Selina Concise Solutions for ICSE Class 7 Biology Chapter 6 Nervous System

Synopsis -

• The interaction of these activities of a living being as per the needs of the body internally or externally is called coordination.
• Nervous coordination is brought about by the nervous system which is made up of the brain, spinal cord, nerves and the sense organs.
• Chemical coordination is brought about through chemical messengers called hormones.
• The nervous system is made up of special cells called nerve cells or neurons.
• The end of the axon terminates in a number of branches called terminal branches.
• The terminal branches of the axon of one neuron lie very close to the dendrites of another neuron. This point of contact is called a synapse.
• A nerve is formed of a bundle of axons (nerve fibres) enclosed in a tubular medullary sheath. There are three kind of nerves as describe
  1. sensory nerve
  2. motor nerve
  3. mixed nerve.
• The nervous sytem of human beings consists of the following three systems:
  1. The central nervous system
  2. The peripheral nervous system
  3. The autonomic nervous system
• The brain has three main parts:
  1. The cerebrum
  2. The cerebellum, and
  3. The medulla oblongata
• The main functions of the spinal cord are:
  1. To control reflexes below the neck.
  2. To conduct messages from the skin and muscles to the brain.
  3. To conduct commands from the brain to muscles of the trunk and limbs.
• The autonomic nervous system consists of a pair of chain of nerves and ganglia found on either side of the backbone. This system controls the involuntary activities of the internal organs.
• Stimulus: Any change in the environment that usually results in change in the activity of the body.
• Response: The activity of the body in response to a received stimulus.
• Impulse: A wave of electrical disturbance that runs through the nerves.
• Receptors : These are sense organs which receives the stimulus.
• Effector: Any muscle or gland where the response occurs.

Review Questions

Multiple Choice Questions:

1. Put a tick mark (✓) against the correct alternative in the following statements:

(a) Medulla oblongata controls
(i) Smelling
(ii) Beating of heart and respiratory movement
(iii) Intelligence and will power
(iv) Balancing the body
Answer: (ii) Beating of heart and respiratory movement
The medulla oblongata is the lowest part of the brain that connects to the spinal cord. It manages automatic functions that keep us alive without us having to think about them.
Teacher's Tip: Remember "M" for Medulla and "M" for Maintenance of life-support functions.
Exam Tip: Always mention that the medulla controls involuntary actions specifically to get full marks.

(b) Spinal cord is an extention of:
(i) Cerebellum
(ii) Cerebrum
(iii) Vertebral column
(iv) Medulla oblongata
Answer: (iv) Medulla oblongata
The medulla oblongata narrows down as it leaves the skull and continues as the spinal cord. This long structure then runs down the center of your back protected by the spine.
Teacher's Tip: Imagine the brain as a lollipop where the medulla is the bottom of the candy and the spinal cord is the stick.
Exam Tip: Do not confuse the vertebral column (bone) with the spinal cord (nerve tissue).

(c) Body posture is mantained by:
(i) Cerebellum
(ii) Cerebrum
(iii) Medulla oblongata
(iv) Spinal cord
Answer: (ii) Cerebrum
The cerebrum is the largest part of the brain and handles complex functions like movement and sensory processing. It helps coordinate how we hold our bodies while moving or standing still.
Teacher's Tip: While the cerebellum handles balance, the cerebrum controls the muscle movements that adjust your posture.
Exam Tip: If both options appear, follow your textbook's specific marking which often highlights the cerebrum for voluntary motor control.

Short Answer Questions:

1. Write one word in the space provided to complete the second pair of the related words pertaining to nervous system.
Memory: cerebrum:: breathing:
Balance: cerebellum:: reasoning:
Answer:
Memory: cerebrum: beathing: medulla oblongata
Balance: cerebellum:: reasoning: cerebrum
The cerebrum is the seat of high-level thinking like logic and memory storage. The medulla oblongata works lower down to regulate life-sustaining rhythms like breathing.
Teacher's Tip: Think of the cerebrum as the "Thinking Brain" and the medulla as the "Living Brain."
Exam Tip: In analogy questions, ensure the relationship between the first pair is exactly mirrored in the second pair.

2. (a) Name three major divisions of the human nervous system.
Answer:
1. The central nervous system (brain and spinal cord)
2. The peripheral nervous system
3. The autonomic nervous system
The central system acts as the main processing hub while the peripheral system consists of all the nerves branching out. The autonomic system handles the background tasks that happen automatically inside your organs.
Teacher's Tip: Think of the CNS as the computer tower and the PNS as the cables connecting the mouse and keyboard.
Exam Tip: List all three systems clearly and briefly state what organs belong to the CNS for a better score.

(b) Name the three main parts of human brain.
Answer:
1. Cerebrum
2. Cerebellum
3. Medulla oblongata
The cerebrum is the big part on top, the cerebellum sits at the back, and the medulla is at the base. Each part has a unique and vital job in controlling how your body works.
Teacher's Tip: Use the "3 C/M" rule: Cerebrum, Cerebellum, and Medulla.
Exam Tip: Check your spelling carefully; "Cerebrum" and "Cerebellum" are very similar but are different parts.

3. Given here is the diagram of a neuron. Name the parts numbered 1-6.
Answer:
1. dendrite
2. dendrite (Terminal Arborization)
3. nucleus
4. axon (Nerve fibre)
5. cell Body (cyton)
6. node of ranvier
7. sheath
The dendrites receive signals while the axon acts like a long wire to send those signals away. The cell body or cyton is the central command center containing the nucleus.
Teacher's Tip: Think of a neuron like a hand: the fingers are dendrites, the palm is the cell body, and the arm is the axon.
Exam Tip: If a diagram question asks for 1-6 but provides 7 answers, label all 7 to show complete knowledge.

Long answer questions

Question 1: With the help of a suitable diagram describe the structure of a neuron.
Answer:
Nervous system consists of special cells called nerve cells or neurons. It has a main cell body called cyton. It gives out many processes called dendrites. From it a very long process is given out. It is called axon or nerve fibre.
The cell body has a nucleus. The dendrites get the message from the organs and send this message to the axon through the cell body. Then the axon sends the message to muscles to contrast or to the gland for secretion.
The neurons make contact with one another through their processes. The axon at its end branches and meets the dendrites of another neuron. The meeting point is called synapse. The message is passed on from one axon to the dendrites of another neuron. How the message goes ? It is like this:
Organ → Message goes to dendrites →Cell body → Axon → Muscles or glands
Neurons are the building blocks of the nervous system and act as messenger cells. They use electrical and chemical signals to send information instantly across the body.
Teacher's Tip: Imagine a game of "telephone" where neurons pass electrical whispers to each other.
Exam Tip: Always include the flow chart (Organ → Dendrites → Cell body → Axon) in your description of nerve impulses.

Question 2: Briefly describe the structure of the cerebrum in human brain, and mention its functions.
Answer:
Brain consists of main three parts and lies in the cranial cavity of skull.
1. The cerebrum
2. The cerebellum
3. The medulla oblongata
Cerebrum - It is very large and form two third of the whole brain. The two hemispheres are separated from each other by a deep longitudinal groove, the median fissure. The outer surface is folded with ridges and grooves. The hemispheres are hollow from inside and their walls have outer and inner portions. The outer portion has cell bodies of the neurons and it is called grey matter.
The wavery edges of the folded layer has large number of neurons to the extent of nine billion. The inner portion of the cerebrum has axons and it is called white matter.
Functions:
1. It controls all the voluntary activities.
2. It is the seat of intelligence, consciousness and will power.
The cerebrum's folded surface allows it to pack billions of neurons into a small space. Its division into grey and white matter helps in processing and then quickly transporting information.
Teacher's Tip: The "ridges and grooves" look like a walnut shell; these folds give you more "brain power."
Exam Tip: Mention "grey matter" and "white matter" specifically when describing the cerebrum's layers.

Question 3: Mention the three functions of spinal cord.
Answer:
Spinal cord has the following functions.
1. It is the centre of reflex actions below the neck.
2. It carries messages from the skin and muscles to the brain.
3. All the stimuli and responses are passed from and to the brain through the spinal cord.
The spinal cord acts as a high-speed highway connecting your brain to the rest of your body. It also handles "emergency" reflex actions so you can react faster than you can think.
Teacher's Tip: Think of the spinal cord as the "Main Cable" connecting a computer to all its parts.
Exam Tip: Clearly number the functions 1, 2, and 3 to make your answer easy for the examiner to grade.

Question 4: Describe three kinds of nerves, giving example of each.
Answer:
A nerve is formed by a group of nerve fibres (axons) encased by tubular medullary sheath. The medullary sheath acts as insulation and do not allow mixing up of impulses of the neighbouring axons (nerve fibres) We have three kinds of nerves:
1. Sensory nerve - It brings impulses from sense organs as these have sensory fibres. These nerve carry the impulses from the sense organs to the brain or to the spinal cord as optic nerve of the eye.
2. Motor nerves - These carry impulses to muscles or glands from the brain or spinal cord. These nerves have only motor fibres as nerves to the muscles of the eye ball.
3. Mixed nerve - It has both sensory and motors fibres as nerve going to the tongue.
Nerves are like insulated electric wires that keep signals from crossing. Sensory nerves tell you what's happening outside, while motor nerves tell your body how to react.
Teacher's Tip: Sensory is "Input," Motor is "Output," and Mixed is "Both."
Exam Tip: Always provide the specific example (like the optic nerve for sensory) to get the "example" marks.

Question 5: What are voluntary and involuntary actions ? Which part of the nervous system controls them ?
Answer:
Voluntary action: When an action is produced with the involvement of thoughts, they are called the voluntary action. For example, writing an article jumping from heights. These actions are produced consciously by our body.
Involuntary action: Actions which take place without consciousness or willingness of an individual are called the involuntary action. Digestion, heart beating, sneezing, etc are few examples of involuntary actions.
1. The cerebral cortex controls our voluntary actions like running and walking etc.
2. Medulla helps in involuntary actions like hearbeat, breathing etc.
Voluntary actions are things you decide to do, like picking up a pen. Involuntary actions are things your body does by itself to keep you safe and healthy.
Teacher's Tip: If you have to think about it, it's voluntary; if it happens while you're asleep, it's involuntary.
Exam Tip: Mention both the definition AND the specific brain part (Cerebrum/Medulla) to fully answer the question.

Additional Questions

I. Multiple choice questions. Tick (✓) the correct choice:

I. Nervous system in humans consists of
(a) brain and nerves
(b) brain and spinal cord
(c) brain, spinal cord and nerves
(d) none of the above.
Answer: (c) brain, spinal cord and nerves
This combination makes up both the central and peripheral components of the system. Without any one of these three parts, messages could not be processed or delivered.
Teacher's Tip: Use the "Rule of Three" for the nervous system: Brain, Cord, Nerves.
Exam Tip: Read all options carefully; option (c) is the most complete answer among the choices.

II. Fill in the blanks:

1. Basic structural unit of the nervous system is the neuron.
Answer: neuron
A neuron is a specialized cell designed to transmit information quickly. Millions of these cells work together to form the brain and nerves.
Teacher's Tip: A neuron is the "building block" of your intelligence.
Exam Tip: Be sure to use the word "structural" and "functional" if asked for a full definition of a neuron.

2. Central nervous system consists of brain and spinal cord.
Answer: brain, spinal cord
These two parts are the most protected organs in the body, covered by bone. They act together as the main "CPU" of the human body.
Teacher's Tip: "Central" means it's right in the middle of your body's command center.
Exam Tip: Don't forget that the spinal cord is just as central as the brain.

3. A neuron consists of cell body, dendrite and axon.
Answer: cell body, dendrite, axon
Information flows into the dendrites, through the cell body, and out along the axon. This one-way street ensures that signals don't get mixed up.
Teacher's Tip: Think of it as a "Receiver," a "Center," and a "Sender."
Exam Tip: List them in the order the impulse travels for better clarity.

4. The neurons carrying impulses from the brain to the muscles are called motor or efferent neurons.
Answer: motor, efferent
Motor neurons trigger movement by sending signals to muscle fibers. They are also called "efferent" because they carry information "exiting" the central system.
Teacher's Tip: "Motor" makes things "Move."
Exam Tip: Learning both terms (motor and efferent) is helpful because examiners might use them interchangeably.

5. Peripheral nervous system consists of nerves.
Answer: nerves
The peripheral system is made of all the nerve threads that reach your skin, organs, and toes. These nerves act like the wiring of a house, connecting everything to the main power box.
Teacher's Tip: "Peripheral" means "on the edge" or "around the outside."
Exam Tip: Remember that the PNS includes both cranial nerves (from brain) and spinal nerves (from cord).

6. The three main parts of the brain are cerebrum, cerebellum and medulla oblongata (brain stem).
Answer: cerebrum, cerebellum, medulla oblongata
Each of these regions handles a different type of task, from thinking to balance to survival. They work in perfect harmony to allow us to live complex lives.
Teacher's Tip: It's like a three-story building: Thinking on top, coordination in the back, and survival at the base.
Exam Tip: If you mention "brain stem," always put "medulla oblongata" in brackets next to it.

III. State whether the following statements are true (T) or false (F):

1. Each neuron consists of three parts called cell body, cyton and axon.
Answer: False. Each neuron consists of three parts called cell body, dendrite and axon.
The term "cyton" is actually just another name for the cell body itself. The three distinct parts required for function are the receiving dendrites, the central body, and the sending axon.
Teacher's Tip: "Cell body" and "Cyton" are identical twins, so they can't be two different parts!
Exam Tip: Always provide the corrected statement when a True/False question is false.

2. The largest part of the brain is the cerebrum.
Answer: True
The cerebrum takes up about two-thirds of the brain's total mass. This size allows it to handle the massive amount of data we process every day.
Teacher's Tip: Big thoughts need a big cerebrum.
Exam Tip: Mentioning that it is divided into two hemispheres adds good detail to your answer.

3. Cerebellum maintains balance of the body.
Answer: True
The cerebellum receives information from the inner ear and muscles to keep you steady. It is the reason you can walk in a straight line or ride a bike.
Teacher's Tip: "Cere-balance" sounds a bit like cerebellum!
Exam Tip: If asked about coordination of muscular activity, the answer is always cerebellum.

4. There are 31 pairs of cranial nerves.
Answer: False. There are 12 pairs of cranial nerves.
Cranial nerves emerge directly from the brain and primarily serve the head and neck. There are actually 31 pairs of spinal nerves, which come from the spinal cord.
Teacher's Tip: Remember "Brain = 12" and "Spine = 31" (31 is just 13 flipped around!).
Exam Tip: Memorizing the exact numbers (12 and 31) is essential for scoring in "Fill in the blanks" or "True/False."

IV. Find the odd-one out, giving reasons:
Axon, cell body, dendrite, cerebellum
Answer: Cerebellum is the odd one out as it is a part of brain while rest three are parts of a neuron.
Axons, cell bodies, and dendrites are microscopic structures that make up a single nerve cell. The cerebellum is a large, visible organ of the central nervous system.
Teacher's Tip: Check if the words are "parts of a cell" or "parts of an organ."
Exam Tip: Always state the category of the "odd one" versus the category of the "remaining three."

V. Define the following:

1. Reflex arc:
Answer: The path that an impulse takes in a reflex action is called a reflex arc.
It usually involves a receptor, a sensory neuron, the spinal cord, a motor neuron, and an effector. This short loop allows the body to react without waiting for the brain to process the thought.
Teacher's Tip: A reflex arc is a "short-cut" for safety.
Exam Tip: Drawing a simple flow diagram of the arc can help clarify your definition.

2. Sensory neuron:
Answer: The neurons which carry impulses from the body parts to the spinal cord or the brain are called sensory or afferent neurons. For example, optic nerve of the eye.
These neurons pick up signals from our surroundings through our sense organs. They "inform" the brain about things like heat, light, and pressure.
Teacher's Tip: Sensory = Senses (Telling you what's happening).
Exam Tip: Use the term "afferent" as a synonym to show extra vocabulary knowledge.

3. Motor neuron:
Answer: The neurons which carry impulses from the brain or spinal cord to the body parts are called motor or efferent neurons.
These neurons send the "orders" from the brain to your muscles. They are what allow you to jump, run, or blink when needed.
Teacher's Tip: Motor = Motion.
Exam Tip: Mention that motor neurons end at "effectors" like muscles or glands.

4. Neuron:
Answer: A neuron or a nerve cell is the basic structural and functional unit of the nervous system.
It is a specialized cell that can conduct electricity to send messages. Everything you think, feel, or do is because of neurons communicating.
Teacher's Tip: The neuron is the "Lego brick" of your brain.
Exam Tip: Always include the phrase "structural and functional unit" in this definition.

VI. Answer the following:

Question 1: Describe the two parts of the nervous system.
Answer:
The nervous system of human has two parts:
1. Central Nervous System (CNS): It consists of the brain and the spinal cord. The brain lies protected inside the skull while the spinal cord is protected within the vertebral column.
2. Peripheral Nervous System (PNS): It consists of nerves arising from the spinal cord (spinal nerves) and the brain (cranial nerves). These nerves link the central nervous system with the various body organs.
The CNS is the "decision maker" and the PNS is the "communication network." Without the PNS, the brain would be cut off from the rest of the body.
Teacher's Tip: CNS is the "Boss," and PNS is the "Messenger."
Exam Tip: Mention the protective bones (skull and vertebral column) to get extra points for detail.

Question 2: What are nerves? Mention the types of nerves found in humans.
Answer:
A bundle of nerve fibres joined together as a tubular sheath that transmits impulses between brain or spinal cord and other body parts is called a nerve. The nerves constitute the peripheral nervous system.
Nerves are of two types in humans:
1. Cranial nerves: They emerge from the brain. There are 12 pairs of cranial nerves.
2. Spinal nerves: They emerge from the spinal cord. There are 31 pairs of spinal nerves.
Nerves act as biological wires that carry electrical signals throughout the body. They are sorted based on where they start: the brain or the spine.
Teacher's Tip: Think of nerves as "bundles of wires" wrapped in protective tape.
Exam Tip: Be sure to mention the specific number of pairs (12 and 31) for each type.

Question 3: Explain the structure of brain.
Answer:
The brain is the main control centre of the nervous system.
It is enclosed within the bony shell of cranium.
It consists ofthree main part:
1. Cerebrum: It is the uppermost and largest part with many ridges and grooves. It is divided into right and left halves called cerebral hemispheres. It controls our thinking, reasoning, intelligence, memory and perception of pain, sound, touch, taste and smell.
2. Cerebellum: It is located under the cerebrum at the back of the head. It maintains balance of the body and coordinates muscular activity.
3. Brain stem (medulla oblongata): It joins the brain to the spinal cord. It controls the activity of internal organs like heartbeat and breathing.
(The diagram shows: CEREBERAL HEMISPHERE, HYPOTHALAMUS, PITUITARY, MIDBRAIN, MEDULLA OBLONGATA, CEREBELLUM.)
The brain's structure is organized so that the most complex thinking happens on top, while basic survival is handled at the bottom. The bony cranium acts like a helmet to keep this soft organ safe from injury.
Teacher's Tip: The "ridges and grooves" in the cerebrum are like extra storage space for your memories.
Exam Tip: When explaining the brain, describe both its physical location (cranium) and its three functional parts.

Question 4: Compare the nervous system and the endocrine system.
Answer:
Nervous system
1. Messages are sent through nerve fibres.
2. It consists of brain, spinal cord and nerves.
3. No hormones are secreted. Messages are sent as impulses.
4. Transmission of impulse is quick.
Endocrine system
1. Messages are sent through blood in the form of hormones.
2. It consists of endocrine glands.
3. Hormones secreted by glands regulate the body activities. .
4. Transmission takes time.
The nervous system is like an "instant message" that travels fast but doesn't last long. The endocrine system is like "snail mail" that takes longer to arrive but can affect the whole body for a long time.
Teacher's Tip: Nervous is "Electrical/Fast," Endocrine is "Chemical/Slow."
Exam Tip: Present your comparison in two columns to make the differences very clear for the teacher.