Electrical Activity And Muscle Contraction Flashcards
What are heart cells called and the 2 types
Myocytes
1- conducting cells : fast spread of AP
2- work cells : cells which generate contraction force
Where are work cells found
In both Atria and ventricles
What are the 2 ways ap can spread in heart
Through conducting fibres
Cell to cell via gap junctions
Which cells have spontaneous depolarisation which causes contraction
SAN
When is the SAN
Right atrium
Where does AP spread from the san
To internodal pathways and then spread across both atria
How is ap spread to both atria before going to the AVN
Through gap junctions
Why is there a delay in ap spread down AVN
To allow all the blood to leave the atria after contraction
How does ap spread to the apex of heart
Down bundle of his , purkinje fibres
What do purkinje fibres on both sides of heart all
Ventricle contraction upwards of the heart
What is the spontaneous depolarisation of the SAN called
Pacemaker potential
What channel opens in the initial depolarisation in the SAN (pacemaker potential)
Non specific cation channels open and cations + flood into cell
Which channels open at the SAN to cause rapid depolarisation once reached threshold
Ca2+ channels
Which channels cause repolarisation at the SAN
Voltage gated K+ channels
Ap in the ventricle cells is different. What causes depolarisation
Voltage gated NA channels
Which channels initially cause repolarisation in ventricle cells
Fast opening K+ channels
Why is there a plateau phase in repolarisation at ventricle cells
Voltage gated ca channels open and counteract the K+ channels leaving the cells
What are the ca2+ called in ventricle AP
Trigger calcium
What happens after plateau phase
Ca channels shut
Slow opening K channels open and cause repolarisation again
Goes to resting potential
How is contraction triggered in ventricle cells
By the trigger ca flooding which bind at the SR to release Ca2+
what are the channels which ca flood out of and later bind to troponin to cause contraction
Ryanodine receptor channels
What are the 2 ways relaxation occurs
Removal of ca back to the sr via ca2ATPase channels
Or
Removal out of the cell via NA/ ca anti Porter
Why can na/ca anti Porter work to remove ca out of cell
Gradient produced by the na/k pump
What factor affects force/ contraction
Number of myosin actin cross bridges which is dependant on number of ca bound to troponin via trigger ca release out of SR
When does muscle contraction first occur in response to an AP
At the plateau phase when trigger calcium enters cell
How does the heart avoid tetanus
It has a long refractory period which allows muscle to relax first via removal of ca
What machine records depolarisation and repolarisation of working cells(contracting)
Electrocardiogram ECG
Why is ecg different to ap
Because it records sum of of electrical activity of all working cells
What is the point in the ecg which is where heart is relaxed
Isoelectric point
Which wave is first in an ecg and what does it represent
P wave
Represents atrial depolarisation
What happens after P wave
QRS complex
What is the dip at Q representing
Initial ventricular depolarisation
What does R represent
Ventricular depolarisation
What does S represent (downward curve at QRS)
Depolarisation upwards by purkinje fibres up the heart muscle
What wave comes after the QRS complex and what does it show
T wave
It shows ventricular repolarisation
What is the interval called between P and the R wave and what does it show
Pr interval
It shows the conduction down the AVN and bundle of His
What is the interval called between S/Q and T
ST interval
Start of repolarisation of the ventricle
What is an irregular rhythm called
Arrhythmias
What are the 2 types of arrhythmia
1- impulse propagation : random AP occurrence and slow firing
2- impulse initiation : uncontrollable AP firing in atria or ventricle = atrial fibrillation/ ventricular fibrillation
