Cardiac Nerves and Refractory Periods

Questions and Answers

What does the left phrenic nerve innervate?

Diaphragm contraction and sensory interactions of most of the thoracic wall.

Where does the right phrenic nerve run?

Laterally to the heart over the subclavian vein and right atrium.

What is ERP (effective refractory period)?

A depolarisation cannot be initiated by an impulse of any strength.

What defines the RRP (Relative Refractory Period)?

A strong impulse like an ectopic can cause depolarisation e.g., R on T. Signup and view all the answers

What are disorders of impulse formation?

Altered normal automaticity, abnormal automaticity, triggered activity, after-depolarisations. Signup and view all the answers

What are disorders of impulse conduction?

Reentry, e.g., anatomic reentry, functional reentry. Signup and view all the answers

What is abnormal automaticity?

Phase 4 shortens by increasing the gradient of slope or the threshold for excitation becomes lower. Signup and view all the answers

Where do the origins of atrial fibrillation (AF) typically occur?

Atria, thoracic veins, pulmonary veins, SVC, vein of Marshall. Signup and view all the answers

What is Atrial Tachycardia (AT)?

Rapid atrial rate originating from atrial tissue (300 bpm) with fibrillatory waves of variable sizes. Signup and view all the answers

Study Notes

Left and Right Phrenic Nerves

Left phrenic nerve innervates the diaphragm and sensory functions of the thoracic wall, running over the left ventricle.
Right phrenic nerve courses laterally over the subclavian vein and the right atrium, playing a crucial role in diaphragm control.

Refractory Periods

Effective Refractory Period (ERP): Represents the timespan during which a new depolarization cannot occur, regardless of the impulse strength.
Relative Refractory Period (RRP): During this phase, a strong impulse, such as an ectopic beat, can provoke depolarization, exemplified by the R on T phenomenon.

Disorders of Impulse Formation

Includes various conditions like altered automaticity, abnormal automaticity, triggered activity, and after-depolarizations, impacting heart rhythm.

Disorders of Impulse Conduction

Involves reentry mechanisms, which can be classified as anatomical or functional, causing synchronization of the heart's electrical signals.

Abnormal Automaticity

Occurs when phase 4 of cardiac action potentials shortens, either due to an increased slope gradient or a decreased threshold for excitation, leading to irregular heart activity.

Origins of Atrial Fibrillation (AF)

Atrial fibrillation can arise from multiple sites including the atria, thoracic veins, pulmonary veins, superior vena cava (SVC), and the vein of Marshall, contributing to its pathophysiology.

Atrial Tachycardia (AT)

Characterized by a rapid atrial rate (up to 300 bpm) originating from atrial tissue, presenting with fibrillatory waves of varying sizes, indicating abnormal atrial electrical activity.

Description

This quiz covers the left and right phrenic nerves and their roles in diaphragm control. It also addresses refractory periods, including ERP and RRP, and disorders of impulse formation and conduction. Test your understanding of these key concepts in cardiac physiology.