Tamil Nadu 10th Standard Science Book Solution | Lesson 15 – Nervous System

Lesson 15. Nervous System

Lesson 15. > Nervous System

I. Choose the best answer

1. Bipolar neurons are found in

1. retina of eye
2. cerebral cortex
3. embryo
4. respiratory epithelium

Ans ; Retina of eye

2. Site for processing of vision, hearing, memory, speech, intelligence and thought is

1. kidney
2. ear
3. brain
4. lungs

Ans ; Brain

3. In reflex action, the reflex arc is formed by

1. brain, spinal cord, muscle
2. receptor, muscle, spinal cord
3. muscle, receptor, brain
4. receptor, spinal cord, muscle

Ans ; Receptor, spinal cord, muscle

4. Dendrites transmit impulse cell body and axon transmit impulse cell body.

1. away from, away from
2. towards, away from
3. towards, towards
4. away from, towards

Ans ; Towards, away from

5. The outer most of the three cranial meninges is

1. arachnoid membrane
2. piamater
3. duramater
4. myelin sheath

Ans ; Duramater

6. There are pairs of cranial nerves and pairs of spinal nerves.

1. 12, 31
2. 31, 12
3. 12, 13
4. 12, 21

Ans ; 12, 31

7. The neurons which carries impulse from the central nervous system to the muscle fibre.

1. afferent neurons
2. association neuron
3. efferent neuron
4. unipolar neuron

Ans ; Efferent neuron

8. Which nervous band connects the twocerebral hemispheres of brain?

1. thalamus
2. hypothalamus
3. corpus callosum
4. pons

Ans ; Corpus callosum

9. Node of Ranvier is found in

1. muscles
2. axons
3. dendrites
4. cyton

Ans ; Axons

10. Vomiting centre is located in

1. medulla oblongata
2. stomach
3. cerebrum
4. hypothalamus

Ans ; Medulla oblongata

11. Nerve cells do not possess

1. neurilemma
2. sarcolemma
3. axon
4. dendrites

Ans ; Sarcolemma

12. A person who met with an accident lost control of body temperature, water balance, and hunger. Which of the following part of brain is supposed to be damaged?

1. Medulla oblongata
2. cerebrum
3. pons
4. hypothalamus

Ans ; Hypothalamus

II. Fill in the blanks

1. __________ is the longest cell in our body.

Ans ; Neuron / Nerve cell

2. Impulses travels rapidly in __________ neurons.

Ans ; Myelinated

3. A change in the environment that causes an animal to react is called __________.

Ans ; Stimulus

4. __________ carries the impulse towards the cell body.

Ans ;  Dendrite

5. The two antagonistic component of autonomic nervous system are __________ and __________.

Ans ; Sympathetic / Parasympathetic

6. A neuron contains all cell organelles except __________.

Ans ; Centriole

7. __________ maintains the constant pressure inside the cranium.

Ans ; Cerebrospinal fluid

8. __________ and __________ increases the surface area of cerebrum.

Ans ; Gyri and Sulci

9. The part of human brain which acts as relay center is __________.

Ans ; Thalamus

III. State whether true or false, if false write the correct statement

1. Dendrons are the longest fibres that conducts impulses away from the cell body. ( False )

• Axon is the longest fibres that conducts impulses away from the cell body.

2. Sympathetic nervous system is a part of central nervous system. ( False )

• Sympathetic nervous system is a part of Autonomic nervous system.

3. Hypothalamus is the thermoregulatory centre of human body. ( True )

4. Cerebrum controls the voluntary actions of our body. ( False )

• Cerebellum controls the voluntary actions of our body.

5. In the central nervous system myelinated fibres form the white matter. ( True )

6. All the nerves in the body are covered and protected by meninges. ( False )

• All the nerves in the body are covered and protected by Epineurium.

7. Cerebrospinal fluid provides nutrition to brain. ( True )

8. Reflex arc allows the rapid response of the body to a stimulus. ( True )

9. Pons helps in regulating respiration. ( True )

IV. Match the following

V. Understand the assertion statement. Justify the reason given and choose the correct choice

1. Assertion is correct and reason is wrong.
2. Reason is correct and the assertion is wrong.
3.  Both assertion and reason are correct.
4. Both assertion and reason are wrong.

1. Assertion: Cerebrospinal fluid is present throughout the central nervous system.
Reason: Cerebrospinal fluid has no such functions.

• Ans : a) Assertion is correct and reason is wrong

2. Assertion: Corpus callosum is present in space between the duramater and piamater.
Reason: It serves to maintain the constant intracranial pressure.

• Ans : d) Both assertion and reason are wrong

VI. Short answer questions

1. Define stimulus.

• Stimulus’ refers to the changes in the environmental condition, that are detected by receptors present in the body.
• Areceptor isa cell or a group of cells that receives the stimuli.
• An effector is a part of the body which can respond to a stimulus.

2. Name the parts of the hind brain.

It is formed of three parts cerebellum, pons and medulla oblongata.

3. What are the structures involved in the protection of brain?

• Brain is protected by skull.
• Brain is covered by three connective tissue membrane or meninges. They are outerDuramater, middle Arachnoid membrane, inner Piamater. Meningeal membranes protect the brain from mechanical injury.
• ‘The brain is suspended in a special fluid environment called cerebrospinal fluid (CSF). It acts as shock absorbing fluid and protects the brain from damage when it is subjected to sudden jerk.

4. Give an example for conditioned reflexes.

Drawing pictures on seeing a human being or a thing is an example of conditioned reflexes which requires conscious effort, acquired as a result of learning and practice.

5. Which acts as a link between the nervous system and endocrine system?

• The hypothalamus is the link between the endocrine and nervous systems.
• The hypothalamus produces releasing and inhibiting hormones, which stop and start the production of other hormones throughout the body.

6. Define reflex arc.
The pathway taken by nerve impulse to accomplish reflex action is called reflex arc.

VIL. Differentiate between

1. Voluntary and involuntary actions.

2. Medullated and non-medullated nerve fibre.

VIII. Long answer questions:

1. With a neat labelled diagram explain the structure of neuron.

Structure of Neuron

• * A neuron typically consists of three basic parts. Cyton, Dendrites and Axon.

Cyton:

• Cyton is also called cell body or perikaryon.
• Tt has a central nucleus with abundant cytoplasm called neuroplasm.
• The cytoplasm has large granular body called Nissl’s granules and the other cell organelles like mitochondria, ribosomes, lysosomes, and endoplasmic recticulum.
• Neurons do not have the ability to divide.
• Several neurofibrils are present in the cytoplasm that help in transmission of nerve impulses to and from the cell body.

Dendrites:

• These are the numerous branched cytoplasmic processes that project from the surface of the cell body.
• They conduct nerve impulses towards the cyton.
• The branched projections increase the surface area for receiving the signals from other nerve cells.

Axon:

• The axon is a single, elongated, slender projection.
• The end of axon terminates as fine branches which terminate into knob like swellings called synaptic knob.
• The plasma membrane of axon is called axolemma, while the cytoplasm is called axoplasm.
• It carries impulses away from the cyton.
• The axons may be covered by a protective sheath called myelin sheath which is further covered by a layer of Schwann cells called neurilemma.
• Myelin sheath breaks at intervals by depressions called Nodes of Ranvier.
• The region between the nodes is called as internode.
• Myelin sheath acts as insulator and ensures rapid transmission of nerve impulses.

Synapse:

• A junction between synaptic knob of axon of one neuron and dendron of next neuron is called synaptic junction.

2. Illustrate the structure and functions of brain.

A human brain is formed of three main parts:

• Forebrain
• Midbrain
• Hindbrain

Forebrain:

• The forebrain is formed of cerebrum and diencephalon.
• The latter consists of dorsal thalamus and ventral hypothalamus.

Cerebrum:

• It is the largest portion forming nearly two-third of the brain.
• The cerebrum is longitudinally divided into two halves as right and left cerebral hemispheres.
• Two cerebral hemispheres are interconnected by thick band of nerve fibres called corpus callosum.
• The outer portion of each cerebral hemisphere is formed of grey matter and is called cerebral cortex.
• The inner or deeper part is formed of white matter and is called cerebral medulla.
• The cortex is extremely folded forming elevations called gyri with depressions between them termed as sulci that increase its surface area.
• Each cerebral hemisphere is divisble into a frontal lobe, a parietal lobe, a temporal lobe and_an occipital lobe.
• These lobes are also known as cerebral lobes and are associated with specific functions.
• Any damage in specific lobe inturn affects its function.
• The cerebrum is responsible for the thinking, intelligence, consciousness, memory, imagination, reasoning and willpower.

Thalamus

• Thalamus present in cerebral medulla is a major conducting centre for sensory and motor signalling.
• It acts as a relay centre.

Hypothalamus:

• It lies at the base of the thalamus.
• It controls involuntary functions like hunger, thirst, sleep, sweating, sexual desire, anger, fear, water balance, blood pressure etc.
• It acts as a thermoregulatory (temperature control) centre of the body.
• It controls the secretion of hormones from anterior pituitary gland and is an important link between nervous system and endocrine system.

Midbrain:

• It is located between thalamus and hind brain.
• The dorsal portion of the mid brain consists of four rounded bodies
• lled corpora quadrigemina that control visual and auditory (hearing) reflexes.

Hindbrain:

• It is formed of three parts cerebellum, pons and medulla oblongata.
  Cerebellum:
• It is second largest part of the brain formed of two large sized hemispheres and middle vermis.
• It coordinates voluntary movements and also maintains body balance.

pons:

• ‘Pons’ a latin word meaning bridge.
• Itis a bridge of nerve fibre that connects the lobes of cerebellum. 5
• It relays signals between the cerebellum, spinal cord, midbrain and cerebrum. Q
• It controls respiration and sleep cycle.

3. What will you do if someone pricks your hand with a needle? Elucidate the pathway of response with a neat labelled diagram.

• If someone pricks my hand with a needle, the stimulus is the pain which is sensed by receptors in our hand. This stimulus in turn triggers an impulse in sensory neuron.
• The sensory neuron transmits or conveys the message to the spinal cord.
• Spinal cord interprets the stimulus and the impulse is passed on to the relay neuron which in turn transmits it to a motor neuron.
• Motor neurons carry command from spinal cord to our arm.
• Muscle in our arm contracts and we withdraw our hand immediately.
• In this example, muscle is an effector organ which has responded to the prick.

4. Describe the structure of spinal cord.

• Spinal cord is a cylindrical structure lying in the neural canal of the vertebral column.
• It is also covered by meninges.
• It extends from the lower end of medulla oblongata to the first lumbar vertebra.
• The posterior most region of spinal cord tapers into a thin fibrous thread like structure called filum terminale.
• Internally, the spinal cord contains a cerebrospinal fluid filled cavity known as the central canal.
• The grey matter of spinal cord is ‘H’ shaped.
• The upper end of letter “H” forms posterior horns and lower end forms anterior horns.
• A bundle of fibres pass into the posterior horn forming dorsal or afferent root.
• Fibres pass outward from the anterior horn forming ventral or efferent root.
• These two roots joins to form spinal nerves.
• The white matter is external and have bundle of nerve tracts.

5. How nerve impulses are transferred from one neuron to next neuron?

•  All the information from the environment are detected by the receptors located in our sense organs such as the eyes, the nose, the skin, etc.
• Information from the receptors is transmitted as electrical impulse and is received by the dendritic tips of the neuron.
• This impulse travels from the dendrite to the cell body and then along the axon to its terminal end.
• On reaching the axonal end, it causes the nerve endings to release a chemical (neurotransmitter) which diffuses across a synapse and starts a similar electrical impulse in the dendrites of the next neuron, then to their cell body to be carried along the axon.
• The flow of nerve impulses from axonal end of one neuron to dendrite of another neuron through a synapse is called synaptic transmission.
• Neurotransmitters are the chemicals which allow the transmission of nerve impulse.
• The important neurotransmitter released by neurons is called Acetylcholine.

6. Classify neurons based on its structure.

Structurally the neurons may be of the following types:

Unipolar neurons:

• Only one nerve process arises from the cyton which acts as both axon and dendron.

Bipolar neurons:

• The cyton gives rise to two nerve processes of which one acts as an axon while another as a dendron.

Multipolar neurons:

• ‘The cyton gives rise to many dendrons and an axon

Unipolar (A), Bipolar (B) and multipolar (C) neurons

X. Higher Order Thinking Skills (HOTS)

1. ‘A’ isa cylindrical structure that begins from the lower end of medulla and extend downwards. It is enclosed in bony cage ‘B’ and covered by membranes ‘C’ As many as ‘D’ pairs of nerves arise from the structure ‘A’

(i) What is A?

• ‘A is Spinal cord.

(ii) Name (a) bony cage ‘B’ and (b) membranes ‘C’

• (a) vertebral column (b) meninges

(iii) How much pairs of nerves does D represent?

• 31 pairs of nerves

2. Our body contains a large number of cells ‘V’ which are the longest cells in the body. L has long and short branch called as ‘M’ and ‘N’ respectively. There is a gap ‘O’ between two ‘LT cells, through which nerves pass.
Impulse transfer by release of chemical substance ‘P’”

(i) Name the cells L.

• Nerve cells or neurons

(ii) What are M and N?

• Axon and Dendrites

(iii) What is the gap O?

• Synapse

(iv) Name the chemical substance P.

• The chemical is Acetylcholine

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