NCERT Solutions for Class 11 Biology Chapter 18 Neural Control and Coordination

NCERT Solutions for Class 11 Chapter 18 Neural Control and Coordination: The Class 11 chapter on neural control and coordination is important for students approaching the board exams. Our meticulously expert-designed NCERT Class 11 Biology Chapter 18 Solutions for the academic year 2024-25 help students explain the concepts for scoring good marks in examinations. The solutions are presented in very simple language for ease of understanding.

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Class	Class 11 Biology
Subject	NCERT Solutions Biology
Chapter	Chapter 18 Neural Control and Coordination
Academic Year	2024 – 25
Content-Type	Text and Images
Medium	English

NCERT Solutions for Class 11 Chapter 18 – Neural Control and Coordination Class 11

Q1:  Briefly Describe the Structure of the Brain. 

Answer:

Structure of the Brain: 

The brain serves as the body’s command and control center. It is shielded by the skull and has three meninges covering it known as Cranial meninges-The dura mater is a fibrous and thick membrane on the outside, the arachnoid is a fragile and thin membrane in the middle, and the pia mater is an extension of the brain tissue on the inside. This layer has a high blood supply and is quite vascular. Forebrain, midbrain, and hindbrain are the three primary divisions of the brain.

1. Forebrain: It is divided into three sections, which are as follows:
   1. Olfactory lobes: These are a pair of very tiny, solid club-shaped entities that are far apart from one another
   2. Cerebrum – It is the largest and most complex. The cerebral hemispheres on the right and left of the brain are separated by a deep gap and are joined by the corpus callosum, a network of myelinated fibers.Diencephalon
   3. It encloses the third ventricle, which is a slit-like chamber. The thick right and left sides of this cavity are referred to as the thalami, its thin floor as the hypothalamus, and its thin ceiling as the epithalamus.
2. Midbrain: It is placed between the thalamus/hypothalamus of the forebrain and the pons of the hindbrain. Its upper surface has two pairs of spherical extensions called corpora quadrigemina and two bundles of fibers termed crura cerebri.
3.  Hindbrain:  It is made up of: 
   1. Cerebellum: The cerebellum is the second largest portion of the human brain. It is made up of two lateral cerebellar hemispheres and a central worm-shaped component called the vermis. The cerebellum has grey matter on the outside, which is composed of three layers of cells and fibers. It also has Golgi cells, basket cells, and granule cells.
   2. Pons Varolii: The pons Varolii is an oval mass that lies above the medulla oblongata. It is mostly made up of nerve fibers that connect various areas of the brain.
   3. Medulla oblongata: This structure extends from the pons Varolii above and connects to the spinal cord below. The midbrain, pons Varolii and medulla oblongata are referred to as the brain stem.

For More Information Read: Human Brain

Q 2: Compare the following:

• (a) Central neural system (CNS) and Peripheral neural system (PNS)
• (b) Resting potential and action potential

Answer:

Comparision between Central neural system (CNS) and Peripheral neural system (PNS) is given below:

Aspect	Central Nervous System (CNS)	Peripheral Nervous System (PNS)
Location	Brain and Spinal Cord	Nerves outside the brain and spinal cord
Function	Processes and integrates information, initiates and coordinates responses	Transmits sensory information to the CNS and carries motor commands from the CNS to muscles and glands
Components	Brain and Spinal Cord	Cranial nerves and spinal nerves
Protection	Protected by bones (skull and vertebrae), cerebrospinal fluid, and meninges	Lacks bony protection; some protection provided by connective tissue coverings
Types of Cells	Neurons and Glial Cells	Mostly neurons
Control of Functions	Controls voluntary and involuntary actions, thoughts, and emotions	Primarily involved in involuntary actions and reflexes
Neurotransmitter Activity	Synaptic transmission	Synaptic transmission
Response Time	Generally slower response time compared to the PNS	Generally faster response time compared to the CNS

Comparision between Resting potential and action potential is given below:

Aspect	Resting Potential	Action Potential
Definition	Stable charge of a neuron at rest	Brief reversal of membrane potential
Membrane Potential	Around -70 mV	Rapid depolarization to around +40 mV
Ion Movement	Maintained by ion gradients	Rapid influx of Na+ and efflux of K+
Channels Involved	Mostly leak channels and pumps	Voltage-gated Na+ and K+ channels
Stimulus	Spontaneous occurrence	Threshold stimulus required
Duration	Persistent	Short-lived
Direction of Ion Movement	Minimal movement	Rapid movement
Role in Neuronal Signaling	Establishes baseline	Mediates electrical signaling

Q3: Explain the following processes:

• (a) Polarisation of the membrane of a nerve fiber.
• (b) Depolarisation of the membrane of a nerve fiber.
• (c) Transmission of a nerve impulse across a chemical synapse.

Solution:

• (a) Polarisation of a nerve fiber membrane:

When a nerve fiber is at rest, it is considered to be in a polarised state. The nerve fiber’s membrane has a resting potential when it is polarised. The following steps occur during the polarization of a nerve fiber’s membrane:

• When a depolarised area of a nerve fiber first begins to become polarised, there are more K + ions outside the nerve fiber and a considerable amount of Na + ions in the axon membrane.
• As the membrane region gets polarised, it becomes more permeable to K + ions and impenetrable to Na + ions and negatively charged proteins.
• A sodium-potassium pump sends 3 Na + ions outside the axon and 2 K + ions into the axon via active transport.
• Because of the flow of sodium and potassium ions, the inner side of the membrane becomes electronegative (negatively charged), while the outer side becomes electropositive (positively charged). This causes the nerve fiber to become polarised.

• (b) Depolarisation of the membrane of a nerve fiber.

When a nerve fiber is activated, it is said to be in a depolarised state. The membrane of the nerve fiber undergoes an action potential when it is depolarized.

During the process of depolarisation of a nerve fiber’s membrane, the following phases occur:

• The axon has a higher concentration of K + ions in a polarised condition, while the concentration of Na + ions is higher outside the axon.
• When a nerve fiber is stimulated, the permeability of the membrane for Na + ions and K + ions reverses.
• The membrane becomes highly permeable to Na + ions.
• There is a fast influx of Na + ions into the axon.
• As a result, the inside of the membrane becomes positively charged, while the exterior of the membrane gets negatively charged.
• Finally, the nerve fiber’s membrane depolarizes and it experiences an action potential.

(c) Transmission of a nerve impulse across a chemical synapse.

• The membranes of the pre-synaptic and post-synaptic neurons combine to form a synapse.
• A gap known as the synaptic cleft may or may not divide two synapses.
• The synaptic cleft separates the pre-and post-synaptic neurons at a chemical synapse.
• The calcium ions in the synaptic cleft enter the synaptic knobs at the axon terminals of the pre-synaptic neuron when an impulse reaches the axon terminal.
• The synaptic vesicles in the pre-synaptic neuron’s synaptic knobs migrate in its direction and fuse with the plasma membrane.
• Acetylcholine, a neurotransmitter, is released by the vesicles in the synaptic cleft. (Empty synaptic vesicles are filled when they return to the cytoplasm of the pre-synaptic neuron.)
• The protein receptors found on the plasma membrane of post-synaptic neurons are where the molecules of acetylcholine bind.
• As a result of this interaction, potassium ions exit the post-synaptic membrane and sodium ions enter the post-synaptic neuron.
• This causes the membrane of the post-synaptic neuron to create an action potential, which then transmits the impulse to the post-synaptic neuron.

Q4: Draw labeled diagrams of the following:

• (a) Neuron 
• (b) Brain

Answer:

(a) The labelled diagram of Neuron is given below:

(b) Brain

Q5: Write short notes on the following:

• (a) Neural coordination
• (b) Forebrain
• (c) Midbrain
• (d) Hindbrain
• (e) Synapse

Answer:

(a) Neural Coordination

Neurons are highly specialized cells that provide neural synchronization. The neurological system functions by nerve impulses and is made up of a network of point-to-point connections between the neurons and the organs. The input and the response—receptors, and effectors—are always coordinated by the neural system. Neural coordination carries out and manages every bodily function. The skin, among other organs, receives the stimulation, and a reaction is produced and conveyed to the muscles or glands. The brain system constantly stores the prior stimulus in memory. Running, walking, writing, and talking are examples of voluntary actions that benefit from neural coordination’s control and symmetry.

(b) Forebrain

The cerebrum, thalamus, and hypothalamus are three components of the cortex.

• Cerebrum: It is the major component of the brain. A fissure in the cerebrum divides the left and right cerebral hemispheres. The corpus callosum connects the hemispheres of the brain. The cerebral cortex is a layer of visible folds made up of cells that cover the cerebral hemisphere. Due to its greyish coloring, it is referred to as grey matter. Many areas of the cerebral cortex don’t appear to have any sensory or motor functions. Association areas carry out a number of complex tasks, such as memory, communication, and intercessory associations. The fibers of the tract are shielded by the myelin coating in the center of the cerebral hemisphere. Because of its impenetrable aspect, white matter is so named. The association areas are in charge of memory, communication, and intercessional associations.
• Thalamus: The Thalamus is a section of the cerebrum that wraps around the center of the forebrain. At this center, sensory and motor signaling are synchronized.
• Hypothalamus: The hypothalamus contains a number of structures that control body temperature, hunger, and thirst. It is linked to the pituitary gland and regulates both growth and sexual behaviors.

(c) Midbrain

It is positioned between the pons of the hindbrain and the thalamus/hypothalamus of the forebrain The midbrain is connected to the brain by a passageway known as the cerebral aqueduct. The corpora quadrigemina, four circular lobes that make up the majority of the dorsal section of the midbrain, are present. The brain stem is made up of the hindbrain and midbrain.

(d) Hindbrain

Pons, cerebellum, and medulla make up the hindbrain. Pons is made up of fiber lines that link various brain areas. In order to accommodate more neurons, the surface of the cerebellum is extremely twisted. The spinal cord and the brain’s medulla are interconnected. Respiratory, cardiovascular, and gastric secretion control centers are located in the medulla.

(e) Synapse

The membranes of the pre-synaptic and post-synaptic neurons combine to form a synapse. A gap known as the synaptic cleft may or may not divide two synapses. Electrical and chemical synapses are two different types of synapses.

Q6: Give a brief account of the Mechanism of Synaptic Transmission.

Answer:

A synapse is the junction of two neurons. It is separated by a cleft and exists between the dendrite of one neuron and the axon terminal of the following neuron. There are two ways synaptic transmission happens.

1. Chemical Transmission: When a nerve impulse reaches the endplate of an axon, acetylcholine, a neurotransmitter, is released across the synaptic cleft. This substance is created in the cell body of the neuron and sent to the axon terminal. Over the cleft, acetylcholine diffuses and binds to receptors on the membrane of the following cell. Depolarization of the membrane and the beginning of an action potential follow from this.
2. Electrical Transmission: In this type of transmission, an electric current is generated in the neuron. The action potential that is brought on by this electric current results in the transmission of nerve impulses across the nerve fiber. This form of nerve conduction is more rapid than the chemical process.

Q7: Explain the Role of Na⁺ in the generation of the action potential.

Answer:

Due to the electrochemical gradient, sodium ions diffuse into the intracellular fluid from the outside. The membrane changes from being positively charged on the inside to being negatively charged outside as the potassium ions exit. The membrane is said to be depolarized as a result of the action potential, a quick shift in the membrane potential.

Read Also: Membrane potential

Q8: Differentiate between:

• (a) Myelinated and non-myelinated axons
• (b) Dendrites and axons
• (c) Thalamus and Hypothalamus
• (d) Cerebrum and Cerebellum

Answer:

(a) Myelinated and non-myelinated axons vs Non-myelinated Axons are:

Aspect	Myelinated Axons	Non-myelinated Axons
Structure	Covered with myelin sheath, speeding up signal transmission	Lack myelin sheath, slowing down signal transmission
Conduction Speed	Faster due to “jumping” action potentials between nodes	Slower as action potentials propagate along the entire axon
Energy Efficiency	More efficient with less ion leakage through myelin	Less efficient with more ion leakage
Protection	Better insulation and protection against damage	More vulnerable to damage and signal loss
Examples	Found in central and peripheral nervous system	Found in sensory neurons, especially for pain perception

• (b) Dendrites and axons vs axons are give below:

Aspect	Dendrites	Axons
Function	Receive incoming signals from other neurons	Transmit signals away from the cell body to other neurons or cells
Structure	Branched extensions from the cell body	Single, elongated projection from the cell body
Size	Typically shorter and more numerous	Longer, with variable lengths
Direction of Signal Flow	Signal reception towards the cell body	Signal transmission away from the cell body
Presence of Myelin	Usually non-myelinated	Can be myelinated or non-myelinated
Synaptic Terminals	Rarely have synaptic terminals	Have synaptic terminals at the axon terminals for signal transmission
Role in Neuronal Signaling	Integrates and processes incoming signals	Transmits signals to other neurons or effector cells

• (c) Thalamus vs Hypothalamus is given below:

Aspect	Thalamus	Hypothalamus
Location	Situated above the brainstem	Located below the thalamus
Function	Acts as a relay station for sensory information, directing it to the appropriate areas of the cerebral cortex	Regulates homeostasis, hormone production, autonomic nervous system, and emotional responses
Hormonal Control	Not primarily involved in hormonal regulation	Controls hormone secretion through the pituitary gland
Role in Sleep/Wake Cycle	Helps regulate sleep and wakefulness indirectly	Directly regulates sleep and wakefulness through the suprachiasmatic nucleus
Relationship with Pituitary	No direct connection with the pituitary gland	Directly connected to the pituitary gland via the hypothalamic-pituitary axis

• (d) Cerebrum vs Cerebellum is as follows:

Aspect	Cerebrum	Cerebellum
Location	Largest part of the brain, located in the uppermost region	Located below the cerebrum, at the back of the brain
Function	Responsible for higher brain functions including cognition, sensory perception, and voluntary motor control	Coordinates voluntary movements, balance, posture, and motor learning
Structure	Comprises two hemispheres connected by the corpus callosum	Consists of two hemispheres with a highly folded surface called the cerebellar cortex
Gray Matter	Contains the cerebral cortex, responsible for conscious thoughts and information processing	Contains the cerebellar cortex, involved in integrating sensory and motor information
White Matter	Comprises nerve fibers connecting different regions of the brain	Comprises nerve fibers connecting the cerebellum to other parts of the brain and spinal cord
Motor Control	Involved in initiating and coordinating voluntary muscle movements	Fine-tunes and regulates motor movements initiated by the cerebrum
Cognitive Functions	Essential for language, memory, attention, and decision-making	Supports procedural memory and motor coordination, but less involved in cognitive functions

Q9: Answer the following:

• (a) Which part of the human brain is the most developed?
• (b) Which part of our central neural system acts as a master clock?

Answer:

• (a)The most developed part is the cerebrum.
• (b)The central nervous system’s hypothalamus serves as a master clock.

Q10: Distinguish between

• (a) afferent neurons and efferent neurons
• (b) impulse conduction in a myelinated nerve fiber and unmyelinated nerve fiber
• (c) cranial nerves and spinal nerves.

Answer: 

• (a) The difference between Afferent neurons and Efferent neurons are:

Aspect	Afferent Neurons	Efferent Neurons
Direction of Signal Flow	Carry sensory information to the CNS	Transmit signals from CNS to muscles/glands
Function	Sense external stimuli	Control movement and glandular secretion
Examples	Skin, eyes, ears sensory neurons	Motor neurons for muscles and glands
Pathway	Signal travels to CNS	Signal originates from CNS
Synaptic Connections	Connect with interneurons in CNS	Directly connect with target cells

• (b) The difference between impulse conduction in a myelinated nerve fiber and unmyelinated nerve fiber:

Aspect	Myelinated Nerve Fiber	Unmyelinated Nerve Fiber
Conduction Speed	Faster due to saltatory conduction, where impulses “jump” between nodes of Ranvier	Slower as impulses propagate continuously along the entire length of the fiber
Energy Efficiency	More energy-efficient with reduced ion leakage through myelin sheath	Less energy-efficient with more ion leakage along the fiber
Protection	Provides insulation and protection, minimizing signal loss and damage	Lacks insulation and is more susceptible to signal loss and damage
Examples	Found in motor neurons and sensory neurons responsible for rapid responses	Found in pain receptors and sensory neurons requiring continuous signal transmission

• (c) The difference between cranial nerves and spinal nerves are:

Aspect	Cranial Nerves	Spinal Nerves
Location	Arise from the brain and exit the skull through openings called foramina	Emerge from the spinal cord and exit the vertebral column through spaces between vertebrae called intervertebral foramina
Number	12 pairs	31 pairs (8 cervical, 12 thoracic, 5 lumbar, 5 sacral, 1 coccygeal)
Function	Primarily innervate structures of the head and neck, controlling sensory and motor functions	Innervate the rest of the body, controlling both sensory and motor functions
Composition	May contain sensory, motor, or mixed (both sensory and motor) fibers	Typically mixed nerves containing both sensory and motor fibers
Examples	Olfactory nerve (I), optic nerve (II), facial nerve (VII)	Sciatic nerve, median nerve, ulnar nerve

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