Question | Answer |
Depolarization of the heart is rhythmic and ? | Spontaneous |
About 1% of cardiac cells have | automaticity— (are self-excitable) |
Gap junctions ensure the heart contracts as a | unit |
The heart has long absolute refractory period of | (250ms) |
During cardiac muscle contraction depolarization opens voltage-gated fast Na+ channels in the | sarrcolemma |
Reversal of membrane potential from | from –90 mV to +30 mV |
Depolarization wave in T tubules causes the SR to release | Ca2+ |
Ca2+ surge prolongs the | depolarization phase |
Ca2+ influx triggers opening of | Ca2+-sensitive channels in the SR |
The duration of the contractile phase is much greater in cardiac muscle than | skeletal muscle |
Repolarization results from | inactivation of Ca2+ channels and opening of voltage-gated K+ channels |
A network of noncontractile (autorhythmic) cells that initiate and distribute impulses to coordinate the depolarization and contraction of the heart | Intrinsic cardiac conduction system |
Have unstable resting potentials (pacemaker potentials or prepotentials) due to open slow Na+ channels
At threshold, Ca2+ channels open
Explosive Ca2+ influx produces the rising phase of the action potential | Autorhythmic Cells |
In the hearts sequence of excitation the Sinoatrial (SA) node (pacemaker) Generates impulses about how many times and does what ? | 75 times/minute (sinus rhythm) and
depolarizes faster than any other part of the myocardium |
In the hearts sequence of excitation the Atrioventricular (AV) node delays impulses approximately by and does what ? | 0.1 second and
Depolarizes 50 times per minute in absence of SA node input |
What is the only electrical connection between the atria and ventricles ? | Atrioventricular (AV) bundle |
what are the two pathways in the interventricular septum that carry the impulses toward the apex of the heart | Right and left bundle branches |
what complete the pathway into the apex and ventricular walls
AV bundle and Purkinje fibers depolarize only 30 times per minute in absence of AV node input | Purkinje fibers |
Defective SA node may result in | Ectopic focus: abnormal pacemaker takes over
If AV node takes over, there will be a junctional rhythm (40–60 bpm) |
Defective AV node may result in | Partial or total heart block
Few or no impulses from SA node reach the ventricles |
Heartbeat is modified by the | ANS |
Cardiac centers are located in the | Medulla oblangata |
Cardio acceleratory center innervates SA and AV nodes, heart muscle, and coronary arteries through | sympathetic neurons |
Cardioinhibitory center inhibits SA and AV nodes through parasympathetic fibers in the | Vagus nerve |
P wave | depolarization of SA node |
QRS complex | ventricular depolarization |
T wave | ventricular repolarization |
Two sounds of the heart (lub-dub) associated with_______of heart valves | Closing |
First sound occurs as | AV valves close and signifies beginning of systole( tricuspid & mitral) |
Second sound occurs when | aortic & pulmonic valves close at the beginning of ventricular diastole. |
all events associated with blood flow through the heart during one complete heartbeat is known as | Cardiac cycle |
Systole | contraction |
Diastole | Relaxation |
What takes place in mid-to-late diastole during the phases of the cardiac cycle | ventricular filling |
AV valves are open
80% of blood passively flows into ventricles
Atrial systole occurs, delivering the remaining 20% | ventricular filling |
volume of blood in each ventricle at the end of ventricular diastole (relaxation) is known as | (End diastolic volume EDV): |
When the Atria is relax and ventricles begin to contract
Rising ventricular pressure results in closing of AV valves
Isovolumetric contraction phase (all valves are closed) this is known as | Ventricular systole |
volume of blood remaining in each ventricle is known as | End systolic volume (ESV |
The P wave represents depolarization of the | atria |
The PR segment = | atrial systole |
The QRS wave represents depolarization of the | ventricles |
The ST segment = | ventricular systole |
The T wave represents repolarization of the | ventricles |
what is the volume of blood pumped by each ventricle in one minute known as | cardiac output |
CO = heart rate (HR) x | stroke volume (SV) |
HR = | = number of beats per minute |
SV = | volume of blood pumped out by a ventricle with each beat |
what is the degree of stretch of cardiac muscle cells before they contract (Frank-Starling law of the heart) known as | preload |
contractile strength at a given muscle length, independent of muscle stretch and EDV | Contractility |
agents increase contractility
Increased Ca2+ influx due to sympathetic stimulation
Hormones (thyroxine, glucagon, and epinephrine) | Positive inotropic |
agents decrease contractility
Acidosis
Increased extracellular K+
Calcium channel blockers | Negative inotropic |
pressure that must be overcome for ventricles to eject blood is known as | afterload |
Positive chronotropic factors | increase heart rate |
Negative chronotropic factors | decrease heart rate |
Norepinephrine causes the pacemaker to fire more | rapidly and increases contractility
fight or flight |
Acetylcholine hyperpolarizes pacemaker cells by opening | K+ channels
The heart at rest exhibits vagal tone (parasympathetic) |
from adrenal medulla enhances heart rate and contractility | Epinephrine |
increases heart rate and enhances the effects of norepinephrine and epinephrine | Thyroxine |
Intra- and extracellular ion concentrations (e.g., Ca2+ and K+) must be maintained for | normal heart functions |
abnormally fast heart rate (>100 bpm) | Tachycardia |
heart rate slower. < 60 bpm
May result in grossly inadequate blood circulation | Bradycardia |
Progressive condition where the CO is so low that blood circulation is inadequate to meet tissue needs | Congestive Heart Failure (CHF) |