Kerala Syllabus 10th Standard Biology Guide Chapter 1 Sensations and Responses
List the variety of experiences experienced by the children and other organisms in the picture.
- A child tasting a mango.
- A snail withdrawing its body into the shell when it ¡s touched.
- Butterfly sipping nectar from flowers.
- The chirping of birds.
- The gentle pat of the breeze.
- The birds fly away on hearing sound.
- Enjoying colourful scenes
- The intoxicating fragrance of flowers.
- Washing the face using cold water.
What are the factors to which children and organisms respond in the picture?
What are stimuli?
The senses that evoke responses in organisms are called stimuli.
What are the differences between internal and external stimuli?
The senses from our immediate surroundings that evoke responses in organisms are called external stimuli. The stimuli that are formed inside the body are called internal stimuli. Hunger and thirst are examples for internal stimuli.
What are receptors.? Write its function also.
There are specialized cells in the sense organs and other parts of the body to receive stimuli. These cells are known as receptors. They receive stimuli and generate suitable impulses.
What are the functions of nervous system?
Normally, responses occur when the impulses generated by the receptors on receiving the stimuli reach the brain. The nervous system controls and co-ordinates these actions.
What are the major parts of nervous system?
Brain, spinal cord and nerves are the major parts of nervous system.
Neuron or nerve cell is the basic structural unit of the nervous system. Like all other cells, the neuron has a cell membrane, cytoplasm and nucleus.
Write the important parts, peculiarities and functions of neuron.
|Cell body (cyton)||It is the main part of neuron. It contains a nucleus and cytoplasm.||It carries impulses from the dendron to axon.|
|Dendron||Short filament from the cell body.||It carries impulses from dendrites to the cell body.|
|Dendrite||Branches of dendron.||Receives impulses from the adjacent neuron.|
|Axon||Longest filament from the cell body.||Carries impulses from the cell body to outside.|
|Axonite||Terminal branches of axon.||Carries impulses to the synaptic knob.|
|Synaptic knob||Tip of axonite.||Secretes neurotransmitter|
What is myelin sheath?
Axons of most of the neurons are repeatedly encircled by myelin, a membrane containing lipid. This is called myelin sheath.
Explain the formation of myelin sheath.
Nerve is a group of axons. Myelin sheath in the nerves is formed of Schwann cells. Myelin sheath in the brain and the spinal cord is. formed of specialized cells called oligodendrocytes.
What is the difference between grey matter and white matter?
The myelin sheath has a shiny white colour. The part of the brain and the spinal cord where myelinated nerve cells are present in abundance is called white matter and the part where nonmyelinated nerve cells are present is called grey matter.
What are the functions of myelin sheath?
The major functions of the myelin sheath are to provide nutrients and oxygen to the axon, accelerate impulses, act as an electric insulator and protect the axon from external shocks.
Explain how impulses are transmitted through neurons.
The outer surface of the plasma membrane of the neuron is positively charged and the inner surface is negatively charged. This is due to the difference in the distribution of certain ions. Impulses are messages conducted through nerves. These impulses transmit in the form of electric charges. Impulses are generated when stimuli evoke changes in polarity in the plasma membrane of receptors, the modified neurons.
The difference in the distribution of ions helps to maintain positive charge on the outer surface and negative charge inside the plasma membrane of the neuron. When stimulated, the ionic equilibrium in the particular part changes. As a result, polarity changes and the outer surface becomes negatively charged while the inner surface becomes positively charged. This change does not persist for long. It regains its original state. But the momentary charge difference in the axon membrane stimulates its adjacent parts and similar changes occur there too.
As this process proceeds, impulses get transmitted through axon. When stimulated, the distribution of ions in that particular part changes and hence the inner surface becomes positively charged and the outer surface becomes negatively charged . This momentary charge difference stimulates its adjacent parts and similar changes occur there too. As this process proceeds, impulses get transmitted as electric charges. Nerve impulses are messages transmitted through the neurons.
What is meant by synapse?
Synapse is the junction between two neurons or a neuron and a muscle cell or a neuron and a glandular cell. Synapse helps to regulate the speed and direction of impulses.
How do impulses pass through synapse?
When electric impulsesfrom the axon reach the synaptic knob, certain chemical substances are secreted from there to the synaptic cleft. These chemical substances are called neurotransmitters. They stimulate the adjacent dendrite or cell and new electric impulses are generated.
What are the different types of synapse?.
Synapse is the junction between two neurons or a neuron and a muscle cell or a neuron and a glandular cell.
Prepare a flow chart of impulses passing through a neuron.
Stimulus → Dendrite → Dendron → Cell body → Axon → Axonite → Synaptic knob → Synapse → Dendrite of adjacent neuron.
What are the different types of neuron?
On the, basis of the direction of impulse, neurons can be classified into sensory neurons and motor neurons. Sensory neurons carry impulses to the brain and spinal cord. Motor neurons carry impulses from the brain and spinal cord to various parts of the body.
What are nerves? Which are they? Write their peculiarities and functions.
Nerves are groups of axons or nerve fibres covered by connective tissue. On the basis of their functions, nerves are further classified into three.
a. Sensory nerve: Formed of sensory nerve fibres. It carries impulses from various parts of the body to the brain and the spinal cord.
eg: Optic nerve
b. Motor nerve: Formed of motor nerve fibres. It carries impulses from brain and spinal cord to various parts of the body.
eg: Hypoglossal nerve
c. Mixed nerve: Formed of sensory nerve fibres and motor nerve fibres. It carries impulses to and from the brain and spinal cord.
eg: Vagus nerve
How is nervous system classified? Write the peculiarities of each part.
The nervous system consists of two parts, namely the central nervous system and the peripheral nervous system. The central nervous system consists of brain and the spinal cord. The peripheral nervous system consists of 12 pairs,of cranial nerves and 31 pairs of spinal nerves.
Prepare a short note about the protection of brain.
The brain is protected inside the skull. It is covered by the meninges, a three-layered membrane. The cerebrospinal fluid is filled within the inner membranes of meninges and the ventricles of the brain.
What are the functions of cerebrospinal fluid?
The cerebrospinal fluid is filled within the inner membranes of meninges and the ventricles of the brain. The cerebrospinal fluid is formed from the blood and is reabsorbed into the blood. The functions of the cerebrospinal fluid are to provide nutrients and oxygen to the tissues of the brain, regulate the pressure inside the brain and to protect the brain from injuries.
Explain the main parts and functions of brain.
Cerebrum is the largest part of the brain and it has numerous fissures and folds. In cerebrum grey matter is seen in the external cortex and white matter is seen in the internal medulla. Cerebrum is the centre of thought, intelligence, memory and imagination. Cerebrum also evokes sensations and controls voluntary movements.
Cerebellum is the second largest part of the brain. It is seen behind the cerebrum as two flaps and has fissures, and grooves. Cerebellum coordinates muscular activities and maintains the equilibrium of the body.
Medulla oblongata :
The rod shaped medulla oblongata is seen below the cerebrum, located near to cerebellum. Medulla oblongata controls involuntary actions like heart beat, breathing, etc.
Thalamus is situated below the cerebrum. It acts as relay station of impulses to and from the cerebrum. Thalamus analyses impulses from the various parts of the body and sends the important ones to the cerebrum.
Hypothalamus is situatedjust below the thalamus and plays a major role in the maintenance of homeostasis.
What is the necessity of wearing helmets while riding two wheelers?
Wearing helmets while riding two wheelers reduces the impact of accident. About 70% to 80 % of death in two wheeler accident is due to the injury of brain
How is the spinal cord protected?
The spinal cord is protected inside the vertebral column. Like the brain, the spinal cord is also covered by meninges.
How does the dorsal root differ from ventral root?
A dorsal root and a ventral root join to form a spinal nerve. Sensory impulses reach the spinal cord through the dorsal root. Motor impulses go out of the spinal cord through the ventral root.
Write about the major functions of the spinal cord.
Impulses from different parts of the body are transmitted to and from the brain through the spinal cord. It also coordinates the repeated movements during walking, running, etc.
What are reflex actions? Write examples also.
The accidental and involuntary responses towards stimuli are called reflex actions.
- Sudden withdrawal of leg while touching a thorn.
- We blink our eyes when objects come towards our eyes.
Explain reflex arc.
Reflex arc is the pathway of impulses in the reflex action.
Prepare a flow chart related to reflex arc.
What is the difference between spinal reflex and cerebral reflex?
Mainly spinal cord acts as the centre of reflex action and such reflexes are called spinal reflexes, eg: Sudden withdrawal of leg while touching a thorn.
But all reflexes are not under the control of the spinal cord. Reflexes under the control of the cerebrum are called cerebral reflexes.
eg: We blink our eyes when light suddenly falls on our eyes.
Is it advisable to lift up people quickly by holding their arms or legs in an accident?
It is not advisable to lift up people quickly by holding their arms or legs in an accident, because these actions may lead to injuries in spinalcord.
What are the changes that take place in the body during emergency situations?
Heart beat increases, breathing rate increases, body shivers and the production of saliva decreases.
Explain autonomous nervous system.
Activities that take place beyond the conscious level are controlled by the autonomous nervous system, a part of the peripheral nervous system. The autonomous nervous system contains the sympathetic system and the parasympathetic system.
Write the action of sympathetic and parasympathetic systems during emergency situations.
|Organ||Sympathetic system||Parasympathetic system|
|Eye||The pupil in the eye dilates||The pupil constricts|
|Salivary gland||Production of saliva decreases||Production of saliva increases|
|Lung||Trachea dilates||Trachea constricts|
|Heart||Heartbeat increases||Heartbeat becomes normal|
|Stomach||Gastric activities slow down||Gastric activities become normal|
|Liver||Glycogen is converted to glucose||Glucose is converted to glycogen|
|Intestine||Peristalsis slows down||Peristalsis becomes normal|
|Urinary bladder||Urinary bladder retains to normal state||Urinary bladder contracts|
Prepare a note on the diseases affecting the nervous system.
Caused by the accumulation of an insoluble protein in the neural tissues of the brain and neurons get destroyed. The major symptoms are loss of memory, inability to recognize friends and relatives and inability to do routine works.
Caused by the destruction of specialized ganglions in the brain due to reduced production ofdopamine, a neurotransmitter. The major symptoms are loss of body balance, irregular movement of musc les, shivering of the body and
Caused by continuous and irregular flow of electric charges in the brain. The
symptoms of epilepsy are due to continuous muscular contraction, frothy discharge from the mouth, clenching of the teeth following which the
patient falls unconscious.
Let Us Assess
The part of the brain which helps to maintain body balance.
c. Medulla oblongata
Identify the relation and fill in the blank.
Irregular flow of charge in the brain : Epilepsy Decreased production of dopamine : ………………….
Analyze the following instances and answer the questions.
- A thorn accidental ly pierces the foot
- The leg is withdrawn
- The thorn is taken out slowly
a. Write the stimuli and responses.
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 were transmitted.
a. Stimuli -touch
Response – withdrawal of leg
b. The thorn is taken out slowly
c. No. Reflex action
Stimulus → receptor → sensoryneuron → intemeuron → motor neuron → related muscle → withdraws the leg.