GSEB Class 11 Biology Solutions Chapter 21 Neural Control and Coordination

 

Question 1. Briefly describe the structure of the following:
1. Brain
2. Eye
3. Ear
Answer:
1. Brain: The human brain is well protected by the skull. Inside the skull, the brain is covered by cranial meninges, which include an outer layer called dura mater, a very thin middle layer called arachnoid, and an inner layer (in contact with the brain tissue) called the pia mater. The brain can be separated into three main parts:

• Forebrain
• Midbrain
• Hindbrain

The forebrain comprises the cerebrum, thalamus, and hypothalamus. The midbrain sits between the thalamus/hypothalamus of the forebrain and pons of the hindbrain. The hindbrain involves the pons, cerebellum, and medulla.
2. Eye: The adult human eyeball is almost a round structure. Its wall is made up of three layers. The outer layer consists of thick connective tissue and is named the sclera. The front part of this is known as the cornea. The middle layer, the choroid, has many blood vessels and appears somewhat blue. The choroid layer is thin over the back two-thirds of the eyeball but thickens in the front part to create the ciliary body. The ciliary body itself moves forward to form a colored, opaque structure called the iris, which is the eye's visible colored section. The eyeball holds a clear crystalline lens, held in position by ligaments connected to the ciliary body. In front of the lens, the opening surrounded by the iris is termed the pupil. The pupil's size is controlled by the iris's muscle fibers. The inner layer is the retina, and it comprises three layers of cells, from inner to outer: ganglion cells, bipolar cells, and photoreceptor cells. There exist two kinds of photoreceptor cells: rods and cones. These cells include light-sensitive proteins called photopigments. Daytime (photopic) vision and color perception are roles of cones, while dim light (scotopic) vision is the role of rods. They possess a reddish-purple protein named rhodopsin or visual purple, which has a derivative of vitamin A. In the human eye, there are three kinds of cones, each with its unique photopigments that react to red, green, and blue light. The optic nerves exit the eye, and retinal blood vessels enter at a point medial to and slightly above the eyeball's posterior pole. Photoreceptor cells are not found in that area, so it's named the blind spot. At the eye's posterior pole, to the side of the blind spot, there is a yellowish pigmented area called macula lutea with a central pit called the fovea. The region between the cornea and the lens is called an aqueous chamber and holds a thin, watery fluid known as aqueous humor. The area between the lens and the retina is called the vitreous chamber and is filled with a clear gel called the vitreous humor.
3. Ear: The ear can be split into three main parts: the outer ear, the middle ear, and the inner ear. The outer ear includes the pinna and the external auditory meatus. The pinna gathers air vibrations that create sound. The external auditory meatus goes inward and reaches the tympanic membrane (eardrum). The middle ear holds three small bones called the malleus, incus, and stapes, which are linked together like a chain. The malleus connects to the tympanic membrane, and the stapes connects to the cochlea's oval window. A Eustachian tube joins the middle ear cavity with the pharynx. This tube assists in balancing pressures on both sides of the eardrum. The fluid-filled inner ear, known as the labyrinth, has two sections: the bony and membranous labyrinths. The bony labyrinth is a set of passages. Inside these passages is the membranous labyrinth, which is surrounded by a fluid called perilymph. The coiled part of the labyrinth is termed the cochlea. The inner ear also features a complex system called the vestibular apparatus, located above the cochlea. The vestibular apparatus is made of three semicircular canals and the otolith organ, which includes the saccule and utricle. Each semicircular canal sits in a distinct plane, at right angles to the others. The saccule and utricle each have a projecting ridge called a macula.
In simple words: The brain is protected by the skull and layers called meninges, divided into three main parts. The eye is a spherical structure with three layers: sclera, choroid (with ciliary body and iris), and retina (with rods and cones), containing fluids and a lens. The ear has outer, middle, and inner sections; the outer collects sound, the middle transmits it via ossicles, and the inner (labyrinth) processes it for hearing and balance.

Exam Tip: When describing biological structures, always mention protective features, main divisions, and the key components with their functions. Use clear, descriptive language for each part.

 

Question 2. Compare the following.
1. Central neural system (CNS) and Peripheral neural system
2. Resting potential and action potential
3. Choroid and retina
Answer:
1. The human neural system is separated into two parts: the central neural system (CNS) and the peripheral neural system (PNS). The CNS involves the brain and spinal cord, serving as the center for processing information and control. The PNS includes all the body's nerves linked with the CNS (brain and spinal cord). The PNS nerve fibers are of two kinds: afferent fibers and efferent fibers. Afferent nerve fibers send impulses from tissues/organs to the CNS, while efferent fibers send controlling impulses from the CNS to the specific peripheral tissues/organs. The PNS is split into two sections: the somatic neural system and the autonomic neural system. The somatic neural system sends impulses from the CNS to the involuntary organs and the body's smooth muscles. The autonomic neural system is further categorized into the sympathetic neural system and the parasympathetic neural system.
2. The electrical potential variation across a plasma membrane that is at rest is known as the 'resting potential'. The electrical potential variation across the plasma membrane at a particular spot A is called the 'action potential', which is actually referred to as a nerve impulse.
3. The middle layer, the choroid, holds many blood vessels and has a bluish shade. The choroid layer is thin across the back two-thirds of the eyeball, but it gets thicker in the front part to form the ciliary body. This ciliary body then extends forward from a colored, opaque structure called the iris, which is the eye's visible colored section. The inner layer is the retina, and it includes three cell layers, from inner to outer: ganglion cells, bipolar cells, and photoreceptor cells. There are two kinds of photoreceptor cells: rods and cones. These cells possess light-sensitive proteins known as photopigments. Daytime (photopic) vision and color perception are roles of cones, while dim light (scotopic) vision is the role of rods.
In simple words: The CNS (brain and spinal cord) processes information, while the PNS (all other nerves) carries signals to and from the CNS, splitting into somatic and autonomic systems. Resting potential is the electrical state of a nerve at rest, while action potential is the rapid change in electrical charge when it fires. The choroid is the eye's middle, vascular layer, forming the ciliary body and iris, whereas the retina is the inner, light-sensitive layer with photoreceptor cells (rods and cones) for vision.

Exam Tip: When comparing, always highlight key differences in structure, function, and location for each pair. For potential differences, emphasize the "resting" vs. "active" state and what causes the change.

 

Question 3. Explain the following processes:
1. The polarisation of the membrane of a nerve fiber
2. Depolarisation of the membrane of a nerve fiber
3. Conduction of a nerve impulse along with a nerve fiber
4. Transmission of a nerve impulse across a chemical synapse.
Answer:
1. Neurons are excitable cells because their membranes are in a polarized condition. Various types of ion channels exist on the neural membrane. These channels permit different ions to pass selectively. When a neuron is not carrying an impulse, or is at rest, the axonal membrane is more permeable to potassium ions \(K^+\) and chloride ions \(Cl^-\), but almost impermeable to sodium ions \(Na^+\). Similarly, the membrane does not allow negatively charged proteins inside the axoplasm to pass. As a result, the axoplasm within the axon has a high concentration of \(K^+\) and negatively charged proteins, and a low concentration of \(Na^+\). Conversely, the fluid outside the axon contains a low concentration of \(K^+\), a high concentration of \(Na^+\), and chloride ions \(Cl^-\), creating a concentration difference. These ion gradients across the resting membrane are kept up by the active movement of ions via the sodium-potassium pump, which moves 3 \(Na^+\) out and 2 \(K^+\) into the cell. Consequently, the outer part of the axonal membrane gains a positive charge, while its inner part becomes negatively charged, making it polarized. The electrical potential difference across the resting plasma membrane is termed the 'resting potential'.
2. When a stimulus is applied to a spot on the polarized membrane, the membrane at spot A becomes easily permeable to \(Na^+\). This causes a swift inflow of \(Na^+\), followed by a reversal of the polarity at that location. This means the outer surface of the membrane becomes negatively charged, and the inner side becomes positively charged. The polarity of the membrane at spot A is thus changed, leading to depolarization. The electrical potential difference across the plasma membrane at spot A is termed the 'action potential', which is actually called a nerve impulse. At nearby spots further along, the axon membrane (e.g., spot B) has a positive charge on the outer surface and a negative charge on its inner surface. As a consequence, a current moves on the inner surface from spot A to spot B. On the outer surface, current moves from spot B to spot A to finish the circuit of current flow. Thus, the polarity at the spot is reversed, and an action potential begins at spot B.
3. The processes involved in creating a nerve impulse and how it travels along an axon. When a stimulus is applied to a spot on the polarized membrane, the membrane at spot A becomes very permeable to \(Na^+\). This causes a quick inflow of \(Na^+\), which then reverses the polarity at that location. This means the outer surface of the membrane becomes negatively charged, and the inner side becomes positively charged. This depolarization at site A creates a localized electric current. This current then flows from the depolarized region (site A) to the adjacent resting region (site B) on the inner surface of the membrane, and from site B back to site A on the outer surface, forming a circuit. This movement of current causes the adjacent region (site B) to depolarize as well, becoming permeable to \(Na^+\). This process repeats, with depolarization spreading sequentially along the axon, like a wave. This continuous transmission of the action potential along the nerve fiber constitutes the nerve impulse conduction. In myelinated nerve fibers, the impulse 'jumps' from one Node of Ranvier to the next, a faster process called saltatory conduction, while in unmyelinated fibers, it's a continuous wave.
4. A nerve impulse moves from one neuron to another through junctions called synapses. A synapse is formed by the membranes of a pre-synaptic neuron and a post-synaptic neuron, which might or might not be separated by a gap known as the synaptic cleft. There are two kinds of synapses: electrical synapses and chemical synapses. In electrical synapses, the membranes of the pre- and post-synaptic neurons are very close together. Electrical current can flow directly from one neuron to the other across these synapses. This transmission across electrical synapses is quite similar to impulse conduction along a single axon and is usually faster. However, electrical synapses are uncommon in our body. In a chemical synapse, the membranes of the pre- and post-synaptic neurons are separated by a fluid-filled space called the synaptic cleft. Chemical messengers, known as neurotransmitters, are involved in transmitting impulses at these chemical synapses.
In simple words: Polarization is when a nerve membrane is at rest, with more positive charge outside and negative inside, maintained by ion pumps. Depolarization happens when a stimulus causes sodium ions to rush in, reversing the charges and creating an action potential. Conduction is how this action potential travels along the nerve fiber by sequential depolarization. Synaptic transmission is when a nerve impulse crosses from one neuron to another, either electrically (fast but rare) or chemically, using neurotransmitters across a synaptic cleft.

Exam Tip: When explaining complex processes like nerve impulse transmission, break them down into logical steps. Clearly define each stage (polarization, depolarization, repolarization, conduction, transmission) and mention the key ions and structures involved.

 

Question 4. Draw labeled diagrams of the following
1. Neuron
2. Brain
3. Eye
Answer:
(1)

(2)

(3)

In simple words: These diagrams show the detailed structures of a neuron, the human brain, and the human eye, each with various labeled parts for better understanding.

Exam Tip: For diagram-based questions, practice drawing and labeling the main parts accurately. Focus on proportional representation and clear labeling for all significant structures.

 

Question 5. Write short notes on the following:
1. Neural coordination
2. Forebrain
3. Midbrain
4. Hindbrain
5. Retina
6. Ear ossicles
7. Cochlea
8. Organ of Corti
9. Synapse
Answer:
1. Neural coordination: Coordination is the process where two or more organs interact and support each other's roles. For instance, when we do physical exercises, the need for energy rises to maintain greater muscle action. The oxygen supply also goes up. This increased oxygen supply makes it necessary for respiration rate, heartbeat, and blood flow through vessels to increase. When physical exercise stops, the activities of nerves, lungs, heart, and kidneys slowly go back to their regular states. So, muscles, lungs, heart, blood vessels, kidneys, and other organs work together during physical exercises. In our bodies, the neural system and the endocrine system together manage and combine all organ activities so they work in a balanced way. The neural system offers a precise network of connections for fast coordination. The endocrine system provides chemical balance through hormones.
2. Forebrain: The forebrain includes the cerebrum, thalamus, and hypothalamus. The cerebrum makes up the largest portion of the human brain. A deep groove splits the cerebrum lengthwise into two halves, known as the left and right cerebral hemispheres. These hemispheres are joined by a bundle of nerve fibers called the corpus callosum. The cell layer covering the cerebral hemisphere is called the cerebral cortex and is arranged in noticeable folds. The cerebral cortex has motor areas, sensory areas, and large parts that are not clearly sensory or motor. These areas, called association areas, handle complex tasks like combining sensory information, memory, and communication. The tract fibers are covered with the myelin sheath, forming the inner part of the cerebral hemisphere, which is called the white matter. The cerebrum surrounds a structure named the thalamus, a key center for sensory and motor signals. The hypothalamus has several centers that manage body temperature, eating, and drinking. It also contains various groups of neurosecretory cells that release hormones called hypothalamic hormones.
3. Midbrain: The midbrain is found between the forebrain's thalamus/hypothalamus and the hindbrain's pons. A channel called the cerebral aqueduct runs through the midbrain. The upper part of the midbrain mostly has four round bumps (lobes) named corpora. Together, the midbrain and hindbrain form the brain stem.
4. Hindbrain: The hindbrain includes the pons, cerebellum, and medulla. The pons contains bundles of fibers that link different parts of the brain. The cerebellum has a very folded surface, which offers more room for many additional neurons. The brain's medulla connects to the spinal cord. The medulla has centers that manage breathing, heart and blood vessel reflexes, and stomach secretions.
5. Retina: The innermost layer is the retina, and it holds three cell layers, from inside to outside: ganglion cells, bipolar cells, and photoreceptor cells. There are two kinds of photoreceptor cells: rods and cones. These cells have light-sensitive parts called photopigments. Daytime (photopic) vision and seeing colors are roles of cones, while dim light (scotopic) vision is the role of rods. Rods contain a reddish-purple protein named rhodopsin or visual purple, which includes a form of vitamin A. In the human eye, there are three types of cones, each with its unique light-sensitive pigments that react to red, green, and blue light. The feelings of different colors happen because of various mixes of these cones and their photopigments. When these cones are all activated equally, we perceive white light.
6. Ear ossicles: The ear ossicles improve how well sound waves travel to the inner ear. A Eustachian tube links the middle ear space with the pharynx. This tube assists in balancing the pressures on both sides of the eardrum.
7. Cochlea: The bony labyrinth is a set of passages. Inside these passages is the membranous labyrinth, which is covered by a fluid called perilymph. The membranous labyrinth itself is filled with a fluid called endolymph. The coiled part of the labyrinth divides into an upper scala vestibuli and a lower scala tympani. The space inside the cochlea, known as the scala media, is filled with endolymph. At the cochlea's bottom, the scala vestibuli finishes at the oval window, while the scala tympani ends at the round window, which opens to the middle ear.
8. Organ of Corti: The organ of Corti is a structure found on the basilar membrane, containing hair cells that act as receptors. These hair cells are arranged in rows on the inner side of the organ of Corti. The base of the hair cells touches the afferent nerve fibers closely. Many small projections called stereocilia extend from the top part of each hair cell. Above these rows of hair cells is a thin, flexible membrane called the tectorial membrane.
9. Synapse: A nerve impulse moves from one neuron to another through connections known as synapses. A synapse is created by the membranes of a pre-synaptic neuron and a post-synaptic neuron, which might or might not have a space between them called the synaptic cleft. There are two kinds of synapses: electrical and chemical.
In simple words: Neural coordination involves organs working together quickly, facilitated by the nervous and endocrine systems. The forebrain includes the cerebrum for complex thought, thalamus for relay, and hypothalamus for basic needs. The midbrain connects brain parts and has visual/auditory centers. The hindbrain contains the pons, cerebellum (for balance), and medulla (for vital functions). The retina is the eye's light-sensing layer with rods (for dim light) and cones (for color). Ear ossicles are tiny bones in the middle ear that amplify sound. The cochlea is the inner ear's coiled part, vital for hearing. The Organ of Corti in the cochlea contains hair cells that convert sound vibrations into nerve signals. A synapse is the junction where nerve impulses pass between neurons.

Exam Tip: For short notes, focus on providing a concise definition, key components, and primary functions for each topic. Use bullet points or short sentences for clarity and easy readability.

 

Question 6. Give a brief account of:
1. Mechanism of synaptic transmission
2. Mechanism of vision
3. Mechanism of hearing
Answer:
1. Mechanism of synaptic transmission: A nerve impulse moves from one neuron to another through junctions called synapses. A synapse is formed by the membranes of a pre-synaptic neuron and a post-synaptic neuron, which might or might not be separated by a gap known as the synaptic cleft. There are two kinds of synapses: electrical synapses and chemical synapses. In electrical synapses, the membranes of the pre- and post-synaptic neurons are very close together. Electrical current can flow directly from one neuron to the other across these synapses. This transmission across electrical synapses is quite similar to impulse conduction along a single axon and is usually faster. However, electrical synapses are uncommon in our body. In a chemical synapse, the membranes of the pre- and post-synaptic neurons are separated by a fluid-filled space called the synaptic cleft. Chemical messengers, known as neurotransmitters, are involved in transmitting impulses at these chemical synapses.
2. Mechanism of vision: Light rays within the visible spectrum focus on the retina after passing through the cornea and the lens, creating electrical signals (impulses) in rods and cones. The light-sensitive compounds (photopigments) in human eyes are made of opsin (a protein) and retinal (a form of vitamin A). Light causes the retinal to separate from opsin, which changes opsin's structure. This change alters membrane permeability. Consequently, electrical potential differences are created in the photoreceptor cells. This produces a signal that then produces action potentials in the ganglion cells, moving through the bipolar cells. These action potentials (impulses) are sent by optic nerves to the brain's visual cortex, where the neural impulses are processed, and the image formed on the retina is identified based on previous memories and experiences.
3. Mechanism of hearing: The outer ear takes in sound waves and guides them to the eardrum. The eardrum shakes in reaction to these sound waves, and these movements are sent through the ear ossicles (malleus, incus, and stapes) to the oval window. The movements then pass through the oval window to the cochlea's fluid, where they create waves in the lymph. These waves in the lymph cause a ripple in the basilar membrane. These motions of the basilar membrane cause the hair cells to bend, pushing them against the tectorial membrane. Consequently, nerve impulses are created in the linked afferent neurons. These impulses are sent by afferent fibers through auditory nerves to the brain's auditory cortex, where the impulses are processed, and the sound is identified.
In simple words: Synaptic transmission is how nerve signals move between neurons via electrical or chemical synapses, with chemical synapses using neurotransmitters across a gap. Vision works by light focusing on the retina, causing photopigments to change, which generates electrical signals that travel to the brain for image recognition. Hearing involves sound waves vibrating the eardrum and ossicles, creating fluid waves in the cochlea that bend hair cells, generating nerve impulses sent to the brain for sound perception.

Exam Tip: When explaining biological mechanisms, start with the input (stimulus) and trace its path through the relevant structures, detailing the changes and transformations that occur at each step until the final output (sensation/response) is reached.

 

Question 7. Answer briefly:
1. How do you perceive the color of an object?
2. Which part of our body helps us in maintaining the body balance?
3. How does the eye regulate the amount of light that falls on the retina?
Answer:
1. In the human eye, there are three kinds of cones, each with its specific light-sensitive pigments that react to red, green, and blue light. The feelings of different colors are created by various mixes of these cones and their photopigments. When these cones are all activated at the same level, we experience white light.
2. The crista and macula are special receptors found in the vestibular apparatus. They are in charge of keeping the body balanced and maintaining posture.
3. The size of the pupil is controlled by the iris's muscle fibers. Photoreceptors, including rods and cones, help manage the quantity of light that reaches the retina.
In simple words: We see colors because our eyes have three types of cones that detect red, green, and blue light, and different combinations create various color perceptions. Our body balance is maintained by special receptors called crista and macula, located in the vestibular apparatus. The eye controls the light hitting the retina using the iris, which adjusts the pupil's size, and photoreceptors also play a role.

Exam Tip: For brief answers, provide direct and concise information. Identify the key biological structures and their specific roles without unnecessary details, ensuring accuracy and clarity.

 

Question 8. Explain the following:
1. Role of \(Na^+\) in the generation of the action potential.
2. Mechanism of generation of light-induced impulse in the retina.
3. The mechanism through which a sound produces a nerve impulse in the inner ear.
Answer:
1. This causes a fast inflow of \(Na^+\), which then reverses the polarity at this spot. This means the membrane's outer surface becomes negatively charged, and its inner side becomes positively charged.
2. Light causes the retinal to separate from opsin, which changes the opsin's structure. This leads to alterations in membrane permeability. Consequently, electrical potential differences are created in the photoreceptor cells. This produces a signal that then generates action potentials in the ganglion cells via the bipolar cells. These action potentials (impulses) are sent by the optic nerves to the brain's visual processing area, where the neural impulses are examined, and the image created on the retina is identified based on prior memory and experience.
3. The vibrations travel through the oval window into the cochlea's fluid, where they create waves in the lymph. These wave movements in the basilar membrane cause the hair cells to bend, pushing them against the tectorial membrane. Consequently, nerve impulses are generated in the linked afferent neurons. These impulses are sent by afferent fibers through auditory nerves to the brain's auditory cortex, where the impulses are processed, and the sound is identified.
In simple words: Sodium ions are crucial for action potential generation; their rapid entry into the nerve cell reverses the membrane's electrical charge. Light triggers vision by changing retinal structure in the eye's photoreceptors, which creates electrical signals sent to the brain. Sound makes us hear when vibrations in the inner ear's cochlea move hair cells, generating nerve impulses that the brain then interprets as sound.

Exam Tip: When explaining biological processes, ensure you highlight the cause-and-effect relationships clearly. For ionic roles, specify whether ions move in or out and how this affects membrane potential. For sensory mechanisms, trace the path from stimulus reception to brain interpretation.

 

Question 9. Differentiate between:
1. Myelinated and non-myelinated axons
2. Dendrites and axons
3. Rods and cones
4. Thalamus and Hypothalamus
5. Cerebrum and Cerebellum
Answer:
1. Myelinated and non-myelinated axons:
The myelinated nerve fibers are covered by Schwann cells, which create a myelin sheath around the axon. These fibers are present in spinal and cranial nerves. Unmyelinated nerve fibers are also surrounded by a Schwann cell, but this cell does not form a myelin sheath around the axon. These are often found in the autonomic and somatic neural systems.
2. Dendrites and axons:
Short fibers that repeatedly branch and extend from the cell body also hold Nissl's granules and are known as dendrites. These fibers send impulses towards the cell body. The axon is a long fiber whose far end branches out. Each branch finishes as a bulb-like shape called a synaptic knob, which contains synaptic vesicles filled with chemical neurotransmitters. Axons send nerve impulses away from the cell body to a synapse or to a neuromuscular junction.
3. Rods and cones:
Daytime vision and color perception are roles of cones. Dim light vision, or twilight vision, is the role of rods. Rods contain a reddish-purple protein named rhodopsin or visual purple, which includes a form of Vitamin A.
4. Thalamus and Hypothalamus:
The cerebrum surrounds a structure named the thalamus, a key center for sensory and motor signals. Another vital part of the brain, the hypothalamus, sits at the base of the thalamus. The hypothalamus has various centers that manage body temperature, eating, and drinking. It also includes several groups of neurosecretory cells that release hormones known as hypothalamic hormones.
5. Cerebrum and Cerebellum:
The cerebrum makes up the largest section of the human brain. A deep groove separates the cerebrum lengthwise into two halves, known as the left and right cerebral hemispheres. The cerebellum has a very folded surface, which helps provide extra space for many more neurons.
In simple words: Myelinated axons have a fatty covering for faster impulse speed, unlike non-myelinated ones. Dendrites receive signals towards the cell body, while axons transmit signals away from it. Rods detect dim light, and cones perceive color. The thalamus relays sensory signals to the brain, while the hypothalamus controls basic bodily functions like hunger and temperature. The cerebrum is the large, upper part of the brain responsible for higher thought, and the cerebellum is at the back, managing coordination and balance.

Exam Tip: For differentiation questions, it is effective to create a table in your mind (or on scratch paper) comparing the two items side-by-side based on criteria like structure, function, location, and key characteristics. This ensures all relevant distinctions are covered.

 

Question 10. Answer the following:
(1) Which part of the ear determines the pitch of a sound?
(2) Which part of the human brain is the most developed?
(3) Which part of our central neural system acts as a master clock?
Answer:
(1) Inner ear
(2) Forebrain (cerebrum)
(3) Somatic neural system.
In simple words: The inner ear handles sound pitch. The forebrain is the most advanced part of our brain. The somatic neural system works like the body's main timekeeper.

Exam Tip: For direct identification questions, recall the specific anatomical structures responsible for each function. Precision in terminology is vital.

 

Question 11. The region of the vertebrate eye, where the optic nerve passes out of the retina is called the
(a) Fovea
(b) Iris
(c) Blind spot
(d) Optic charisma
Answer: (c) Blind spot
In simple words: The area where the optic nerve leaves the retina and where no photoreceptor cells are found is known as the blind spot. This means there is no vision in that specific region.

Exam Tip: Remember that the blind spot is a physiological scotoma on the retina where the optic nerve fibers exit the back of the eye, containing no light-sensitive cells.

 

Question 12. Distinguish between:
(1) Afferent neurons and Efferent neurons
(2) Impulse conduction in a myelinated nerve fiber and Unmyelinated nerve fiber.
(3) Aqueous humor and vitreous humor
(4) Blind spot and yellow spot
(5) Cranial nerves and spinal nerves
Answer:
(1) Differences between afferent neurons and efferent neurons:
Afferent neurons: The afferent nerve fibers convey signals from tissues/organs to the Central Nervous System (CNS).
Efferent neurons: The efferent fibers send controlling signals from the CNS to the relevant peripheral tissues/organs.

(2) Differences between impulse conduction in a myelinated nerve fiber and unmyelinated nerve fiber:
Myelinated nerve fiber: These nerve fibers are covered with Schwann cells, which create a myelin sheath around the axon.
Unmyelinated nerve fiber: These nerve fibers are wrapped by a Schwann cell that does not create a myelin sheath around the axon.

(3) Differences between the aqueous humor and vitreous humor:
Aqueous humor: The space between the cornea and the lens is known as the aqueous chamber and holds a thin watery fluid called aqueous humor.
Vitreous humor: The space between the lens and the retina is called the vitreous chamber and is filled with a clear gel called the vitreous humor.

(4) Differences between the blind spot and yellow spot:
Blindspot: Photoreceptor cells are not present in that specific area, which is why it is called the blind spot.
Yellow spot: At the posterior pole of the eye, lateral to the blind spot, there is a yellowish pigmented spot named macula lutea with a central pit called the fovea.

(5) Differences between cranial nerves and spinal nerves:
Cranial nerves: Humans have 12 pairs of cranial nerves that either originate from or terminate in different parts of the brain.
Spinal nerves: Humans have 31 pairs of spinal nerves. A pair of spinal nerves originates from each segment of the spinal cord.
In simple words: This answer provides key distinctions between various pairs of biological structures, covering how different types of neurons carry signals, the role of myelin, the fluids within the eye, specific retinal areas, and the two major categories of nerves.

Exam Tip: When distinguishing between biological terms, focus on clear, concise definitions, structural differences, and functional variations. Organizing your answer with sub-headings for each pair helps clarity.