Class 10th Science Chapter 6 – Control and Coordination | Reflex Action and Reflex Arc

Control and Coordination

Reflex Action and Reflex Arc | Class 10 Science | CBSE + Foundation + Competitive

🧠 Reflex Action and Reflex Arc

1. Reflex Action – प्रतिवर्ती क्रिया

Reflex Action: A reflex action is a quick, automatic and involuntary response to a stimulus.

प्रतिवर्ती क्रिया: किसी उद्दीपन (Stimulus) के प्रति शरीर द्वारा की जाने वाली त्वरित, स्वतः एवं अनैच्छिक प्रतिक्रिया को प्रतिवर्ती क्रिया कहते हैं।

Examples / उदाहरण:

• Touching a hot object and immediately withdrawing the hand.
• गरम वस्तु को छूने पर हाथ तुरंत पीछे खींच लेना।
• Blinking of eyes when an object suddenly approaches.
• तेज प्रकाश में आँखों की पुतली का सिकुड़ना।
• Coughing or sneezing in response to irritation.

2. Why is Reflex Action Fast?

Reflex actions are generally coordinated through the spinal cord rather than waiting for the brain to initiate the immediate response.

प्रतिवर्ती क्रिया में तत्काल प्रतिक्रिया के लिए संदेश को पहले मस्तिष्क तक पहुँचाकर वापस लाने की आवश्यकता नहीं होती। इससे प्रतिक्रिया बहुत तेज होती है।

However, information also reaches the brain, allowing us to become consciously aware of the stimulus.

CBSE Point: Reflex action does not mean that the brain receives no information. The spinal cord can coordinate the immediate response, while information can simultaneously travel upward to the brain.

3. Reflex Arc – प्रतिवर्ती चाप

Reflex Arc: The pathway followed by nerve impulses during a reflex action is called a reflex arc.

प्रतिवर्ती चाप: प्रतिवर्ती क्रिया के दौरान तंत्रिका आवेग जिस मार्ग से होकर गुजरता है, उसे प्रतिवर्ती चाप कहते हैं।

Animated Reflex Arc – प्रतिवर्ती चाप का एनिमेटेड चित्र

Stimulus → Receptor → Sensory Neuron → Relay Neuron → Motor Neuron → Effector → Response

4. Components of Reflex Arc

Component	Function / कार्य
Receptor	Detects the stimulus. उद्दीपन को पहचानता है।
Sensory Neuron	Carries impulse from receptor towards CNS.
Relay / Interneuron	Connects sensory neuron with motor neuron, mainly within CNS.
Motor Neuron	Carries impulse from CNS to effector.
Effector	Muscle or gland that produces the response.

5. Example – Withdrawing Hand from a Hot Object

Suppose a person accidentally touches a hot object.

Step 1: Heat stimulates receptors in the skin.
Step 2: Sensory neuron carries the impulse towards the spinal cord.
Step 3: A relay neuron in the CNS passes the information to a motor neuron.
Step 4: Motor neuron carries the impulse to the arm muscle.
Step 5: The muscle contracts.
Step 6: The hand is withdrawn quickly.

Stimulus → Receptor → Sensory Neuron → Relay Neuron → Motor Neuron → Muscle → Response

6. Reflex Action vs Voluntary Action

Reflex Action	Voluntary Action
Usually automatic and involuntary.	Performed consciously.
Very rapid.	Usually comparatively slower.
Often coordinated by spinal cord.	Generally involves conscious brain control.
Example: withdrawing hand from hot object.	Example: writing with a pen.

7. Reflex Arc and Brain

The spinal cord can coordinate an immediate reflex response.

At the same time, sensory information can travel to the brain. Therefore, after the hand is withdrawn, the person may consciously feel pain and become aware of what happened.

Important: Reflex action is not simply "brain is not involved"; rather, the immediate motor response can be coordinated at the spinal level.

8. Types of Neurons Involved

Neuron	Direction	Function
Sensory Neuron	Receptor → CNS	Carries sensory impulses.
Relay Neuron	Within CNS	Connects neurons.
Motor Neuron	CNS → Effector	Carries motor impulses.

9. Key Terms – महत्वपूर्ण शब्द

Stimulus A change in surroundings that produces a response. Receptor Structure that detects a stimulus. Impulse Electrical signal travelling through a neuron. Effector Muscle or gland producing the response. CNS Brain + Spinal Cord. Reflex Arc Pathway of impulse during reflex action.

10. 30 MCQs – Multiple Choice Questions

Q1. What is a reflex action?

A) A slow voluntary response

B) A quick automatic response to a stimulus

C) A learned intellectual activity

D) A hormonal response only

Answer: B – Reflex action is quick, automatic and generally involuntary.

Q2. The pathway followed by a nerve impulse during a reflex action is called:

A) Reflex arc

B) Synapse

C) Brain pathway

D) Hormonal pathway

Answer: A

Q3. Which part usually coordinates the immediate withdrawal reflex?

A) Cerebrum

B) Cerebellum

C) Spinal cord

D) Retina

Answer: C

Q4. Which neuron carries impulses from receptor to CNS?

A) Motor neuron

B) Sensory neuron

C) Relay neuron

D) Effector neuron

Answer: B

Q5. Which structure acts as an effector in withdrawal of hand?

A) Muscle

B) Retina

C) Spinal cord

D) Receptor

Answer: A

Q6. Which is the correct sequence of a typical reflex arc?

A) Motor → Receptor → Sensory → Muscle

B) Brain → Muscle → Receptor → Sensory

C) Receptor → Sensory → Relay → Motor → Effector

D) Receptor → Motor → Sensory → Effector

Answer: C

Q7. Reflex actions are generally:

A) Automatic

B) Deliberate

C) Always learned

D) Always hormonal

Answer: A

Q8. A receptor primarily performs which function?

A) Contracts muscle

B) Detects stimulus

C) Pumps blood

D) Produces urine

Answer: B

Q9. Which neuron carries impulses from CNS to an effector?

A) Sensory neuron

B) Receptor

C) Motor neuron

D) Relay neuron only

Answer: C

Q10. Which is an example of reflex action?

A) Writing an essay

B) Reading a book

C) Playing chess

D) Withdrawing hand from a hot object

Answer: D

Q11. CNS stands for:

A) Central Nervous System

B) Cellular Neural System

C) Central Neuron Structure

D) Controlled Nervous Signal

Answer: A

Q12. Which two structures form the CNS?

A) Brain and muscles

B) Brain and spinal cord

C) Spinal cord and glands

D) Receptors and muscles

Answer: B

Q13. Relay neuron is mainly found:

A) In blood

B) In muscles

C) In the CNS

D) In bones

Answer: C

Q14. Which part produces the actual physical response in a reflex?

A) Effector

B) Receptor

C) Sensory neuron

D) Brain only

Answer: A

Q15. The withdrawal of hand from a hot object protects the body by:

A) Increasing digestion

B) Reducing immediate tissue damage

C) Increasing blood sugar

D) Stopping respiration

Answer: B

Q16. Which of the following is NOT normally a component of a reflex arc?

A) Receptor

B) Sensory neuron

C) Motor neuron

D) Red blood cell

Answer: D

Q17. A stimulus is:

A) A change that can produce a response

B) A type of muscle

C) A hormone

D) A blood cell

Answer: A

Q18. Which action is generally voluntary?

A) Withdrawal from a pin prick

B) Blinking in response to dust

C) Writing your name

D) Sneezing

Answer: C

Q19. What happens at the end of a reflex arc?

A) Effector produces response

B) Stimulus disappears before detection

C) Blood is filtered

D) Food is digested

Answer: A

Q20. The immediate advantage of a reflex action is:

A) It is slow

B) It provides rapid protection

C) It requires conscious thinking first

D) It always involves hormones

Answer: B

Q21. Which sequence correctly represents information flow?

A) Motor → CNS → Receptor

B) Effector → Receptor → Brain

C) Receptor → Sensory neuron → CNS

D) Muscle → Motor neuron → Receptor

Answer: C

Q22. Which sequence correctly represents motor output?

A) CNS → Motor neuron → Effector

B) Effector → Motor neuron → CNS

C) Receptor → Motor neuron → CNS

D) Brain → Sensory neuron → Muscle

Answer: A

Q23. Which statement is correct?

A) Every reflex requires conscious decision first.

B) Reflex actions can provide rapid protective responses.

C) Reflex actions never involve neurons.

D) Reflex arcs consist only of muscles.

Answer: B

Q24. Pain from a hot object is detected initially by:

A) Receptors in skin

B) Motor neurons

C) Muscles

D) Blood cells

Answer: A

Q25. Which part connects sensory and motor pathways in a typical spinal reflex?

A) Red blood cell

B) Relay neuron

C) Tendon

D) Bone

Answer: B

Q26. The hand is withdrawn because the motor neuron activates:

A) An effector muscle

B) A sensory receptor

C) A red blood cell

D) A digestive enzyme

Answer: A

Q27. Which one is NOT a feature of a typical reflex action?

A) Rapid

B) Automatic

C) Protective

D) Always consciously planned

Answer: D

Q28. Reflex action mainly helps an organism to:

A) Avoid immediate danger

B) Digest all food

C) Produce red blood cells

D) Form bones

Answer: A

Q29. Which is the best definition of reflex arc?

A) A blood circulation pathway

B) A pathway of nerve impulse during reflex action

C) A digestive pathway

D) A pathway of hormones only

Answer: B

Q30. Information about the reflex stimulus can also reach the:

A) Brain

B) Stomach only

C) Kidney only

D) Bone marrow only

Answer: A

11. 2 Marks Questions – 2 अंक

2 Marks Q1. What is reflex action?

Answer: Reflex action is a quick, automatic and involuntary response to a stimulus. Example: withdrawing hand from a hot object.

2 Marks Q2. Define reflex arc.

Answer: The pathway followed by nerve impulses during a reflex action is called reflex arc.

2 Marks Q3. Name the three main types of neurons involved in a typical reflex arc.

Answer: Sensory neuron, relay/interneuron and motor neuron.

2 Marks Q4. What is the function of a receptor?

Answer: A receptor detects a stimulus and initiates a sensory nerve impulse.

2 Marks Q5. Why are reflex actions important?

Answer: They provide rapid protective responses and help reduce injury from potentially harmful stimuli.

12. 3 Marks Questions – 3 अंक

3 Marks Q6. Explain the pathway of a reflex arc.

Answer: Stimulus is detected by receptor → sensory neuron carries impulse to CNS → relay neuron connects it to motor neuron → motor neuron carries impulse to effector → effector produces response.

3 Marks Q7. Differentiate between sensory and motor neurons.

Answer:
1. Sensory neuron carries impulses from receptor to CNS.
2. Motor neuron carries impulses from CNS to effector.
3. Sensory input enters the CNS, whereas motor output leaves the CNS.

3 Marks Q8. Why does a person withdraw his hand immediately after touching a hot object?

Answer: Heat stimulates skin receptors. The sensory impulse travels to the spinal cord, where a reflex pathway activates motor neurons. The arm muscles contract and withdraw the hand rapidly.

3 Marks Q9. What are stimulus, receptor and effector?

Answer:
Stimulus: A change capable of producing a response.
Receptor: Detects the stimulus.
Effector: Muscle or gland that produces the response.

3 Marks Q10. Why is spinal cord important in reflex action?

Answer: The spinal cord acts as an important integration centre for many reflexes. It allows a rapid motor response through the reflex arc while sensory information can also be transmitted to the brain.

13. 4 Marks Questions – 4 अंक

4 Marks Q11. Explain reflex action with the example of touching a hot object.

Answer:
1. Heat acts as the stimulus.
2. Receptors in skin detect heat/pain.
3. Sensory neuron carries impulse to spinal cord.
4. Relay and motor neurons activate arm muscles, causing withdrawal.

4 Marks Q12. Explain the role of sensory, relay and motor neurons in reflex action.

Answer:
• Sensory neuron carries information from receptor to CNS.
• Relay neuron connects sensory and motor neurons in CNS.
• Motor neuron carries the command from CNS to effector.
• The effector produces the final response.

4 Marks Q13. Differentiate between reflex and voluntary actions.

Answer:
1. Reflex action is automatic; voluntary action is consciously controlled.
2. Reflex action is usually very rapid; voluntary actions may take longer.
3. Reflex action often involves spinal coordination; voluntary action involves conscious brain control.
4. Example: withdrawal from heat vs writing.

4 Marks Q14. Explain why reflex action is considered a protective mechanism.

Answer: Reflex action occurs rapidly and automatically. It reduces the time between detection of a harmful stimulus and the muscular response. Thus, the body can withdraw from heat, sharp objects or other harmful conditions before greater injury occurs.

4 Marks Q15. Draw and label a reflex arc.

Answer: The diagram should show:
Receptor → Sensory Neuron → Spinal Cord/Relay Neuron → Motor Neuron → Effector.

The arrows must correctly indicate the direction of the nerve impulse.

14. 5 Marks Questions – 5 अंक

5 Marks Q16. Describe the complete mechanism of reflex action.

Answer:
1. A stimulus acts on a receptor.
2. Receptor generates a nerve impulse.
3. Sensory neuron carries the impulse towards the CNS.
4. Relay neuron passes information to a motor neuron.
5. Motor neuron carries the impulse to the effector, which produces the response.

5 Marks Q17. Explain the importance of reflex arc in human beings.

Answer:
• Provides rapid responses.
• Helps protect the body from injury.
• Reduces delay in responding to harmful stimuli.
• Uses an efficient neuronal pathway.
• Allows immediate spinal coordination while information can also reach the brain.

5 Marks Q18. Explain the difference between reflex action and voluntary action with examples.

Answer:
Reflex action is rapid, automatic and generally involuntary, e.g. withdrawing hand from heat.

Voluntary action is consciously initiated and controlled, e.g. writing, walking deliberately or raising a hand.

Reflex actions provide rapid protection, whereas voluntary actions allow conscious decision-making.

5 Marks Q19. Describe the role of spinal cord in reflex action.

Answer: The spinal cord receives sensory information, connects sensory neurons to appropriate motor pathways through interneurons and coordinates the immediate motor response. It therefore acts as an important centre for many reflexes.

5 Marks Q20. Explain the functions of the components of a reflex arc.

Answer:
Receptor – detects stimulus.
Sensory neuron – carries impulse to CNS.
Relay neuron – connects sensory and motor pathways.
Motor neuron – carries impulse to effector.
Effector – produces response.

15. 6 Marks Questions – 6 अंक

6 Marks Q21. Explain reflex action and reflex arc in detail with a suitable example.

Answer:
Reflex action is a quick, automatic and involuntary response to a stimulus.

For example, when a person touches a hot object, receptors in the skin detect the stimulus. The sensory neuron carries the impulse to the spinal cord. A relay neuron connects it with a motor neuron. The motor neuron carries the impulse to the arm muscle. The muscle contracts and the hand is withdrawn.

The complete pathway is:
Stimulus → Receptor → Sensory Neuron → Relay Neuron → Motor Neuron → Effector → Response.

6 Marks Q22. Describe the complete reflex arc involved in withdrawing the hand from a hot object.

Answer:
1. Hot object provides stimulus.
2. Skin receptors detect heat/pain.
3. Sensory neuron carries impulse to spinal cord.
4. Relay neuron connects sensory neuron with motor neuron.
5. Motor neuron carries impulse to arm muscle.
6. Muscle contracts and hand is withdrawn.

6 Marks Q23. Explain why reflex actions are faster than many voluntary actions.

Answer:
Reflex actions can be coordinated through a relatively short pathway involving the spinal cord. The immediate response does not have to wait for conscious processing by the brain. Therefore, the motor response can occur very quickly. Information can nevertheless reach the brain so that the person becomes aware of the stimulus.

6 Marks Q24. Explain the role of receptors, neurons and effectors in reflex action.

Answer:
Receptor: Detects the stimulus.
Sensory neuron: Carries information towards CNS.
Relay neuron: Connects sensory and motor neurons.
Motor neuron: Carries command towards effector.
Effector: Muscle or gland that produces the response.
Overall: These components work together to produce a rapid protective response.

6 Marks Q25. Explain reflex action with a labelled diagram of reflex arc.

Answer:
The student should draw and label:
Receptor → Sensory Neuron → Spinal Cord → Relay Neuron → Motor Neuron → Effector Muscle.

The diagram should clearly indicate the direction of the nerve impulse and the final response.

6 Marks Q26. Compare reflex action and voluntary action on six suitable points.

Answer:
1. Reflex – automatic; Voluntary – conscious.
2. Reflex – generally involuntary; Voluntary – under conscious control.
3. Reflex – rapid; Voluntary – may be comparatively slower.
4. Reflex – often coordinated through spinal pathways; Voluntary – conscious control mainly involves brain pathways.
5. Reflex – protective; Voluntary – purposeful.
6. Example: withdrawing hand from heat vs writing.

6 Marks Q27. What would happen if the sensory neuron of a reflex arc were damaged?

Answer:
If the sensory neuron is damaged, the stimulus information may not reach the CNS normally through that pathway. As a result, the corresponding reflex response may be weakened, delayed or absent. Sensation from the affected region may also be impaired depending on the location and extent of damage.

6 Marks Q28. What would happen if the motor neuron of a reflex arc were damaged?

Answer:
The sensory signal may reach the CNS, but the motor command would not be transmitted normally to the effector muscle through the damaged motor neuron. Therefore, the expected muscular response could be weak or absent.

6 Marks Q29. Explain the statement: “Reflex action is protective but the brain is still informed.”

Answer:
The spinal cord can coordinate the immediate motor response without waiting for conscious brain processing. This makes the response rapid and protective. At the same time, sensory information can travel through ascending pathways to the brain. Thus, the person becomes aware of pain or the stimulus after or around the time of the immediate response.

6 Marks Q30. Explain the importance of reflex arc in maintaining safety and survival.

Answer:
Reflex arcs:
1. Detect potentially harmful stimuli quickly.
2. Provide rapid responses.
3. Reduce exposure to harmful conditions.
4. Protect tissues from injury.
5. Coordinate appropriate muscular responses.
6. Allow the nervous system to respond before conscious decision-making is completed.

16. HOTS / Application Based Questions

HOTS 1: A student accidentally touches a hot iron and immediately withdraws his hand. Why does withdrawal occur before he consciously thinks about the pain?

Answer: The immediate response is coordinated through a spinal reflex pathway, allowing the hand to be withdrawn rapidly. Conscious awareness of pain involves subsequent processing in the brain.

HOTS 2: If a person sees a dangerous object approaching and intentionally moves away, is it necessarily a reflex action?

Answer: Not necessarily. A consciously planned movement is a voluntary action. Reflex action is automatic and involuntary.

HOTS 3: Why is a reflex arc usually shorter than a pathway requiring conscious response?

Answer: It can use a rapid spinal pathway for immediate coordination rather than waiting for conscious processing before initiating the motor response.

17. CBSE Golden Points – परीक्षा के लिए महत्वपूर्ण बिंदु

⭐ Golden Point 1: Reflex action = quick + automatic + generally involuntary response.

⭐ Golden Point 2: Reflex arc = pathway followed by nerve impulse during reflex action.

⭐ Golden Point 3: Sensory neuron carries information towards CNS.

⭐ Golden Point 4: Motor neuron carries information from CNS to effector.

⭐ Golden Point 5: Relay neuron connects sensory and motor pathways in CNS.

⭐ Golden Point 6: Effector may be a muscle or gland.

⭐ Golden Point 7: Spinal cord coordinates many immediate reflex responses.

⭐ Golden Point 8: The brain can receive information about the stimulus even when the immediate response is coordinated by the spinal cord.

18. One-Line Revision – त्वरित पुनरावृत्ति

Question	Answer
What is reflex action?	Quick automatic response to stimulus.
What is reflex arc?	Pathway of impulse during reflex action.
Immediate reflex centre?	Spinal cord for many reflexes.
Receptor function?	Detects stimulus.
Sensory neuron?	Receptor → CNS.
Relay neuron?	Connects neurons within CNS.
Motor neuron?	CNS → Effector.
Effector?	Muscle or gland.
Classic example?	Withdrawal of hand from hot object.

19. Diagram Labelling Practice

For board examinations, practise labelling the following:

• Stimulus
• Receptor
• Sensory neuron
• Spinal cord
• Relay neuron
• Motor neuron
• Effector muscle
• Direction of nerve impulse
• Response

20. Final Exam Formula

Stimulus → Receptor → Sensory Neuron → CNS/Relay Neuron → Motor Neuron → Effector → Response

Remember: Reflex action is mainly about the rapid protective response, while reflex arc describes the neural pathway through which that response is produced.