15. Nervous System

I. Choose the Correct Answer.

1. Bipolar neurons are found in _______

(a) retina of eye
(b) cerebral cortex
(c) embryo
(d) respiratory epithelium

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

(a) kidney        (b) ear
(c) brain         (d) lungs

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

(a) brain, spinal cord, muscle
(b) receptor, muscle, spinal cord
(c) muscle, receptor, brain
(d) receptor, spinal cord, muscle

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

(a) away from, away from
(b) towards, away from
(c) towards, towards
(d) away from, towards

5. The outer most of the three cranial meninges is ______

(a) arachnoid membrane
(b) piamater
(c) duramater
(d) myelin sheath

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

(a) 12, 31        (b) 31, 12
(c) 12, 13         (d) 12, 21

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

(a) afferent neurons
(b) association neuron
(c) efferent neuron
(d) unipolar neuron

8. Which nervous band connects the two cerebral hemispheres of brain?

(a) thalamus
(b) hypothalamus
(c) corpus callosum
(d) pons

9. Node of Ranvier is found in ______

(a) muscles      (b) axons
(c) dendrites    (d) cyton

10. Vomiting centre is located in:

(a) medulla oblongata
(b) stomach
(c) cerebrum
(d) hypothalamus

11. Nerve cells do not possess _______

(a) neurilemma            (b) sarcolemma
(c) axon                       (d) dendrites

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?

(a) Medulla oblongata
(b) cerebrum
(c) pons
(d) hypothalamus

II. Fill in the blanks.

1. Axon is the longest cell in our body.

2. Impulses travels rapidly in Myelin sheath of neurons.

3. A change in the environment that causes an animal to react is called reactions or responses

4. Dendrites carries the impulse towards the cell body.

5. The two antagonistic components of the autonomic nervous system are Sympathetic and Parasympathetic

6. A neuron contains all cell organelles except Golgi apparatus in axon

7. Cerebrospinal fluid maintains the constant pressure inside the cranium.

8. Gyri and Sulci increases the surface area of cerebrum.

9. The part of the human brain which acts as a relay centre is Thalamus

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

1. Dendrons are the longest fibres that conduct impulses away from the cell body.
Answer:           False
Correct Statement: Axons are the longest fibres that conduct impulses away from the cell body.

2. The sympathetic nervous system is a part of the central nervous system.
Answer:           False
Correct Statement: Sympathetic nervous system is a part of the autonomic nervous system.

3. Hypothalamus is the thermoregulatory centre of the human body.
Answer:           True

4. The cerebrum controls the voluntary actions of our body.
Answer:           True

5. In the central nervous system, myelinated fibres form the white matter.
Answer:           False
Correct Statement: In the central nervous system, two types of matter such as white matter or grey matter, is formed, with respect to the presence or absence of myelin sheath.

6. All the nerves in the body are covered and protected by meninges.
Answer:           False
Correct Statement: The brain is covered by three connective tissue membrane or meninges.

7. Cerebrospinal fluid provides nutrition to brain.
Answer:           True

8. Reflex arc allows the rapid response of the body to a stimulus.
Answer:           True

9. Pons helps in regulating respiration.
Answer:           True

IV. Match the following

1. Nissil’s granules

(c) Cyton

2. Hypothalamus

(a) Forebrain

3. Cerebellum

(d) Hindbrain

4. Schwann cell

(b) Peripheral Nervous system

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

(a). Assertion is correct and Reason is wrong
(b). Reason is correct and the assertion is wrong
(c). Both assertion and reason are correct
(d). Both assertion and reason are wrong

1. Assertion: Cerebrospinal fluid is present throughout the central nervous system.
Reason: Cerebrospinal fluid has no such functions.
Answer:
(a) Assertion is correct and Reason is wrong

2. Assertion: Corpus callosum is present in space between the dura mater and pia mater.

 Reason: It serves to maintain constant intracranial pressure.
Answer:
(d) Both assertion and reason are wrong

VI. Short Answer Questions.

1. Define the stimulus.

The changes in the environmental condition, that are detected by receptors present in the body are called stimulus.

2. Name the parts of the hind brain.

Hind brain consists of cerebellum, pons and medulla oblongata.

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

The brain is covered by three connective tissue membrane or meninges.

  • Dura mater, which is the outermost thick fibrous membrane.
  • Arachnoid membrane, which is the middle thin vascular membrane providing a web-like cushion.
  • Pia mater, which is the innermost, thin delicate membrane richly supplied with blood. Meningeal membranes protect the brain from mechanical injury.

4. Give an example for conditioned reflexes.

Common examples of conditioned reflexes are playing a musical instrument, tying shoelaces or the neck-tie without being attentive, watering of the mouth after seeing or smelling favourite food.

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

The hypothalamus controls the secretion of hormones from the Anterior Pituitary gland and is an important link between the nervous system and the endocrine system.

6. Define reflex arc.

The path along which the reflexive impulse travel is called reflex arc.
(OR)
The path way taken by nerve impulse to accomplish reflex action is called reflex arc.

VII. Differentiate between

1. Voluntary and involuntary actions.

Voluntary Action

Involuntary Action

1. The actions which are under the control of our will, eg. Eating, walking.

1. The actions, which are not under our control, eg. Breathing, Heartbeat

2. Controlled by the brain.

2. Controlled by the spinal cord.

3. Voluntary Action results in muscular action.

3. Involuntary actions result in a muscular action or secretions of some glands.

2. Medullated and non-medullated nerve fibre.

Medullated nerve fibre

Non-medullated nerve fibre

1. Nerve fibre is covered by a protective sheath, called the Myelin sheath, which is covered by Neurilemma.

1. Nerve fibre is covered by a single sheath, Neurilemma.

2. Nodes of Ranvier are present.

2. Nodes of Ranvier are absent.

3. They appear white.

3. They appear grey.

4. They carry nerve impulses, much faster than non-medullated nerve fibre.

4. They carry nerve impulses, much slower than medullated nerve fibre.

5. They are present in the white matter of brain, spinal cord and in the cranial and spinal nerves.

5. They are present in the grey matter of the brain and spinal cord and in the autonomic nerves.

VIII. Long Answer Questions.

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

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Structure of Neuron: A neuron consists of three basic parts namely Cyton, Dendrites and Axon.
(a) Cyton: Cyton is called cell body or perikaryon. It has a central nucleus with abundant cytoplasm called neuroplasm. The cytoplasm has a large granular body called Nissl’s granules and the other cell organelles like mitochondria, ribosomes, lysosomes, and endoplasmic reticulum. Neurons do not have the ability to divide. Several neurofibrils are present in the cytoplasm that help in the transmission of nerve impulses to and from the cell body.

(b) 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.

(c) Axon: The axon is a single, elongated, slender projections. 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 protein 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 an internode. Myelin sheath acts as an insulator and ensures the rapid transmission of nerve impulses.
A junction between synaptic knob of the axon of one neuron and dendron of next neuron is called Synaptic Junction. Information from one neuron can pass to another neuron through these junctions, with the release of chemicals known as neurotransmitters, from the synaptic knob.

2. Illustrate the structure and functions of the brain.

A human brain is formed of three main parts forebrain, midbrain and hindbrain.
1. Forebrain: The forebrain is formed of Cerebrum and Diencephalon. The diencephalon consists of dorsal thalamus and ventral hypothalamus.
(a) Cerebrum: It is the largest portion and nearly forms two-third of the brain. The cerebrum is longitudinally divided into two halves, as of right and left cerebral hemispheres by a deep – cleft called median cleft. The 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 the surface area. Each cerebral hemisphere is divisible into a frontal lobe, a parietal lobe, a temporal lobe and an occipital lobe. These lobes are also known as cerebral lobes.

(b) Thalamus: Thalamus present in the cerebral medulla is a major conducting centre for sensory and motor signalling. It acts as a relay centre.

(c) Hypothalamus: It lies at the base of the thalamus. It controls the secretions of hormones from the anterior pituitary gland.

2. Midbrain: It is located between thalamus and Hindbrain. The dorsal portion of the midbrain consists of four rounded bodies called corporaquadrigemina, that control visual and auditory (hearing) reflexes.

3. Hindbrain: It is formed of three parts Cerebellum, Pons and Medulla Oblongata.

  • Cerebellum: It is the second-largest part of the brain formed of two large-sized hemispheres and middle vermis.
  • Pons: It is a bridge of nerve fibre that connects the lobes of the cerebellum. It relays signals between the cerebellum, spinal cord, midbrain and cerebrum.
  • Medulla Oblongata: It is the posterior-most part of the brain, that connects the spinal cord and various parts of the brain.

Functions of Brain:

Structure

Functions

1. Cerebral cortex

Sensory perception, Intelligence, consciousness, control of voluntary functions, language, thinking, memory, decision making, creativity, reasoning and will power.

2. Thalamus

Acts as Relay Station.

3. Hypothalamus

Temperature control, anger, thirst, hunger, urination, the important link between the nervous system and endocrine glands, sleep, sweating, sexual desire, fear, water balance, blood pressure.

4. Midbrain

Visual and Auditory reflexes.

5. Cerebellum

Maintenance of posture and balance, and co-ordinate voluntary muscle activity.

6. Pons

Respiration and Role in the sleep-wake cycle.

7. Medulla Oblongata

Cardiovascular, respiratory and digestive control centres, vasomotor centres to control heartbeat, contraction of blood vessels. It also regulates vomiting and salivation.

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

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


  • When the hand is pricked by a needle, the stimulus is the prick (touch) pain, which is sensed by a receptor called touch or pain receptors in the skin in our hand. This stimulus in tum triggers an impulse in a sensory neuron.
  • The sensory neuron transmits or conveys the message to the spinal cord.
  • The spinal cord interprets the stimulus and the impulse is passed on to the relay neuron, which in tum transmits it to a motor neuron.
  • Motor neurons carry command from the spinal cord to our arm.
  • The muscle in our arm contracts and we withdraw our hand immediately from the needle prick. Muscle is the effector organ which has responded to the prick (pain).

4. Describe the structure of the spinal cord.
Answer:
The 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 terminate.

Internally, the spinal cord contains a cerebrospinal fluid-filled cavity, known as the central canal. The grey matter of the spinal cord is ‘H’ shaped. The upper end of the letter, ‘H’ forms posterior horns and lower end forms anterior horns. A bundle of fibres pass into the posterior horn forming the dorsal or afferent root. Fibres pass outward, from the anterior horn forming the ventral or efferent root. These two roots joins to form spinal nerves. The white matter is external and has a bundle of nerve tracts. Spinal cord conducts sensory and motor impulses to and from the brain. It controls the reflex actions of the body.

5. How nerve impulses are transferred from one neuron to next neuron?
Answer:
All the information from the environment is detected by the receptors, located in the sense organs such as the eyes, nose, skin and 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 electrical signal reaches the brain or spinal cord. The response from the brain (or spinal cord) is similarly passed on to the effector organs such as the muscle or gland cell, that undergoes the desired response.

6. Classify neurons based on its structure.
Answer:
The neurons are classified, based on their structures:

(a) Unipolar neurons: Only one nerve process arises from the cyton, which acts as both axon and dendron. It is found in early embryos, but not in the adult.

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(b) Bipolar neurons: The cyton gives rise to two nerve processes, of which one acts as an axon, while another acts as a dendron. Bipolar neurons are found in the retina of the eye and olfactory epithelium of nasal chambers.

(c) Multipolar neurons: The cyton gives rise to many dendrons and an axon. Multipolar neurons found in the cerebral cortex of the brain.

IX. Higher Order Thinking Skills (HOTS) Questions

1. ‘A’ is a 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’.

  1. What is A?
  2. Name (a) bony cage ‘B’ and (b) membranes ‘C’
  3. How much is D?

Answer:

  1. A is spinal cord.
  2. (a) Bony cage is Vertebral column
    (c) is Meninges
  3. D is 31 pairs of spinal nerve.

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

  1. Name the cells L
  2. What are M and N?
  3. What is gap O?
  4. Name the chemical substance P?

Answer:

  1. Neuron
  2. Axon and Dendrites
  3. Synaptic Junction (knob)
  4. Neurotransmitter (Acetylcholine)