14.1.2: The Reflex Arc
Automatic. Rapid. Involuntary. SURVIVAL.
⚡ EXAMINER FOCUS: Reflexes are NOT conscious. They bypass the brain for SPEED.
What is a Reflex Action?
⚡ AUTOMATIC
You do NOT decide to do it. It happens WITHOUT thinking.
🚀 RAPID
Faster than conscious thought. Milliseconds.
🛡️ PROTECTIVE
Prevents injury BEFORE your brain processes pain.
📚 SYLLABUS DEFINITION:
"A REFLEX ACTION is an automatic, rapid, and involuntary response to a stimulus."
⚠️ EXAMINER TRAP:
Students often write: "Reflex actions are controlled by the brain."
❌ WRONG! Reflexes bypass the brain. They are coordinated by the SPINAL CORD (CNS) via the RELAY NEURONE.
✅ Examples of Reflex Actions:
- •Pulling hand away from hot object
- •Pupil reflex: Pupils constrict in bright light
- •Knee-jerk reflex: Leg kicks when tendon tapped
- •Blinking: When object approaches eye
🎯 KEY TAKEAWAYS:
- Reflexes are automatic, rapid, and involuntary
- The pathway is: Stimulus → Receptor → Sensory → Relay → Motor → Effector → Response
- Reflexes are coordinated by the RELAY NEURONE in the spinal cord (CNS), NOT the brain
- Effectors can be muscles (contraction/movement) or glands (secretion/chemicals)
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