Online Lab 1 - Intro-transcript

Introduction to Heart Rate Control

• Focus on neural and hormonal control mechanisms regulating heart rate in humans and other animals.

• Use of cane toad heart as an animal model due to similarities with human physiological function.

• Structure of online laboratory class:

  • Theoretical background review.

  • Video presentation of cane toad dissection and experimental setup.

  • Data analysis presentation.

  • Experimental data available for download.

Cardiac Physiology

• Sinoatrial Node:

  • Located in the right atrium, contains specialized pacemaker cells.

  • Produces rhythmic electrical signals initiating heart contraction.

  • Signal spreads throughout right atria via internodal pathways and from cell to cell through gap junctions.

  • Simultaneous activation of both atria, promoting coordinated blood flow into ventricles.

• Atrioventricular Node (AV Node):

  • Delays electrical signal from atria to ventricles, allowing time for atrial contraction and ventricular filling.

  • Signal moves from AV node through bundles of His to ventricle muscle tissue, resulting in ventricular contraction.

• Cane Toad Heart:

  • Three-chambered heart: two atria and one ventricle.

  • Blood flow:

    • Deoxygenated blood from body via veins to sinus venosis.

    • Blood moves to right atrium and then to single ventricle, directed to lungs and skin.

  • Oxygen absorption through the skin in amphibians helps minimize mixing of oxygenated and deoxygenated blood.

Cardiac Output and Regulation

• Cardiac Output:

  • Amount of blood ejected from the heart per minute, influenced by heart rate and contraction strength.

  • Increased during exercise due to higher heart rate and stronger contractions, enhancing blood flow to muscles.

  • Decreases during rest to match lower blood flow needs.

• Autonomic Nervous System Control:

  • Heart rate modulation through sympathetic and parasympathetic innervation of the sinoatrial node.

  • Sympathetic Activation:

    • Occurs during exercise through stimulated sensory afferents in the medulla.

    • Increases heart rate via norepinephrine release at the sinoatrial node.

    • Augments force of contraction via norepinephrine at ventricular tissue.

    • Enhanced by adrenaline release from adrenal glands in systemic circulation.

  • Parasympathetic Activation:

    • Occurs post-exercise with reduced sensory input leading to increased parasympathetic activity.

    • Acetylcholine release decreases heart rate by reducing electrical rhythm frequency.

Experiments Overview

• Three main experiments:

  1. Examine effects of neurotransmitters and hormones on cane toad heart rate pre and post-application.

  2. Determine types of cell surface receptors activated by neurotransmitters using receptor blocking drugs: atropine and propranolol.

  3. Investigate pacemaker location in the toad heart using silk thread ligature to disrupt electrical pathway transmission.

Experimental Apparatus

• Setup:

  • Exposed toad heart with ventricular tip connected to a force transducer via surgical thread.

  • Force transducer converts mechanical movement into electrical signals (voltage changes).

  • Heart contractions pull string, altering voltage, which is amplified by a Power Lab data acquisition system.

  • Visualization of heart rate changes on a personal computer screen during interventions (e.g., neurotransmitter addition).

Conclusion

• Summary of how the experiments will illustrate both the practical and theoretical aspects of cardiac physiology using the cane toad as a model.