contractions
where does the Bundle of HIS (AV BUNDLE) originates from
AV node
what is the function of the BUNDLE OF HIS
it works as a connecting pathway for the electrical activity between the atrium and the ventricles
the BUNDLE OF HIS divides into what?
and where does it move?
it divides into left and right bundle branches
and moves into left and right ventricles
how many action potentials does the Bundle of HIS make
30 AP/minute
what are purkinje fibres and its functions
they are terminal fibres that stimulate the contraction of the contractile ventricular myocardium
how many action potentials are made in the purkinje fibres
30 AP/minute
which part of the conduction system stimulates the contraction of the atrial contractile myocardium
a. AV node
b. Bundle of his
c. SA node
d. Purkinje fibres
c. SA Node
which of the following parts of the conduction system stimulates the contractile ventricular myocardium
a. AV node
b. Bundle of his
c. SA node
d. Purkinje fibres
d. purkinje fibres
what would happen if any part of the conduction system is damaged? give an example
the next fastest portion of the conduction system will take over and become the pacemaker
eg: if the SA node is damaged then the AV node will take over
what would happen if the SA node is damaged and the AV node takes over
the atium (left and right) may not contract and the ventricles will contract a less number of times per minute (50 beats per minute)
what device can help if the SA/AV node gets damaged? explain how this device can help with the stimulation of the heart
artificial pacemakers can be inserted in place to stimulate ventricular contraction if the SA/AV node gets damaged
Action potentials of non-contractile auto-rhythmic cardiac muscle cells involve what part of the conduction system
SA and AV node only
describe the pacemaker cells
- self excitable
- have electrical activity only
- no contractile activity
why do auto rhythmic cells have a low K+ permeability
because the K+ voltage gates are closed
describe the 1st step process of action potentials in auto-rhythmic cardiac muscle cells (depolarization)
- Na ions slowly move inside the cell thru Na+ voltage gates
- cause a slow depolarization towards a unique threshold value for pacemaker cells: -40 mv
what happens during the process of action potentials when the threshold is reached in auto rhythmic cardiac muscle cells
once threshold is reached an action potential is made
what happens to the Na+ voltage gates when Action potential is made in the auto rhythmic cardiac muscle cells
Na+ voltage gates close
what voltage gates open when action potential is reached in the auto rhythmic cardiac muscle cells? and what ions are involved
- Calcium voltage gated channels open and Calcium ions moves into the cells causing more depolarization
when do calcium voltage-gated channels close in auto rhythmic cardiac muscle cells
at peak depolazrization = +10 mv
During the repolarization phase of auto rhythmic cardiac muscle cells what voltage gates open?
K+ voltage gates
T or F: K+ voltage gates open at the SAME TIME Ca2+ voltage gates closes at peak depolarization
True
describe what occurs during the repolarization phase of auto rhytmic cardiac muscle cells
- K voltage gates open and K+ ions rushes out of the cell causing repolarization
- K+ voltage gates closes when membrane potential moves back down to threshold value (past -40mv)
- Na+ channels open at -50 mv so that a new pacemaker potential can start
the resting membrane potential of contractile myocardial fibres is?
-90 mv
what portion of the conduction system spreads action potential to contractile fibres? via what?
Purkinje fibres
- via gap junctions
what are the steps of the action potentials in contractile ventricular myocardium
- depolarization
- plateau phase
- repolarization
what occurs during depolarization phase of the contractile ventricular myocardium
- Na+ voltage gates open and Na+ rushes in to the cell
- occurs quickly
- membrane potential jumps to 30 mv
T or F:
during depolarization in the contractile ventricular myocardium it uses the same Na voltage gates channels as used in neurons and skeletal muscle
true
what happens to the Na+ voltage gates during the plateau phase of contractile myocardium
- close and becomes inactivated
when do Na+ channels becomes activated again after remaining inactive in the plateau phase
when the membrane potential returns to -70 mv
in the plateau phase of contractile ventricular myocardium what happens to the Calcium ions and the voltage gates?
slow voltage gates opens and calcium moves into the cell maintaining depolarization
what happens when SOME K+ channels open during the plateau phase
it makes a slight drop in the membrane potential
how is the depolarization maintained during the plateau phase?
Slow voltage Calcium gates open and moves calcium into the cell
K+ voltage gates open which makes k ions move out of the cell
describe what occurs during repolarization of the contractile ventricular myocardium
- Calcium channels close
- More K+ voltage gates open = more K ions out of the cell
- membrane potential moves back to resting value
during the excitation contraction coupling in myocardial cells describe what happens to the voltage calcium channels
- open voltage calcium channels of the action potentials from the ventricular myocardium cause an increase in calcium concentration from the outside to the sarcoplams
is there enough calcium to stimulate contraction in the myocardium when open voltage gated calcium channels increase the entry of calcium ions from the extra cell fluid during the action potential of contractile myocardium?
no because there isnt enough calcium to fully saturate the troponin and stimulate contraction
how does stimulation of the myocardium occur if there isn’t enough calcium to fully saturate the troponin
depolarization of the muscle fibre opens chemically gated calcium channels in the sarcoplasmic reticulum
even more calcium enters and binds to troponin which initiates contraction
contraction of the heart occurs via the?
sliding filament mechanism
when does contraction occur in the heart
begins a few milliseconds after action potential begins
how long does the action potential lasts
250 miliseconds
how long does a twitch lasts
300 miliseconds
why do contraction of the heart almost finishes when action potential is over
this make sure that summation doesnt happen so that tetanus does not happen
why is tetanus dangerous for us?
because it would stop the heart
blood flow would stop
how does the heartbeat to prevent tetanus
contraction continuously alternates with relaxation
