Edexcel iGCSE Biology-3.40 Simple Reflex Arc- Study Notes- New Syllabus
Edexcel iGCSE Biology-3.40 Simple Reflex Arc- Study Notes- New syllabus
Edexcel iGCSE Biology-3.40 Simple Reflex Arc- Study Notes -Edexcel iGCSE Biology – per latest Syllabus.
Key Concepts:
3.40 describe the structure and functioning of a simple reflex arc illustrated by the withdrawal of a finger from a hot object
Reflex Arc – Structure & Function
🌱 Introduction
A reflex arc is the simplest neural pathway for a rapid, automatic response to a stimulus.
Purpose: Protects the body from harm and allows quick reactions without waiting for the brain.
Reflexes are involuntary and very fast.
🧩 Components of a Reflex Arc
- Receptor
Specialized cells in sense organs that detect a stimulus (e.g., heat, pain, pressure). Converts stimulus into an electrical impulse. - Sensory (Afferent) Neuron
Transmits the impulse from the receptor to the CNS (spinal cord). Direction: receptor → CNS. - Relay (Inter) Neuron
Located in spinal cord. Receives impulse from sensory neuron and connects to motor neuron. Can modulate response. - Motor (Efferent) Neuron
Carries impulse from CNS to effector (muscle or gland). Direction: CNS → effector. - Effector
Muscle or gland that produces a rapid response (e.g., muscle contracts to pull away, gland secretes).
🔥 Example: Withdrawal from a Hot Object
| Step | Event | Details |
|---|---|---|
| 1 | Stimulus | Heat from hot object touches finger. |
| 2 | Receptor activation | Heat-sensitive receptors in skin detect high temperature. |
| 3 | Sensory neuron | Impulse travels along sensory neuron to spinal cord. |
| 4 | Relay neuron | In spinal cord, impulse is passed to motor neuron. |
| 5 | Motor neuron | Impulse travels to muscles in the arm. |
| 6 | Effector response | Muscles contract → finger and hand withdraw from hot object. |
🔹 Key Features of Reflex Arc
- Rapid: Signal bypasses brain initially → prevents injury.
- Automatic/Involuntary: No conscious thought needed.
- Protective: Maintains safety and homeostasis.
- One-way signal: Receptor → sensory neuron → relay neuron → motor neuron → effector.
📌 Quick Recap
Reflex arc = fast, automatic neural response.
Components: Receptor → Sensory neuron → Relay neuron → Motor neuron → Effector.
Example: Withdrawal reflex from hot object.
Advantage: Protects body from immediate harm.
✨ Tip: “R-S-R-M-E” → Receptor, Sensory, Relay, Motor, Effector.