Lecture on Autonomic Inputs and the Heart

Introduction

• Previous lecture focused on the conduction pathway of the heart.
• The heart operates as its own central nervous system with specialized cardiac muscle cells.
• It can adapt to changes in blood flow autonomously.
• Today's focus: autonomic inputs, which include the sympathetic and parasympathetic nervous systems.

Autonomic Nervous System Overview

• Part of the peripheral nervous system.
• Manages involuntary physiological processes.
• Helps anticipate environmental changes.
• Composed of:
  • Sympathetic Nervous System
  • Parasympathetic Nervous System
  • Enteric Nervous System

Sympathetic and Parasympathetic Nervous Systems

• Sympathetic Nervous System:
  • Deals with stressors (any change from the body's baseline).
  • Increases heart rate and strength of contraction.
  • Acts like a fire alarm: widespread alert.
• Parasympathetic Nervous System:
  • Returns body to baseline post-stressor.
  • Slows down heart rate.
• Enteric Nervous System:
  • Controls gastrointestinal system.
  • Integrates with both sympathetic and parasympathetic systems.

Heart Conduction System and Autonomic Inputs

• SA Node and AV Node are key parts of the conduction system.
• Sympathetic fibers innervate SA node, AV node, and Purkinje fibers to enhance heart function.
• Parasympathetic fibers mainly innervate SA node and AV node to reduce heart activity.

Effects on Heart Rate

• Sympathetic activity increases the heart rate by making action potentials more frequent.
• Parasympathetic activity decreases the heart rate by slowing down action potentials.
• Adrenal glands can release epinephrine to further stimulate heart rate.

Sympathetic Nervous System and Cardiac Output

• Cardiac Output: The volume of blood the heart pumps per minute.
• Normal cardiac output is about 5 liters/min.
• During increased sympathetic activity (such as stress or exercise), cardiac output can increase significantly.
• Right atrial pressure is important; low pressure allows for better blood flow into the heart.

Conclusion

• Sympathetic stimulation raises cardiac output to handle stressors.
• Future lectures will cover the vascular network.

These notes summarize the key points of the lecture on autonomic inputs and their impact on the heart's function. They cover the autonomic nervous system's role, its components, and how sympathetic and parasympathetic activities affect heart rate and cardiac output.