Introduction to Physiological Control

Study Notes

Control systems consist of interconnected components designed to elicit a desired response despite external disturbances.
Control emphasizes achieving a specific status, while regulation focuses on modifying system properties for stability and responsiveness.

Open-loop systems cannot compensate for unpredicted disturbances (e.g., programmable thermostats adapt based on time but not weather).
Actions are primarily programmed in neural circuits, combining innate and learned responses.
Sensory feedback is crucial for correcting actions to avoid errors (e.g., lifting a surprisingly light suitcase).
Servomechanisms amplify forces based on predictions (e.g., power steering in cars).

Central to automatic control, closed-loop systems utilize feedback for regulation.
Feedback is defined as reinserting past performance results into the system to improve control.
Norbert Wiener pioneered this concept, coining the term "cybernetics" to apply control theory to both biological and artificial systems.
Example of closed-loop control: a thermostat adjusts the temperature by comparing a feedback signal to a set point.

Most regulatory mechanisms incorporate both open and closed-loop controls.
Athletes exemplify this integration by executing learned actions while compensating for unexpected changes (like wind).
Autonomic regulation in the body features predictive mechanisms (e.g., cardiovascular adjustments before standing).

Homeostasis refers to the stability of the internal environment vital for life.
Claude Bernard introduced the idea of maintaining stable internal conditions, highlighting the need for feedback mechanisms.
Homeostasis entails coordinated actions to secure food, water, and temperature regulation, all directed toward sustaining internal stability.

Muscle Stretch Reflex: a reaction to a stretch triggered by tapping; involves a feedback signal from muscle spindles to the spinal cord to adjust muscle action.
Baroreflex: regulates cardiovascular responses by reacting to changes in arterial pressure using baroreceptors and feedback to the central nervous system.
Reflexes tend to be responses to immediate stimuli, while feedback mechanisms can address ongoing disturbances and oscillations in control.

Physiological systems exhibit versatility with integrated open and closed-loop regulation strategies, unlike fixed tasks in artificial systems.
Physiological components often remain unknown, necessitating system identification through data rather than predetermined models.
Extensive interactions (cross-coupling) exist among physiological systems, demonstrated in various reflex and regulatory mechanisms.
Adaptive controls and hierarchical structures allow for adjustments based on specific circumstances (e.g., muscle stretch reflex adaptations).
Embedded feedback mechanisms establish working points through nonlinear characteristics rather than comparisons to external set points, maintaining stability despite internal variations.