Lecture Notes: Control Systems and Homeostasis

Introduction to Control Systems

• Physiological Importance: Control systems maintain a constant internal environment (homeostasis) despite external changes.
• Dynamic Physiology: Enables activities like running and leaping while maintaining cell and molecular stability.
• Nervous System Role: Works with physiological systems to facilitate homeostasis.

Control Systems Basics

• Question: What kind of control generates homeostasis?
• Focus: Discuss control systems abstractly before delving into physiological specifics.

Thermostat Example: Negative Feedback

• Temperature Control: Illustrates negative feedback system.
• Components:
  • State Variable: The temperature being controlled.
  • Set Point: Desired temperature.
  • Integrating Center: Thermostat controlling the furnace.
• Mechanical Operation: Old school thermostats operate mechanically, modern versions are digital.
• Feedback Loop:
  • Furnace heats room when below set point; turns off above set point, creating oscillations around set point.
  • Error: Difference between state variable and set point, critical for control system operation.
  • Thresholds: High (tau) and low (-tau) thresholds determine furnace activation/deactivation.
• Rules for Control:
  • Furnace on/off decisions based on error relative to thresholds.
  • Flowchart representation of control systems showing integrating center, efferent, and afferent pathways.
  • Efferent Pathway: Action influencing state variable.
  • Afferent Pathway: Sensory input influencing efferent response.

Negative Feedback

• Aim: Maintain state variable around set point.
• Utility: Useful for homeostasis in physiological systems (temperature, blood pressure, ion balance, etc.).

Positive Feedback

• Key Differences:
  • State variable-driven efferent pathway.
  • Exponential rise characteristic; requires external shutdown to prevent runaway effect.
• Example: Sodium voltage-gated channels during action potential in cells.

Feedforward Control

• Characteristics:
  • No feedback loop.
  • Efferent response independent after initiation, simple and fast-acting.
• Application: Seen in reflex arcs (musculoskeletal, autonomic).

Summary of Control Types

• Feedforward Control: Simple, fast, without feedback.
• Negative Feedback: More complex, allows modulation, essential for homeostasis.
• Positive Feedback: Rapid, exponential rise, requires shutdown; not suited for homeostasis.

Conclusion

• Focus on Negative Feedback: Predominantly used in physiological control systems for maintaining homeostasis.
• Course Outlook: Future lectures will further explore these concepts in physiological contexts.