Regulation of Stroke Volume & Heart Rate Flashcards
Describe the role of the pacemaker cells in regulating heart rate.
Pacemaker cells, typically found in the sinoatrial node, depolarize to threshold first, initiating an action potential that spreads through the heart to cause contractions.
How does the sympathetic nervous system affect heart rate?
The sympathetic nervous system, responsible for the fight or flight response, increases heart rate by releasing noradrenaline and adrenaline, which act on adrenergic receptors to increase the slope of the pacemaker potential.
Define tachycardia.
Tachycardia is the technical term for an increased heart rate, often caused by factors like sympathetic nervous system activation.
What is the role of the parasympathetic nervous system in heart rate regulation?
The parasympathetic nervous system, responsible for rest and digest functions, decreases heart rate by releasing acetylcholine, which acts on muscarinic receptors to hyperpolarize pacemaker cells.
Describe the influence of preload on stroke volume.
Preload, a term coined by Starling, refers to the initial length of the cardiac muscle and influences the energy of contraction, as per Starling’s law.
How does the parasympathetic nervous system affect heart rate?
The parasympathetic nervous system decreases heart rate by releasing acetylcholine, which hyperpolarizes pacemaker cells and slows down the firing of action potentials.
What is bradycardia?
Bradycardia refers to a decreased heart rate, often caused by factors like parasympathetic nervous system activation.
Define stroke volume.
Stroke volume is the amount of blood pumped by the heart in one contraction, influenced by factors like preload, afterload, and contractility.
Define the term ‘preload’ in the context of muscle physiology.
Preload refers to the initial resting length of the muscle before contraction, which is correlated with the tension or strength of the subsequent muscle contraction.
How does the number of crossbridges between actin and myosin filaments affect muscle contraction strength according to the Starling curve?
Optimal crossbridge formation at peak tension results in a strong muscle contraction. Fewer crossbridges at larger muscle lengths lead to weaker contractions, while excessive overlap hinders crossbridge formation, reducing efficiency.
Describe the application of the length-tension relationship from skeletal muscle to cardiac muscle.
The length-tension relationship, commonly applied to skeletal muscle, is also relevant to cardiac muscle. In cardiac muscle, the end diastolic volume, which stretches the muscle, influences the strength of contraction and stroke volume.
Do changes in venous return affect cardiac muscle contraction and stroke volume?
Yes, increasing venous return stretches the cardiac muscle more, leading to a stronger contraction and increased stroke volume. Conversely, decreasing venous return results in less muscle stretching, weaker contractions, and lower stroke volume.
Explain the significance of end diastolic volume in relation to cardiac muscle contraction.
End diastolic volume represents the volume of blood filled into the ventricles before contraction. It influences the stretching of cardiac muscle, affecting the strength of contraction and stroke volume in the heart.
Describe the importance of the mechanism discussed in the content.
The mechanism ensures self-regulation and closely matched stroke volumes of the left and right ventricles to prevent blood accumulation on one side.
Define afterload in the context of the content.
Afterload is defined as the load against which the muscle tries to contract, particularly referring to the pressure the ventricle must overcome to push the aortic valve open.
