Nervous System

Imagine our nervous system as this incredible communication network, constantly relaying information to help us navigate the world and keep our internal machinery running smoothly. You’re spot on – the neuron is indeed the fundamental building block, the individual “messenger” in this vast network.

the axon, that long, slender fiber, is the transmission cable, carrying the electrical message, or nerve impulse, away to its destination. Sensory nerves are our informants, bringing news from our senses – the sights, sounds, smells, tastes, and touches – back to the central command. And those clever mixed nerves that do double duty are like multi-lane highways carrying traffic in both directions!

The Central Nervous System (CNS), comprising the brain and spinal cord, is truly the control hub. You’ve accurately described the main parts of the brain and their primary responsibilities. The cerebrum, with its wrinkled surface, is where our higher-level thinking, learning, memories, and conscious movements reside – it’s the seat of our intellect. The cerebellum, tucked away at the back, is the master of coordination, balance, and posture, ensuring our movements are smooth and precise. And the medulla oblongata, at the base of the brainstem, takes care of those essential, unconscious functions that keep us alive, like breathing and heartbeat.

The spinal cord, that vital extension from the brainstem, acts as the main communication superhighway between the brain and the rest of the body. And its role in reflex actions is so important for our safety! You’ve clearly explained how these rapid, automatic responses bypass conscious thought, allowing us to react instantly to potential harm. Thinking about the stimulus as the trigger, the response as our action, the receptors as the detectors, and the effectors as the actors really clarifies how this protective mechanism works. 

Essentially, this chapter paints a picture of a remarkably organized and efficient system that allows us to perceive, think, act, and maintain our internal balance.

REVIEW QUESTIONS

Multiple Choice Questions:

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

(a) Medulla oblongata controls

1. Smelling
2. Beating of heart and respiratory movement
3. Intelligence and will power
4. Balancing the body

(b) Balance of body is controlled by:

1. Spinal cord
2. Cerebellum
3. Cerebrum
4. Medulla

(c) The smell of good food causes watering of your mouth. It is a

1. Natural reflex
2. Acquired relfex
3. Inborn reflex
4. Ordinary reflex

(d) The structural and functional unit of nervous system is a

1. Axon
2. Nephron
3. Neuron
4. Texon

Short Answer Questions:

Question 1.
Name the two types of coordination which take place in our body.
Answer:
First, we have nervous coordination, which acts like the body’s super-speedy messaging system. Imagine a complex web of communication lines – that’s your nervous system, complete with the command center (brain), the main relay station (spinal cord), and countless messengers (nerves). These messengers use rapid-fire electrical and chemical signals to transmit information almost instantly. A classic example is that split-second reaction when you encounter something unexpectedly hot; your nervous system snaps into action, telling your hand to move now!

Then there’s chemical coordination, a more gradual but enduring form of communication. This relies on hormones, which are like chemical couriers produced by specialized glands known as endocrine glands. These hormones journey through the bloodstream to reach their intended recipients – specific organs and tissues – where they exert their influence on a wide array of bodily processes. Think about the significant changes that unfold during puberty; those are driven by the slow and steady work of hormones circulating throughout your system.

Question 2.
You are driving your bicycle at a fast speed. Suddenly, a small boy comes in front of your cycle and, without wasting any time in thinking, you immediately apply the brakes, and the accident is avoided. What name is given to such an action?
Answer:
That split-second, automatic response your body unleashes to dodge danger is precisely what we call a reflex. Think of it as an innate survival mechanism, a lightning-quick emergency crew that springs into action even before your conscious mind catches up. It’s your body’s immediate “move now!” command, expertly crafted to shield you from harm without a second thought.

Question 3.
Given below is the diagram of a neuron. Name the parts numbered 1-5.

Answer:Dendrites: Picture these as the neuron’s numerous receivers, those branch-like extensions reaching out from the main cell body. Their role is to capture incoming signals broadcast by nearby nerve cells.

Cell body (or Soma): Envision this as the neuron’s central command unit. It contains all the vital machinery, including the nucleus, and serves as the integration hub where all the received signals are processed.

Axon hillock: This is a crucial junction, marking the origin of the axon as it extends from the cell body. It acts as the neuron’s decision threshold, determining whether an incoming signal is potent enough to trigger an electrical impulse down the axon.

Axon: Think of this as a long, insulated cable stretching outward from the cell body. Its primary function is to conduct electrical messages away from the neuron, heading towards other cells. The segmented appearance indicates the presence of a myelin sheath, which significantly accelerates the transmission of these signals.

Axon terminals (or Synaptic terminals): These are the branching endpoints of the axon. They serve as the neuron’s communication outposts, releasing chemical messengers known as neurotransmitters to relay signals to other neurons, muscle fibers, or glands at specialized connections called synapses.

Question 4.
Write one word in the space provided to complete the second pair of the related words pertaining to the nervous system.
Memory : cerebrum : : breathing :
Balance : cerebellum : : reasoning :
Answer:
Memory is primarily associated with the cerebrum, just like breathing is mainly controlled by the medulla.

Similarly, balance is a key function of the cerebellum, while reasoning is a higher-level cognitive function primarily handled by the cerebrum.

Question 5.
Differentiate between the following pair of terms:
(a) Stimulus and impulse
(b) Receptor and effector
(c) Motor nerve and sensory nerve
Answer:
(a) Stimulus and Impulse:

Think of a stimulus as the starting gun – it’s any change our body notices, whether it’s a loud noise or a sudden drop in temperature. The impulse is the swift message that follows, a rapid electrical and chemical signal created by our nervous system to carry information about that stimulus along our nerves. So, the stimulus gets things going, and the impulse is how our body quickly communicates what’s happening.

(b) Receptor and Effector:

A receptor is like a specialized sensor, a cell or nerve ending designed to pick up specific signals from our surroundings or inside our bodies. It’s the first to receive the news. An effector is the body part that then acts on that news, carrying out a response based on the signals it receives from the nervous system. This usually involves muscles moving or glands releasing something. Receptors sense the world, and effectors make things happen.

(c) Motor Nerve and Sensory Nerve:

A sensory nerve acts like an information pipeline, carrying signals from our sensory organs all the way to our brain and spinal cord. It’s the route for all the “what’s going on” messages. A motor nerve is also a pipeline, but it carries signals in the opposite direction, from the brain and spinal cord out to our muscles and glands. These are the “okay, now do this” instructions. Sensory nerves bring information in, and motor nerves carry instructions out.

Question 6.
(a) Name the three major divisions of the human nervous system.
(b) Name the three main parts of the human brain.
Answer:
(a)

1. The central nervous system (brain and spinal cord)
2. The peripheral nervous system
3. The autonomic nervous system

(b)

1. Cerebrum
2. Cerebellum
3. Medulla oblongata

Question 7.
Give the function of each of the following:
(a) Olfactory nerve:
(b) Optic nerve:
(c) Facial nerve:
Answer:
(a) Olfactory nerve: Think of this as your sense of smell’s dedicated messenger. Its job is to pick up scent molecules in your nose and relay that information as electrical signals directly to your brain, allowing you to perceive different odors.

(b) Optic nerve: This is the crucial pathway for your sense of sight. It takes the visual information captured by your eyes – everything from light and color to shapes and movement – and transmits it as electrical signals to your brain, where it’s processed into the images you see.

(c) Facial nerve: This is a versatile nerve with a number of important roles, primarily controlling the muscles in your face that allow you to make expressions like smiling, frowning, and raising your eyebrows. It’s also responsible for your sense of taste on the front part of your tongue, controlling tear and saliva production, and even plays a role in hearing.

Long answer questions

Question 1.
With the help of a suitable diagram describe the structures of a neuron.
Answer:A neuron has a central cell body (soma) containing the nucleus. ¹ Branching out from the cell body are dendrites, which receive signals. ² A long projection called the axon carries signals away from the cell body, often covered by a segmented myelin sheath for faster transmission. ³ The axon ends in axon terminals, which transmit signals to other cells. ⁴

Question 2.
Briefly describe the structure of the cerebrum in human brain and mention its functions.
Answer:
The cerebrum, the brain’s largest part, has a wrinkly surface called the cerebral cortex, packed with nerve cells. It’s divided into a left and right hemisphere connected by nerve fibers. This is our brain’s command center for thinking, memory, language, reasoning, sensory processing (sight, touch, hearing), and voluntary movements. Although each side has some unique roles, they constantly collaborate for all these complex functions.

Question 3.
Mention the three functions of the spinal cord.
Answer:
The spinal cord acts as the body’s main communication line, relaying sensory information to the brain and carrying movement commands back. ¹ It also manages quick, protective reflexes and houses the neural circuits for rhythmic actions like walking.

Question 4.
With the help of suitable examples, describe reflex action.
Answer:
Sensory nerves are your body’s information gatherers. They have special sensors that detect changes (like touch, temperature, taste, etc.) and send electrical signals about these changes to your brain and spinal cord.

Motor nerves are your body’s action commanders. They receive signals from your brain and spinal cord and relay these instructions to your muscles and glands, causing movement or the release of substances.

Mixed nerves are two-way communication lines. They contain both sensory and motor fibers, allowing for simultaneous information flow to and from the central nervous system within the same nerve.

Question 5.
Describe three kinds of nerves, giving the example of each.
Answer:
Sensory nerves: Think of these as the body’s dedicated information gatherers. They’re constantly relaying data from your senses – the sights your eyes capture, the sounds your ears pick up, the textures your skin feels – straight to your brain and spinal cord, the central processing unit. So, if you accidentally touch a scorching pan, it’s the sensory nerves that immediately shoot off that urgent “Too hot!” alert.

Motor nerves: These are your body’s movement orchestrators. They carry out the instructions issued by your brain and spinal cord, delivering orders to your muscles and glands to initiate actions or responses. When you decide to reach for a cup, it’s the motor nerves that transmit the precise “move your arm and hand now!” signals.

Mixed nerves: Imagine these as highly efficient, two-way communication highways for nerve signals. They cleverly bundle both sensory and motor fibers within the same nerve pathway, allowing for a simultaneous flow of incoming sensory reports and outgoing motor commands. A prime example is the sciatic nerve in your leg, which handles both the sensations you feel in your leg and the muscle movements that allow you to walk and move.

Question 6.
Differentiate between natural reflex and conditioned reflex. Give examples to illustrate your answer.
Answer:Natural reflexes are built-in, automatic responses you’re born with. Think of them as your body’s factory settings for immediate protection.

• Example: Yanking your hand away instantly after touching something scorching hot.

Conditioned reflexes, on the other hand, are learned responses developed through experience and association. They’re like custom programs your body creates.

• Example: A dog salivating at the sound of a bell because it has learned that the bell precedes food.