Question
Compare the nervous system and endocrine system as means of control and coordination. How does a reflex arc work?
(CBSE Class 10 — Control and Coordination)
Nervous vs Endocrine Comparison
flowchart TD
A["Control & Coordination"] --> B["Nervous System"]
A --> C["Endocrine System"]
B --> B1["Fast response (milliseconds)"]
B --> B2["Electrical impulses via nerves"]
B --> B3["Short-lived, precise effect"]
B --> B4["Targets specific organ"]
C --> C1["Slow response (seconds to hours)"]
C --> C2["Chemical signals (hormones) via blood"]
C --> C3["Long-lasting, widespread effect"]
C --> C4["Targets multiple organs"]
B --> D["Example: pulling hand from flame"]
C --> E["Example: growth, puberty changes"]Solution — Step by Step
The nervous system uses electrical impulses to send messages. It has three parts:
- Brain — The control centre. Cerebrum (thinking), cerebellum (balance), medulla (involuntary actions like breathing)
- Spinal cord — Relay centre between brain and body; handles reflex actions
- Nerves — Sensory nerves (carry info to brain), motor nerves (carry commands to muscles)
Response time: milliseconds. The effect is immediate but short-lived.
The endocrine system uses hormones (chemical messengers) secreted by glands into the blood:
| Gland | Hormone | Function |
|---|---|---|
| Pituitary | Growth hormone | Controls growth |
| Thyroid | Thyroxine | Controls metabolism (needs iodine) |
| Pancreas | Insulin | Lowers blood sugar |
| Adrenal | Adrenaline | Fight-or-flight response |
| Testes | Testosterone | Male puberty changes |
| Ovaries | Oestrogen | Female puberty changes |
Response time: seconds to hours. Effects are slower but last longer.
A reflex action is an automatic, involuntary response to a stimulus — like pulling your hand away from a hot plate.
The path (reflex arc):
- Receptor (skin) detects the stimulus (heat)
- Sensory neuron carries the message to the spinal cord
- Relay neuron (in spinal cord) processes the information
- Motor neuron sends command to the effector
- Effector (muscle) pulls the hand away
The brain is NOT involved — this is why reflexes are so fast. The brain learns about it a fraction of a second later (that is when you feel the pain).
Why This Works
The nervous system handles situations requiring quick, precise responses (touching fire, catching a ball). The endocrine system manages slow, long-term processes (growth, metabolism, reproduction). Together, they ensure the body responds appropriately to both immediate dangers and gradual changes.
Reflex arcs bypass the brain for speed — the spinal cord makes the decision. This evolutionary adaptation saves precious milliseconds that could mean the difference between minor and severe injury.
Alternative Method — Feedback Mechanism
The two systems often work together through feedback mechanisms:
Example: Blood sugar regulation
- Blood sugar rises → Pancreas releases insulin → Sugar stored → Blood sugar falls
- Blood sugar falls → Pancreas releases glucagon → Sugar released → Blood sugar rises
This is negative feedback — the response opposes the change, maintaining balance.
For CBSE, always draw the reflex arc diagram — it carries 3 marks. Label all five parts: receptor, sensory neuron, relay neuron (in spinal cord), motor neuron, effector. Show the direction of the impulse with arrows. The most commonly drawn reflex is “hand touching a hot object.”
Common Mistake
Students confuse “reflex action” with “involuntary action.” All reflex actions are involuntary, but not all involuntary actions are reflexes. Heartbeat is involuntary (controlled by medulla oblongata in the brain), but it is not a reflex. Reflexes are sudden responses to specific stimuli, mediated by the spinal cord, not the brain.