SSLC Biology: Chapter 01 Sensations and Responses - Questions and Answers


Questions and Answers for Class 10 Biology അറിയാനും പ്രതികരിക്കാനും | Text Books Solution Biology (English Medium) Chapter 01 Sensations and Responses

Class 10 Biology Chapter 01 Sensation and Responses
* Study Notes
* Stimulus:  the senses that evoke responses in organisms
* External stimuli:- Sound, touch, heat, pressure, cold
* Internal stimuli:- Hunger, thirst, infection …
The Nervous system generates and coordinates responses through impulses.

* Human nervous system 
The human nervous system includes receptors that receive stimulus and generates impulses, nerves – carries impulses and brain and spinal cord – they control and coordinate life activities according to impulses.

* Neurons (nerve cells):- The structural and functional units of the nervous system.

* Myelin sheath: 
⦁ Most neurons are repeatedly encircled by Schwann cells to form a myelin sheath.
⦁ In the brain and spinal cord, myelin sheath formed by oligodendrocytes. 
* Function: 
⦁ Provide Oxigen and nutrients to axon
⦁ Accelerates impulses
⦁ Act as an electric insulator
⦁ Protect the axon from external shocks 
* Myelin sheath has a shiny white colour
⦁ Myelinated nerves are seen in abundance in the brain and spinal cord – White matter
⦁ Non-myelinated nerves are present in abundance – Grey matter 

* Synapse: The junction between neurons or between neurons and muscles or glands. It regulates the speed and direction of impulses.
The impulses are transmitted across the synaptic cleft only through a chemical (neurotransmitter), secreted from the synaptic knobs. Acetylcholine and Dopamine are neurotransmitters.
* Impulse generation:
When stimulated, this ionic equilibrium (polarity) changes there and the outer surface becomes negatively charged and the inner becomes positively charged. As a result, impulse generated. 

* Impulses are electrical messages conducted through nerves.
Transmission of impulse: Impulse due to stimulus – dendrites – dendrons – cyton – axon – axonites – synaptic knob – secretion of neurotransmitter to the synaptic cleft –stimulation in the adjacent dendrites – impulse forms.

* Types of neurons:
Sensory: Carry impulses from sense organs to the brain and spinal cord.
Motor: Carry impulses from the brain and spinal cord to different organs.
Mixed: Carry impulses from brain and spinal cord to different organs and vice versa

* Classification of the human nervous system:
a. Central nervous system (Brain and Spinal cord)
b. Peripheral nervous system (12 pair Cranial nerves and 31 pair Spinal nerves)
* A few peripheral nerves act as Autonomous nervous system (Sympathetic nerves and parasympathetic nerves)

I. Central nervous system 
A. Brain: Protected inside a hard skull and is covered by three-layered meninges. Cerebrospinal fluid, a fluid formed inside the meninges, also protects it.
CSF provides nutrients and oxygen to brain tissues, regulates the pressure inside the brain and protects the brain from injuries.
Five functional parts of the brain are,
1. Cerebrum: largest part with fissures and folds. The cerebral cortex is grey coloured. Centre of thought, imagination, intelligence and memory. Evokes sensations, Controls voluntary movements.
2. Cerebellum: seen as 2 flaps, behind the cerebrum. Coordinates muscular activities and maintains the equilibrium of the body.
3. Medulla oblongata: rod-shaped lower part. Controls involuntary actions like heartbeat and breathing.   
4. Thalamus: the seat of the cerebrum. Acts as a relay station of impulses to and fro the cerebrum and also analyses the impulses.
5. Hypothalamus: seen below the thalamus. Plays a major role in the maintenance of homeostasis.

B. Spinal cord: protected inside the vertebral column and is covered by the meninges. The central canal is filled with cerebrospinal fluid. Outer white matter while inner grey matter. Spinal nerves originate from the spinal cord as dorsal root  (sensory) and ventral root (motor).
The spinal cord transmits impulses from different parts of our body  to and fro the brain., Coordinates the repeated movements during walking, running etc.      Also affects certain reflex actions.
* Reflex action: the accidental and involuntary responses of the body, in response to a stimulus.
a. Cerebral reflexes (Eg:-Blinking of eyes, sudden fright when hearing a loud noise or seeing a snake, sneezing)
b. Spinal reflexes (Eg:- On touching a hot object, the hand is withdrawn, withdrawal of  the leg when a spine pierce into the feet)

* Reflex arc: the pathway of impulses in a reflex action. 
This includes,
a. stimulus receiving receptor
b. sensory neuron        
c. inter neuron
d. motor neuron           
e. affecting muscles.
    
II. Peripheral nervous system 
Peripheral nervous system including 12 pair cranial nerves and 31 pair spinal nerves. It connects the central nervous system with different organs of our body.
The autonomous nervous system, a part of the peripheral nervous system controls the activities of different organs beyond the conscious level. The sympathetic system and parasympathetic system together form the autonomous nervous system. 
The sympathetic system helps to prepare for overcome the emergency situation. And parasympathetic system helps to regain all stimulated activities into normal.

* The sympathetic system includes the ganglion network on both sides of the vertebral column and related nerves. The nerves from the brain and the last ganglions from the spinal cord constitute the parasympathetic system.

* The disorders of the nervous system 


* Questions and Answers

1. The brain has a fluid that is formed from blood and reabsorbed into the blood.
(a) Identify the fluid.
(b) What are the functions of that fluid?
Answer:
a) Cerebrospinal fluid
b) Provides nutrients and oxygen to brain tissues, protects the brain from injuries

2. Complete the table by placing the following statements suitably in the table given below
(i) Part of the Central nervous system
(ii) Part of the peripheral nervous system
(iii) Covered with meninges
(iv) All nerves from here are mixed nerves
(v) Cerebral ventricles are filled with CSF
(vi) Central canal is filled with CSF
(vii) Site of memory and imagination
Answer:

3. Mention any three physiological activities retarded due to the action of the Sympathetic system.
Answer:
Production of saliva
Gastric activities
Intestinal peristalsis

4. Mention any three physiological activities that came into a normal state by the action of the Parasympathetic system
Answer:
Heartbeat
Gastric activities
Intestinal peristalsis

5. Observe the illustration and answer the questions.

a) Identify A and B.
b) Write any two functions of B.
Answer:
a) A- axon, B - myelin sheath
b) provide nutrients and oxygen to the axon, accelerate impulses, act as an electric insulator and protect the axon from external shocks.

6. Analyse the illustration and answer the questions.
Different parts of the body ------(A)----> Central nervous system -----(B)----> Different parts of the body.
a) Identify the nerves indicated A and B.
b) Name the nerve that performs the functions of both nerves A and B.
Answer:
a) A- Sensory nerve B- Motor nerve
b) Mixed nerve

7. Analyse the given statements and answer the questions.
A- "The sympathetic system stimulates all physical activities".
B - " The sympathetic system stimulates some physical activity and reduces certain functions".
(a) Which statement do you agree with? Justify your answer.
Answer:
B - " The sympathetic system stimulates some physical activity and reduces certain functions".
Production of saliva decreases, Gastric activities slow down, Peristalsis in the intestine slows down.

8. Some physical activity will change when you feared.
a) Identify the part of the autonomous nervous system that regulates physical activity in this context.
b) What are the changes made by this system to the organs heart, liver, and salivary glands?
Answer:
a) Sympathetic system
b) Heartbeat increases, Glycogen is converted to glucose, Production of saliva decreases.

9. "Synapse has a major role in controlling the direction of  impulses "
Justify the statement citing appropriate evidence.
Answer:
Neurotransmitters secrete from the synaptic knob to the synaptic cleft. So impulse can travel only from a neuron's axonite to the dentrite of another neuron through a synapse. For this reason, the Synapse has a major role in controlling the direction of impulse.

10. The main symptoms of a disease affecting the nervous system are given below. Analyze the symptoms and answer the questions.
Loss of body balance.
Irregular movement of muscles.
Profuse salivation.
a) Identify the disease.
b) Write the causes of this disease.
Answer:
a) Parkinson's disease.
b) Destruction of specialised ganglions in the brain. Decrease in the production of the neurotransmitter, dopamine in the brain.

11. Formation of impulses in a neuron is illustrated below.
a) Which factor in diagram A causes charge difference?
b) What difference can you observe in diagram B, when compared to diagram A.? Write the reason.
Answer:
a) Stimulus
b) In diagram A, in the stimulated part the inner side of the membrane became positively charged and the outer side became negatively charged.
In diagram B, the momentary charge difference stimulates its adjacent parts and similar changes occur there too. As this process proceeds, messages are transmitted through the axon.

12. “Impulses are formed due to the change in the distribution of ions on either side of the plasma membrane of a neuron”
a) What changes occur to the charges on either side of the plasma membrane during impulse formation?  Which factor causes this.?
b) How does charge difference transmits from one part of the neuron to the other?
Answer:
a) Outer side of the plasma membrane becomes positively charged and the inner part becomes negatively charged. The difference in the charge on either side of the plasma membrane is due to stimulus.
b) Stimulus changes the equilibrium of ions on either side of the plasma membrane. So at the stimulated part outer side of the membrane has a negative charge and the inner side has a positive charge. This momentary charge difference stimulates its adjacent parts and similar changes occur there too. As this process proceeds, messages are transmitted through the axon.

13. Identify the odd one and write the common feature of others.
Touch, Sound, Smell, Thirst
Answer: Thirst - Others are external stimuli

14. Identify the word pair relationship and fill the blanks.
Myelin sheath: Covers and protects axon.
................................: Covers and protects the brain
Answer: Meninges

15. Find out the correct statements related to myelin sheath from those given below.
a) Dendrons of all neurons are covered with a myelin sheath.
b) Myelin sheath in the nerves are made up of Schwann cells and that of the brain and spinal cord is formed of oligodendrocytes.
c) Myelin sheath has a dark colour.
d) Myelin sheath reduces the speed of impulses through the axon.
Answer:
b) Myelin sheath in the nerves are made up of Schwann cells and that of the brain and spinal cord is formed of oligodendrocytes.

16. A fluid fills the internal membranes of Memninges.
a) Identify the fluid?
b) Write any one function of this fluid.
Answer:
a) Cerebrospinal fluid.
b) Provides nutrients and oxygen to the tissues of the brain, regulate the pressure inside the brain and protect the brain from injuries.

17. Identify the parts of the nervous system with each of the following functions.
a) Plays a major role in the maintenance of homeostasis.
b) Acts as a relay station of impulses
Answer:
a) Hypothalamus
b) Thalamus

18. Analyse the following statements and write the reasons for each.
a) Cerebral cortex is called Grey matter.
b) The spinal nerves are mixed nerves.
Answer:
a) The cell body and the nerve parts without myelin sheath form the cerebral cortex. So cerebral cortex is called Grey matter.
b) The spinal nerves are mixed nerves because they contain the sensory nerve fibres carrying impulses to the spinal cord and motor nerve fibres carrying impulses to different body parts.

19. Prepare a flow chart using the words given below related to reflex arc.
Motor neuron, receptor, muscle, interneuron, sensory nerve
Answer:
receptor
⬇
sensory nerve
⬇
interneuron
⬇
Motor neuron
⬇
muscle

20. Which of the following statements are correct in connection with the transmission of impulse through synapse?
a) Transmits from the cell body of one neurone to the cell body of the adjacent neuron.
b) Transmits from the synaptic knob of one neurone to the dendrite of an adjacent neuron.
c) Transmits from the synaptic knob of one neurone to the axonite of the adjacent neurone.
d) Transmits from the dendrite of one neurone to the axonite of the adjacent neurone.
Answer:
b) Transmits from the synaptic knob of one neuron to the dendrite of an adjacent neuron.

21. Which of the following indicates white matter?
a) The part where the cell body and axon of nerves are present.
b) The part where the cell body and non-myelinated neurons are present.
c) The part of the brain and the spinal cord, where myelinated neurons are present in abundance.
d) The part where a large number of axons are present.
Answer:
c) The part of the brain and the spinal cord, where myelinated neurons are present in abundance.




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