CHAPTER - 3

1. CHAPTER - 3 LIFE PROCESSES - CONTROL AND CO-ORDINATION

2. 3.1 IMPORTANCE OF NERVOUS SYSTEM • All organisms have an unique property to respond to the changes in theenvironment. This property of responding to changes in the environment is called Irritability Examples 1. If we touch an Earthworm it moves away from the place. 2.If we place plants in the shade, they grow towards the source of light. 3.A person runs away from the snake the moment he sees it. In this example snake is the stimulus and running away from it, is the response. • This kind of response indicates that living organisms have a mechanism to identify or sense the stimulus in the environment. • This information is sent to the organ which has the ability to respond to such changes.

3. In multicellular organisms, a co-ordination between various organ systemsis brought about in two general ways; namely control by nervous system and control by endrocrinesystem • Nervous system consists of Receptors ,Effectors ,Conductors.

4. 3.2 HUMAN NERVOUS SYSTEM • The nervous system of all vertebrates including man is made up of nerve cells called neurons and supporting cells. • The nervous system has three basic components namely central nervous system (CNS), peripheral nervous system (PNS) and autonomic nervous system (ANS).

5. 3.21 CENTRAL NERVOUS SYSTEM (CNS) • Brain and spinal cord are the components of central nervous system • They are covered by three membranes namely outer dura mater, middle arachnoid and inner piamater. These membranes are called meninges. • Space between the meninges is filled with a watery fluid called cerebro-spinal fluid (CSF). • This fluid flows from brain to spinal cord and back to brain and protects brain and spinal cord from injuries and provides nutrients to the cells in brain and spinal cord. • Besides these, brain is protected by a bony case called cranium

6. BRAIN • The brain is very well developed and has reached complexity resulting in a high mental capacity. • Brain is divided into three parts Fore brain,Midbrain and Hind brain(continues as spinal cord) Fore brain : It shows two major parts called cerebrum and dienchephalon. Cerebrum: • Cerebrum is the largest part of the brain. It consists of two equal halves called cerebral hemispheres (right and left) separated by a groove. • Cerebrum shows two regions namely an outer cortex and inner medulla. • Cortex is composed of cytonsand forms the grey matter, the medulla is composed of nerve fibres (axons and dendrites) and forms the white matter. • The cortex is deeply folded into ridges called convolutions which increase the surface area of the cerebrum. • The high degree of intelligence of the human being is supposed to be result of the great development of cortex.

7. MID BRAIN : Mid brain is a small region of brain made up of nerve fibresconnecting cerebrum to the cerebellum. • It serves mainly as relay station through which impulses move from hind brain to the forebrain. It is concerned with receiving impulses from eyes and ears. • HIND BRAIN : Hind brain consists of three parts namely pons varoli, cerebellum and medulla oblongata.

8. SPINAL CORD • Spinal cord is a long and cylindrical structure passing through vertebral column. • It is composed of a large number of nerve cells and nerve fibres. • It has grey matter in the centresurrounded by white matter. • Thirty one pairs of nerves arise from the spinal cord and their branches reach several partsof the body namely heart, lungs, stomach, urinary bladder and sex glands. • Thespinal nerves are made up of both sensory and motor nerve fibres. • Spinal cord co-ordinates the movements of limbs and organs in the body by reflex actions.

9. REFLEX ACTION AND REFLEX ARC : • A reflex action is an automatic response to an external stimulus. • Spinal cord is the centre of such reflex actions. • These are independent of the brain. For example, when we step on a thorn unknowingly, immediately we take away our leg. Similarly, when we touch a hot object we withdraw our hands. • The pathway of the nerve impulse in.olvedin reflex action is called reflex arc.

10. IT CONSISTS OF FIVE DISTINCT PARTS : • 1. A receptor (sense organ) that receives stimulus. • 2. A sensory neuron that conducts the impulse from the receptor to the spinal • cord or the hind brain. • 3. An association neuron which transmits the impulse from the sensory neuron • to a motor neuron. • 4. A motor neuron through which the impulses pass on to an effector. • 5. An effector where the action takes place in response to the stimulus.

11. 3.22 PERIPHERAL NERVOUS SYSTEM • Peripheral nervous system includes twelve pairs of cranial nerves and thirty one pairs of spinal nerves.

13. 3.23 AUTONOMIC NERVOUS SYSTEM (ANS) • The autonomic nervous system consists of a special set of peripheral nerves that supply nerves to organs such as heart, lungs, digestive tract and other internal organs. • It regulates a variety of functions which are not under the control of the will. • It consists of two parts, the sympathetic system and the para-sympathetic system with opposite actions. • For example, the sympathetic system stimulates the pupil in the eye to dilate, where as the para sympathetic system causesitto constrict.

14. 3.3 THE SENSE ORGANS When we look at a rose we get an idea about its colour, size and shape with the help of our eyes. By touching it, we feel the softness of its petals and by touching its thorns we feel the pain. We sense its smell with our nose. • The organs through which we sense the objects in our environment are known as sense organs. We have five sense organs namely eyes, ears, nose,tongueand skin, by means of which we are able to see, hear, smell, taste and touch, respectively. • Sensory nerves carry impulses from sense organs to the brain. • Motornerves carry messages from brain to the muscles. • Mixed nerves are both sensory and motor in function. • The longest nerve fibres are about one meter long. They stretch from the base of spinal cord to the tip of the toe. • A sense organ receives the stimuli from the objects around us. • Eachstimulus is then passed on to the brain through a sensory nerve. The brain interprets and recognises the stimulus. This results in a set of information about the object.

15. 3.31 HUMAN EYES • Eyes are the organs of sight and are stimulated by light. We can get to know the colour, size, shape and distance of an object with the help of eyes. • The eye balls are situated infront of the face in bony sockets of skull. • Eacheye ball is held by three pairs of muscles by means of which we can move our eye up and down and in various directions. • The eyes are covered by the eyelids situated above and below the eye ball. Eyelids with the eye lashes prevent the dust particles from entering eyes. • The eye brows protect eye from small particles that fall from above to the eye. • The hairs of the eye brows help to shade the eyes from bright illumination. • Lacrymalglands situated in the outer region of the upper eyelid, produce secretions to keep the surface of the eye moist and wash • out dirt and foreign particles. • The secretion contains some salts and is an antiseptic.

16. STRUCTURE OF EYE : • The wall of the eye is made up of three layers namely sclerotic, choroid and retina.

17. The area between the cornea and the lens is filled with a fluid called aqueous humour. • The relatively thick fluid filling the space behind the lens is called vitreous humour. • Both these fluids help in refraction of light rays and maintain the shape of the eye ball.

18. Retina lines the inner surface of the eye. • It contains numerous nerve fibresand receptors. • The receptor cells are of two types namely rods and cones. • Rods are sensitive to dim light and cannot distinguish colours. • Cones are sensitive to bright light and can distinguish colours • A large number of cones are located opposite to the pupil where the most clear and sharp image is formed. • This part is some what depressed and is known as the yellow spot (fovea). • The sensory fibresof the retina form a bundle of nerves and emerge from the eye ball as the optic nerve. • The cones and the rods are absent at the exit of the optic nerve. No image is perceived at this spot and it is therefore called the blind spot.

19. FUNCTIONING OF THE EYE : • The light rays reflected from the object are focussedon the retina to form the image. • The retinal cells exposed to the light in the region of the image are stimulated by photochemical reactions. • Thesecells convert the stimulations into electrical impulses which pass along the optic nerve to the visual centre in the cerebrum. • The interpretation of these impulses in the cerebrum, results in vision. • The human eye, however adjusts itself to near and far objects by altering the focal length of the lens. • When the lens focuses the image of a near by object, the muscles around the lens contract and convexity of the lens increases. • When we see a distant object the convexity of the lens decreases and eye ball becomes flat. This property of the lens in human eye is called accommodation.

20. DISORDERS ASSOCIATED WITH EYE

21. FIRST AID FOR THE REMOVAL OF FOREIGN BODIES IN THE EYES • The foreign bodies that get into the eye may be flies, dust particles, sparks or pieces of metals or wood in a work shop. • In such a case do not rub the eye as the eye ball will be injured. • If the foreign particle is visible try to remove it with the help of a clean handkerchief. • The foreign body can be removed by causing the flow of tears. Close the eye for a few seconds pulling one eye lid over the other till tears collect. • The foreign body will be moved to a corner by the tears. Then it can be wiped out. • It can also be removed by keeping the eye in a clean bowl of cold water or boric lotion, open and close the eye several times inside the water or boric lotion. The particle gets washed out.

22. 3.32 HUMAN EARS • The human ears are the sense organs meant for hearing and maintenance of body balance. The ear is divided into three parts - the outer ear, the middle ear and the inner ear. Inner Ear • The inner ear is enclosed in a bony cavity of the skull. • The inner ear is a delicate organ surrounded by a fluid called perilymph. • The inner ear has two main parts namely utriculus and sacculus. • The upper part is the utriculus which is connected to three semi circular canals. • The lower part is the sacculus which has an appendage called cochlea. Outer Ear • The outer ear consists of pinna, auditory canal and the tympanic membrane. • The ear pinna is a cartilagenous organ covered with skin. • It collects the sound waves and directs them into the auditory canal. • The auditory canal has hairs at its opening that prevent tiny particles entering the ear. • The wax secreting cells on the inner lining of the auditory canal produce wax which entangle small organisms and dust. • At the inner end of the auditory passage there is an obliquely placed membrane called tympanum or ear drum. • Tympanum separates the external ear from the middle ear. • Sound waves from outside cause the tympanum to vibrate.

23. Middle Ear • The middle ear consists of three small bones called the malleus (hammer) incus (anvil) and stapes (stirrup). • The stirrup is close to the oval window or fenestra ovalis. • The vibrations of the tympanum are transmitted across the middle ear by the movements of these three bones. • The middle ear is connected to the throat by an air passage called eustachian tube which equalizes the air pressure on the two sides of the ear drum. • The entire ear is filled with a fluid called endolymph. • Utriculusand semicircular canals are concerned with balancing of the body. • Cochlea occupies a large part of the internal space and encloses a very delicate structure called organ of corti. • Thereceptorspresent in the organ of corti join together to form the auditory nerve.

24. MECHANISM OF HEARING • The sound waves directed by the pinna to the tympanum, through the auditory canal make the tympanum to vibrate. • These vibrations are carried to the internal ear through the chain of bones in the middle • ear. • The vibrations are further conducted to the organ of corti through perilymph • and endolymph. • These wave impulses are picked up by receptors in the organ of corti and are carried through auditory nerve to the cerebrum which interprets the sound. • The act of hearing is brought about within a fraction of a second.

25. 3.33 THE NOSE • Nose is the organ of smell and breathing. • The nasal cavities are lined by the olfactory epithelium. • The receptors of smell are situated in the epithelial lining of the upper part of the nasal cavity. • They are connected with the olfactory nerve and it carries impulses to the brain, whenever smell is detected. • Molecules escaping from substances may be carried by the inhaled air. • On reaching the olfactory epithelium, they get dissolved in the mucus and stimulate the receptors. • The stimulation is passed through the olfactory nerve to the brain which interpretsthemessage as the sensation of smell. • First aid : If a pea or a button or a bead gets into the nose accidentally, give a pinch of snuff to the person. It causes a violent sneezing and the foreign body will be thrown out. If this does not work then take the help of a Doctor.

26. 3.34 THE TONGUE • Tongue is the organ of taste. • It iscoveredby a mucus membrane. It encloses numerous tiny sensorycellscalled the taste buds. • Thetastebud is composed of a cluster of cells with the receptors lying in a small depression on the surface. • Food dissolved in the saliva entersthepores of the taste buds and chemically stimulates the sensorycells. • These cells convert these chemical stimuli into electrical impulses that pass along sensory neurons to the brain which interprets these impulses as taste. • There are four basic types of taste. They are sweet, salt, sour and bitter. • The taste buds of sweetness are distributed in the front, those of salt taste at the anterior margin, those of sour taste at the sides and those of bitter taste at the posterior region of the tongue.

27. 3.35 THE SKIN : • The skin is an important sense organ. • It receives the sensations of touch, pressure, pain, heat and cold. • You feel hot when you sit in front of an oven and feel cold when you move outside the house in winter. The pain of pricks, the touch and the pressure are experienced by all of us. • All these stimuli are perceived by the respective sense receptors distributed all over the skin. Touch receptors are near the surface of the skin. • The pressure receptors and the pain receptors are all over the body and are deeply situated.

28. 3.4 THE ENDOCRINE SYSTEM • Apart from the nervous system, control and co-ordination of the various body functions in animals are carried out by the endocrine system. • You have studied about some glands and their secretions like saliva, gastric juice, bile etc. • A gland is an organ whose cells are specialised for producing a particular secretion. Sometimes, a highly specialised single cell constitutes a gland. • Thereare two types of glands in all vertebrates including man. • They are glands with ducts (exocrine glands) and glands without ducts (endocrine glands). • Exocrine glands discharge their secretions through the ducts to their target organs. Example : salivary glands and pancreas. • Endocrine glands discharge their secretions directly into blood stream. • Chemical substances secreted by the endocrine glands are called ‘hormones’. • They reach the respective organs through the blood and control and co-ordinate the activities of the organs. • Theorgans on which hormones act are called target organs. • Since hormones carry the stimuli from one part of thebody to another they are called chemical messengers.

29. On chemical analysis, hormones are found to be either proteins, amino acids or steroid compounds. • Hormones are produced in very minute quantities , yet they are highly effective. • The excess secretion from an endocrine gland is called hypersecretionand inadequate secretion is called hyposecretion. Both these conditions result in disorders. • The major endocrine glands in the human body are pituitary, thyroid, parathyroid, adrenals, islets of langerhans and gonads.

30. FUNCTIONS OF PITUITARY GLAND • It influences the rate of growth of the body. • It influences the secretion of hormone from thyroid gland, activity of the adrenal gland,secretionof milk from mammary glands, excretion of water from the kidneys and contraction of muscles of uterus. • It also influences the development of ovary and testis. • If the secretion of growth hormone is more prior to puberty, growth rate will be very high and this condition is called gigantism. • If the growth hormone is secreted less prior to puberty, growth rate is retarded and this condition is called dwarfism. • The excess secretion of growth hormone in adults results in a disease called acromegaly. • The symptom of this disease is disproportionate growth of bones particularly in jaws, nose, hands and legs.

31. 3.42 THE THYROID GLAND : • Thyroid gland is located close to the trachea in the neck. • It secretes a hormone called Thyroxin. • It is an amino acid in combination with iodine. • Thyroxin increases the rate of metabolism. • It increases the production of heat in the body, promotes growth and differentiation of tissues. • Sinceit affects indirectly the growth of the body, it is also called the ‘personality hormone’. • Thyroid disorders : Clinical thyroid disorders are caused either due to little (hypothyroidism) or too much (hyperthyroidism) of the hormone secretion.

32. Hypothyroidism : It is a condition in which the thyroid gland fails to produce enough thyroxin to meet the normal requirements of the body. It causes many abnormalities, like simple goitre, myxedima and cretinism. • Simple Goitre : If there is deficiency of iodine in the food, thyroid gland increases in size. This results in the swelling of the throat. Goitre can cured by administering iodine along with food and water.Goitrecases are found in areas where iodine is less in soil and water. It is an endemic disease. Usually coastal people do not suffer from goitre because sea water and soil are rich in iodine.

33. Myxoedema: This is a condition caused and produced by an underactivity ofthe thyroid gland in an adult. Its symptoms are low metabolic rate, loss of mentaland physical vigour, increase in weight, thickening of the skin and lower rateof heart beat. This can be cured by providing thyroxin in proper doses.Cretinism : This condition is produced in children born without a properlyfunctioning thyroid. Its symptoms are stunted growth, retarded mental development,bow legs, defective teeth, Protrusion of the tongue and loose wrinkled skin. Theseeffects can be prevented if proper treatment is given in time.Hyperthyroidism : This is a condition that results from an overactivity of thethyroid gland. Excess secretion of thyroxin results in high metabolic rate,protrusion of the eye balls, high blood pressure, nervous tension, irritability,profuse sweating, weight loss and fatigue.

34. 3.43 THE PARATHYROID GLANDS • There are four very small parathyroid glands embedded in the tissues of the thyroid gland. They secrete a hormone called parathormone. • This hormone controls the amount of calcium salts in blood and bone. • A deficiency of this hormone leads to painful muscle cramps. • Excess of parathormoneremoves calcium from the bones making them soft and spongy.

35. 3.44 THE ADRENAL GLANDS : (SUPRARENAL GLANDS) • There are two adrenal glands - one on the upper part of each kidney. • Each adrenal gland has two parts - the outer cortex and inner medulla. • These two parts secrete different hormones. • The adrenal cortex secretes many hormones; one of these is known as cortisone. • It regulates the rate of metabolism and the concentration of salts in the blood. • The adrenal medulla secretes three hormones namely adrenaline, Noradrenaline and dopamine. Adrenaline is normally present in the blood in small quantities. • Adrenaline is secreted in excess quantities at times of fear, anger or other emotional stress condition and prepares the body to face the emergency. • Since adrenaline brings a coordination of several events like increased heart beat, rate of respiration, dialation of pupils and others of the body to face an emergency, it is often referred to as the “emergency hormone”.

36. 3.45 THE ISLET OF LANGERHANS • Pancreas is a mixed gland with a portion functioning as an exocrine gland and another portion functioning as endocrine gland. • The cells of endocrine pancreas are called Islets of Langerhans. • They secrete two hormones – insulin and glucagon. • Insulin promotes the conversion of glucose to glycogen for storage in liver and muscle. • Insulin is liberated when the blood glucose levels are high, • usually when food is digested and absorbed. • If sufficient insulin is not produced, glucose level in blood increases and it is excreted through urine. This condition is called diabetes mellitus. • Usually diabetes is identified by the presence of sugar in urine. Frequent urination and thirst are two other common symptoms of diabetes. This disease can be controlled by the administration of insulin injections. • Glucagon is secreted when the blood glucose levels are low. It influences the conversion of glycogen into glucose. This glucose is released into the blood and supplied to the tissues.

37. 3.46 GONADS • Apart from producing gametes, gonads (testes and ovary) also secrete hormones. • The testis secrete the male sex hormones called androgens. • The most common hormone is testosterone. It is responsible for the appearance of the male secondary sexual characters at puberty such as, beard, moustache and the low pitch voice. • Deficiency of Testosterone results in under-sexed individuals whose masculine characters are developed to a low degree. • The ovaries secrete female sex hormones called estrogens, the most common of which is estradiol. • These hormones promote the development of feminine characteristics at puberty such as, the development of uterus, mammary glands and the changes during menstrual cycle and pregnancy. • Deficiency of estrogens causes infertility. • Corplusluteumis an yellow body in the ovary which secretes the hormone progesterone. • It influences the ultimate uterine changes necessary for pregnancy. • Deficiency of estrogens may cause sterility.

38. Afterstudying the unit you will ............... 1. recognise the importance of nervous system in co-ordinating the various functions of other systems in the body. 2. Explain the parts of C.N.S. and their functions. 3. Recognisethe role of P.N.S. and ANS in the function of nervous system. 4. Identify the different sense organs of the human body. 5. Suggest measures to take care of the sense organs. 6. Explain the significance of endocrine glands influencing various activities in the human body. 7. Draw a neat diagram to show parts of human brain, eye and ear. 8. Explain how skin is a sensory organ.

39. Activities : 1. With the help of your teacher, study the parts of a mammalian brain (Generally a sheep’s brain can be procured easily than any other) 2. Make a list of reflex action that you would have shown in a day. 3. Prepare model of human brain using plaster of paris or clay.

40. EXERCISES I. Choose the correct answer : 1. The structure that controls reflex actions is a) Medulla Oblongata b) Cerebrum c) Cortex d) Spinal Cord 2. The outer surface of the eye ball is covered by a membrane called a) Fovea b) Conjunctiva c) Pericardium d) Tympanum 3. The passage which connects middle ear to throat a) Auditory Canal b) Eustachian tube c) Wind pipe d) Oesophagus 4. The part of the tongue where we find the taste buds responsible to feel sweet taste is at : a) Posterior region b) Central region c) Lateral sides d) Anterior region 5. A gland embedded in another gland : a) Parathyroid b) Pituitary c) Gonad d) Adrenal

41. I. Answer the following questions 1. What is irritability? 2. Name the three divisions of the nervous system in man. 3. What is reflex action? Give examples. 4. Draw a neat diagram of vertical section of human brain and label the parts. 5. Draw a neat diagram of vertical section of the eye ball and label the parts. 6. How is human eye adapted for close and distant visions? 7. Which are the three main parts of the ear? 8. Mention the functions of the parts of the inner ear. 9. Draw a neat diagram of the human ear and label the parts. 10. How is nose helpful to feel the sense of smell? 11. What structures enable the skin to function as a sense organ? 12. What is a gland? Which are the two types of glands in our body? 13. What is Simple goitre? How is it caused? 14. Name the harmonesrecreted by gonals. 15. Where are parathyroid glands situated? What is the effect of the harmones secreted by them? 16. What are the functions of the following? 1) Optic nerve 2) Utriculus 3) Ear drum 4) Eustachian tube 5) Taste buds.