NERVOUS SYSTEM

CENTRAL NERVOUS SYSTEM

The central nervous system consists of brain and spinal cord.

Human Brain
À Brain is the highest coordinating centre in the body.
À It is present in the bony box in the skull called cranium. It is surrounded by three membranes called meninges.
À The space present between the membranes is filled with a cerebrospinal fluid that protects the brain from mechanical shocks and acts like a cushion.
À The brain is divided into three regions- forebrain, midbrain and hindbrain.

Human Brain It consists of three parts

Forebrain
1.Cerebrum
2Hypothalamus


2.Midbrain

3.Hindbrain
1.Cerebellum
2.Pons
3. medulla oblongata

Cerebrum1. It is the most complex and largest part of the brain.
2..It is the site of our faculties such as learning, reasoning, intelligence, personality and memory. All our thoughts, sensations, actions and movements are controlled by the cerebrum.

3.The cerebrum has different areas for performing different functions.
1. Sensory area: The information is received from the sense organs like eyes, ears, nose, tongue, and skin and gives sensation of feelings.
2. Motor areas: Instructions are sent to various organs or muscles to do various types of activities.

3. Association areas: They register and store information and respond by interpreting past experiences, they are associated with reasoning, learning and intelligence.
4. In cerebrum five lobes are present to control specific activities.

1. Occipital lobe…Visual reception
2. Temporal lobe…Auditory reception
3. Parietal lobe……Perception of general sensation like touch, smell, temperature and conscious association.
4. Frontal lobe……Muscular activities, both voluntary and involuntary. It also includes speech, thought and memory etc.

HYPOTHALAMUS
Controls and regulate body temperature, hunger, thirst, blood pressure etc.

MIDBRAIN

The midbrain controls reflex movement of the head, neck and trunk in response to visual and auditory stimuli.
It also controls eye muscles, change in pupil size and shape of the eye lens.
HINDBRAIN

Cerebellum…..
1. Controls and coordinates precise and accurate movements such as walking in a straight line, riding a bicycle and picking up a pencil, etc.
2. It also helps in maintaining posture and balance of the body.
Pons…..It acts as a bridge carrying all sensory and motor neurons between brain and spinal cord.
Medulla Oblongata…..1. Posterior most part of the brain. Continues into spinal cord.
2.Have reflex centers to control activities like swallowing, coughing, sneezing, vomiting, heart beat, swallowing and breathing etc.

REFLEX ACTION

REFLEX ACTION

Reflex action is a rapid automatic and involuntary response to a stimulus which is not under the control of the brain.
If we unknowingly touch a hot object, we immediately move our hand away from it. So moving our hand away on touching a hot plate is an example of reflex action.
A knee jerk, coughing, yawning, blinking of eyes, sneezing, salivation, movement of diaphragm during breathing are all examples of reflex actions.


REFLEX ARC





The nerve pathway involved in a reflex action is called a reflex arc.
If we unknowingly touch a hot object, this heat is sensed by a heat receptor (Thermo receptor) in our hand.
The receptor starts an impulse in a sensory neuron, which transmits the message to the spinal cord.
The impulse is passed to the relay neuron, which is in turn passes to motor neuron.
The motor neuron passes the impulse to a muscle in our arm.
The muscle of arm is an effector organ because it responds to the stimulus.

Stimulus → Receptor → Sensory neurons
↓
Effector organs ← motor neurons ← spinal cord

Dear students this is the diagram of reflex arc.

Dear students If diagram of reflex arc is asked

SENSE ORGANS

Animals have five sense organs.
1. Photoreceptor - respond to light……..eyes
2. Phonorceptor - respond to sound……ears
3. Olfactory receptor - respond to smell…….nose
4. Chemoreceptor - respond to chemicals…tongue
5. Thermo receptor - respond to heat ……..skin

CONTROL AND COORDINATION IN HUMANS

Control and Coordination in Humans

There are two types of coordination of activities in humans. These are:
Nervous system
Endocrine system
In human beings, nervous system and endocrine system work together to control and coordinate all our activities such as our physical actions, our thinking processes and our emotional behavior.
Human Nervous System
Nervous system is composed of two main components:
Central nervous system(CNS): It includes brain and spinal cord
Peripheral system (PNS): It includes all the nerves arise from brain (cranial nerves) and spinal cord (spinal nerves).These nerves are present outside the CNS and connect brain and spinal cord to all parts of the body.

STRUCTURE OF A NEURON

Nervous system is made of special cells called neurons. The neurons carry messages in the form of electrical impulses or nerve impulses. A neuron has three components:
Cell body or cyton
Dendrites
Axon.
Cell body or cyton

1. The cell body contains a nucleus and cytoplasm. In the cytoplasm are embedded different cell organelles like mitochondria, Golgi apparatus, endoplasmic reticulum etc. 2.From the cell body extend out two kinds of protoplasmic extensions the cell body – dendrites and axons.
Dendrites
Dendrites are short and branched processes. They carry the impulse towards the cell body.

Axon
1. It is a long process, may be several centimeters long. It conducts nerve impulses away from the cell body.
2. The axon has an insulating and protective sheath of myelin around it.
Neurons are of three types:
Sensory neurons: They carry nerve impulses from receptors to the central nervous system. They carry stimulus from receptors.
Receptors → CNS
Motor neurons: They take nerve impulses from CNS to effector organs that may be a muscle or gland.
CNS → Effector
Interneuron or relay neurons: They are found only in CNS and make links between sensory and motor neurons.

SYNAPSE

3. There is no physical connection between the neurons at synapse and so the impulse has to pass through the synapse to be passed on to other neurons.


How do we detect that we are touching a hot object?

All information from our environment is detected by the tips of dendrite of nerve cells. These receptors are usually located in our sense organs, such as the inner ear, the nose, the tongue, the skin and the eyes.
1. Hot object is a stimulus. When a stimulus acts on a receptor, a chemical reaction is set off that creates electrical impulse.
2.This impulse travels from the dendrite to the cell body and then travel along its axon.
3.At the end of axon synapse is present; a microscopic gap between two neurons, thus electrical impulse can not directly pass between two neurons.
4. At the end of axon, the releases small amount of a chemical substance called acetylcholine into the synapse. This chemical substance starts a similar electric impulse in the dendrite of the next neuron. As acetylcholine transmits impulse of one neuron to another so it is called as neurotransmitter.
5. In this way it can be transmitted to a third neuron and so on. Finally reaches to the brain. The motor neurons bring message from the brain in the form of electrical impulse to the effector organs like muscles and glands.

Transport of materials in plants

TRANSPORT OF FOOD AND OTHER SUBSTANCES IN PLANTS

1.Leaves make food by the process pf photosynthesis. The food made by leaves is in the form of simple sugar (glucose). Other types of substances are called plant hormones are released from the tips of roots and shoots. Now every part of the plant needs food and other substances. So these substances are to be transported to all the parts of the plants like roots, stems, growing

regions etc. The movement of food from leaves to other parts of the plant is called Trans location. In plants, phloem Trans locates the food and other substances.

2.Phloem consists of sieve tubes and companion cells. Sieve tubes are living cells which contain cytoplasm but do not have nucleus. So its function is supported by companion cell. Each sieve tube has a companion cell next to it.

3.Food is prepared in the Mesophyll cells of a leaf. Food is trans located in the form of sucrose. The movement of water and dissolved minerals in xylem is always upward (from soil to leaves). The movement of food can be upward as well as down ward depending upon the needs of the plants.




The mechanism of transport of food in a plant.:-

1.The movement of food in the phloem takes place by utilizing energy. The areas where the nutrients are stored known as sink (e.g. root) and where they originate as source ( leaf). The movement of food is always from the source to the sink.

2.At source, leaves food is prepared in the form of glucose. Glucose is converted into sucrose. Sucrose enters into the phloem at the expense of energy from ATP.

3.The osmotic concentration of phloem will increase. Water now enters into sieve tubes by the ocess of osmoses due to which the hydrostatic pressure in the phloem tissue rises.

4.This high pressure produce in the phloem tissues allow the movement of food to all parts of the plants having low pressure in their tissues. At sink, sucrose move from the phloem into the storage site or growing parts of the plants. Water will also move out from phloem. Hydro static pressure will decrease in phloem at sink.

5.A pressure gradient is set up in the phloem with high pressure at source and low pressure at sink. So the phloem sap with food will move from source to the sink. The phloem transports food according to the need of the plant e.g., in spring even the sugar stored in the roots or stem tissue of a plant would be transported through phloem to the buds which need energy to grow.

Transport of water in plants
Plants need raw materials like CO2, water and minerals for photosynthesis and for various other purposes such as making of proteins. For plants soil is the richest source of water and minerals. Roots absorb these substances and transport to the various parts of the plant. The water and minerals dissolved in it move through special tissue present in plants called xylem. Xylem consists of two kinds of elements called tracheids and vessels. Vessels and tracheids of the roots, stems and leaves are interconnected to form a continuous system of water conducting channels reaching all parts of the plant.

1. The cells of root actively take up ions from the soil. This creates a difference in the concentration of these ions between the root and soil. Inside the root the concentration of ions is more than the soil. Cell of the root is hypertonic in nature. So water moves cosmetically into the root from the soil. Water reaches then to the xylem this result in hydrostatic pressure in the xylem. This pressure is known as root pressure that forces the water up in the plant.

2. However, this pressure is not enough to move water in tall plants. To move water in tall plants, plants use another process known as transpiration pull.

3. According to transpiration pull, water is lost in the form of water vapours through the stomata. Stomata take water from the deeper cells. Finally the water is taken from the xylem vessels of the leaf.

4. The water is in the xylem behaves like a solid column because of strong force of attraction between water molecules.

5. The evaporation of water molecules from the cell of the leaf creates a suction which pulls water from the xylem cells of root. The lose of water in the form of vapour from the aerial parts of the plant is known as transpiration.

SIGNIFICANCE OF TRANSPRATION

1 It helps in the absorption and upward movement of water and minerals from roots to the leaves.
2 It also helps in the temperature regulation. It protects the plant from heat injury.

How water is transported at night in plants.?

Ans:- During the day, when the stomata are open, the transpiration pull becomes the major driving force in the movement of water in the xylem. During night, when stomata are closed, the transport of water is through root pressure.

structure of human heart

Heart is a pumping organ that keeps the blood continuously moving in the blood vessels. It is a blunt conical organ of about 12cm long and 9 cm broad. Its narrow apex is pointed downward and to the left. Heart is enclosed in a doubled walled sac, called pericardium. In between the two layers fluid filled space; the fluid is called pericardia l fluid and it prevents any friction between the heart walls and the surrounding tissues.

Human heart consists of four chambers. The two upper chambers are called atria (or auricles) and the two lower ones the ventricleTwo auricles are separated by an interatrial septum.
Two ventricles are separated by an interventricular septum Septum prevents the mixing of oxygenated blood and deoxygenated blood. The right auricle and right ventricle guarded by tricuspid valves. The left atrium and left ventricle are guarded by bicuspid valve. Both the valves are attached to chordae tendinae, the tough strands of connective tissue which in turn are attached to the papillary muscles of ventricles.

Heart is made of special muscles cells called cardiac muscles Bicuspid and tricuspid valves allows only unidirectional flow of blood i.e. from atria to ventricles Ventricles are far thicker walled than atria because ventricles pump out the blood with force to the different parts of the body, Left ventricles are far thicker walled than right ventricles as it is pumping the blood to different parts of the body a right ventricle is only up to lungs From right atrium the deoxygenated blood enters the right ventricle through tricuspid valves From right ventricle the deoxygenated blood is pumped out through pulmonary artery to lungs for oxygenation. Oxygenated blood from left atrium enters the left ventricles through bicuspid valve. From left ventricle, the oxygenated blood is pumped out into aorta, the largest artery which takes the blood to the body. In the tissues a capillary network allows the exchange of gases and food substances. Finally the deoxygenated blood flows through venules and then veins. This blood is returned to the right atrium through inferior and superior vena cava and inferior vena cava pour deoxygenated blood to the right atrium. Pulmonary veins from lungs pour oxygenated blood into left atrium. Right atrium pours deoxygenated blood into right ventricles right ventricles. Left atrium pours oxygenated blood into left ventricle.
CARDIAC CYCLE

1.contraction of atria.
right atrium recieves blood from vena ceva and pours into right ventricle. left atrium recieves blood from pulmonary vein and pours into left ventrical.
2.Contraction of both ventricles (Atria start relaxing):
from right ventricle, deoxygenated blood flows to the lungs through pulmonary artery.From left ventricle pours blood into aorta sends blood to the various parts of the body.