IGCSE Study Buddy: Coordination and Response (Part 1)

Introduction

• Focus on topic 14 from Cambridge IGCSE Biology syllabus.
• Importance of coordination and response in organisms.

Nervous System Overview

• Purpose: Coordinate and regulate body functions for homeostasis.
  • Receives and processes environmental and internal information.
  • Generates responses to maintain a stable internal environment.

Example

• Cold exposure triggers neurons to alert the brain, initiating shivering for heat generation.

Components of the Nervous System

• Millions of neurons (nerve cells) transmitting information as electrical impulses.
• Central Nervous System (CNS): Brain and spinal cord.
• Peripheral Nervous System (PNS): All nerves outside the brain and spinal cord.

Types of Neurons

• Sensory Neurons: Carry impulses from sense organs to CNS.
• Relay Neurons: Found in CNS, connect sensory and motor neurons.
• Motor Neurons: Carry impulses from CNS to effectors (muscles/glands).
• Identification:
  • Sensory Neurons: Long, cell body in the middle of axon.
  • Relay Neurons: Short, small cell body at one end, many dendrites.
  • Motor Neurons: Long, large cell body, long dendrites.

Stimulus, Receptors, and Effectors

• Stimulus: Change in environment detected by sensory neurons (e.g., light, sound).
• Receptor: Detects stimulus, generates electrical impulse to CNS.
• Effector: Responds to CNS signals resulting in action (muscles/glands).

Example: Fire

• Stimulus: Fire.
• Receptor: Skin receptors detect fire.
• Effector: Arm muscles retract arm away from fire.

Voluntary vs. Involuntary Responses

• Voluntary Response: Conscious action (e.g., raising hand in class).
  • Initiated by the brain.
• Involuntary Response: Automatic reaction (e.g., pulling hand from heat).
  • Quick, does not involve the brain initially.
  • Important for survival, faster than voluntary responses.

Reflex Arc

• Pathway of nerve impulse in an involuntary response.
• Process:
  1. Stimulus: Fire detected.
  2. Receptor: Skin receptor cells.
  3. Sensory Neuron: Sends impulse to spinal cord.
  4. Relay Neuron: Connects sensory to motor neuron in spinal cord.
  5. Motor Neuron: Impulse to effector (arm muscle).
  6. Effector: Muscle contracts, arm retracts.
• Diagram: Visualizes stimulus to response pathway.

Synapses

• Junctions between neurons; neurons do not touch.
• Structure:
  • Vesicles with neurotransmitter molecules.
  • Synaptic gap.
  • Receptor proteins.
• Process:
  1. Impulse in neuron A causes neurotransmitter release.
  2. Neurotransmitter diffuses across synaptic gap.
  3. Binds to receptor proteins on neuron B.
  4. Stimulates impulse in neuron B.
• Function: Ensures one-directional impulse travel.

Conclusion

• Summary of part 1: Coordination and Response.
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