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Questions and Answers
What is the primary function of contractile cells in the heart?
What is the primary function of contractile cells in the heart?
What is the result of sympathetic stimulation on the heart?
What is the result of sympathetic stimulation on the heart?
What is the role of autorhythmic cells in the heart?
What is the role of autorhythmic cells in the heart?
What ion is involved in the depolarization of the SA node?
What ion is involved in the depolarization of the SA node?
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What is the effect of parasympathetic stimulation on the heart?
What is the effect of parasympathetic stimulation on the heart?
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What is the function of funny channels in the heart?
What is the function of funny channels in the heart?
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What determines the force of contraction in cardiac muscle?
What determines the force of contraction in cardiac muscle?
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What is the effect of digitalis on the heart rate?
What is the effect of digitalis on the heart rate?
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In which direction does the depolarization wave spread in the ventricles?
In which direction does the depolarization wave spread in the ventricles?
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What is the name of the wave that represents the depolarization of the atria?
What is the name of the wave that represents the depolarization of the atria?
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What is the term for a heart rate that is faster than normal?
What is the term for a heart rate that is faster than normal?
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What is the term for a restricted blood flow to the heart?
What is the term for a restricted blood flow to the heart?
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What is the effect of G-protein on calcium channels?
What is the effect of G-protein on calcium channels?
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What is the term for an abrupt reduction in coronary blood flow to a segment of myocardium?
What is the term for an abrupt reduction in coronary blood flow to a segment of myocardium?
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Study Notes
Heart Function and Electrical Conduction
- Heart relaxation occurs when ventricles fill with blood.
- Contraction of the heart occurs from the apex to the base.
Cardiac Muscle Cells
- Contractile cells make up the bulk of atrial and ventricular walls and produce powerful contractions to propel blood.
- Ca2+ binding to troponin triggers muscle contraction.
- Autorhythmic cells (pacemakers) control and coordinate contractile cells.
Action Potentials
- The first action potential occurs in the SA node, resulting in depolarization.
- The second action potential occurs in the myocardium, resulting in contraction.
- Cardiac muscle cells can generate action potentials spontaneously without nervous stimulation.
Ion Channels and Stimulation
- Funny channels (If) are more permeable to sodium than potassium, allowing depolarization.
- Sympathetic stimulation alters permeability to different ions, exciting beta 1 receptors and increasing heart rate.
- Catecholamines (e.g., adrenaline) stimulate the heart.
- Parasympathetic stimulation increases pacemaker potential, hyperpolarizing SA node cells and slowing the heart rate.
Depolarization and Repolarization
- Depolarization of the SA node involves calcium.
- Sodium is involved in myocardium depolarization.
- The cardiac action potential has three stages: rapid depolarization, plateau, and repolarization.
Calcium-Induced Calcium Release and Muscle Contraction
- Calcium-induced calcium release triggers muscle contraction.
- Cardiac muscle contraction can be graded, with calcium levels determining the force of contraction.
- G-proteins open calcium channels, increasing calcium release and muscle contraction.
Drugs and the Heart
- Digitalis blocks the sodium-potassium channel, increasing intracellular sodium and calcium, and slowing the heart rate.
Electrical Conduction in the Heart
- The SA node, internodal pathways, AV node, AV bundle, bundle branches, and Purkinje fibers coordinate contraction in the heart.
- The atria contract while the ventricles relax, and vice versa.
Electrocardiogram (EKG)
- An EKG represents the summed electrical activity of all cells recorded from the surface of the body.
- Waves, segments, and intervals are used to analyze the EKG.
- The axis of the EKG represents the general movement of the waveform.
EKG Components
- The P wave represents atrial depolarization and systole.
- The PR interval is the time from the onset of the P wave to the beginning of the QRS complex.
- The QRS complex represents ventricular depolarization.
- The ST segment represents the time at which the entire ventricle is depolarized.
- The Q-T interval represents ventricular repolarization.
Abnormal Heart Rhythms
- Tachycardia: a heart rate faster than normal.
- Bradycardia: a heart rate slower than normal.
- Arrhythmia: an irregular heartbeat.
Heart Pathologies
- Ischemia: insufficient blood flow to the heart.
- Hypoxia: low levels of oxygen.
- Anoxia: absence of oxygen.
- Myocardial infarction: abrupt reduction in coronary blood flow to a segment of myocardium.
- Stenosis: restricted blood flow.
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Description
This quiz covers the mechanisms of cardiac muscle contraction, including the role of autorhythmic and contractile cells, action potentials, and calcium ions.
