Kerala State Syllabus 10th Standard Biology Solutions Chapter 1 Sensations and and AnswersResponses
Questions and Answers
Page 5Question 1 -Children and other organisms have a variety of experiences? What are they?
Answer:
•A child tasting a mango.
•A snail withdrawing its body into the shell when it is touched.
•Feel cold when washing face.
•Birds are flying when making sound.
Question 2.
What are the factors to which children and organisms respond here?
Answer:
•Touch
•SoundTasteSmall
Stimulus: The senses that evoke responses in organisms are called stimuli. These are two types, external and internal stimuli.
External stimuli: Sound, touch, heat, chemicals, pressure, cold radiations.
Internalstimuli:Hunger,touch,infection,pressure variation third exhaust
Page 8• Nerve cells or receptors that are capable of receiving stimuli from within the body and external environment are located in sense organs.• Nerve cells are capable of receiving stimuli from within the body and external environment. They also transmit messages to and from central nervous system and organs.• The function of the nervous system is to generate and coordinate responses according to internal and external changes.• The nervous system includes the brain, spinal cord, nerves, and receptors.
Neuron
A neuron has mainly the following parts a cyton (cell body), impulse receiving dendrons and branches of dendrons is dendrites, impulse transmitting axon and branches of axon is aconites, synaptic knobs for secreting neurotransmitter. In certain neurons, the nerve fibers are covered by myelin sheath, made up of white Schwann cells.
Formation of myelin sheath:
Schwann cells, a part of nervous tissues repeatedly encircle the axon to form the myelin sheath. Myelin sheath in the brain and spinal cord is formed of specialized cells called Oligodendrocytes. The myelin sheath has a shiny white colour.
Functions of myelin sheath:
•Provide nutrients and oxygen to the axon.
•Accelerate impulses.
•Act as an electric insulator.
•Protects the axon from external shocks.
•Gives white appearance (white matter) to the neural parts.
Generation Of Impulses
The difference in the distribution of ions maintains positive charge on the outer surface and negative charge inside the plasma membrane of the receptor part of neuron. When stimulated, this ionic equilibrium (olarity) changes tNervousNervoushere and the outer surface becomes negatively charged and inner become positively charged. As a result, impulse generated. This charge difference stimulates its adjacent parts and similar changes occur there too. Thus a continuous flow of the impulse becomes possible.
Charges on either side of the plasma membrane in a resting state:Positive charge on the outer surface and negative charge inside the plasma membrane of the neuron.
Charges in the distribution of ions on both sides of the plasma membrane when it gets stimulated:
When stibrainmulated, the ionic equilibrium in a particular part changes. As a result polarity changes and the outer surface becomes negatively charged while the inner surface becomes positively charged. The change does not persist for long.
Nerves
Nerves are groups of axons or nerve fibers. They are covered by connective tissue.
Sensory nerve:
Carry impulses from various parts of the body to the brain and the spinal cord. Formed by the union of sensory nerve fibers.
Motor nerve:
Carry impulses from brain and spinal cord to various parts of the body. Formed by the union of motor nerve fibres.
Mixed nerve:
Formed by the union of sensory and motor fibres. Carry sensory impulses from the receptors to the brain or spinal cord. Carry motor impulses from brain or spinal cord to different parts of the body.
Nervous System
The nervous system consists of two parts, namely the central nervous system and the peripheral nervous system.
Brain
The brain contains the greatest number of neurons in the nervous system.
Protection of the brain:
The brain is protected inside a hard skull and is covered by a three-layered membrane, called the meninges. Cerebrospinal fluid, a fluid formed inside the meninges. It regulates the pressure inside the brain and to protect the brain from injuries.
Nourishment of the brain:
The cerebrospinal fluid formed from blood is reabsorbed into the blood. It provides nutrients and oxygen to the tissues of the brain.
Different parts of brain:Human brain has outer cerebrum, cerebellum and medulla oblongata and inner thalamus and hypothalamus.
spinal cord
Spinal cord, which is the continuation of medulla oblongata, is situated within the vertebral column and is covered by a three-layered membrane, called meninges. The outer part of spinal cord is white matter and inner is grey matter. The central canal at its center is filled with CSF. There are 31 pairs of spinal nerves arising from the spinal cord. A dorsal root and a ventral roof join to form a spinal nerve.
Reflex Actions:
Reflex actions are the accidental and involuntary responses of the body in response to a stimuli. There are cerebral and spinal reflexes.
Reflex Arc:
Reflex arc is the pathway of impulses in the reflex action
.Autonomous nervous system:
The autonomous nervous system is composed of the sympathetic system and the parasympathetic system.
There are many activities which occur beyond our conscious area. Such activities are controlled by the autonomous nervous system. The endocrine system is also associated with the nervous system for performing this function.
Sensations and Responses Let Us Assess
Question 1.
The part of the brain which helps to maintain body balance,
a) Cerebrum.
b) Cerebellum.
c) Medulla oblongata.
d) Thalamus.
Answer:
b) Cerebellum.
Question 2.
Identify the relationship and fill in the blanks.
Irregular flow of charge in the brain: Epilepsy.
Decreased production of dopamine:….?
Answer:
Parkinsons.
Question 3
Analyse the following instances and answer the questions.
1) a thorn accidentally pierce the foot.
2) the leg is withdrawn.
3) the thorn is taken out slowly.
a) Write the stimuli and response.
b) Which is the conscious response?
c) Was the leg withdrawn after sensing the pain? Which action took place there? Prepare an illustration showing the parts through which the impulses transmitted.
Answer:
a) A thorn accidentally the foot (stimulus) and the leg is withdrawn (response).
b) The thorn is taken out slowly.c) No, reflex action.
Stimulus → Receptor → Sensory nerve → Interneuron → motor nerve → related muscle → Withdrawl of leg.
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