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

Last Updated : 01 Jun, 2023
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NCERT Solutions for Class 11 Chapter-18 Neural Control and Coordination: The chapter on neural control and coordination is important for students approaching the board exams. This article introduces NCERT solutions designed to help students explain the concepts of further learning and how to write to get good grades on exams. The solutions are presented in very simple language for ease of understanding.

Solution NCERT Chapter 18 Neural Control and Coordination of Class 11 explains how physical activity enhances the blood’s oxygen supply. For instance, you will notice that the energy required to maintain greater muscular activity increases when you exercise. And the increased supply of oxygen necessitates a rise in the rate of breathing, pulse, and blood flow through blood vessels. The functions of your neurons, lungs, heart, and kidney gradually return to normal once you stop exercising. Revise the basic concepts of Neural Control and Coordination for quick revision and class notes

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.

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.

Q 2: Compare the following:

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

Answer:

  • (a) Central neural system (CNS) and Peripheral neural system (PNS)

Central Neural System (CNS)

Peripheral Neural System (PNS)

The brain and spinal cord make up the CNS.

The PNS is made up of spinal nerves and cranial nerves.

The skull and vertebral column protect the spinal cord and brain, respectively.

PNS is not protected by any structures.

There are no subdivisions within CNS.

The somatic nervous system and the autonomic nervous system are two subsystems of the PNS.

The CNS analyses the data and regulates how the body reacts to impulses.

PNS nerves send signals to the CNS and the CNS sends responses to various body organs.

The CNS’s nuclei are collections of neurons.

Ganglia is a group of neurons in the PNS

  • (b) Resting potential and action potential

Resting Potential

Action Potential

It is the potential difference across the membrane while the neuron is in the resting phase (difference in electric charge).

It is the potential differential across the membrane that occurs when the neuron is activated or aroused.

The neuron has a negatively charged inner and a positively charged outside.

The neuron has a positively charged inner and a negatively charged outside.

K+ ions can pass more easily through the neuron’s plasma membrane.

Na+ ions are more easily passed via the neuron’s plasma membrane.

To keep the resting potential constant sodium-potassium-ATPase pump is activated and pumps Na + ions outside the neuron.

The sodium-potassium ATPase pump transfers Na + ions into the cell by working in reverse.

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:
Polarization of Nerve Fiber

 

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.
Depolarization of 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.

Synaptic Transmission

 

  • 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) Neuron

Neuron Structure

C

(b) Brain

Human 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.

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

Myelinated Axons

Non-myelinated Axons

There is a myelin sheath.

There is no myelin sheath.

There are Ranvier nodes.

There are no Ranvier nodes.

It is located in the brain, spinal cord, and autonomous nervous system’s grey matter.

It can be discovered in the brain, spinal cord, and autonomous nervous system’s white matter.

Nerve impulses go from node to node.

Nerve impulse conduction is fluid.

Compared to non-myelinated axons, impulse conduction is 50 times faster.

The impulse’s conduction moves slowly

  • (b) Dendrites and axons

Dendrites

Axons

They are quick processes. Axons are lengthy processes. Dendrites direct impulses toward the neuron’s cell body. Impulses are carried by axons outside the neuron’s cell body. Dendrites are always branching. Axons might or might not be branched. Nissl’s granules can be seen in the neuroplasm. The neuroplasm is devoid of Nissl’s granules.
  • (c) Thalamus and Hypothalamus
Thalamus
Hypothalamus It is entirely composed of grey matter. It is composed of grey and white matter. No hormones are secreted by the thalamus. Specific hormones secreted by the brain regulate the pituitary gland’s activity. It’s located above the midbrain. It is located near the thalamic base It houses the nerve centers responsible for pain, heat, and cold sensations. It has centers that regulate homeostasis, blood pressure, and body temperature.
  • (d) Cerebrum and Cerebellum

Cerebrum

Cerebellum

It is the greatest portion of the brain. It is the brain’s second-largest region. The forebrain contains it. The hindbrain contains it. There are two cerebral hemispheres in the brain. The central vermis and the two lateral cerebellar hemispheres make up the cerebellum’s three lobes. It is the location of intelligence and memory. It is the location of posture and body equilibrium.

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) Afferent neurons and Efferent neurons

Afferent Neurons

Efferent Neurons

They transport sensory signals to the central nervous system from receptors.

They transport motor impulses from the brain to the muscles and other effector organs.

They can be found in the sense organs.

The spinal cord and the brain both contain them.

These neurons are sensory ones.

These are motor neurons.

  • (b) impulse conduction in a myelinated nerve fiber and unmyelinated nerve fiber
Impulse Conduction in a Myelinated Nerve Fibre
Impulse Conduction in Non-myelinated Nerve Fibre The path of an impulse is node to node. The impulse traverses the complete length of the nerve fiber. Conduction speed is 50 times faster than in non-myelinated nerve fibers. The rate of conduction is slower. Less energy is used during impulse transmission. More energy is used during impulse transmission.
  • (c) cranial nerves and spinal nerves

Cranial Nerves

Spinal Nerves

The cranial nerves come in 12 pairs. The spine has 31 pairs of nerves They originate in the brain and spread to other body parts They start in the spinal cord and spread to other bodily regions. They could be mixed, sensory, or motor. They have a mixture of nerves.

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