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

NCERT Solutions for Class 11 Biology Chapter 18 (Neural Control and Coordination) explain how the nervous system controls and coordinates different activities of the body. The chapter covers neurons, the transmission of nerve impulses, synapses, reflex actions, and the structure and functions of the human brain. Students can learn how the nervous system helps the body respond to different stimuli and work in a coordinated way.

NCERT Solutions for Class 11 Biology Chapter 18 by ALLEN explain how nerve impulses are generated and transmitted, how signals pass between neurons, and how different parts of the brain work, including the hypothalamus and cerebellum. Students can also learn how reflex actions take place and how the spinal cord helps control them. These solutions help students revise NCERT topics, answer textbook questions, and prepare for school exams and NEET.

1.0Class 11 Biology Chapter 18 Neural Control and Coordination: Key Concepts

Class 11 Biology Chapter 18, Neural Control and Coordination, explains how the nervous system receives information, processes it, and controls different activities of the body. The chapter covers neurons, the human nervous system, the structure and functions of the brain, the transmission of nerve impulses, synapses, and reflex actions.

Neural System: Learn how neurons receive and transmit information to help the body respond to different stimuli.
Human Neural System: Understand the two main parts of the nervous system: the central nervous system (CNS), which includes the brain and spinal cord, and the peripheral nervous system (PNS), which includes cranial and spinal nerves.
Structure and Types of Neurons: Study the structure of a typical neuron and learn about unipolar, bipolar, and multipolar neurons.
Generation and Conduction of Nerve Impulses: Understand polarization, depolarization, and repolarization and how electrical signals travel along the axon.
Transmission Across Synapses: Learn how nerve impulses pass between neurons through electrical and chemical synapses and the role of neurotransmitters.
Structure of the Human Brain: Study the forebrain, midbrain, and hindbrain, including the cerebrum, thalamus, hypothalamus, corpora quadrigemina, pons, cerebellum, and medulla oblongata.
Reflex Action and Reflex Arc: Understand how the body produces quick, involuntary responses and how sensory neurons, interneurons, and motor neurons take part in a reflex action.

2.0Detailed NCERT Textbook Solutions : Class 11 Biology Chapter 18

Briefly describe the structure of the Brain:
Ans. The brain is the central information processing organ of our body, and acts as the 'command and control system'. It controls the voluntary movements, balance of the body, functioning of vital involuntary organs (e.g., lungs, heart, kidneys, etc.), thermoregulation, hunger and thirst, circadian (24-hour) rhythms of our body, activities of several endocrine glands and human behaviour. It is also the site for processing of vision, hearing, speech, memory, intelligence, emotions and thoughts. The human brain is well protected by the skull. Inside the skull, the brain is covered by cranial meninges consisting of an outer layer called dura mater, a very thin middle layer called arachnoid and an inner layer (which is in contact with the brain tissue) called pia mater. The brain can be divided into three major parts: (i) forebrain, (ii) midbrain, and (iii) hindbrain
Compare the following :
(a) Central neural system (CNS) and Peripheral neural system (PNS).
(b) Resting potential and action potential.
Ans.
(a) CNS : It lies along the mid-dorsal axis of the body. It is a hollow, dorsally placed structure. The CNS includes the brain and the spinal cord and is the site of information processing and control.
PNS : PNS comprises of all the nerves of the body associated with the CNS (brain and spinal cord). It carries information to and from the CNS.
(b) Resting potential : Outside the plasma membrane of a nerve fibre is the extracellular fluid which is positively charged with respect to the cell contents inside the plasma membrane. A resting nerve fibre shows a potential difference between inside and outside of this plasma membrane. This difference in the electrical charges across the plasma membrane is called the 'resting potential'. A membrane with resting potential across it, is said to be electrically polarized.
Action potential : Action potential is another name of nerve impulse. The contents inside a cell at the excited state becomes positively charged with respect to extracellular fluid outside it. This change in polarity across the plasma membrane is known as an action potential. The membrane with reversed polarity across it is said to be depolarized.
Explain the following processes:
(a) Polarisation of the membrane of a nerve fibre.
(b) Depolarisation of the membrane of a nerve fibre.
(c) Transmission of a nerve impulse across a chemical synapse.

Ans.

(a) Different types of ion channels are present on the neural membrane. These ion channels are selectively permeable to different ions. When a neuron is not conducting any impulse, i.e., resting, the axonal membrane is comparatively more permeable to potassium ions $(K^{+})$ and nearly impermeable to sodium ions $(Na^{+})$ . Similarly, the membrane is impermeable to negatively charged proteins present in the axoplasm. Consequently, the axoplasm inside the axon contains high concentration of $K^{+}$ and negatively charged proteins and low concentration of $Na^{+}$ . In contrast, the fluid outside the axon contains a low concentration of $K^{+}$ , a high concentration of $Na^{+}$ and thus form a concentration gradient. These ionic gradients across the resting membrane are maintained by the active transport of ions by the sodium-potassium pump which transports $3 Na^{+}$ outwards for $2 K^{+}$ into the cell. As a

result, the outer surface of the axonal membrane possesses a positive charge while its inner surface becomes negatively charged and therefore is polarised. The electrical potential difference across the resting plasma membrane is called as the resting potential.
(b) When a stimulus is applied at a site on the polarised membrane, the membrane at the site A becomes freely permeable to $Na^{+}$ . This leads to a rapid influx of $Na^{+}$ followed by the reversal of the polarity at that site, i.e., the outer surface of the membrane becomes negatively charged and the inner side becomes positively charged. The polarity of the membrane at the site A is thus reversed and hence depolarised.
(c) Transmission of a nerve impulse across a chemical synapse : At a chemical synapse, the membranes of the pre- and post- synaptic neurons are separated by a fluid- filled space called synaptic cleft. Chemicals called neurotransmitters are involved in the transmission of impulses at these synapses. The axon terminals contain vesicles filled with these neurotransmitters. When an impulse (action potential) arrives at the axon terminal, it stimulates the movement of the synaptic vesicles towards the membrane where they fuse with the plasma membrane and burst to release their neurotransmitters in the synaptic cleft. The released neurotransmitters bind to their specific receptors, present on the post-synaptic membrane. This binding opens ion channels allowing the entry of ions which can generate a new potential in the post-synaptic neuron. The new potential developed may be either excitatory or inhibitory.

Draw labelled diagrams of the following:
(a) Neuron
(b) Brain

Ans.

ques-4-sol-class-11-biology-chapter-18

Write short notes on the following:
(a) Neural coordination
(b) Forebrain
(c) Midbrain
(d) Hindbrain
(e) Synapse
Ans.
(a) Neural coordination : When higher animals respond to various stimuli, each response to a specific stimulus generally involves many organs (parts) of their bodies. Therefore, it is necessary that all the concerned organs (parts) of the body should work in a systematic manner to produce the response. The working together of various organs (parts) of the body of multicellular organism in a proper manner to complement the functions of each other is called coordination. This is achieved by three overlapping processes of nervous systemsensory input, integration and motor output.

(b) Forebrain : The forebrain consists of cerebrum, thalamus and hypothalamus. Cerebrum forms the major part of the human brain. A deep cleft divides the cerebrum longitudinally into two halves, which are termed as the left and right cerebral hemispheres. The hemispheres are connected by a tract of nerve fibres called corpus callosum. The layer of cells which covers the cerebral hemisphere is called cerebral cortex and is thrown into prominent folds. The cerebral cortex is referred to as the grey matter due to its greyish appearance. The neuron cell bodies are concentrated here giving the colour. The cerebral cortex contains motor areas, sensory areas and large regions that are neither clearly sensory nor motor in function. These regions called as the association areas are responsible for complex functions like intersensory associations, memory and communication. Fibres of the tracts are covered with the myelin sheath, which constitute the inner part of cerebral hemisphere. They give an opaque white appearance to the layer and, hence, is called the white matter. The cerebrum wraps around a structure called thalamus, which is a major coordinating centre for sensory and motor signaling. Another very important part of the brain called hypothalamus lies at the base of the thalamus. The hypothalamus contains a number of centres which control body temperature, urge for eating and drinking. It also contains several groups of neurosecretory cells, which secrete hormones called hypothalamic hormones. The inner parts of cerebral hemispheres and a group of associated deep structures like amygdala, hippocampus, etc., form a complex structure called the limbic lobe or limbic system. Along with the hypothalamus, it is involved in the regulation of sexual behaviour, expression of emotional reactions (e.g., excitement, pleasure, rage and fear), and motivation.

(c) Midbrain : The midbrain is located between the thalamus/hypothalamus of the forebrain and pons of the hindbrain. A canal called the cerebral aqueduct passes through the midbrain. The dorsal portion of the midbrain consists mainly of four round swellings (lobes) called corpora quadrigemina.

(d) Hindbrain : The hindbrain comprises pons, cerebellum and medulla. Pons consists of fibre tracts that interconnect different regions of the brain. Cerebellum has very convoluted surface in order to provide the additional space of many more neurons. The medulla of the brain is connected to the spinal cord. The medulla contains centres which control respiration, cardiovascular reflexes and gastric secretions. Three major regions make up the brain stem; mid brain, pons and medulla oblongata. Brain stem forms the connections between the brain and spinal cord.

(e) Synapse : A nerve impulse is transmitted from one neuron to another through junctions called synapse.

Give a brief account of mechanism of synaptic transmission.
Ans. Transmission of a nerve impulse across a chemical synapse : At a chemical synapse, the membranes of the pre- and post- synaptic neurons are separated by a fluid- filled space called synaptic cleft. Chemicals called neurotransmitters are involved in the transmission of impulses at these synapses. The axon terminals contain vesicles filled with these neurotransmitters. When an impulse (action potential) arrives at the axon terminal, it stimulates the movement of the synaptic vesicles towards the membrane where they fuse with the plasma membrane and burst to release their neurotransmitters in the synaptic cleft. The released neurotransmitters bind to their specific receptors, present on the post-synaptic membrane. This binding opens ion channels allowing the entry of ions which can generate a new potential in the post-synaptic neuron. The new potential developed may be either excitatory or inhibitory.
Explain the role of $Na^{+}$ in the generation of action potential.
Ans. The action potential is largely determined by $Na^{+}$ ions. The action potential results from the following sequential events
(i) Disturbance caused to the membrane of a nerve fibre by a stimulus results in leakage of $Na^{+}$ into the nerve fibre.
(ii) Entry of $Na^{+}$ lowers the trans-membrane potential difference.
(iii) Decrease in potential difference makes the membrane more permeable to $Na^{+}$ than to $K^{+}$ ions so that more $Na^{+}$ enter the fibre than $K^{+}$ leave it.
(iv) Accumulation of $Na^{+}$ in the nerve fibre initiates depolarisation (action potential), making the axonic contents positively charged relative to the extracellular fluid.
(v) With continued addition of $Na^{+}$ the potential reaches zero and then plus 40-50 millivolts. This is the peak of action potential.
(vi) Permeability of a depolarised membrane to $Na^{+}$ then rapidly drops, there are now as many $Na^{+}$ on the inside of the membrane as on the outside.
Differentiate between
(a) Myelinated and non-myelinated axons
(b) Dendrites and axons
(c) Thalamus and Hypothalamus
(d) Cerebrum and Cerebellum

Ans.

(a) Differences between myelinated and non-myelinated axons are as follows:

Myelinated axons	Non-myelinated axons
Axons have Schwann cells, which form myelin sheath.	Myelin sheath is absent.
Nodes of Ranvier are present at intervals.	Nodes of Ranvier are absent.
Voltage-gated ion channels are concentrated at the nodes; depolarisation occurs only in the nodes.	Voltage-gated, ion channels are spread all over the axon; depolarisation occurs all along the length of nerve fibre.
Ion exchange can occur only at the nodes.	Ion exchange occurs all over the surface.
Action potential does not propagate over inter nodes, and jumps from node to node.	Action potential propagates all along the axon.
Nerve impulse conduction is saltatory.	Nerve impulse conduction is smooth.
These carry nerve imulses much faster than non-medullated nerve fibres.	These carry nerve impulses much slower than medullated nerve fibres.
These are present in the white matter of brain and spinal cord and in cranial and spinal nerves.	These are present in autonomic nerves.

(b) Axon and dendrites can be differentiated as follows:

Axon	Dendrites
Single per neuron.	Usually many per neuron.
Arises from a conical projection, the axon hilock, from the discharging end of neuron.	A rises directly from the receiving surface of the neuron.
Very long (may be several metres) and of uniform diameter (0.25 – over 10 mm).	Very short (generally under 1.5 mm) and tapering.
Branched at the distal end only.	Much branched, practically all along.
Terminal branches enlarged to form synaptic knobs at the tips.	No knobs at the tips of the branches.
Have neurotransmitter-containing vesicles in the knobs.	Do not have such vesicles anywhere.
Conduct impulses away from the cyton.	Conduct impulses towards the cyton.

(c) Thalamus and hypothalamus can be differentiated as follows:

Thalamus	Hypothalamus
It is present on the right and left sides of the third ventricle.	It is present at the floor of the third ventricle.
Each thalamus acts as a relay centre for sensory impulses, except those of smell; as reflex centre for muscular and glandular activities; and as a perceiving centre for crude sensation such as extremes of heat, cold, pain, etc.	The hypothalamus contains centres for maintaining homeostasis by regulating body temperature, heat beat, water balance and blood pressure; controls hunger, thirst, sexual arousal, and feeling of pain, pleasure, anger and fear; and controls the hypophysis.

(d) Cerebrum and cerebellum can be differentiated as follows :

Cerebrum	Cerebellum
It is the largest part of the brain, forming four-fifths of its weight.	It is the second largest part of the brain, forming one-eighth of its mass.
It is a part of the forebrain.	It is a part of the hindbrain.
In consists of 2 cerebral hemispheres each comprising 4 lobes : frontal, occiital, parietal, temporal.	It consists of two cerebellar hemispheres and a median vermis.
White matter does not form arbor vitae.	White matter form arbor vitae.
It initiates voluntary movements, and is a seat of will, intelligence, memory etc.	It maintains posture and equilibrium.

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?

Ans.

(a) Cerebrum (cerebral hemispheres).
(b) Pineal gland present in diencephalon of forebrain acts as a master clock, which maintains biological rhythm.
10. Distinguish between
(a) Afferent neurons and efferent neurons
(b) Impulse conduction in myelinated nerve fiber and unmyelinated nerve fiber
(c) Cranial nerves and spinal nerves Ans.
(a)

Afferent neurons	Efferent neurons
They conduct impulses from the receptors to CNS.	They conduct impulses from CNS to be effectors.
They are sensory in nature.	They are motor in nature.

(b) Differences between myelinated and nonmyelinated axons are as follows:

Myelinated axons	Non-myelinated axons
Axonshave Schwann cells, which form myelin sheath.	Myelin sheath is absent.
Nodes of Ranvier are present at intervals.	Nodes of Ranvier are absent.
Voltage-gated ion channels are concentrated at the nodes; depolarisation occurs only in the nodes.	Voltage-gated, ion channels are spread all over the axon; depolarisation occurs all along the length of nerve fibre.
Ion exchange can occur only at the nodes.	Ion exchange occurs all over the surface.
Action potential does not propagate over intermodes, and jumps from node to node.	Action potential propagates all along the axon.
Nerve impulse conduction is saltatory.	Nerve impulse conduction is smooth.
These carry nerve imulses much faster than non-medullated nerve fibres.	These carry nerve impulses much slower than medullated nerve fibres.
These are present in the white matter of brain and spinal cord and in cranial and spinal nerves.	These are present in autonomic nerves.

(c)

Carnival nerves	Spinal nerves
The nerves that arise from or join the brain are called cerebral or cranial nerves.	Spinal nerves arise from the spinal cord.
There are 12 pairs of cranial nerves in humans.	There are 31 pairs of spinal nerves in humans.
They are numbered I to XII in Roman numerals.	They are classified into five groups cervical 8 pairs, thoracic 12 pairs, lumbar 5 pairs, sacral 5 pairs and coccygeal 1 pair.

3.0NCERT Class 11 Biology – Chapter-Wise Solutions & Explanations

Study Class 11 Biology with chapter-wise NCERT Solutions and answers to all textbook questions. Revise important topics, understand each chapter, and prepare for your Biology exams.

Chapter Number	Chapterwise NCERT Solutions
Chapter 1	The Living World
Chapter 2	Biological Classification
Chapter 3	Plant Kingdom
Chapter 4	Animal Kingdom
Chapter 5	Morphology of Flowering Plants
Chapter 6	Anatomy of Flowering Plants
Chapter 7	Structural Organisation in Animals
Chapter 8	Cell: The Unit of Life
Chapter 9	Biomolecules
Chapter 10	Cell Cycle and Cell Division
Chapter 11	Photosynthesis in Higher Plants
Chapter 12	Respiration in Plants
Chapter 13	Plant Growth and Development
Chapter 14	Breathing and Exchange of Gases
Chapter 15	Body Fluids and Circulation
Chapter 16	Excretory Products and their Elimination
Chapter 17	Locomotion and Movement
Chapter 19	Chemical Coordination and Integration

4.0Key Features of NCERT Solutions for Class 11 Biology Chapter 18

Generation of Nerve Impulses: Understand how sodium and potassium ions move across the neuronal membrane during the generation and transmission of nerve impulses.
Functions of Brain Regions: Learn the functions of different brain regions, including the hypothalamus, cerebrum, cerebellum, and limbic system.
Transmission Across Synapses: Understand how nerve impulses pass through electrical and chemical synapses and how neurotransmitters help transmit signals between neurons.
Reflex Action and Reflex Arc: Learn the pathway of a reflex action, including the roles of sensory neurons, the spinal cord, and motor neurons.
Prepared by ALLEN Expert Faculty: Study clear explanations of nervous system structures and functions based on the NCERT Class 11 Biology syllabus.
Node of Ranvier and Saltatory Conduction: Understand how nerve impulses travel faster along myelinated axons by moving from one node of Ranvier to the next.
Complete NCERT Exercise Solutions: Get clear answers to NCERT textbook questions to revise Neural Control and Coordination and prepare for school exams and NEET.