Reflex action and the reflex arc
A reflex action is a sudden, automatic response, such as pulling your hand off a hot pan. Its path, the reflex arc, runs through the spinal cord, without the brain.
What is a reflex action?
Some dangers need an answer at once, with no time to think. A reflex action is a quick, automatic response to a stimulus. It is usually controlled by the spinal cord, without the thinking brain deciding. It is involuntary: it happens without conscious thought. Every reflex starts with a stimulus and ends in a muscle action or a gland secretion. Examples: pulling your hand back from a hot pan or a needle (muscle). Tears washing dust out of your eye (gland). Closing your eyes in a dust storm. Shivering in the cold (muscle) and sweating in the heat (gland).
The reflex arc
The impulse also travels up the spinal cord to the brain, so you **feel the pain a moment after** your hand has moved.
Natural reflex vs conditioned reflex
Voluntary action vs reflex action
| Feature | Voluntary action | Reflex action |
|---|---|---|
| Controlled by | Cerebrum (brain) | Spinal cord |
| Thinking | Needed; done by choice | Not needed; automatic |
| Speed | Slower, after thought | Immediate |
| Examples | Choosing a study stream, making new friends, writing | Pulling your hand away when a needle pricks it, blinking when dust flies |
How to draw the reflex arc
- Draw a cross-section of the spinal cord as an oval, with a butterfly-shaped gray matter in the middle and white matter around it.
- Draw a receptor in the skin of the hand and a sensory neuron running from it into the spinal cord.
- Inside the gray matter, draw a short association neuron joining the sensory neuron to a motor neuron.
- Draw the motor neuron running out to a muscle in the arm; label the muscle effector.
- Add arrows from receptor to effector to show the path of the impulse, and label every part.
When hot oil splashes from the kadai while frying puris, your hand jerks back before you think: that is a reflex. Your mouth watering at the smell of biryani from a neighbour's kitchen is a conditioned reflex.
2 marks: “What is a reflex action? Give two examples.” A sudden, automatic response to a stimulus, controlled by the spinal cord without thinking. Examples: pulling the hand away from a hot object; tears flowing when dust enters the eye.
2 marks: “What is a conditioned reflex? How is it different from a natural reflex?” A reflex learned through experience, such as the mouth watering at the smell of a favourite food. A natural reflex is inborn and needs no learning, such as blinking or coughing.
5 marks: “Your hand jerks away from a hot pan before you feel the pain. Name this kind of action, trace the impulse along its pathway, and draw that pathway with every part labelled.” A reflex action: a sudden, automatic response controlled by the spinal cord. Path: receptor in the skin → sensory neuron → association neuron in the spinal cord → motor neuron → arm muscle (effector); the brain is informed later, so pain is felt after the hand moves; labelled diagram with arrows.
Parts of the reflex arc: Ram Sees Red, Moves Elbow: Receptor, Sensory neuron, Relay (association) neuron in the spinal cord, Motor neuron, Effector.