CBSE Class 10 Science Control And Coordination Notes Set D

CONTROL & CO-ORDINATION

9.1 INTRODUCTION :

All the living organisms show the irritability or sensitiveness. It is the property to give response to the stimulus. The stimulus can be external or internal. The living organisms adapt themselves to the external and internal factors with proper adjustment. This adjustment of the vital activities of life is called co-ordination. The working of one system is co-ordinate with that of other system .e.g., During eating our body performs several kinds of coordinated activities. The  nose differentiates the smell of food and hand serve as the organs of ingestion. the alimentary canal and glands help in the digestion of food. Thus various organs perform co-ordinate activities.

9.1 (a) Control and Co-ordination :

Control and co-ordination also help to maintain a steady state of stability and steady state within an organism in constantly changing environment. The mechanism of maintaining internal steady state is called homeostasis. A mountaineer feels lack of oxygen  a high altitudes In order to cope with this condition, more number of RBCs are produced. It is the internal environment (physiologically) that adjusts to the external stress i.e. lack of oxygen. Similarly mammals are capable of maintaining a constant body temperature. The vital activities of an organism are controlled by endocrine system and nervous system. There are two types of co-ordinations i.e., nervous and hormonal co-ordination. In animals both hormones and neurons (structural and functional unit of nervous system) are involved in regulating and coordinating the various vital activities. In plants only chemical (phytohormones) co-ordination is present.

9.2  CHEMICAL CO-ORDINATION IN PLANTS :

9.2 (a) Movements in Plans :

The plants are fixed in the soil so they cannot avoid various stimuli by moving away. There is no ‘brain-like’ structure in plants to adapt themselves according to the changes in their surroundings. Still the plants show the positive or negative responses to light, water, gravity, touch etc. The movements of plants due to stimuli are called the tropic or curvature movements. The response of a part of the plant to light is called phototropism. The stem is positively phototropic (grown towards light) while the root is negatively phototropic. The growth response of a part of plant to gravity (attraction force of the earth) is called geotropism. The shoot is negatively geotropic while the root is positively geotropic. Chemotropism is due to the chemical stimulus e.g. growth of pollen tube. The Response to a stimulus, independent o direction, is called nastic movement. The Leaves of Mimosa pudica (Touch-me-not) droop own (bend) on touching.

9.2 (b) Effect of Light :

Flowering and seed germination are regulated by the duration of light, This phenomenon called photoperiod sum. Plants respond to this stimulus (light duration) with the help of phytochorme pigment. Phytochrome is a proteinacesous pigment and controls several light dependent developmental processes like germination, growth and flowering. Phytochrome exists in two forms Pr and Pfr . Pfr is active form and both are intervconvertible.

9.2 (c) Photoperiodism and Flowing :

It is a physiological change occurring in plants in response to relative length of the day and light. The term photoperiodism was used by Graner and Allard for the response of plants to photoperiods expressed in the form of flowering. On the basis of photoperiod there are three classes of plants.

(i) Shor day plants       (ii) Long day plants   (iii) Day neutral plants

9.2 (b) Vernalization and Flowering :

The term vernalization was coined by Lysenko for promotion of flowering by a previous cold treatment. For flowering in winter varieties, winter cold treatment is necessary. In nature, plant requiring cold treatment usually behaves as biennial. The germinate and grow vegetatively in first season and produce flowers during second seasons after getting the cold treatment. The suitable temperature for vernalizatin is 40C and time period varies from 4 days to 3 months.

Table : Difference between phototropism and photoperiodism

GROWTH REGULATORS :

The growth regulators are the important chemical affecting growth. Growth hormones (phytohormones) are the natural growth substances which are produced in any part of the plant and are transferred to another part and there they influence the growth of plant. The growth regulators consist of auxins , gibberellins, cytokinins, ethylene and abscisic acid. Except abscisic acid, ethylene the three are called growth hormones and ethylene, abscisic acid are growth inhibitor.

9.3 (a) Auxins :

Auxins are the growth hormones which were first discovered by Charls Darwin. Auxins are the weak organic acids which can promote elongation and growth. These are produced in the apical meristem (tips of root and stem), young leaves, flower  buds and fruits. The first discovered plant hormone was identified as indole acetic acid (I.A.A.).

(i) Functions of auxins :

(A) Cell enlargement and elongation : Auxins loose the cell wall, increase membrane permeability and synthesis wall microfibirlls. All these activities result in the cell enlargement and elongation.

(B) Tissue culture

(C) Apical dormancy : The presence of terminal or apical bud involves the failure of lateral bud growth. It is due to the secretion of IAA. Removal of apical bud results in the growth of lateral buds.

(D) Root formation : Auxins can induce adventitious roots in stem cuttings.

(E) Cell division

(F) Parthenocarpy : Application of synthetic as well as natural auxins to unpollinated pistils produces parthenocarpic fruits (seedless fruits). Parthenocarpy is the phenomenon of development of seedless fruits without pollination and fertilization. This phenomenon is applies in seed bearing fruits like grape, banana, papaya, tomato etc.

(G) Curvature movements

(H) Abscission

(I) Lead and fruit fall : 2, 4 -D (2, 4- dichorophenoxy acetic acid) is applied to avoid pre-harvest fruit drop in oranges and apples.

(J) Flowering : Auxins generally inhibit flowering but in pineapple it cause flowering.

(K) Weedcides :  The auxins play important role in weed control.

(L) Storage : Applied for potato storage.

9.3 (b) Gibberallins :

Gibberellins have a unique property of increasing the height of plants but they do not cause curvature. The gibberellins were firs discovered in Japan by Yabuta and Sumuki. E. Kurosawa obtained extracts from rice plants which were infected with fungus Gibberella fujikuroi. These rice plants were taller and sterile.

(i) Functions of gibberellins : The physiological effects of gibberellins on plant growth are as follows :

(A)Cell elongation : Gibberellins cause stem elongation and expansion of leaves in intact plants.

(B) Stem elongation : These induce stem elongation in genetically dwarf varieties (pea, maize & Cabbage) It is called bolting.

(C) Seed germination

(D) Flowering

(E) Parthenocarpy            

(F) Counteract dormancy : Natural dormancy of buds, tubers, rhizomes and some seeds can be over come by gibberellins.

(G) Induction of maleness : GA3 induces the formation of male flowers on genetically female plants in Cucurbits.

(H) Induction of aerial stem

(I) Increase in size of fruits : Application of gibberellins increase bunch length and fruit size in grapes.

9.3 (c) Cytokinins :

The cytokinins are chemically basic growth hormones which promote cell division in plants. This group of phytohormones was discovered when Carlos Mille isolated the crystalline substance from degraded DNA material. This substance was named as kinetin.

(i) Function of cytokinins : The important physiological effects of these cytokinins on plant growth are as follows :

(A) Cell division : One of the main functions of cytokinins is in cell division and more particular cytokinesis.

(B) Secondary growth : Cytokinins overcome apical dominance and promote the growth of lateral bunds.

(D) Senescence : Cytokinins can inhibit or delay senescence (ageing). Leaves treated with cytokinins, retain chlorophyll for longer period i.e., they remain green for a longer period.

(E) Morphogenesis : A natural balance between auxins and cytokinins is responsible for differentiation of stems and roots (morphogenesis). When cyntokinins are in excess, lateral buds develop while roots are formed if relatively more auxins are present.

(F) Induction of flowering

(G) Callus growth

9.3 (d) Ethylene :

This is a gaseous plant hormone which is produced by almost all the fleshy fruits during ripening. Ethylene is autocatalytic in nature. Higher concentration of auxins induce ethylene formation.

(i) Functions of ethylene : The important function of ethylene are as follows :

(A) Fruit ripening : It is used for artificial ripening of fleshy fruits in the shops.

(B) Abscission layer : Ethylene accelerates the abscission of leaves, flowers and fruits.

(C) Senescence : Ethylene induces yellowing of leaves and downward bending. This results in the senescence in the plants.

(D) Growth : It promotes transverse expansion but it inhibits longitudinal growth.

(E) Flowering : It induced flowering in pineapple.

(F) Dormancy : It breaks the dormancy of several organs of plants except lateral buds.

(G) Induction of femaleness : If has feminizing effect. This increases the number of female flowers in Cucurbits.

9.3 (e) Abscisic Acid (A.B.A.) :

Stress hormone of plants is called as abscisic acid. It is also known as dormin. Addicott and his co-workers isolated as substance from young cotton bolls and named it as Abscisic acid. This acid is now isolated from dormant seeds, buds and other parts of the plants. Abcisic is a growth inhibitor. Abscisic acid has no stimulating effect on any aspect of growth.

(i) Functions of abscisic acid :

(A) Growth : A.B.A. has antagonistic property to growth promoting hormones (auxins, gibberellins and cytokinins). Thus it keeps the growth under check.

(B) Dormancy : A.B.A. induces dormancy in buds towards the approach of unfavorable conditions. it causes natural dormancy in seeds and tubers.

(C) Abscission : It promotes abscission in leaves, flowers and fruits and causes ageing in plants.

(D) Wilting : During drought it closes the stomata and checks loss of water by transpiration. This ensures the survival of plant undergoes wilting.

(E) Resistance : It promotes cold hardiness.

(F) Flowering and seed development : It is known to inhibit the process of flowering, fruit formation and seed development.

9.4 CHEMICAL CO-ORDINATION IN ANIMALS :

Coordination in animals is brought about by the secretions of endocrine glands. Endocrine glands are ductless glands which secrete the chemical substances called hormones, Directly pour into the blood. Any chemical substance which is formed is the tissues of endocrine glands are carried by the blood the other parts of the body for its specific actions is termed as hormone. As organ which responds to such a hormone is known as target organ.

9.4 (a) Characteristics of Hormones :

(i)  They are the secretions of endocrine glands.

(ii) They are produced at a place and act on target organs which are mainly away from their source.

(iii) They are poured directly into the blood steam.

(iv) They are required in very small quantities.      

(v) they are specific in function.

(vi) Chemically they are mainly proteins.  Some of them may be amino acids, steroids etc.

(vii) They are harmful if present in less or excess amounts.

Viii) Hormones are immediately destroyed after their action is over.

9.4 (b) Feedback Mechanism :

Endocrine glands interact with each other, so that secretion of one gland may stimulate or depress the activity of another. The amount of hormone released by an endocrine gland is determined by the body’s need at any given time e.g. The hypophysis produces a hormone that stimulates the thyroid to produce its hormone; in turn the thyroid secretion induces the hypophysis to produce less thyroid stimulating its hormone; in turn the thyroid secretion induces the hypophysis to produce less thyroid stimulating hormone. This is known as the ‘negative feedback’. This feed-back helps bring about a steady state in the body which is called as homeostasis.

9.5  VARIOUS ENDOCRINE GLANDS PRESENT IN THE HUMAN BODY ARE :

(i)     Pituitary gland (or Hypophysis)         (ii)           Pineal gland                       (iii)         Thyroid gland

(iv)  Parathyroid gland                              (v)           Thymus gland                   (vi)          Adrenal gland

(vii) Pancreas                                           (viii)       Ovaries                             (ix)          Testes

9.5 (a) Pituitary Gland (or Hypophysis):

It is a small ovoid structure attached to the base of brain (hypothalamus) by a short stalk called infundibulum placed just behind the optic chiasma where the optic nerve from each eye meet. Pituitary gland is also known as the master gland as it controls other endocrine glands. This gland consist of three lobes-anterior, middle and posterior. Each lobe of the pituitary gland secretes different sets of hormones.

(i) Hormones of anterior pituitary :

(A) Growth hormone (GH) : This hormone promotes and regulates the process of growth in the body. It’s deficiency during childhood lead to dwarfism  and over secretion leads to gigantism.

(B) Adrenocorticotrophic hormone (ACTH) : This regulates the activities of adrenal cortex. It mainly stimulates the adrenal cortex to secrete corticosteroid hormone which defends the human body under stress.

(C) Thyroid stimulating hormone (TSH) : As is clear from its name it controls the functioning of thyroid gland. It stimulates thyroid gland to secrete thyroxin.

(D) Follicle stimulating hormone (FSH) : It stimulates the production of gametes, stimulates the development of ovarian follicles in females, and its equivalent in the males stimulates sperm production.

(E) Luteinising hormone (LTH) : In causes ovulation and formation of corpus luteum, which secretes progesterone in females and stimulates the testis to produce testosterone in males.

(F) Luteorophic hormone (LTH) : This is also known as prolactin. This hormone stimulates growth of mammary glands during pregnancy and promotes lacation after deliver. Prolactin level rise during pregnancy and is very high during lactation.

(ii) Hormones of middle pituitary:

(A)  Melanocyte stimulating hormone (MSH) : This is the only hormone secreted by middle pituitary which controls the growth and development of melanocytes responsible for skin colour.

(iii) Hormones of posterior pituitary :

(A) Vasopressin or Antidiuretic hormone (ADH): This causes the reabsorption of water into the blood from the collecting tubules of the kidney’s thereby concentrating the urine and reducing it volume.

(B) Oxytocin : This hormone stimulates uterus contractions as the time of child birth and causes release of mil from mammary glands. It is also known as birth hormone or milk ejecting hormone.

9.5 (b) Pineal Gland :

It is a small gland reddish-grey in colour, about the size of a pea, attached to the roof of the third ventricle of the brain. It contributes in regulating gonadal development. It control development & concentration of melanin.

9.5 (c) Thyroid Gland :

The thyroid gland consist of two label joined together by an isthmus. It is situated in the lower part of the neck and when enlarged it forms goitre. Two hormones secreted by the thyroid gland are :

(i) Thyroxine : It is the principal hormone secreted by the thyroid gland and its main role is to increase the metabolic rate of he organs and tissues of the whole body. 60% of thyroxine consists of iodine, an element which is essential for the gland to enable it to synthesize its hormone. The basal metabolic rate (B.M.R.) is increased in hyperthyroidism and reduced in hypothyroidism.

(ii) Calcitonin : This hormone lowers the calcium level in the ways :

(A) By inhibiting renal tubular calcium reabsorption.

(B) By inhibiting bone calcium reabsorption.

1. Hypothyroidism : This results from lack or deficiency of thyroid hormone secretion. It is manifested differently in children as compared with adults. Cretinism affects children and is due to congenital defect of either absence or defect of the gland. In this disease growth is stunded, the features are coarse, frequently the child has a protruding tongue and an enlarged abdomen; the mentality of the child is low and retarded. Myxoedema is the condition caused by thyroid deficiency in adults. It affects woman more frequently than men. It is characterized by puffy face, thick skin, dry cough, cold and loss of hair. There is a deposition of mucin and fluid retention in extracellular spaces. B MR is lowered Iodine deficiency causes simple goitre.
2. Hyperthyroidism : This results from excessive secretion and over action of thyroid hormones, As excessive amount of thyrozine is poured into the blood and the metabolism of the body is speeded up. The person starts loosing weight, has an increased pulse rate, suffers from nerves excitement and there is protrusion of eye balls. These toxis sings and symptoms are responsible for the condition being known as toxic goitre. Other names are thyrotoxicosis, exophathalamic goiltre and grave’s disease.

9.5 (d) Parathyroid Gland :

These are small ovoid pea shaped glands. They lie on the posterior surface of the thyroid gland. Usually there are two pairs of parathyroid glands, a superior pair and an inferior pair. The parathyroid secretion, parathormone has two main functions.

(i) It regulates the balance between the calcium in bones and in extracellular tissue fluid, thus affecting the amount of calcium in the blood.

(ii) It also controls the excretion of phosphates in the urine, probably by reducing tubular reabsorption of phosphorus by the kidney tubule.

9.5 (e) Thymus Gland :

This gland is situated in the thorax in midline under the sternum in front of trachea. It has two lobes which are further divided into many lobules. it secretes a hormone namely thymosin. It is one of the sites of lymphocyte formation in children. Recently thymus has assumed importance because of its role in immunological process. It helps in producing antibodies.

9.5 (f) Adrenal Glands :

These are two small semilunar structure lying one each on upper pole of the kidneys. That is why they are also known as supra renal glands. Each gland consists of two structurally and physiologically separate parts known as cortex and medulla. The cortex occupies outer peripheral portion which is yellowish in colour and medulla is inner brownish part. Cortex secretes three different kinds of hormones known as corticosteroids. They are :

(i) Mineral corticoids : These regulate sodium and potassium balance in the body.

(ii) Glucocorticoids : These derive their name from their influence on carbohydrate metabolism e.g. Glycogenesis is promoted in liver.

(iii) Sex hormones : Small quantities of sex hormones as androgens and oestrongen are produced by adrenal glands which influence sexual development and growth.

Adrenal medulla is important in raising defence mechanisms and supplementing sympathetic action in the body. It secretes two hormones.

(i) Adrenaline : It is a stress hormone causes increases in systolic blood pressure, dilation of coronary

blood vessels, increased sweating and increase in metabolic rate. It brings restlessness, muscle fatigue and anxiety.

(ii) Noradrenalin : It is a general vasoconstrictor, Increases both systolic and diastolic pressures. Both of these hormones are helpful in emergency conditions. Thus are called as “fight or flight response”.

9.5 (g) Pancreas :

Pancreas is the only heterocrine gland in the human body. It acts as exocrine as well as endocrine gland. It acts as exocrine as it secretes pancreatic juice which is poured into the duodenum with the help of pancreatic duct. The endocrine tissue of the pancreas is in the form of clumps of secretory cells known as the islets of Langerhans. he islet cells are of three-alpha, beta and delta.

(i) Insulin is secreted by the beta cells and like other hormones, passes directly into the blood. Insulin is required to convert glucose into glycogen (glycogenesis) and store it in  liver. Deficiency of insulin due to defect in islets of Langerhans results in diabetes mellitus, a condition in which blood glucose in high and is passed in the urine.

(ii) The alpha cells of pancreas secrete glucagon, the metabolic effects of which are opposite to those of insulin. It causes the breakdown of liver glycogen, thereby releasing glucose into the blood stream.

(iii)  The third hormone somatostating is secreted by the delta cells of the islets of Langerhans. It is able to inhibit the secretion of many hormones. As it inhibits the release of growth hormone of pituitary gland, it is also known as growth hormone release inhibiting hormone (GHRIH).

9.5 (h) Ovaries :

Ovaries secrete three hormone :

(i) Oestrogen : FSH from the anterior pituitary controls the secretion of oestrogen by acting on the Graffian follicles. This hormone effects the development of female sex characters. The oestrogen secretion influences the follicular phase. Its secretion in maximum during evaluation period. Moreover during pregnancy the oestrogen secretion by placenta keeps of increasing till full term.

(ii) Progesterone : It is secreted by corpus luteum. This hormone in contrast to oestrogen which is produced continuously during the reproductive years, is secreted only after ovulation. Progesterone prepares the uterus for receiving the embryo. It prepares inner lining of the uterus i.e. endometrium to receive the in implanting embryo for about a week. If ovum gets fertillized, the corpus luteum continues to play a role in maintaining the pregnancy for the first three months, after which the placenta takes over the role of corpus luteum by secreting progesterone itself. This hormone is essential for the maintenance of pregnancy and is therefore called pregnancy hormone. If pregnancy does not follow ovulation, corpus luteum degenerated and breaks down due to the lack of progesterone.

(iii) Relaxin : This hormone is secreted during later stage of pregnancy and leads to relaxation of muscles of the pelvic area to enable easy child birth and reduce the pressure on the foetus.

9.5  (i) Testes :

Testosterone is the main testicular hormone secreted by interstitial cells of the testis. It is mainly concerned with the development an maintenance of male sex characters and enhancing the process of spermatogenesis.

9.6 NERVOUS CO-ORDINATION IN ANIMALS :

In animals two kinds of co-ordination -nervous & chemical are present. The nervous co-ordination is brought about by the nervous system and the chemical co-ordination by hormones. Both the systems work an integrated system. Infect such a control and coordination requires.

(i) Gathering information about changes in the external environment.

(ii) Transmitting this information to the internal cells located away from the body surface and.

(iii) Exchange of information between the ells situated away from each other

1. Nervous system in animals : Except, Sponges, all multicellular animals posses simple or complex nervous system. Ina all these animals, nervous system is comprised of specialized cells called neurons or nerve cells to respond to stimuli and coordinate animal activities. Nerve cells are the structural & Functional units of nervous system.
2. Nervous system of Hydra : Hydra belongs to phylum Cridaria (Coelenterate) of the group invertebrate. The nervous system in hydra is merely a network of nerve cells joined to one another and spread throughout the body between the two gem layers, outer epidermis & inner gastrodermis. This network is called as nerve net. When the body of hydra receives certain stimulus at a particular region from the environment, the nerve cells present at the region send impulses in all the direction through the network of nerve call spread throughout the body. In this way, nerve network coordinates responses to different stimuli in Hydra without the existence of central control region i.e. brain.
3. Nervous system is grasshopper (as Insect) : In insets, the nervous system consist of a brain, ganglia (singular ganglion) & nerve cord. A mass of nerve cells is called ganglion. The nerve cord run along the entire length of the body. At interval, it has ganglia. Small nerves are given out from each ganglion. Near the anterior end of the insect body, a large bilobed ganglion, called the brain, is present. Thus the nervous system of grass hopper consist of a rain, a long nerve cord, the ganglia and nerves spreading form the nerve cord.

10.1 NERVOUS SYSTEM IN HUMAN :

The nervous system of human beings consists of central & peripheral nervous systems. Neuron is the structural & functional unit of nervous system. It is the longest cell found in the body. They unit the receptor and effector organs with each other. The nervous system is composed of neurons. These are surrounded by a connective tissue called neuroglia. Impulses from recptors run through neurons. The number of neurons are almost fixed for a particular species.

10.1 (a) Struture :

Each neuron consist of  a cell body called cyton and a number of branches (nerve fibres) arising from the cyton. Neuron does not divide. Cyton contains a nucleus within the cytoplasm & Nissl’s granules (formed of RER with ribosomes) and fine thread like  fibres, called neurofibrils.

(i) Dendrites : These are short, several, much branched & contain granules. They carry impulse towards the cyton.

(ii) Axon : It is a large, single and unbranched structure. It has not nissl’s granules. It carries impulses from cyton to the effector organs like glands, muscles etc. It is a typical nerve fibre consisting of a central thin cytoplasm cylindrical axis continuous with the body. It’s cytoplasm is called axoplasm. Axis cylinder is enclosed in a thin permeable membrane called axolemma or nerve membrane. A layer of fatty material called myelin or medullary sheath is found outside the axolemma. Such fibres are called myelinated (medullated) fibres. They seems to be white. Nerve fibres lacking myelin sheath are called non-myelinated & appear grey in colour. Myelin in interrupted at intervals by circular constrictions called Nodes of Ranvier. Terminal branches of axon are called telodendria. Each telodendron ends in a swollen knob called synaptic knob or terminal button. Synaptic knob of one serve fibre (axon) forms synapse with the dendrites of another neuron. Synapse is a very fine gap between two neurons. Thus, in the entire nervous system neurons are linked together.

10.1 (b) Types of Neurons or Nerve Fibres :

(i) Motor : It carries impulses from brain and spinal cord to effector organs.

(ii) Sensory : It transmits impulse from sensory organs to central nervous system. 

10.1 (c) Types of Nervous System :

(i) Central nervous system : It consists of the brain and the spinal cord. The brain is covered by cranium & spinal cord is covered by vertebral column Both are also surrounded by three membranes of the connective tissues called meninges.

1. Outer most Duramater
2. Middle Arachnoid
3. Inner most Piamater. The space between the membrane is filled with a fluid called cerebrospinal fluid that protect the brain from mechanical shocks. The brain can be differentiated into three main regions fore brain, mid brain & hind brain.

(A) Fore brain : It consists of olfactory lobes, cerebrum and diencephalon.

1. Olfactory lobes : These are a pair of small, solid, cube shaped bodies. They are fully covered by cerebrum. They receive impulse for smell.
2. Cerebrum : It is the largest part of the brain. It consists of two cerebral hemispheres joined by a band of nerve fibres called corpus callosum. Surface of cerebral hemisphere is made up of gray metter, called cerebral cortex. It becomes highly folded to increase area for accommodation of more neurons. The folds are called gyri & depression between them, are called sulci. Deep and wide sulci are called fissures. Fissures divide each cerebral hemisphere into four lobes

(i) Occipital lobe                 : Region for visual perception

(ii) Frontal lobe                   : For muscular activities

(iii) Parietal lobe                 : For touch, smell, temperature and conscious association. 

(iv) Temporal lobe             : For auditory reception

Cerebrum has sensory areas where impulses are received from sense organs (receptors). Similarly it has a general motor area from where impulses are sent to effector organs (Muscles & glands)

Diencephalon : It encloses a cavity called third ventricle. It consists of thalamus and hypothalamus. Thalamus serves as a relay centre for sensory and motor impulses from spinal cord and medullaoblongata to cerebrum. It recognizes sensory impulses of heat, cold, pain, light & pressure. Floor of third ventricle is called hypothalamus. It possesses control centres for hunger, thirst, thermoregulation, sleep, sex, stress etc.

(B) Mid Brain : It consists of two heavy fibre called Crura cerebri. These tracts connect fore brain to the hind brain. These are the centres for control of eye movement and hearing responses.

(C) Hind brain :

1. Cerebellum : Very large & well developed. It controls coordination and adjustment of movements (equilibrium) and posture.
2. Pons varolii : it lies above the medulla oblongata. It controls some aspects of respiration.
3. Medulla oblongata : It is the posterior most part of the brain and continues into the spinal cord. It controls involuntary functions of the body such as heart beat, rate of breathing, secretion of saliva, swallowing, coughing, sneezing, vomiting etc.
4. Spinal Cord : It lies in the vertebral column. It starts from medulla oblongata and extends downward. It is also protected by three meninges and cerebrospinal fluid. It also acts as a centre for spinal reflexes.

(ii) Peripheral nervous system : It included cranial nerves and spinal nerves. It mainly controls the voluntary activities of the body. Cranial nerves also called cerebral nerves arise from brain. There are 12 pairs of cranial nerves in man and 31 pairs of spinal nerves arise from spinal cord.

(iii) Autonomic nervous system : It controls Involuntary activities of internal organs such as hear, blood vessels, glands & smooth muscles of alimentary canal & uterus. It is subdivided into

1. Sympathetic
2. Parasympathetic system.

Organs receive nerves from both sympathetic and parasympathetic nerve fibres. They have opposite effects on the organs if one is stimulatory, the other is inhibitory. 

10.1 (d) Effect of Sympathetic and Parasympathetic System :

10.1  (e) Reflex Action:

Reflex action is the name given to the response which is at the level is spinal cord itself. It is a rapid automatic response to a stimulus by an organ or a system of organs, which does not involve the brain for its initiation. A reflex action is an unconscious (without will) and involuntary response of effectors (muscles or glands) to a stimulus.

10.1 (f) Reflexes are of Two Types :

Simple or unconditioned and continued reflexes.

(i) Simple reflex : It is an inborn response to a stimulus. Where learning is not required. These are mostly protective in function  e.g. knee jerk occurred immediately when patella tendon of leg is sharply tapped, quick closing of eyelid when an object suddenly comes in fort of eyes (corneal reflex) etc.

(ii) Conditioned reflex : These are not inborn. They are acquired by experience, training & learning. e.g. Learning of cycling or driving of scooter etc.

10.1 (g) Electro Encephalogram (EEG) :

An instrument called electro encephalograph can record electrical activity of brain. The activity of brain is recorded as electrical potentials such a record is called Electro Encephalogram. By placing two electrodes on the scalp and leading via suitable amplifier to ink writing device, record of four different types of waves is obtained. These waves are named as alpha, beta, delta and theta and vary in frequency. These waves give the characteristic activity of brain which is very useful for clinical purposes.