Clase 20 Fisiología Cardíaca 5 - Excitación rítmica del corazón (IG:@doctor.paiva)

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This section introduces the topic of cardiac physiology, focusing on the rhythmic excitation of the heart and the specialized system responsible for cardiac contraction.

Rhythmic Excitation of the Heart

• The discussion delves into the generalities of cardiac excitation, highlighting key components such as the sinoatrial node (SA node), atrioventricular node (AV node), His bundle, and Purkinje fibers.

• Emphasis is placed on the role of Purkinje fibers in transmitting action potentials to ventricular muscles, controlling cardiac excitation and conduction.

• The automaticity of the heart's contraction is attributed to the specialized system known as the cardiac conduction system or pacemaker system, which generates rhythmic electrical impulses for muscle contraction and rapid conduction throughout the heart.

Specialized Cardiac Conduction System

• The specialized system is highlighted for its dual functions: generating rhythmic electrical impulses for muscle contraction and conducting these stimuli rapidly across the heart.

• Detailed exploration of the sinoatrial node (SA node) as a pacemaker in a healthy heart, initiating signals that propagate through the cardiac conduction system.

• Further elucidation on how signals from SA node travel to other parts of the heart via internal pathways, leading to ventricular contractions through Purkinje fibers.

Excitability Mechanisms

This segment focuses on understanding nodal excitability mechanisms within specific components like SA nodes.

Sinoatrial Node Characteristics

• Description of SA node as an ellipsoid structure with specialized cardiac muscle lacking contractile properties but crucial for initiating electrical impulses.

• Specific location details provided for SA node within superior posterolateral wall of right atrium, emphasizing its dimensions and direct connection to atrial muscle fibers.

Nodal Action Potentials

• Comparison drawn between action potentials in ventricular muscles and SA nodes, highlighting differences in resting membrane potential and ion channel activities.

• Explanation provided regarding why SA nodal action potentials are less negative due to natural permeability to sodium and calcium ions, leading to depolarization at threshold levels.

Mechanisms Behind Nodal Excitability

• Addressing common questions about less negative potentials in SA nodes linked to ion permeability dynamics involving sodium and calcium channels.

Despolarization Cycle in the Heart

This section delves into the process of depolarization in the heart, focusing on key structures like the sinoatrial node and atrioventricular node, as well as the conduction velocities involved.

Depolarization Process

• The signal from the sinoatrial node travels to both the atrioventricular node and the left atrium through internal pathways.

• Conduction velocities differ, with muscle atrial velocity at 0.3 meters per second and internal pathways faster at approximately meters per second.

• Both atria contract simultaneously due to rapid conduction via internal pathways, although there is a slight delay in right atrial contraction.

• The impulse from the sinoatrial node to the atrioventricular node takes 0.03 seconds, highlighting the importance of this delay region.

Atrioventricular Node Function

• The atrioventricular node acts as a delay mechanism allowing ventricles to fill properly before contracting.

• Specific delays occur within the atrioventricular node, crucial for coordinated heart function.

• Slow conduction in this region is attributed to fewer intercalated discs, leading to decreased ion flow between cells.

Conduction Pathways in Heart

This part explores how specific structures like Purkinje fibers contribute to efficient signal transmission within the heart.

Purkinje Fiber System

• Purkinje fibers facilitate rapid signal transmission due to increased intercalated discs allowing for enhanced ion flow.

• Anatomical barriers separate different heart regions electrically, ensuring unidirectional signal propagation towards vital nodes.

• These barriers prevent cross-stimulation between chambers or regions, maintaining proper cardiac rhythm.

Rhythmic Signal Transmission

• Unidirectional signaling towards critical nodes ensures coordinated heart contractions without interference.

• Detailed discussion on branches of His bundle and their role in directing signals efficiently within the heart.

Purkinje Fiber Speed

• Signals travel swiftly through His bundle branches towards Purkinje fibers before reaching ventricular muscles rapidly.

Ventricular Contraction and Signal Transmission

In this section, the speaker discusses the speed of ventricular contraction and the transmission of signals within the heart.

Ventricular Contraction Speed

• The speed of ventricular contraction ranges from 0.3 to 0.5 meters per second.

• The muscle contraction in the ventricle spirals towards the surface.

• It takes approximately 0.03 seconds for the signal to travel from the Purkinje network to reach the last cell in the ventricular muscle.

Signal Transmission Delays

This part focuses on summarizing signal delays during transmission within different parts of the heart.

Signal Delay Summary

• From sinus node to atrioventricular node: 0.3 seconds.

• Delay in bundle of His: 0.9 seconds.

• Further delay in Purkinje fibers: 0.4 seconds.

• Total time for signal transmission from sinus node to ventricular muscle: Approximately 2 seconds.

Heart's Electrical System and Impulse Generation

Exploring impulse generation and frequencies within different nodes of the heart's electrical system.

Impulse Generation Details

• Sinus node sends signals at a rate of 70 to 80 impulses per minute.

• Atrioventricular node transmits between 40 to 60 impulses per minute.

• Purkinje system discharges between 15 to 40 impulses per minute.

Dominance of Sinus Node in Heart Control

Discussing how the sinus node plays a crucial role in controlling heart rhythm over other nodes.

Sinus Node Dominance

• Sinus node dictates heart rhythm due to its rapid discharge frequency.

• It triggers impulses before atrioventricular nodes or Purkinje system reach their excitation threshold.

Backup Systems in Case of Node Damage

Exploring backup mechanisms if primary nodes are damaged or dysfunctional.

Backup Mechanisms

• If sinus node is damaged, atrioventricular node takes control but at a slower pace (40–60 beats/min).

• If both sinus and atrioventricular nodes are impaired, Purkinje system assumes command at a slower rate (15–40 beats/min).

eleva el borde sagrado eleva el potencial de reposo de la salvación nasal y las células y nos salva que facilitaba por ende será mucho más fácil que llegue al umbral de excitación y causa una despolarización y en consecuencia en potencia lección y es por eso que aumenta la frecuencia cardíaca perfecto de bibliografía utilice el tratado de fisiología gayton jaula edición número 13

The text discusses how raising the sacred edge increases the resting potential of nasal salvation and cells, making it easier to reach the excitement threshold, leading to depolarization and increased heart rate. Reference is made to Gayton's Physiology textbook, 13th edition.

Key Points:

• Raising the sacred edge enhances the resting potential of nasal salvation and cells.

• Facilitation aids in reaching the excitement threshold more easily.

• Depolarization occurs as a result of reaching the excitement threshold.

• Increased heart rate is a consequence of depolarization.