Edexcel iGCSE Biology-3.36 Nervous & Hormonal Control- Study Notes- New Syllabus

Nervous vs Hormonal Communication

📝 Introduction

• Living organisms must respond to changes in their surroundings called stimuli.
• These responses help the body survive and maintain a stable internal environment.
• The body uses two main communication systems:
  • Nervous system → fast electrical responses
  • Hormonal (endocrine) system → slower chemical responses
• Both systems work together to control body activities in a coordinated way.

⚡ Nervous System – Fast Communication

What is the Nervous System?

• A system that controls body responses using electrical impulses.
• Messages travel through special cells called neurons (nerve cells).
• Controlled mainly by the brain and spinal cord (CNS).

How Nervous Communication Works

• A stimulus is detected (e.g. heat, light, pain).
• Receptors in sense organs detect the change.
• Electrical impulses are sent through sensory neurons to the CNS.
• CNS processes the information.
• Motor neurons carry impulses to effectors (muscles or glands).
• Effectors produce a quick response.

Key Features of Nervous Communication

• Very fast response.
• Short duration of action.
• Highly specific (only one muscle or gland is affected).
• Uses electrical signals.
• Works through a fixed pathway of neurons.

Examples

• Pulling hand away from a hot object.
• Blinking when something approaches the eye.
• Knee-jerk reflex action.

💉 Hormonal System – Chemical Communication

What is the Hormonal System?

• A system that uses hormones to control body activities.
• Hormones are chemical messengers released by endocrine glands.
• Hormones are carried in the bloodstream to target organs.

How Hormonal Communication Works

• An endocrine gland detects a change in the body.
• The gland releases a hormone into the blood.
• The hormone travels throughout the body.
• Only target cells with specific receptors respond.
• The target organ produces a response.

Key Features of Hormonal Communication

• Slower response compared to nervous system.
• Long-lasting effects.
• Can affect many organs at the same time.
• Uses chemical signals (hormones).
• Carried by blood, not nerves.

Examples

• Insulin lowers blood glucose levels after eating.
• Adrenaline prepares the body for “fight or flight”:
  • Increases heart rate
  • Increases breathing rate
  • Increases blood glucose release

⚖️ Differences Between Nervous and Hormonal Systems

🔗 How Both Systems Work Together

• The nervous system handles quick reactions.
• The hormonal system controls long-term processes.
• Both systems ensure the body responds properly to changes.
• Together they help maintain homeostasis (stable internal conditions like temperature and glucose level).

🌟 Why Two Systems Are Needed

• Some responses must be instant → nervous system is used.
• Some processes need long-term regulation → hormonal system is used.
• Using both systems gives better control and balance in the body.

📊 Quick Comparison

• Nervous system = fast message through wires (nerves).
• Hormonal system = slow message through blood (chemicals).
• Nervous = quick action.
• Hormonal = long control.

📌 Quick Recap
Nervous = fast, electrical, short-term, specific.
Hormonal = slow, chemical, long-term, widespread.
Both = vital for coordination + survival.