Lecture Notes: Response to Environmental Stimuli

Introduction

• Living organisms need to respond to environmental changes to survive and reproduce.
• Stimuli (singular: stimulus): changes in the environment that organisms detect and respond to.

Detection and Response Mechanisms

• Organisms have evolved various receptors to detect stimuli.
• Humans have senses like sight and hearing to detect different stimuli and coordinate responses.

Internal and External Responses

• Organisms must respond to changes in both external and internal environments.
• Homeostasis: maintaining a constant internal environment for optimal metabolic function (e.g., water, CO2, glucose, pH, salt, temperature).

Receptors and Effectors

• Receptors: specialized cells for detecting stimuli.
• Effectors: cells (often muscles or glands) that carry out the response.
  • Example: Moving hand away from hot surface.

Human Response Systems

• Two main systems connecting receptors to effectors:
  1. Nervous System
     • Rapid communication via electrical impulses.
     • Involves neurons.
     • Instantaneous responses, short-lived, localized.
  2. Endocrine System
     • Slow response via hormones in the blood.
     • Long-lasting effects, can affect large areas or multiple cells.

Systems Comparison

• Nervous System:
  • Communication: Electrical impulses.
  • Speed: Instant.
  • Duration: Short-lived.
  • Scope: Localized.
• Endocrine System:
  • Communication: Hormones.
  • Speed: Slower.
  • Duration: Long-lasting.
  • Scope: Widespread effects.

Conclusion

• Both systems complement each other and the body chooses which system to use based on the stimulus.