Week 10
Regulation of Organ Function by Nerve Impulses
Every organ's function is regulated by nerve impulses.
Example: A frog muscle, with its nerve connected to electrodes, can be stimulated electrically.
When stimulated, a control lamp lights up, indicating the muscle contraction.
Contraction is recorded on a slow rotating drum coated with soot.
Autonomic Actions of Vegetative Organs
Vegetative organs (e.g., intestines, heart) function largely automatically.
Their performance is regulated by increasing or inhibiting nerve impulses.
Nerve impulses enable coordination of a single organ's action with overall organism function.
Heart functionality can vary in:
Speed (faster or slower)
Strength (stronger or weaker)
Otto Lurvy's Contribution
Otto Lurvy explored how nerve signals are transmitted to organs.
Key physiological question: What mechanism transmits a nervous impulse to an effector?
Stimulation of a nerve raises an impulse at the stimulation site, propagating to nerve endings.
Propagated impulse is accompanied by an electrical wave called the action potential.
Understanding Augmenter vs. Inhibitory Nerves
Augmenter Nerves:
Stimulation increases organ activity, understandable through electrical wave propagation.
Inhibitory Nerves:
The electrical wave decreases or stops effector organ activity, which cannot be explained by the electrical hypothesis alone.
Chemical Transmission Hypothesis
Consideration of chemical transmission mechanisms became necessary.
Drugs such as adrenaline and muscarine affect vegetative organs similar to nerve stimulation in opposite directions.
This raised the idea of a chemical mechanism underlying the nervous effect.
Identification of Chemical Substances
Lurvy proposed that nerve endings contain chemicals that are released when stimulated.
These chemicals induce reactions in the effector organs.
By 1921, Lurvy's experiment on the frog's heart confirmed this hypothesis.
Augmentary substance identified: noradrenaline
Inhibitory substance identified: acetylcholine
Experimental Evidence
Classical Experiment by Otto Lurvy (1921):
Frog heart suspended in a damp chamber connected to nutrient solution via cannula.
Nerves positioned above electrodes for electrical stimulation.
Apex of the heart connected to an indicator for contraction registration.
Stimulation Observations
Vagus Nerve Stimulation:
Control lamp flashes blue when stimulated.
Observed that oscillations in heart contraction decrease with stimulation.
After stimulation ceases, amplitude returns to original height.
Sympathetic Nerve Stimulation:
Triggered by a flashing red lamp.
Results in rapid increase of heart oscillations.
Lurvy's 1921 Publication
Otto Lurvy published findings about humoral transmission of heart nerve reactions.
Further experiments involved two frog hearts:
One heart electrically stimulated; contraction recorded on a curve.
Fluid extracted transferred to second heart, affecting its oscillations without electrical stimulation.
Implications of Chemical Mediators
Substances liberated during vagus stimulation affect the second heart similarly.
Sympathetic stimulation leads to increased heart power, demonstrated through fluid transfer.
Chemical Mechanisms and Enzymatic Action
Acetylcholine recognized as secreted substance by vagus and cholinergic nerves.
Noradrenaline/Adrenaline act as mediators for the sympathetic effect.
Role of Cholinesterase
Acetylcholine quickly destroyed by cholinesterase enzyme.
Observed via color change indicating acetylcholine's breakdown.
Cholinesterase inhibition results in prolonged effects from vagus stimulation.
Increased concentration of acetylcholine maintained, leading to prolonged vagus effects.
Impact of Lurvy's Research
Research findings validated for transmission of impulses across all efferent peripheral nerves.
Recognition of chemical nature of nerve effects significantly influenced biology.
Led to advances in diagnostics and therapeutics within modern medicine.
Otto Lurvy and Sir Henry Dale were awarded the Nobel Prize for Medicine in 1936 for their contribution.