Biological Rhythms: From Clocks to Chaos
Henri Poincaré started it all
Norbert Wiener & Cybernetics
**************************************************** Late 1975
Outline Homeostasis -- in many forms Biological oscillators Starting and stopping oscillators (Bifurcations in physiological dynamics) Forcing oscillators: Single vs. Periodic Conclusions
Outline Homeostasis in all of its forms Biological oscillators Starting and stopping oscillators (Bifurcations in physiological dynamics) Forcing oscillators: Single vs. Periodic
Homeostasis
Externally Induced Fluctuations
Ion Channel Current Fluctuations
“Spontaneous” Fluctuations
Noise vs. Chaos
Outline Homeostasis in all of its forms Biological oscillators Starting and stopping oscillators (Bifurcations in physiological dynamics) Forcing oscillators: Single vs. Periodic
Maintained by a periodic process
Different Perturbations Different Effects
Homeostatis in the Kidney
Islets of Langerhorns: Constant Glucose Stimulus
Mutual Inhibition in the Lobster Cells 1 & 2 both active but they inhibit each other
Same in the Mouse Spinal Cord Reciprocal Neural Oscillators
Making the Pupil Oscillate A negative feedback system
Neural Inhibition
Outline Homeostasis in all of its forms Biological oscillators Starting and stopping oscillators (Bifurcations in physiological dynamics) Forcing oscillators: Single vs. Periodic
Gut: Tapping in to an Oscillator Electrical Mechanical Electrical Mechanical
Soft Excitation (Supercritical Hopf Bifurcation) Cardiac Cell Model (McAllister, Noble, Tsien)
Schematically
More Soft Excitation Lung volume Phrenic activity Uterine pressure waves in dysmenorrhea
Still More Soft Excitation Arterial occlusion Fictive swimming
Female orgasm
Visual Hysteresis Hard Excitation?
Hard Excitation (Subcritical Hopf Bifurcation) Squid activity
Male orgasm
Outline Homeostasis in all of its forms Biological oscillators Starting and stopping oscillators (Bifurcations in physiological dynamics) Forcing oscillators: Single vs. Periodic
Single Pulse Perturbation--Heart
Single Pulse Perturbation--Squid Annihilation of action potentials with residual signs of limit cycles
Periodic Perturbation/Forcing Control 2:1 3:2 1:1 2:2 2:3 “Chaos” 3:1 2:1 3:2 (walking) 3:2 (running)
Conclusions Homeostasis can be like a (mathematical) steady state Varieties of homeostasis: steady, oscillating, ??chaotic?? Types of bifurcations: Soft and Hard Direct analogies between behaviour and mathematical properties Understanding normal biological properties ↔ understand disease Every example has been studied mathematically