Electrical Activity and Cardiodynamics

Contractile cell

small, single central nucleus containing sarcomeres/myofibrils; branched with connections to several adjacent cells

Intercalated discs

the connections between contractile cells; contains gab junctions and desmosomes

Desmosomes

physically tie the cells together and allows for the cells to pull on each other when contracting

Gap junctions

connect the cytoplasm of one cell directly to the cytoplasm of another cell allowing minerals/water to flow directly from one cell to another

Calcium channel blockers

powerful medications given to patients to reduce the calcium in myocytes causing contractions to be less forceful

Electrocardiogram (ECG/EKG)

a recording of electrical events in the heart, representing the sum of electrical activity in the whole myocardium over time (not a measure of a single cell)

P wave

atria depolarizing

QRS complex

ventricles depolarizing

T wave

ventricles repolarizing

Fibrillation

chaotic deflections, no steady heartbeat, EKG looks like a squiggle; heart attack

Defibrillator

gives a massive shock to the heart causing all of the cells to contract at once so that all cells go back to baseline/in synch with each other so that pacemakers can reestablish the normal beat

Systole

contraction of the myocardium

Diastole

relaxation of the myocardium

Isovolumetric Contraction

ventricles contract inward but blood does not leave the ventricles yet; building pressure in the ventricles, beginning stage of ventricular systole

Isovolumetric relaxation

all valves close not allowing blood back into the ventricles as the ventricles relax

Ejection

once there is enough pressure built during isovolumetric contraction, the semilunar valves will release ejecting the blood into the vessels

Heart sounds

occur when valves close (end of QRS complex and end of T wave)

Blood Pressure

pressure exerted by blood onto the wall of the container; directly related to volume of blood (occurs in chambers and vessels)

electrical event

the distribution of electrical excitation (initiated by pacemaker cells) passed to the contractile cells

mechanical event

the contraction of myocardial cells, exerting pressure on the blood driving it through and out of the heart

cardiac cycle steps

1. action potential in atria pacemaker cells
2. action potential passes to contractile cell in both atria (atria systole)
3. electrical signal transmits from atria through the Purkinje fibers
4. Purkinje fibers pass signals to both ventricles causing those cells to contract (ventricular systole); atrial diastole at the same time
5. ventricles relax (ventricular diastole)

Cardiodynamics

the control of cardiac output

Cardiac output

the volume of blood pumped by the left ventricle in one minute

equation for cardiac output

CO = HR x SV (mL/min)

End Diastolic Volume

the amount of blood in the left ventricle just before contraction

End Systolic Volume

the amount of blood left in the left ventricle after contraction (it is never empty)

Stroke Volume

the amount pumped out of the left ventricle during systole

Medulla Oblongata

part of the brainstem that drives the autonomic nervous system

Cardiovascular Center

part of the medulla oblongata that regulates heart activity

cardioacceleratory center

increases heart rate by causing the sympathetic neurons to release more NE at the SA node

cardioinhibitory center

slows heart rate by causing parasympathetic neurons to release acetylcholine at the SA node

Sympathetic

fight or flight system

Parasympathetic

rest and digest system

Sympathetic tone

the constant firing of action potentials in vessels that sustain a low level of contraction in the smooth muscle cells creating partial vasoconstriction

Vasoconstriction

the degree of constriction to reduce blood flow in a vessel

Vasodilation

the degree of dilation of the vessel to increase blood flow

Preload

stretch on ventricle wall during diastole (fill)

Contractility

force produced during contraction, at a given preload

Beta blockers

block receptors for epinephrine and NE \= decrease contractibility of muscle

Calcium channel blockers

decrease calcium entry or release in contractile cells; decrease workload on the heart (less strong contractions)

Afterload

force the ventricle needs to produce to open the semilunar valve and eject blood

Ejection Fraction

the percentage of EDV pumped out in one beat (normal is 50 to 75%)