Cardiovascular Physiology Overview

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Questions and Answers

Which statement correctly describes the function of contractile cells in the heart?

They initiate electrical activity.

They produce contractions and generate force. (correct)

They control and coordinate the heartbeat.

They are responsible for the conduction of electrical impulses.

What is a key characteristic of auto-rhythmic cells?

They have more striations than contractile cells.

They contain many contractile fibers.

They initiate and distribute electrical activity. (correct)

They make up the majority of heart muscle.

What structural feature is unique to cardiac muscle cells compared to skeletal muscle cells?

Multiple nuclei per cell.

Specialized ion channels in the sarcolemma. (correct)

Uniform fiber anchoring at each end.

Absence of intercalated discs.

Why are gap junctions and intercalated discs important in cardiac muscle cells?

They enable electrical signals to pass quickly from cell to cell. Signup and view all the answers

What is the primary reason that cardiac muscle fibers are not anchored at the ends?

To allow for greater sarcomere shortening and lengthening. Signup and view all the answers

What effect does increased vagal tone have on heart rate?

Decreases heart rate via parasympathetic stimulation Signup and view all the answers

Which neurotransmitter is responsible for sympathetic stimulation of the heart?

Noradrenaline Signup and view all the answers

What is the primary role of the autonomic nervous system (ANS) concerning heart function?

Modulating the cardiac activities Signup and view all the answers

What effect describes the force of contraction in response to sympathetic action on the ventricles?

Inotropic effect Signup and view all the answers

Which effect relates to the rate of impulse conduction through the AV node?

Dromotropic effect Signup and view all the answers

What is the primary role of Ca2+ in cardiac muscle contraction?

It induces the release of Ca2+ from the sarcoplasmic reticulum. Signup and view all the answers

Which characteristic distinguishes the action potential in cardiac muscle from that in skeletal muscle?

Cardiac muscle action potentials are wider and have a longer contraction phase. Signup and view all the answers

Why can't cardiac muscle be tetanized?

The action potential duration is very long in cardiac muscle. Signup and view all the answers

What initiates the action potentials in the heart?

Autorhythmic cells in the conducting system. Signup and view all the answers

How does the action potential spread to contractile cells in cardiac muscle?

Through gap junctions. Signup and view all the answers

What role do ATP-dependent pumps play after cardiac muscle contraction?

They pump Ca2+ back into the sarcoplasmic reticulum and out of the cell. Signup and view all the answers

Where are autorhythmic cells primarily located in the heart?

Throughout the conducting system, including the sinoatrial node. Signup and view all the answers

What component is responsible for exposing myosin binding sites during contraction?

Ca2+ binding to troponin. Signup and view all the answers

What role does the A-V node play in the conduction system of the heart?

It is responsible for the slowest conduction of signals. Signup and view all the answers

How does the fibrous skeleton impact electrical activity in the heart?

It separates atrial and ventricular electrical activity. Signup and view all the answers

What is the main function of the SA node?

To serve as a pacemaker for the heart. Signup and view all the answers

What is the significance of the delay in conduction at the AV node?

It ensures atrial contraction occurs before ventricular contraction. Signup and view all the answers

What happens during the absolute refractory period of a myocyte?

Sodium channels are inactivated and unexcitable. Signup and view all the answers

What allows the Purkinje fibers to rapidly carry signals throughout the ventricles?

Dense connections with gap junctions. Signup and view all the answers

How does the SA node regulate heart rate?

By having the shortest cycle of repolarization and depolarization. Signup and view all the answers

What prevents excessively fast rates of atrial contraction from affecting the ventricles?

The diameter of cells at the A-V node. Signup and view all the answers

Study Notes

Cardiac Cell Types

Two main cardiac muscle cell types: contractile cells (99% of heart muscle) and autorhythmic cells.
Contractile cells produce contractions and generate force; activated by membrane potential changes.
Autorhythmic cells initiate and distribute electrical activity; control heartbeat without contributing to contraction.

Structure of Cardiac Muscle Cells

Cardiac muscle cells are striated, short, branched, with a single, central nucleus.
They contain gap junctions and intercalated discs for cell connectivity.
Specialized ion channels, including voltage-gated Ca²⁺ channels, are present in the sarcolemma.

Action Potential in Cardiac Muscle

Action potentials (AP) spread from autorhythmic cells to contractile cells via gap junctions.
AP travels along the plasma membrane to T-tubules, causing Ca²⁺ release from the sarcoplasmic reticulum (SR).
Ca²⁺ binds to troponin, leading to muscle contraction through cross-bridge cycling.

Cardiac vs. Skeletal Muscle Action Potential

Cardiac muscle AP is wider and has a prolonged contraction phase compared to skeletal muscle.
Cardiac muscle cannot undergo summation or tetanus due to a long refractory period.

Intrinsic Conduction System

Autorhythmic cells generate action potentials through sinoatrial (SA) node, atrioventricular (AV) node, Bundle of His, and Purkinje fibers.
SA node is the primary pacemaker, facilitating the fastest recovery from refractory periods.

Electrical Signal Pathway

Signals originate from SA node, traveling through internodal pathways and atrial muscle.
AV node conducts signals slower, allowing atrial contraction before ventricular contraction.

Fibrous Cardiac Skeleton

The fibrous skeleton electrically separates atria from ventricles to control impulse conduction.
Only the AV node and Purkinje fibers penetrate this barrier, preventing atrial impulses from directly stimulating ventricular muscle.

Timing and Delay in Conduction

Shortest repolarization cycle occurs at SA node, ensuring it fires first and regulates heart rate.
The AV node introduces a delay allowing complete atrial contraction and blood flow into ventricles before ventricular contraction.

Refractory Periods in Myocytes

Absolute refractory period: myocyte unexcitable post-stimulation due to all sodium channels being inactivated.
Relative refractory period: some sodium channels reset, allowing weak AP in response to external stimulation.

Autonomic Nervous System (ANS) Influence

ANS modulates (does not generate) heart rate, with vagal influences dominant at rest.
Changes in heart rate can result from adjustments in sympathetic and vagal activity on the SA node.

Sympathetic and Parasympathetic Effects

Sympathetic stimulation increases heart rate (positive chronotropic effect) via noradrenaline binding to β1 receptors.
Parasympathetic stimulation decreases heart rate (negative chronotropic effect) via acetylcholine and influences K⁺ and Ca²⁺ ion conductance.

Inotropic and Dromotropic Effects

Inotropic effects: sympathetic impact increases force of heart contractions.
Dromotropic effects: influence impulse conduction speed through the AV node.
Bathmotropic effects: regulate threshold attainment and automatism in AV node and ventricles.

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Description

Explore the fundamentals of cardiovascular physiology with a focus on the electrical activity of the heart and its ionic basis. This quiz will help you understand the different cardiac cell types, their structure, and function. Join the learning adventure and deepen your knowledge in this vital area of medical science!