Neuron: The Basic Unit
Cell body (Cyton): Contains the nucleus.
Dendrites: Receive signals.
Axon: Sends signals away.
Types of Neurons:
Sensory: Carry signals to the CNS.
Motor: Send signals from CNS to muscles/glands.
Interneurons: Connect sensory and motor neurons.
Divisions of the Nervous System
Central Nervous System (CNS): Brain and spinal cord (control center).
Peripheral Nervous System (PNS): Nerves outside CNS.
Somatic: Controls voluntary actions.
Autonomic: Manages involuntary functions.
Brain & Spinal Cord
Cerebrum: Controls thinking, memory, and voluntary actions.
Cerebellum: Coordinates movement and balance.
Medulla: Regulates breathing, heartbeat.
Spinal Cord: Relays signals and controls reflexes.
Reflex Actions
Fast, automatic responses (e.g., pulling hand from heat).
The reflex arc includes:
Receptor → 2. Sensory neuron → 3. Relay neuron → 4. Motor neuron → 5. Effector.
This system ensures quick reactions for survival.
EXERCISE
1. MULTIPLE CHOICE TYPE (Select the most appropriate option in each case).
1) The insulating sheath covering the neural axon is called.
(a) plasmalemma
(b) neurolemma
(c) dura mater
(d) pia mater
Ans: (b) neurolemma
2) Which one of the following pairs of brain parts and its function is not correctly matched?
(a) Cerebrum – Memory
(b) Cerebellum – Balance of body
(c) Medulla oblongata – controls activities of internal organs
(d) Pons – Consciousness
Ans: (d) Pons – consciousness
3) A mixed nerve is one which
(a) carries sensations from 2 or more different sense organs
(b) contains both sensory and motor fibres
(c) has a common root but branches into two or more nerves to different organs
(d) has two or more roots from different parts of the brain.
Ans:(b) Contains both sensory and motor fibres
B. VERY SHORT ANSWER TYPE:
Question 1: Name the following:
(a) The fluid that is present inside and outside the brain.
(b) The junction between two nerve cells
(c) The part of the brain which is concerned with memory
(d) The part of the human brain which controls body temperature.
Ans: (a) Cerebrospinal fluid
(b) Synapse
(c) Cerebrum
(d) Hypothalamus
2) Note the relationship between the first two words and suggest the suitable word/words for the fourth place.
(a) Stimulus: Receptor:: Impulse: …………….
(b) Cerebrum: Diencephalon:: Cerebellum: ……………….
(c) Receptor: Sensory nerve:: Motor nerve: ……………….
Ans:
(a) Stimulus: Receptor:: Impulse: Effectors
(b) Cerebrum: Diencephalon:: Cerebellum: Medulla oblongata
(c) Receptor: Sensory nerve:: Motor nerve: Effector
3) Complete the following statements by choosing the correct alternative from the choice given in brackets:
(a) The dorsal root ganglion of the spinal cord contains cell bodies of (motor/sensory/intermediate) neurons.
(b) Cerebellum is the part of the brain which is responsible for
(i) conducting reflexes in the body
(ii) maintain posture and equilibrium
(iii) controlling thinking memory & reasoning
(c) Reflex action is controlled by
(i) brain
(ii) spinal cord
(iii) autonomic
(iii) peripheral nervous system
Ans: (a) Sensory
(b) Maintaining posture and equilibrium
(c) Spinal cord
C. SHORT ANSWER TYPE:
1) Mention where in human body are the following located and state their main function:
(a) corpus callosum
(b) central canal
Ans: (a) Corpus Callosum : The corpus callosum is a wide, thick bundle of nerve fibers located deep within the center of the brain. It acts as the primary communication link between the left and right cerebral hemispheres. Its main function is to allow these two sides of the brain to share information, ensuring they can work together to coordinate complex functions like thinking, memory, and voluntary movements.
(b) central canal : The central canal is a thin, fluid-filled space located in the center of the spinal cord. It’s filled with cerebrospinal fluid (CSF), which performs two vital functions. First, it helps to nourish the surrounding spinal cord tissues by delivering essential nutrients. Second, it acts as a protective cushion, absorbing shocks and guarding the spinal cord from physical damage.
2) State whether the following statements are true (T) or false (F).
(a) The main component of the white matter of the brain is perikaryon
(b) The arachnoid layer fits closely inside the pia mater.
(c) A double chain of ganglia, one on each side of the nerve cord belongs to the spinal cord.
(d) Dura mater is the outermost layer of the meninges.
Ans: (a) False
(b) False
(c) True
(d) True
3) Differentiate between following pairs with reference to the aspect in brackets.
(a) cerebrum and cerebellum (function)
(b) sympathetic nervous system and para – sympathetic nervous system (overall effect on body)
(c) Sensory nerve and motor nerve (direction of impulse carried)
(d) medulla oblongata & cerebellum (function)
(e) cerebrum and spinal cord (arrangement of cytons and exons of neurons).
Ans: (a) cerebrum and cerebellum (function)
| cerebrum | cerebellum |
| The cerebrum is responsible for higher-level functions such as thought, memory, speech, voluntary actions, and the interpretation of sensory information. | The cerebellum’s primary role is to coordinate and regulate muscular activity, maintaining posture, balance, and fine motor skills. |
| It is the largest part of the brain and is divided into two hemispheres | It ensures movements are smooth and precise. |
(b) sympathetic nervous system and para – sympathetic nervous system (overall effect on body)
| sympathetic nervous system | para – sympathetic nervous system |
| Sympathetic Nervous System: This system prepares the body for a “fight or flight” response in stressful situations. | The parasympathetic system promotes a “rest and digest” state. It conserves energy by slowing the heart rate, constricting pupils, stimulating digestion, and lowering blood pressure. |
| It increases heart rate, dilates pupils, inhibits digestion, and raises blood pressure to mobilize energy resources. | It is most active during periods of relaxation |
(c) Sensory nerve and motor nerve (direction of impulse carried)
| Sensory nerve | motor nerve |
| These nerves carry impulses from sensory organs (like the skin, eyes, and ears) to the central nervous system (brain and spinal cord). | These nerves carry impulses from the central nervous system to muscles or glands, causing them to respond. |
| They are also known as afferent nerves. | They are also known as efferent nerves |
(d) medulla oblongata & cerebellum (function)
| medulla oblongata | cerebellum |
| The medulla controls vital, involuntary functions essential for survival, such as breathing, heart rate, blood pressure, and reflexes like sneezing and coughing. | The cerebellum focuses on coordination and regulation of voluntary motor movements, balance, and posture. It does not control involuntary actions. |
| It forms the lower part of the brainstem. | It does not control involuntary actions |
(e) cerebrum and spinal cord (arrangement of cytons and exons of neurons).
| cerebrum | spinal cord |
| The cerebrum has gray matter on the outside (cortex) and white matter on the inside. | The spinal cord has the opposite arrangement, with gray matter on the inside (forming an H-shape) and white matter on the outside. |
| The gray matter contains the cytons (cell bodies) of neurons, while the white matter consists of myelinated axons. | The central gray matter contains the cytons, and the surrounding white matter consists of axons. |
4) Given below are two structures, write their special functional activity.
(a) cerebellum and …………….
(b) Myelin sheath and ……………
Ans:
(a) Cerebellum maintains balance of the body and coordinates muscular activity.
(b) Myelin sheath acts like an insulation and prevents mixing of impulses in the adjacent axons.
5) Write the functions of the following:
(a) synapse
(b) Association neuron
(c) medullary sheath
(d) Medulla obiongata
(e) cerebellum
(f) Cerebrospinal fluid
Ans: (a) Synapse
Think of a synapse as a tiny meeting point between two nerve cells. Its job is to pass messages from one neuron to another using special chemicals called neurotransmitters. When an electrical signal reaches the synapse, these chemicals jump across the gap like a molecular bridge, triggering the next neuron to continue the message.
(b) Association Neuron (Interneuron)
These are the brain’s middlemen. Found only in the brain and spinal cord, they link sensory neurons (which bring information in) with motor neurons (which send commands out). Without them, your body couldn’t process information – like when you pull your hand from hot water before even thinking about it.
(c) Medullary Sheath (Myelin Sheath)
This fatty wrapping around nerve fibers acts like insulation on an electrical wire. It speeds up nerve signals by forcing them to “jump” between uncovered spots (nodes of Ranvier) rather than traveling the whole length. When this sheath deteriorates (as in multiple sclerosis), nerve signals slow down dramatically.
(d) Medulla Oblongata
Your body’s autopilot center. This thumb-sized area at the brain’s base keeps you alive without conscious effort – maintaining your heartbeat, controlling breathing rhythms, and regulating blood pressure. Even when you’re in deep sleep, your medulla keeps these vital functions running smoothly.
(e) Cerebellum
The brain’s built-in movement coach. This cauliflower-shaped structure at the skull’s back fine-tunes every motion – from threading a needle to riding a bike. It constantly adjusts muscle activity based on balance signals from your inner ear and feedback from your muscles, making movements precise and coordinated.
(f) Cerebrospinal Fluid (CSF)
Imagine your brain floating in a shock-absorbing water bed. When doctors do a spinal tap, they’re checking this fluid for signs of infection or neurological disorders. It completely refreshes itself every few hours.
6) what do we refer to in the nervous system when we say:
(a) sensory, motor and mixed ………………..
(b) somatic and autonomic …………………..
(c) Natural and conditioned …………………
(d) sensory, motors and association ……………….
(e) Gray and white ………………………………
Ans: (a) Sensory, Motor, and Mixed Nerves
Sensory Nerve: Carries signals from sense organs (eyes, skin, etc.) to the brain/spinal cord (CNS).
Motor Nerve: Carries signals from the CNS to muscles or glands to trigger actions.
Mixed Nerve: Contains both sensory and motor fibers, allowing two-way communication (e.g., spinal nerves).
(b) Somatic vs. Autonomic Nervous System
Somatic: Controls voluntary movements (e.g., walking, lifting objects) via skeletal muscles.
Autonomic: Regulates involuntary functions (e.g., heartbeat, digestion) without conscious effort.
(c) Natural vs. Conditioned Reflexes
Natural Reflex: Innate, automatic (e.g., pulling hand from fire, blinking at bright light).
Conditioned Reflex: Learned through repetition (e.g., salivating at the sound of a food bell).
(d) Sensory, Motor, and Association Neurons
Sensory Neuron: Sends signals from senses to CNS.
Motor Neuron: Carries commands from CNS to muscles/glands.
Association Neuron (Interneuron): Connects sensory and motor neurons within the CNS for processing.
(e) Gray Matter vs. White Matter
Gray Matter: Contains neuron cell bodies (cytons) and dendrites; found in brain cortex and spinal cord’s H-shaped core. Processes information.
White Matter: Made of myelinated axons (fat-covered for speed); forms inner brain regions and outer spinal cord areas. Transmits signals
7) Rearrange the following in correct sequence pertaining to what is given within brackets at the end.
(a) Effector …….. sensory neuron ………. Receptor…….. motor neuron………. Stimulus……. central nervous system………. Response (Reflex arc)
(b) repolarization……. Depolarization…….. Resting….. (polarised) (during conduction of nerve impulse through a nerve fibre)
(c) axon endings ……… nucleus …….. Dendrites ……… axon…….. perikaryon ………. Dendron……. (Neutron structure)
(d) diencephalon ………. Cerebellum …….. medulla oblongata ………. Pons ….. Cerebrum ……. mid-brain (sequence of parts of the human brain).
Ans: (a) Stimulus — receptor — sensory neuron — central nervous system — motor neuron — effector — response
(b) Resting — depolarization — repolarization
(c) Dendrites — Dendron — perikaryon — nucleus — axon — axon endings
(d) Cerebrum — diencephalon — midbrain — cerebellum — pons — medulla oblongata
D. LONG ANSWER TYPE:
1) (a) What is meant by reflex action?
A reflex action is the body’s lightning-fast, automatic response to danger or sudden stimuli—no thinking required. It’s like an emergency alarm system that bypasses the brain for speed, keeping us safe from harm.
How It Works (The Reflex Arc):
Stimulus Detected – A receptor (e.g., skin) senses danger (like heat from a hot pan).
Signal to Spinal Cord – A sensory neuron zips the message to the spinal cord.
Instant Decision – Instead of waiting for the brain, the spinal cord instantly relays the signal to a motor neuron.
Rapid Reaction – The motor neuron commands a muscle (like your arm) to jerk away—before you even feel the pain.
Why It Matters:
Protection: Prevents burns, falls, or injuries before the brain processes the threat.
Speed: Since the signal skips the brain, reactions happen in milliseconds.
Examples: Knee-jerk reflex, blinking when something flies at your eye, or pulling your hand from a sharp object.
(b) State whether the following are simple reflexes conditioned reflexes or neither of the two:
(i) Sneezing: …………….
(ii) Blushing: ……………….
(iii) Contraction of eye pupil: …………………..
(iv) Lifting up a book: …………………..
(v) Knitting without looking: …………………..
(vi) sudden application of brakes of the cycle on sighting an obstacle in front …………….
Ans: (i) Sneezing is a simple reflex. It’s an involuntary and automatic protective response triggered when irritants are detected in the nasal passages. Sensory nerves in the nose send a signal to the brainstem, which instantly commands muscles to forcefully expel air to clear the irritant. This happens without conscious thought.
(ii) Blushing is not a simple reflex. Although it’s an involuntary response, it’s a complex physiological reaction linked to emotions and higher brain functions. The autonomic nervous system is activated by emotions like embarrassment, which causes blood vessels in the face to dilate and the cheeks to redden.
(iii) Pupil contraction is a simple reflex. When the eye is exposed to bright light, sensory receptors send a signal to the brainstem. The brainstem immediately sends a motor signal to the muscles of the iris, causing the pupil to constrict. This action protects the retina from damage by excessive light.
(iv) Lifting a book .This is a conscious and deliberate movement initiated by the cerebrum. The cerebrum sends a signal down the motor nerves to activate the specific muscles needed for the task. Because it’s voluntary, you can choose to control or stop the action at any time.
(v) Knitting without looking is a conditioned reflex. This is a learned, automatic response developed through repeated practice. The brain creates strong neural pathways (muscle memory) that allow the complex sequence of movements to be performed automatically, without conscious effort.
(vi) Emergency braking is a conditioned reflex. This is a learned response developed through driving experience and training. When a driver perceives a danger, their brain triggers a rapid, automatic reaction. The action feels involuntary due to the ingrained neural pathways formed from practice, which enable an instant response.
2) What are the advantages of having a nervous system?
Ans: Speed and Coordination
The nervous system is like your body’s high-speed communication network. It uses specialized cells called neurons to send electrical and chemical signals. This rapid transmission allows for quick coordination of your body’s actions, from simple reflexes, like pulling your hand away from a hot stove, to more complex movements, like catching a ball. This speed is crucial for responding to a threat or danger, ensuring your survival.
Adaptation and Learning
This function is what makes you uniquely you. Your nervous system is incredibly adaptable; it can change its structure and function in response to new experiences, a concept known as neuroplasticity. This is the basis of learning and memory. When you learn a new skill, like riding a bike, your brain forms new connections between neurons. These connections become stronger with practice, allowing you to perform the task more efficiently. This ability to learn from past experiences helps you adapt to your environment and develop complex behaviors.
Regulation and Homeostasis
Your body’s internal environment needs to be stable, a state called homeostasis. The nervous system, in partnership with the endocrine system (the body’s hormone system), plays a vital role in maintaining this balance. It regulates involuntary functions you don’t have to think about, such as heart rate, blood pressure, and body temperature. For example, if you get too hot, your nervous system signals your sweat glands to start working and your blood vessels to dilate, helping you cool down.
Sensation and Perception
This function allows you to experience the world around you. Your sense organs—your eyes, ears, nose, tongue, and skin—are equipped with specialized cells that detect different types of information, like light, sound, chemicals, and pressure. The nervous system receives these signals and processes them into meaningful information. Sensation is the raw data collected by your sense organs, while perception is your brain’s interpretation of that data, allowing you to see colors, hear music, and feel a breeze.
3) Why do you call the spinal cord and the brain the central nervous system?
Ans: The brain and spinal cord form the central nervous system (CNS) because they are the main control centers of the body. They function as a central processing unit, receiving information, interpreting it, and sending out instructions.
Function and Role
The CNS is responsible for most of the body’s functions, including thought, movement, and sensation. Think of the brain as the body’s command center and the spinal cord as the main communication highway. The brain processes information and makes decisions, while the spinal cord relays signals between the brain and the rest of the body. This central role in controlling and coordinating all bodily activities is why they are called the central nervous system
4) What is the difference between reflex action and voluntary action?
Ans: A reflex action is a quick, automatic response to a stimulus, like pulling your hand away from something hot. It happens without thinking because the signal goes to the spinal cord and straight back to the muscles, skipping the brain for speed. This helps protect the body from harm.
A voluntary action is a deliberate, conscious response. For example, when you decide to pick up a book, the signal goes to your brain for processing before a command is sent to your muscles. This makes the response slower than a reflex action.
5) Draw a labelled diagram of a myelinated neuron.
Ans:
6) During a street fight between two individuals, mention the effects on the following organs by the autonomous nervous system, in the table given below : (one has been for you as an example)
| Organ | Sympathetic System | Parasympathetic System |
| e.g. Lungs | Dilates bronchi and bronchioles | Constricts bronchi and bronchioles |
| 1. Heart | ||
| 2. Pupil | ||
| 3. Salivary gland |
Ans:
| Organ | Sympathetic System | Parasympathetic System |
| e.g. Lungs | Dilates bronchi and bronchioles | Constricts bronchi and bronchioles |
| 1. Heart | Accelerates heartbeat | Retards heartbeat |
| 2. Pupil | Dilates | Constricts |
| 3. Salivary gland | Inhibits the secretion of saliva causing the drying of the mouth | Stimulates the release of saliva |
E. STRUCTURED / APPLICATION/SKILL TYPE:
1) Two hungry boys (A and B) enter a restaurant and find a table decorated as follows: Boy B starts salivating but not A. Explain the reason for this difference.
Ans: Boy B’s ,His brain has associated the sight and smell of the food with the pleasure of eating. This learned connection causes his salivary glands to release saliva in anticipation of the meal.
Boy A, on the other hand, appears unfamiliar or repulsed by the food in front of him. Because he lacks a positive association or a conditioned reflex for that specific dish, his body does not produce the same anticipatory salivary response. His lack of salivation suggests that his brain hasn’t learned to link that particular food with a rewarding eating experience.
2) Given below are a few situations. What effective change will occur in the organ/body part mentioned and which part (sympathetic or parasympathetic) of the autonomic nervous system brings it about?
| Situation | Organ/body part | Change/action | Part of autonomic nervous system involved |
| 1. You have entered a dark room | Eye | ||
| 2. Your body is consuming lot of glucose while running a race | Liver | ||
| 3. You are chewing a tasty food | Salivary gland | ||
| 4. You are running a race | Adrenal gland | ||
| 5. You are retiring to bed for sleep | Heart | ||
| 6. You are shivering in intense cold | Body hairs |
Ans:
| Situation | Organ/body part | Change/action | Part of autonomic nervous system involved |
| 1. You have entered a dark room | Eye | Pupil dilates | Sympathetic |
| 2. Your body is consuming lot of glucose while running a race | Liver | Glycogen is converted into glucose in liver | Sympathetic |
| 3. You are chewing a tasty food | Salivary gland | Salivation increases | Parasympathetic |
| 4. You are running a race | Adrenal gland | Release of adrenaline and noradrenaline increases | Sympathetic |
| 5. You are retiring to bed for sleep | Heart | Heart rate slows down | Parasympathetic |
| 6. You are shivering in intense cold | Body hairs | Hair raised | Sympathetic |
3) Given below is the partially incomplete scheme of the components of the peripheral nervous system. Fill up the blanks numbered (1) – (8):
Ans:
REVIEW QUESTIONS:
A. MULTIPLE CHOICE TYPE: (Select the most appropriate option in each case).
1) Which part of the eye is grafted in a needy patient from a donated eye?
(a) Conjunctiva
(b) Cornea
(c) Choroid
(d) Ciliary muscles
Ans: (b) Cornea
2) Which part of our ear is shaped like a snail shell?
(a) Semi circular canals
(b) Cochlea
(c) Stapes
(d) Eustachian tube
Ans: (b) Cochlea
3) The three parts of human ear contributing in hearing are-
(a) cochlea, ear ossicles and tympanum
(b) semicircular canals, utriculus and sacculus
(c) eutachian tube, tympanum and utriculus
(d) perilymph, ear ossicle and semicircular canals.
Ans: (c) eutachian tube, tympanum and utriculus
4) The region in the eyes where the rods and cones are located is the
(a) retina
(b) cornea
(c) choroid
(d) sclera
Ans:(a) retina
B.VERY SHORT ANSWER TYPE:
1) Name the following:
(a) The photosensitive pigment present in the rods of the retina.
(b) The part which equalizes the air pressure in the middle and external ear.
(c) The ear ossicle attached to the tympanum
(d) The outermost covering layer of the brain
(e) The tube which connects the cavity of the middle ear with the throat
(f) The part of the eye responsible for its shape.
(g) The nerves which transmit impulse from ear to the brain
(h) The photoreceptors found in the retina of the eye.
(i) The eye defect caused due to shortening of the eye ball from front to back.
Ans: (a) Rhodopsin
(b) Eustachian tube
(c) Hammer
(d) Dura mater
(e) Eustachian tube
(f) Cornea
(g) Auditory nerves
(h) Rods and cones
(i) Hypermetropia
2) Note the relationship between the first two words and suggest the suitable word/words for the fourth place.
(a) Cones : Iodopsim :: Rods : ……………….
(b) sound : ear drum :: Dynamic balance : ……
Ans:(a) Cones: Iodopsin:: rods: rhodopsin
(b) Sound: ear drum:: dynamic balance: semi-circular canals
3) Which one or more of the expressions in column II are appropriate for the items listed in column I? write the correct matching pairs-
| Column I | Column II |
| (i) The blind spot | (a) colour of the eye |
| (ii) the yellow spot | (b) shape of the lens |
| (iii) Ciliary muscle | (c) protective covering of the brain |
| (iv) Iris | (d) basic unit of brain |
| (v) Meninges | (e) free of rod cells |
| (f) vitreous humour | |
| (g) centre of the retina | |
| (h) no sensory cells |
Ans:
| Column I | Column II |
| (i) The blind spot | (h) no sensory cells |
| (ii) the yellow spot | (g) centre of the retina |
| (iii) Ciliary muscle | (b) shape of the lens |
| (iv) Iris | (d) basic unit of brain (e) free of rod cells |
| (v) Meninges | (c) protective covering of the brain |
C. SHORT ANSWER TYPE:
1) Differentiate between members of each of the following pairs with reference to what is asked in brackets.
(a) Myopia and hyperopia (cause of the defect)
(b) Rods and cones (sensitivity)
(c) Semi-circular canal and cochlea (Senses perceived)
(d) Rod and cone cells (pigment contained)
(e) Dynamic balance and static balance (Definition)
Ans:
(a) Myopia and hyperopia (cause of the defect)
| Myopia | hyperopia |
| The eyeball is either too long or the cornea is too curved. | The eyeball is too short or the cornea is not curved enough. |
| This causes light to focus in front of the retina instead of directly on it, making distant objects appear blurry. | This causes light to focus behind the retina, making close objects appear blurry. |
(b) Rods and cones (sensitivity)
| Rods | cones |
| These photoreceptor cells are highly sensitive to low light levels. | These cells are less sensitive to light and require bright light to function. |
| They are responsible for night vision and peripheral vision, but they do not detect color. | They are responsible for sharp vision and the detection of color. |
(c) Semi-circular canal and cochlea (Senses perceived)
| Semi-circular canal | cochlea |
| These three fluid-filled loops in the inner ear are responsible for sensing dynamic balance. | This snail-shaped structure is responsible for the sense of hearing. |
| They detect rotational movements of the head and help us maintain our balance while moving. | It converts sound vibrations into nerve impulses that are sent to the brain. |
(d) Rod and cone cells (pigment contained)
| Rod | cone cells |
| Contain the pigment rhodopsin, which is highly sensitive to light and allows for vision in dim conditions. | Contain three different types of pigments (photopsins), each sensitive to a different wavelength of light (red, green, or blue). |
(e) Dynamic balance and static balance (Definition)
| Dynamic balance | static balance |
| This is the ability to maintain equilibrium while the body is in motion. | This is the ability to maintain equilibrium while the body is at rest. |
| It is controlled by the semi-circular canals and involves detecting changes in speed and rotation. | It is controlled by the utricle and saccule in the inner ear and involves detecting the position of the head relative to gravity. |
2) State whether the following statements are True (t) or False, correct them by changing any one single word in each.
(a) Deafness is caused due to rupturing of the pinna
(b) Semi circular canals are concerned with static (positional) balance.
Ans:
(a) False Correct statement: Deafness is caused due to rupturing of the eardrum.
(b) False Correct statement: Semicircular canals are concerned with dynamic balance.
3) Mention, where in living organisms are the following located and state their main functions:
(a) Fovea centralis
(b) Organ of corti
Ans: a) Fovea Centralis
The fovea centralis is a tiny depression in the retina packed with cone cells, enabling sharp, detailed, and color vision. It’s crucial for tasks like reading or recognizing faces.
b) Organ of Corti
Located in the cochlea, the organ of Corti houses hair cells that turn sound vibrations into nerve signals. These signals travel to the brain, allowing us to hear. It’s essential for detecting pitch and volume.
4) Mention if the following statements are true (T) or false (F) Give reason.
(a) Sometimes medicines dropped into the eyes come into the nose and even throat (b) Ciliary muscles regulate the size of the pupil
(c) yellow spot of the retina is the region of colour vision
(d) The auditory nerve is purely for perceiving sound
(e) Malleus incus and stapes are collectively called the ear ossicles
(f) Flavor and taste are one and the same thing.
(g) short-sightedness and hyperopia are one and the same thing
(h) Blind spot is called so because no image is formed on it.
Ans: (a) True
(b) False/ Ciliary muscles regulate the size of the lens.
(c) True
(d) False/The auditory nerve responsible for sound as well as for the body balance. (e) True
(f) False/ flavour is a combination of taste and smell.
(g) False/ short-sightedness is myopia and hyperopia is long-sightedness.
(h) True
5) Given below are two sets (a) and (b) of five parts in each. Rewrite them in the correct sequence.
(a) Cochlea, tympanum, auditory canal, ear ossicles, oval window.
(b) Conjunctiva, retina, cornea, optic nerve, lens
Ans: (a) Auditory canal, tympanum, ear ossicles, oval window, cochlea
(b) Conjunctiva, cornea, lens, retina, optic nerve
6) Given below are certain structures. Write against them their functional activity.
(a) organ of corti and ……………….
(b) Olfactory nerve and ……………..
(c) retina and ……………………….
(d) Taste bud and …………………..
Ans:(a) Organ of Corti and hearing
(b) Olfactory nerve and smell
(c) Retina and vision
(d) Taste bud and taste
7) Answer the following:
(a) What is a lacrimal gland?
(b) In what two ways is the yellow spot different from the blind spot?
(c) Name an old age eye defect. What happens in it?
(d) What is meant by the power of accommodation of the eye?
(e) Mention the characteristics of the image that falls on the retina of the eye.
Ans:(a) Lacrimal Gland : The lacrimal gland is indeed a tear gland located in the upper, outer part of the eye orbit. Its secretion, known as tears, serves several crucial functions. Tears lubricate the surface of the eye, keeping it moist and comfortable. They also help to wash away dust, debris, and other foreign particles that can irritate the eye. Furthermore, tears contain an enzyme called lysozyme, which has antibacterial properties and helps kill germs, protecting the eye from infection.
(b)The yellow spot (or macula lutea), is a region in the retina with the highest concentration of cones, specialized photoreceptor cells responsible for sharp, color vision. It’s the part of the eye that provides the most detailed sight.This area has no photoreceptor cells (cones or rods), meaning it can’t detect light, creating a “blind” spot in your visual field.
c)Presbyopia and Cataracts: Presbyopia is an age-related condition where the eye’s lens loses its flexibility, making it difficult to focus on close objects. It’s often called “age-old far-sightedness.” Cataracts, also common with age, occur when the eye’s lens becomes cloudy or opaque. This clouding scatters light, leading to blurred vision and, if left untreated, can cause blindness.
(d) Power of Accommodation of the Eye: The eye adjusts its lens’s focal length to focus on near or far objects. Ciliary muscles contract to thicken the lens for near vision and relax to thin it for distant vision.
(e) Characteristics of the Image on the Retina
Real (formed by actual light rays),
Inverted (upside down, corrected by the brain),
Diminished (smaller than the object).
8) What is meant by optical illusion? Give one example.
Ans: They happen because the brain uses shortcuts to interpret visuals quickly. For example, the Müller-Lyer illusion makes two equal-length lines seem different due to arrow directions—outward arrows make a line look shorter, while inward arrows make it appear longer. This shows how our brain misjudges shapes and depth at times.
9) Where are the following located? Briefly mention the function of each:
(a) oval window
(b) Cochlea
(c) Semicircular canals
(d) Utriculus
Ans: (a) Oval Window
The oval window links the middle ear to the inner ear. It passes sound vibrations from the stapes bone to the cochlea’s fluid. Its small size helps amplify these vibrations, improving hearing.
(b) Cochlea
A spiral-shaped, fluid-filled structure in the inner ear. It converts sound vibrations into electrical signals for the brain, enabling hearing.
(c) Semicircular Canals
Three fluid-filled loops in the inner ear that sense head rotations, helping maintain balance.
(d) Utriculus (Utricle)
A sac in the inner ear’s vestibule that detects linear motion (e.g., forward/backward movement) and head tilt, aiding balance.
10) Name the four principal tastes and the respective regions of the tongue concerned with their perception.
Ans: Tip: Sweeter and salty tastes.
Sides: Salty and sour flavors.
Back: Bitter tastes—likely to spot toxins quickly.
This slight variation helps with taste perception and protection.
11) Complete the following table by filling in the blank spaces.
| Structure | Function |
| Yellow Spot | ____________ |
____________ | Transfers impulse from inner ear to brain |
____________ | Helps to change the focal length of the eye lens |
| Spinal cord | ____________ |
| Oval window | ____________ |
| ____________ | Dynamic equilibrium |
Ans:
| Structure | Function |
| Yellow Spot | Region of the brightest vision |
| Auditory nerve | Transfers impulse from inner ear to brain |
| Ciliary muscle | Helps to change the focal length of the eye lens |
| Spinal cord | Conducts impulses |
| Oval window | Sets fluid in cochlear canal into vibration |
| Semicircular canals | Dynamic equilibrium |
D. LONG ANSWER TYPE:
1) Describe the mechanism of focusing the image of a distant object in your eye when you raise your head after reading a book.
Ans: When shifting focus from a nearby to a distant object:
Ciliary muscles relax, reducing contraction.Suspensory ligaments tighten, pulling the lens.
The lens flattens and thins, increasing focal length.This reduces converging power, helping distant objects focus clearly on the retina.
2) Sometimes you remember a vivid picture of a dream you saw. What is the role of your eyes in this experience?
Ans: Scientists think these movements match the dream images your brain creates—like “scanning” the dream scene. It’s not real vision, just your visual cortex and eyes reacting to the dream. This idea is called the “scanning hypothesis.” Essentially, your eyes follow the dream’s visuals as if they were real.
3) By closing the eyes and gently pressing them by your palms, you may see some specks of brilliant light. How do you get this sensation while there is no light entering your eye
Ans: When you press on your closed eyes, the pressure stimulates the retina—the light-sensitive layer at the back of your eye. Normally, the retina responds to light, but physical pressure can also trigger its cells, sending false signals to your brain. These signals are interpreted as flashes or specks of light, called phosphenes, even though no actual light is present. It’s like your eyes “tricking” your brain into seeing something that isn’t there.
4) Explain the terms ‘adaptation’ and ‘accommodation’ with reference to the eye.
Ans: Adaptation: Adaptation is the eye’s ability to adjust to varying levels of light intensity. This is a slower process that allows us to see in both bright and dim conditions. The main mechanisms are:
- Pupil size: The pupil, which is a hole in the center of the iris, automatically constricts in bright light to limit the amount of light entering the eye and dilates in dim light to allow more light in.
- Retinal sensitivity: The photoreceptor cells (rods and cones) in the retina also adjust their sensitivity. Rods are more active in low light, and cones are more active in bright light.
Accommodation: This is a rapid process that enables clear vision whether we’re looking at a faraway mountain or a nearby book. The primary mechanism is:
- Ciliary muscles and lens: The ciliary muscles surrounding the lens change its shape. When focusing on a nearby object, these muscles contract, making the lens thicker and increasing its converging power.
5) You do not enjoy watching a movie from a very short distance from the screen in a cinema hall. Why?
Ans: Watching a movie from a very short distance in a cinema is uncomfortable because:
Strain on Eyes – Sitting too close forces your eyes to constantly move to see the entire screen, causing fatigue.
Distorted View – The screen appears overly large, making it hard to focus on the whole picture at once.
Neck Discomfort – You may need to tilt your head up or sideways for long periods, leading to neck pain.
Poor Immersion – Being too close can make the image feel overwhelming, reducing the cinematic experience.
A moderate distance provides a balanced and enjoyable view.
6) Enumerate the common defects of vision, their causes and the possible methods of correcting them.
Ans: Common Vision Defects and Corrections
Myopia (Nearsightedness)
- Cause: The eyeball is too long or the cornea is too curved, causing light to focus in front of the retina instead of on it. This makes distant objects appear blurry.
- Correction: Concave lenses (glasses or contact lenses) are used to diverge the light rays before they enter the eye, pushing the focal point back onto the retina.
Hypermetropia (Farsightedness)
- Cause: The eyeball is too short or the cornea is not curved enough, causing light to focus behind the retina. This makes nearby objects appear blurry.
- Correction: Convex lenses are used to converge the light rays, moving the focal point forward onto the retina.
Astigmatism
- Cause: An irregularly shaped cornea or lens, which causes light to scatter and focus at multiple points on the retina, resulting in blurred vision at all distances.
- Correction: Cylindrical lenses are prescribed to correct the uneven curvature of the eye.
Presbyopia
- Cause: A natural, age-related stiffening of the eye’s lens, which reduces its ability to change shape and focus on near objects. This is why many people need reading glasses after age 40.
- Correction: Convex lenses in the form of reading glasses or bifocals are used to help with near vision.
Cataracts
- Cause: The natural lens of the eye becomes cloudy or opaque, usually due to aging. This significantly reduces vision clarity.
- Correction: The only effective treatment is surgery to remove the cloudy natural lens and replace it with a clear, artificial intraocular lens.
Color Blindness
- Cause: A genetic condition where the cone cells in the retina, which are responsible for color vision, are either absent or not functioning correctly.
- Correction: There is no cure, but certain specialized glasses or contact lenses can help some people distinguish between colors more effectively.
7) Name the three ear ossicles. How do they contribute to the mechanism of hearing?
Ans:Malleus (hammer): Attached to the eardrum.
Incus (anvil): Connects the malleus and stapes.
Stapes (stirrup): The smallest bone, pressing against the oval window (inner ear entrance).
They convert low-pressure eardrum vibrations into high-pressure vibrations for the inner ear’s fluid, ensuring efficient sound transmission for clear hearing.
8) What is meant by the power of accommodation of the eye? Name the muscles of the eye responsible for the same …………
Ans: The eye adjusts its focus for near and far objects by changing the lens shape—this ability is called accommodation.
Ciliary muscles control this process:
For near vision: They contract, loosening the suspensory ligaments, making the lens thicker (more curved).
For distant vision: They relax, tightening the ligaments, making the lens thinner (flatter).
This ensures clear vision at varying distances.
E. STRUCTURED / APPLICATION / SKILL TYPE:
1) With reference to the functioning of the eye, answer the questions that follow:
(a) What is meant by the power of accommodation of the eye?
(b) What is the shape of the lens during (1) near vision (2) distant vision?
(c) Name the two structures in the eye responsible for bringing about the change in the shape of the lens.
(d) Name the cells of the retina and their respective pigments which get activated (1) in the dark and (2) in the light.
Ans:
(a) Power of accommodation of the eye:
The ability of the eye lens to adjust its focal length to see both near and distant objects clearly by changing its shape.
(b) Shape of the lens during:
Near vision – Thicker (more convex)
Distant vision – Thinner (less convex)
(c) Two structures responsible for changing lens shape:
Ciliary muscles (contract or relax)
Suspensory ligaments (loosen or tighten)
(d) Retina cells and their pigments:
In the dark – Rods (activated; contain rhodopsin pigment)
In the light – Cones (activated; contain iodopsin pigment)
2) With reference to the human ear, answer the questions that follow
(a) Give the technical term for the structure found in the inner ear.
(b) Name the three small bones present in the middle ear. What is the biological term for them collectively?
(c) Name the part of the ear associated with (1) static balance (2) hearing (3) dynamic balance.
(d) Name the nerve, which transmits messages from the ear to the brain.
Ans:
(a) Inner Ear Structure: The bony labyrinth is a hard, maze-like structure in the inner ear. It includes:
Cochlea – Turns sound vibrations into nerve signals for hearing.
Semicircular Canals & Vestibule – Sense head movements and position to help with balance.
(b) Middle Ear Bones: The three ear ossicles—malleus, incus, and stapes—are correctly identified along with their function of transmitting sound.
(c) Ear Parts & Functions: The specific functions of the inner ear components are correctly matched:
Static balance: The utricle and saccule detect the head’s position.
Hearing: The cochlea is the primary organ for hearing, converting vibrations into nerve signals.
Dynamic balance: The semicircular canals are responsible for sensing head movement and rotation.
(d) Ear-to-Brain Nerve: The auditory nerve (also known as the vestibulocochlear nerve) is correctly identified as the nerve that sends both auditory and balance signals to the brain.
3) The figure below compares a part of our eye with a part of a photographic camera.
(a) name the corresponding parts of the eye the camera shown here that are comparable in function.
(b) Explain the mode of working and the functions of the parts of the eye mentioned above
Ans: (a) Corresponding Parts
Iris (Eye) ↔ Diaphragm (Camera)
Pupil (Eye) ↔ Aperture (Camera)
(b) Working & Functions
The iris (a muscle in the eye) controls the pupil’s size—shrinking in bright light to limit light entry and expanding in dim light to allow more light for clear vision.
Similarly, a camera’s diaphragm adjusts the aperture size—widening for low-light shots (more light) and narrowing for bright scenes (less light)—to ensure proper exposure.
4) Given below is a diagram depicting a defect of the human eye. Study the same and answer the questions that follow:
(a) Name the defect shown in the diagram
(b) Give two possible reasons for this defect
(c) Name the parts labelled 1 to 4
(d) Name the type of lens used to correct this eye defect
(e) Draw a labelled diagram to show how the above mentioned defect is rectified using the lens named above.
Ans: (a) Defect shown: Myopia (nearsightedness).
(b) Two possible reasons: The eyeball is too long, or the cornea/lens has an excessive curvature.
(c) Parts labelled 1 to 4: While the diagram wasn’t included, your assumption of common eye parts (cornea, lens, retina, optic nerve) is a logical and safe one.
(d) Corrective lens: A concave lens is the correct lens type.
(e) Diagram explanation: The explanation that a concave lens diverges light rays to properly focus the image on the retina is spot-on
5) The figure below is the sectional view of a part of the skull showing a sense organ:
(i) Name the sense organ
(ii) What are the parts labelled ‘m’, “I” and “s”? What do these three parts constitute collectively?
(iii) what do you call the part shown in the form of a spiral? What is its function?
(iv) Name the part labelled “tm”? What is its function?
Ans: (i) The diagram shows the ear.
(ii) Labeled parts:
m: Malleus
i: Incus
s: Stapes
Together, they form the ear ossicles.
(iii) The spiral-shaped part is the cochlea, which converts sound vibrations into nerve signals for the brain.
(iv) “tm” is the tympanic membrane (eardrum). It vibrates when sound hits it and passes these vibrations to the malleus.
6) Given below is the diagram of a part of the human ear. Study the same and answer the questions that follow:
(i) Give the collective biological term for malleus, Incus and stapes
(ii) Name the parts labelled A, B, and C in the diagram
(iii) state the functions of the parts labelled ‘A’ and ‘B’
(iv) Name the audio receptor region present in the part labelled ‘A’
Ans:(i) Ear Ossicles
The malleus, incus, and stapes are three small bones in the middle ear that transmit sound vibrations.
(ii) Labeled Parts
A: Cochlea – Spiral-shaped inner ear part that converts sound into nerve signals.
B: Eustachian tube – Connects middle ear to throat, balancing air pressure.
C: Tympanic membrane (eardrum) – Thin membrane separating outer and middle ear, vibrating in response to sound.
(iii) Functions
Cochlea (A): Changes sound vibrations into electrical signals for the brain.
Eustachian tube (B): Keeps ear pressure equal for proper eardrum movement.
(iv) Sound-Detecting Region
The organ of Corti in the cochlea detects sound using hair cells that turn vibrations into nerve signals.
7) Draw a labelled diagram of the inner ear. Name the part of the inner ear that is responsible for static balance in human beings.
Ans:
8) Have a look at the posture of this girl who is reading a book and answer the questions which follow:
(a) Name the problem she is facing
(b) What are the two conditions shown in sections A and B of the eye as applicable to her.
(c) What kind of looking glasses does she need?
Ans: (a) Problem she is facing
The girl is facing a condition called myopia (nearsightedness). This is a common vision problem where a person can see nearby objects clearly, but distant objects appear blurry. Her poor reading posture—holding the book too close—is a known risk factor for the development and progression of myopia.
(b) Conditions shown in sections A and B
While the images don’t have explicit sections A and B, typical diagrams for this type of question illustrate two conditions:
- Section A would likely show a normal eye where the image is focused directly on the retina. * Section B would represent a myopic eye, where the image is focused in front of the retina because the eyeball is too long or the cornea is too curved.
(c) Kind of looking glasses she needs
She needs glasses with concave lenses. They correct myopia by diverging the light rays before they enter the eye, pushing the focal point back onto the retina so that the image is clear.
