Nervous System in Animals – Long Answer Questions (CBSE Class 10 Science)
Medium Level (Application & Explanation)
Q1. Describe how the CNS and PNS work together when you accidentally touch a hot object. Trace the full flow of information.
Answer:
When you touch a hot object, sensory neurons in the skin detect the heat as a stimulus. They send signals to the spinal cord via the PNS.
The spinal cord (part of the CNS) quickly forms a reflex arc with interneurons, sending an immediate message through motor neurons to the arm muscles to pull back. This is a reflex action.
The message also travels upward to the brain for awareness and later learning (“Don’t touch that again!”), but the immediate pullback happens first for protection.
Thus, the PNS carries signals to and from the CNS, while the CNS coordinates a fast and safe response.
This coordination shows the steps: sensory input → integration → motor output, ensuring survival by reducing injury time.
Q2. Explain the structure of a neuron and how each part helps in rapid message transmission.
Answer:
A neuron is the basic unit of the nervous system and acts like a messenger. It has three main parts:
Dendrites: Short, branching processes that receive signals from other neurons and carry them to the cell body. More dendrites mean better reception.
Cell body (soma): Contains the nucleus and controls neuron activities. It processes incoming signals and decides whether to start a nerve impulse.
Axon: A long fiber that carries the impulse away from the cell body to other cells. Many axons have a myelin sheath (fatty covering) that acts like insulation and allows the impulse to travel faster.
The axon ends in axon terminals, which pass messages to the next cell across a synapse.
Direction of flow is usually: dendrites → cell body → axon → axon terminals, helping signals move quickly and in an orderly way.
Q3. How does an electrical nerve impulse travel along a neuron? Describe resting potential, action potential, and propagation in simple terms.
Answer:
At rest, a neuron has a resting potential: the inside is more negative than the outside. This is like a battery waiting to be used.
When a stimulus reaches a certain level, the neuron fires an action potential. Tiny charged particles (ions) move, and the inside becomes briefly positive. This change is the impulse.
The action potential moves like a wave along the axon, as one part triggers the next. This is called propagation of the nerve impulse.
A myelin sheath speeds this movement by letting the impulse “jump” between gaps (nodes) for faster conduction.
After the impulse passes, the neuron returns to resting potential and is ready for the next signal.
In short: resting state → stimulus → action potential → impulse travels → reset, allowing quick communication in the body.
Q4. What happens at a synapse when one neuron passes a message to another? Why are neurotransmitters important?
Answer:
Neurons do not touch each other; they are separated by a small gap called a synapse.
When an electrical impulse reaches the axon terminal of neuron A, it triggers the release of neurotransmitters (chemical messengers) into the synaptic gap.
These neurotransmitters cross the gap and bind to receptors on the membrane of neuron B. This binding starts a new electrical impulse in neuron B.
The signal thus changes from electrical (in the axon) to chemical (in the synapse) and back to electrical in the next neuron.
Neurotransmitters are essential because they allow signals to jump the synaptic gap, ensure one-way transmission, and help control the strength and duration of the message.
Example: Swatting a mosquito involves fast synaptic transfer between sensory and motor pathways for quick action.
Q5. Differentiate between the somatic and autonomic parts of the PNS with suitable examples from daily life and animals.
Answer:
The Peripheral Nervous System (PNS) has two main parts:
Somatic nervous system: Controls voluntary actions. Example: Choosing to raise your hand, writing, or a dog running to fetch a ball on command. It uses motor neurons to control skeletal muscles.
Autonomic nervous system: Controls involuntary actions like heartbeat, breathing rate, digestion, and pupil size. Example: A cat’s pupils constrict in bright light; your heart rate increases when you are scared.
Both systems work together. While the somatic system lets you act by choice, the autonomic system keeps your body running automatically.
This division helps ensure both conscious movement and automatic control, which is vital for survival in humans and other animals.
High Complexity (Analytical & Scenario-Based)
Q6. You are cycling when a dog suddenly barks loudly. Explain the complete nervous system response, including any reflexes, conscious decisions, and autonomic changes.
Answer:
The loud bark is picked up by sensory neurons in your ears (hearing). The signal travels to the brain (CNS) for processing.
The brain quickly assesses the sound as a possible threat (integration) and sends motor commands via motor neurons to your leg and hand muscles to slow down, steer, or stop.
At the same time, the autonomic nervous system may increase heart rate, breathing rate, and alertness (fight-or-flight readiness), preparing your body to respond.
If you need to brake quickly, your actions may include learned reflex-like responses (fast, practiced motor patterns) that reduce reaction time.
After the immediate response, the brain evaluates the situation and calms the body if the threat is gone, showing how sensory input, integration, and motor output happen rapidly and together.
Q7. In the ruler-drop reflex activity, what factors can affect reaction distance, and how does the reflex arc help reduce reaction time? Suggest ways to improve your performance.
Answer:
The reflex arc involves sensory neurons → spinal cord (interneurons) → motor neurons, allowing a quick response without waiting for full brain processing.
Reaction distance can be affected by:
Level of attention and fatigue.
Practice and familiarity with the task.
Distractions in the environment.
Hand dominance and muscle readiness.
Small delays at the synapse and nerve conduction speed.
To improve performance:
Practice to strengthen neural pathways for faster responses.
Minimize distractions and maintain good posture.
Use your dominant hand and keep eyes focused on the ruler’s base.
Ensure you are rested and alert.
This activity demonstrates how the spinal cord can manage fast protective actions and why trained responses help in real-life tasks like driving.
Q8. Compare and contrast reflex actions and learned responses using suitable examples. Why does the body need both types?
Answer:
Reflex actions are automatic, fast, and usually controlled by the spinal cord. Example: Blinking when something comes close to the eye or pulling your hand away from a hot surface. They protect the body from harm by reducing delay.
Learned responses are voluntary and require brain processing and practice. Example: A dog sitting on command or a person balancing on a bicycle. They become faster with repetition but are not instant at first.
Differences:
Speed: reflexes are fastest; learned responses improve with practice.
Control: reflexes are involuntary; learned actions are voluntary.
Pathway: reflex arc (spinal cord) vs more complex brain circuits.
The body needs both: reflexes for immediate safety and learned responses for skilled, adaptable behaviors in changing environments.
Q9. Predict the effects on body responses if the myelin sheath is damaged or if synaptic transmission is blocked. Use simple logic based on impulse transmission.
Answer:
If the myelin sheath around axons is damaged, impulse speed decreases. Messages may become slow or uncoordinated. This could cause delayed responses, poor muscle control, or slower reflexes because myelin normally helps signals travel faster.
If synaptic transmission is blocked (neurotransmitters can’t cross the synapse or bind to receptors), signals will not pass from one neuron to the next. This can lead to weak or absent actions, such as failure to move a muscle on time or inability to sense a stimulus properly.
Together, these problems show why both fast electrical conduction and proper chemical signaling are essential. The body relies on quick, accurate communication for safety, coordination, and regular functions like blinking, walking, and reacting to danger.
Q10. Design a simple investigation to test whether dominant-hand use affects reaction time in the ruler-drop activity. Explain your plan and the nervous system logic behind it.
Answer:
Plan:
Recruit several students. Each performs the ruler-drop test ten times with the dominant hand and ten times with the non-dominant hand.
Keep conditions constant: same ruler, same drop height, similar lighting, and minimal distractions.
Record the distance fallen before catching. Convert distance to time using a chart or compare distances directly.
Calculate average reaction distance for each hand and compare within each student and across the group.
Nervous system logic:
The dominant hand may have stronger neural pathways due to frequent use, leading to faster synaptic transmission and more efficient motor control.
Repeated trials reduce random errors and show the benefit of practice on the reflex pathway.
This investigation links sensory input, spinal processing, and motor output to ...
