Year 12 First Term Biology Notes PDF

Mr. CHUKS 2023/2024 YEAR 12 BIOLOGY ENOTE Biology is the most powerful technology ever created. DNA is software, proteins are...

Mr. CHUKS 2023/2024 YEAR 12 BIOLOGY ENOTE Biology is the most powerful technology ever created. DNA is software, proteins are hardware, and cells are factories. Arvind Gupta. The world has a huge number of trillion-dollar problems wanting to be solved, and biology is the only way to do that. Biology is a software process. Our bodies are made up of trillions of cells, each governed by this process. You and I are walking around with outdated software Mount Olive College, running in our bodies, which evolved in a very Ezi,Umunya, Umunya, different era. Ray Kurzweil Anambra State. mountolivecollege.org “Impossible” is not a scientific term Biology Department, Mount Olive College, Anambra State.  AWARD PAGE A Page that potentially belongs to All TERM 3 BIO CHAMPIONS Best students in individual year groups for the 2022/2023 Academic session Year 12 Elijah Ifunanya Year 11 Ezenekwe Chizitelum Year 10 Onyekwelu Maduabuchi Year 9 Egbo Lois Year 8 Elijah Emeka Year 7 Udoye Chinechetam MOST IMPROVED STUDENTS Students who dramatically improved through hard work and consistency Year 12 Okoye Chidinma Year 11 Ezeafulukwe Jessica Year 10 Anosike Chisom Year 9 Zina Madueke Year 8 Ozoh Nneka Year Chinmdindu Overcomer PRACTICAL SQUAD OF TERM 1 Students who distinguished themselves during Biology practical sessions Ifenweobi Michael Nwadinogbu-Ikenna Chisom Ezeafulukwe Jessica Ekeh Christabel Umeike Jessica Okafor Precious Agbo Chinenye Okereke Mmesoma Category Name of Student Undisputed Best Student in Asiegbu Adaobi Biology Practical in 2022/2023 Session Biologist of Term 3 Ezenekwe Chizitelum Emeka Elijah Students with overall best result Biology Department, Mount Olive College, Anambra State.  Overall Most Resourceful Okereke Mmesoma In the Laboratory Congratulations to the Awardees of Term 3, 2022/2023 Session! Dethrone them if you dare Catch them if you can………………………… Biology Department, Mount Olive College, Anambra State.  2023/2024 ACADEMIC YEAR 12 BIOLOGY SCHEME OF WORK FOR TERM 1 WEEKS TOPICS CONTENTS 1 - Revision of Work from Year - Structure and Functions of the reproductive parts of 11 plants. - Beginning of Term Test Arrangement of reproductive organs in different parts of - Reproductive System in plants. Plants Diagrammatical illustrations of placentation / Pollination / Differences / Agents / Differences 2 - Regulation of the Internal - Definition of Homeostasis Environment of Organisms - Homeostatic organs / substances involved. - Kidney, Liver, Skin and roles played by the organs in Homeostasis. 3 - Regulation of the Internal - The Endocrine glands: hormones Environment of Organisms - Glands that secrete each hormone and process (II) involved. 4 - Plant Hormones - Plant Hormones ( Auxins): Functions / Effects of auxin development on bud development / Leaf fall - Modern Auxin Application - Practicals 5 - Nervous Coordination - The Organization of the Nervous System: CNS / PNS - The Brain: Position, Structure and Function. - The Spinal cord: Position, Structure and Function 6 2023/2024 TERM 1 MIDTERM BREAK 7 - Nervous Coordination (II) - Peripheral Nervous System: Somatic and Autonomic Nervous System / Parasympathetic and Sympathetic Nervous System - Structures and Functions of Neurones - Reflex and Voluntary Actions - Experiment on Dog, Food and Bell (Ivan Pavlov) 8 Sense Organs - Definition - Organs involved / Organ of Smell / Mechanism of Smelling - Adaptation of Survival – Animals that sniff for hunting e.g dog - Organ of Taste - Organ of Hearing 9 Sense Organs - As receptors - The Organ of Sight and its various parts - Functions of the parts of the eye - Image formations - Eye defects 10 Sense Organs - Correction of Eye defects - The Skin as a receptor - Functions / Parts / Illustrations WAEC model Diagram Practice for all the Organs Considered 11 REVISION 12 EXAMINATION Welcome to Year 12 I know you are good to go! Biology Department, Mount Olive College, Anambra State.  UNIT 1 Regulation of the Internal Environment Specific Objectives 1. Explain Homeostasis 2. List the main organs and substances involved in homeostasis (control mechanism). 3. Describe the structure and functions of these organs kidney, skin, liver. 4. Name some kidney and liver diseases, explaining briefly their symptoms and effects. 5. Discuss the remedy for unhealthy conditions of the liver and kidney. Introduction Organisms usually find themselves in a constantly evolving environment full of a range of stimuli moving from one end of the spectrum to another. Therefore, there is a need for a self-regulating process by which a living organism can maintain internal stability while adjusting to changing external conditions and this is what we refer to as Homeostasis. Homeostasis (homeo: same/steady, stasis: state) is a phenomenon in which the body regulates its functions to keep the internal conditions as stable as possible. Homeostasis is necessary because the body cells need to have suitable conditions around them for proper functioning. These conditions include the presence of proper concentration of chemicals, proper temperature, and a suitable pH (degree of salinity or acidity), osmotic pressure etc. inside its cells. However, these conditions inside our body as well as inside other organisms keep fluctuating within a narrow range. Tolerance to any change from this range differs in different organisms. Hence, Organisms adopt a variety of measures to cope with such changes. Structures of Homeostasis Biology Department, Mount Olive College, Anambra State. Homeostasis takes place at all levels of living organism. - In one celled organisms such as Amoeba and Paramecium, the adjustment involves the whole body using contractile vacuole to collect and expel excess water. - In higher animals such as mammals, the adjustments are the tissues, organs and system levels. Structures that carry out this homeostasis in the mammalian body are the kidney, liver, skin, ductless glands (hormones), and brain (providing overall control of the homeostatic process in the body). Homeostasis is the process by which a fairly constant internal environment is maintained in an organism. The Mechanism of Homeostasis Adjustment of physiological systems within the body is called homeostatic regulation, which involves four parts or mechanisms: (1) the set point or norm (2) the receptor, (3) the control center, and (4) the effector. - Set point or the norm - This is the normal level of any factor in the body. The set point may have a small or large range. For example, the normal set point of human body temperature is C (with 0.5 C plus or minus - The receptor (sensory detectors) receives information that something in the environment is changing or that there is a deviation from the set point. - The control center or integration center receives and processes information from the receptor about the deviation from the set point. It interprets the new information and then sends the command for correction. - The effector responds to the commands of the control center by either opposing or enhancing the stimulus in order to restore the set point. - This ongoing process continually works to restore and maintain homeostasis. This mechanism is regulated by the Negative Feedback Mechanism. Negative feedback is a regulatory mechanism in which a 'stimulus' causes an opposite 'output' in order to maintain an ideal level of whatever is being regulated. Homeostatic mechanism: An example 1. During body temperature regulation, temperature receptors in the skin communicate information to the brain (the control center) 2. The Brain (hypothalamus) signals the effectors: blood vessels and sweat glands in the skin. 3. The effectors drive into action to bring about the needed response Biology Department, Mount Olive College, Anambra State.  Kidney as a Structure of Homeostasis In Year 11, we established that the mammalian kidney is a bean-shaped, reddish-brown organ located in the posterior end of the abdomen. We also discovered longitudinally that two distinct regions are observed; an outer cortex and an inner medulla. Several narrow tubules called urinary tubules (nephrons) pass through the two regions stated above. The tubules open at the tips of triangular- shaped masses of tissues called pyramids. The pyramids open into a funnel-shaped cavity called the pelvis. The kidney has many tiny capillaries which are branches of the renal artery and the renal vein. The pelvis continues as the ureter, a long narrow tube connecting the kidney to the urinary bladder. The kidneys maintain homeostasis by controlling the amount of water, ions, and other substances in the blood. Kidneys also secrete hormones that have other homeostatic functions. The homeostatic functions of the kidney are grouped into two namely: (i) Osmoregulatory functions and (ii) Excretory functions Osmoregulation (water balance in the body) is defined as the process by which living organisms balances the amount of water to mineral salts in its body fluids. 1. Kidney as an Osmoregulator: (A) Water Balance – - When the body is dehydrated (little water in the body) which results from drinking a small quantity of water or losing water through sweat on a hot day, the osmotic pressure of the blood increased. - The osmoreceptors in the hypothalamus detect the changes in the osmotic pressure as the water content drops. - This stimulates the pituitary gland to secrete more anti-diuretic hormone (ADH) or vasopressin into the blood. - The secretion from above makes the walls of the urinary tubules more permeable so that more water is reabsorbed into the blood by osmosis; therefore less water is lost from the body as concentrated urine. - When the body is hydrated (too much water in the body) which results from drinking a large quantity of water or on cold days when we sweat less. - The osmotic pressure of the blood is lowered and less ADH is secreted. - The walls of the kidney become less permeable. - More water is lost from the body as dilute urine (B) Maintenance of acid-base balance of the body – - The acid-base balance of the body fluid is maintained by the kidney. The PH of human blood is between 7.35 and 7.45 (neutral). Anything below or above this range is dangerous to the body. - If the acid content of the blood get higher, the cells of the distal convoluted tubules reabsorb more hydroxyl ions (OH) from the urine and more hydrogen ions (H+) or acid are therefore excreted with the urine. - On the other hand, if the hydroxyl ions content of the blood get higher, less hydrogen ions are produced by the cells of distal convoluted tubule while more hydroxyl ions are excreted with the urine. In this way, the acid-base balance of the body is maintained (C) Control of blood sodium ions and pH levels: - When the concentration of sodium ions in the blood is higher than normal, the excess is excreted. - If it is lower, then more sodium ions are reabsorbed. This process is regulated by inhibiting or stimulating the secretion of the hormone aldosterone. Biology Department, Mount Olive College, Anambra State. Other kidney functions 1. Excretion of urea 2. Elimination of undesirable substances like toxins. 3. Produces heat during cold. Diseases of the kidney Diseases Case Definition Effects Remedies Kidney This is a condition in which tiny 1. Passing urine is 1. Drink sufficient Stone solids e.g calcium phosphate present with great difficulty water and other fluid in urine blocks the nephron or 2. Severe abdominal such as fruit juices kidney tubules. When the solid pain is experienced. during hot to prevent becomes too large, it forms a kidney 3. High blood the urine from stone. pressure may be becoming concentrated experienced 2. Avoid food item that are hard to digest 3. Avoid excessive intake of food containing calcium. 4. Drug capable of dissolving kidney stones may be given to the patient (oral acid) 5. Surgery may be used to remove the stones. Diuresis The removal of excess watery urine 1. Thirst and 1. Do not use fans and from the body through the kidneys. dehydration occur due air condition in cold The situation occurs when the to excessive removal weather kidney tubules fail to reabsorb water of body fluid. 2. Avoid excessive from the glomerular filtrate back to 2. High blood drinking of alcohol the blood. pressure may result 3. People lacking ADH Causes 3. It can lead of loss and aldosterone should 1.Diseases such as diabetes of serum electrolytes be treated. insipidus and pituitary diseases from the body 4. Kidney transplant 2.Lack of a hormone called 4. Loss of appetite, may be done on the aldosterone causing excess sodium weakness, fatigue and patient ions to be excreted nausea 3.Drinking of excessive alcohol 5. Death may occur if 4.Heart failure, renal failure and not treated. kwashiorkor Nephritis This may be caused by 1. Puffiness in the 1. All food items must or oedema streptococcus infection in the throat, face be properly washed or ear, nose or elsewhere. 2. Watery swellings in well cooked The poison produced by the germs the feet and ankles a 2. Drinking water must when carried by the blood to the condition known as be properly boiled and kidneys damage the glomeruli. This oedema. filtered will hinder the function of ultra- 3. Kidney become 3. Dialysis machine filtration in the glomerulus. The swollen (artificial kidney) for glomerulus become inflamed and 4. Dizziness, fatigue, filtering out waste from causing them to become more high blood pressure, the n ’s blood and permeable than normal. convulsion, back pain, body fluid. headache, fever and vomiting may result. 5. Protein and blood cells pass into the Biology Department, Mount Olive College, Anambra State. 2 major interventions usually given to kidney diseaseurine patients as a last line resort are: Dialysis: process whereby the patient’s blood is passed through the machine (dialyser) by tubes which convey his blood through the machine and back to his body. As the blood passes through the machines, waste products pass into fluid via the machine Kidney transplant, a surgical process of replacing a damaged or non-functioning kidney with a healthy kidney usually extracted from a willing compatible donor. The Liver as an Organ of Homeostasis The liver is the largest gland in the body weighing about 1.25kg. It is dark-red, spongy and lobed. The lobes are caudate lobe, left lobe, right lobe and medium lobe. It is located below the diaphragm by a ligament and partly overlaps the stomach. Underside of the right lobe is a gall bladder containing a bile duct which leads from the liver to the duodenum. Blood is supplied to the liver by hepatic artery and hepatic portal vein. Hepatic vein carries blood away from the liver. The liver also doubles as an accessory organ within the digestive system and is responsible for maintaining sugar levels in the blood as part of homeostasis. After a large meal, the liver converts extra glucose into glycogen, a polysaccharide that stores glucose. Biology Department, Mount Olive College, Anambra State. Excess glucose in blood – Insulin – Glycogen in Liver Deficiency of glucose in blood – Glucagon - Glucose FUNCTIONS OF THE LIVER 1. Blood sugar regulation (Blood sugar constant) - Glucose in the blood stream is maintained at a constant level called sugar constant, as low level of glucose would be injurious to tissue of certain organs such as the brain that cannot store glucose. - Surplus glucose is converted by the liver cells into glycogen for storage under the control of hormone called insulin. Glycogen is converted to glucose by another hormone called glucagon in order to maintain a constant blood sugar level. The liver also converts fructose and glucose for use by the body. 2. Regulation of blood protein (Deamination) – is the process by which amino acids are split into its two components – the amino group (RNH) and the carboxyl group (COOH). - The amino group which is harmful is converted into harmless urea which are excreted while the carboxyl group is processed as carbohydrate and stored in the liver as glycogen 3. Detoxification – is a process taking place in the liver where poisons or harmful substances such as drug, organic compounds produced by bacteria are converted into harmless substances which are later excreted from the body. Some enzymes present in the liver cells convert toxic products into non-toxic compounds which are later excreted by the kidney. For example, hydrogen peroxide which is split into water and oxygen by enzyme called catalase in the liver. 4. The liver makes and secretes bile which is used for emulsification of fat in the process of digestion. The bile is stored in the gall bladder (bile is 98% water and 2% bile salts, bilirubin, inorganic salts and cholesterol). 5. Formation of red blood cells in foetus but in the adult, the bone marrow of long bone form red blood cells. 6. Regulation of lipids by removing the lipid from blood and convert them to glucose and oxidize them to release energy during aerobic respiration. 7. The liver produces heat which is distributed to all part of the body by blood circulation thus regulating the body temperature. 8. The liver manufactures essential blood proteins like fibrinogen, prothrombin, globulin which are needed in blood clotting. 9. The liver break downs worn-out red blood cells in adults to form the bilirubin. 10. The liver manufactures vitamin A from carotene and stores fat soluble vitamin A, / and D 11. The liver acts are reservoir of blood storing (up to 1,500 cm of blood) and regulation of blood volume and pressure in general circulation. 12. Production of heat as a by-product of its numerous metabolic activities. Biology Department, Mount Olive College, Anambra State. Diseases of the Liver Diseases Case Definition Effects Remedies Diabetes The disease is caused as a result of I su s D ug h Mellitus the inability of the liver cell to continuous C b h d sh u d convert excess glucose in the blood dehydration be avoided to glycogen due to the failure of the I c us pancreas is produce a hormone exhaustion or insulin, therefore excess sugar left in muscular weakness the blood and lost through urine. It may lead to blurred vision and loss of weight Infective This disease is caused by Loss of appetite, 1. Fruit and Hepatitis inflammation and destruction of nausea, weakness, vegetable must (or viral liver cells by viruses. Faeces of fever, head ache, be properly hepatitis) infected person many be carried to diarrhoea, abdominal, washed with source of drinking water or food or discomfort, pain, clean water. palm wine. It may also be yellow eyes, and skin 2. Drinking water must transmitted by transfusion of blood be boiled with filter. of an infected person to an 3. Faces of an infected uninfected person. person must be buried deeply or burnt. 4. Flies should not be allowed to perch on food. Gall These are stony masses formed in 1. Abnormal pains, i. Drink sufficient Stones the gall bladder or bile duct. These chills and fever. water or fruit juice are mostly precipitation of 2. Skin and eyes turn ii. Reduce consumption cholesterol. The gall stones obstruct yellow due to the of food containing the flow of bile, subjecting the gall concentration of cholesterol and avoid bladder to infections. It also cause bilirubin in the blood being overweight high concentration of bilirubin in the and tissues. iii. Gall stones can be blood, tissue and bile which will 3. It may lead to removed by oral result in overweight. cancer of the liver. administration of a bile acid or by sugar in case of large stone Cancer of It is the abnormal outgrowth or I ds g n Th c nc s c the liver uncontrollable swelling of cell weakness. be destroyed using which do not retain the normal Th b d s radiotherapy or function of the tissues in which they exhausted chemotherapy arise. This continuous outgrowth Lv ns n eventually will prevent the liver be done from performing its normal role. Cirrhosis This is a disease condition in which G n w kn ss f Av d nc f of the liver the damaged liver cells become the body. alcoholic drinking replaced by useless fibrous tissues, L ss f. Sug b d n making the liver firm and irregular. on the patient This can be caused by excessive Liver transplant may drinking of alcohol and hepatitis. be done Jaundice caused by increase in the blood The symptom of bilirubin level due to excessive jaundice is yellowing breakdown of red blood cells of skin or eye white. observed in sickle cells or chronic Biology Department, Mount Olive College, Anambra State.  malaria patients and obstruction of bile duct by gall stones or diseases of the liver Amoeba The parasitic amoeba (Entamoeba It produces an enzyme Liver histolytica) which causes amoeba that destroys liver Abscess dysentery is also responsible for this tissue and cause an infection. The parasite gets into the abscess to form. liver from large intestine via the Abscess is an hepatic portal vein. inflamed swelling containing pus. The Skin as a Homeostatic Organ The skin is the largest organ of the body which covers its entire surface. It is composed of an outer epidermis, an inner layer of dermis and a layer of subcutaneous fat under the skin (below the dermis). An average skin is between 1-2 mm thick. The skin acts as a thermoregulator to keep the body temperature fairly constant. The starting point in any homeostasis is the identification of its set or the normal point. The set point of human body temperature is taken as 37°C, which is also called the normal or core body temperature. The core body temperature refers to the temperature of the combined portion of the trunk, head and upper part of arms and legs. Whenever the core body temperature departs from the normal, the body takes corrective measures. For example: If the temperature falls, there is increased heat production in the body along with prevention of heat loss. If body temperature rises there is cooling to give out excess heat. Before going into the specific role of the skin as a thermoregulator, it is very important to note that the body makes use of 2 regulatory systems in temperature control and they are: Physiological and Behavioural regulation. - Physiological regulation: These refer to actions like changes in blood circulation like vasodilation or vasoconstriction, sweating or not sweating, increase or decrease in cell metabolism, shivering, etc. All these adjustments are not under the control of will. - Behavioural regulation: It includes the conscious and subconscious acts. For example: When it is hot we often: Fan ourselves (to promote evaporation of sweat); - Move to any shaded or cooler place - Stretch out the limbs while resting in the bed. When it is cold we - Move to warmer places (open - Wrap ourselves inside blanket (to cut sunshine or in front of heat radiators) down heat radiation) - Prevent entry of cold winds (close the - Fold either arms or both arms and legs windows) tightly close to the body (to reduce radiation of heat from the body. Biology Department, Mount Olive College, Anambra State.  The Skin and Thermoregulation The principal heat-regulating centre is located in the hypothalamus, a part of the forebrain. This part acts like a thermostat. When the body has to face cooling below the n u , ‘sw ch s n’ s ds u the heat-producing processes nd s u n us ‘shu s ff’ the heat-losing ones. When the body faces overheating during summer or after intense physical exercise, it accelerates h c ng c ss nd ‘sw ch s ff’ h h - producing ones. The rise in body temperature It may be caused by hot weather, vigorous exercise, high fever or exposure to solar radiation. An increase in body temperature stimulates temperature receptors in the hypothalamus to send nerve impulses to the skin. These impulses stimulate processes that get rid of excess body heat. These processes include 1. Vasodilation: The expansion (dilation) of blood capillaries beneath the skin epidermis and relaxation of capillaries in deep layer of the skin. This allows more blood flow near the surface and heat is lost through the epidermis into the air by convection and radiation, thus reducing the temperature. 2. Sweating: Sweat glands are stimulated by nerve impulses to secrete large amount of sweat which evaporates and cools the body. Other mammals lose heat by (panting) i. e. evaporation of water through the mouth, nose and tongue. We often speed up evaporation of sweat by using fans. The fans by themselves do not cool the air; it is the movement of air that increases evaporation of the sweat to produce more cooling. 3. Decreasing metabolic rate: This minimizes heat production within the body. 4. Lowering of hairs: Erector muscles relax keeping the hair flat on the skin surface. Fall in body temperature Thermoregulation in cold weather is achieved in two ways: preventing loss of body heat and generating more body heat. Due to cold weather, the following processes occur: 1. Vasoconstriction: The narrowing or contraction of the blood capillaries beneath the skin surface and expansion of those ones in deep layers. As a result, less blood flows near the surface of the skin. Therefore, less heat is lost by convection and radiation, thus making the person look pale and blue. With the reduced blood supply to the sweat glands in the skin, there is less or no secretion of the sweat and thus there is no evaporation of water and no loss of heat 2. Shivering: rhythmic contractions of skeletal muscles to produce heat. 3. Increasing metabolic rate: The thyroid gland is stimulated by the hypothalamus to produce hormone thyroxine which increases the metabolic rate; hence more heat is produced especially by the liver. 4. Raising of hairs: Erector muscles contract to raise the hairs to trap air which is a bad conductor of heat. Biology Department, Mount Olive College, Anambra State.  UNIT 2 HORMONAL COORDINATION Students should be able to: 1. Explain what hormones are. 2. Name the substances produced by each gland. 3. List the glands in the body. 4. List some endocrine gland with their position and their functions. 5. State the effect of over production or under production of homones. Introduction The Endocrine System The endocrine system is made up of organs called endocrine glands. Endocrine glands produce and release different hormones that target specific things in the body and therefore regulate the functioning of the organism. These glands that are located at various parts of the body secrete a substance called HORMONES. Biology Department, Mount Olive College, Anambra State. Contrariwise, another type of glands exist which are called the Exocrine glands – these are glands of external secretion. These glands secrete substances on the body surface through a duct. Salivary glands, mammary glands, lacrimal glands, sweat glands, are some of the exocrine glands. Exocrine glands release their secretions (sweat, tears, saliva, milk and digestive juices) through ducts to where they are needed. Endocrine glands have no ducts, they are referred to as ductless glands because their secretions are delivered directly into the bloodstream and not through ducts. HORMONES Hormones are chemical substances produce in small quantities by specific cells of one part of the body in response to stimuli and carried to all or some parts of the body by the blood stream in animals or vascular system in plants where they produce a response. The activities of the various parts of the bodies in higher animals are controlled and coordinated by two coordinating systems namely the nervous and endocrine system. The nervous system which we shall study later in detail acts swiftly, instantly and electrically while the endocrine system acts slowly and chemically. In animals, hormones are manufactured in ductless (endocrine glands) and delivered directly into the blood stream where they are circulated to target organs to exert their effects. These effects could either be to speed up or slow down biological reactions. Hence, hormones can coordinate the body functions in a place far away from where they are produced. A few hormones like thyroxine and other growth hormones exert their effects on all body cells. Hormones (usually needed in a small amount) are active in homeostasis, growth and development. After their actions, hormones are inactivated in the liver and excreted in the urine. A hormone can be defined as a chemical messenger that is produced in one part of an organism and brings about a specific effect in a target organ some distance away. Nature and Function of Hormones – Hormones at a glance  Hormones are secreted from their sources directly into the blood.  Blood carries the hormone to the target cells which respond to it.  Hormones regulate the physiological processes.  They are produced in very small quantities and are biologically very active.  For example, adrenaline is active even at a concentration of 1 in 300 million parts.  Their excess and deficiency, both, cause serious disorders.  Chemically, the hormones may be water-soluble proteins (peptides), glycoproteins and amines or lipid-soluble steroids.  The extra hormones are not stored in the body and are excreted out. Animal Hormones There are basically 5 groups of animal hormones secreted by different glands and they are tabulated as follows: Pituitary Hormones The pituitary gland can be found below the hypothalamus in the part of the brain called the forebrain. It consists of anterior and posterior lobes both of which release hormones. The anterior lobe of the pituitary gland secretes a growth hormones, prolactin and 4 tropic hormones Pituitary Biology Department, Mount Olive College, Anambra State. hormones regulate the activities of other endocrine glands through a homeostatic mechanism. H nc , h u s c d “ s g nd” as it controls the activities of other glands. The hormones of the pituitary gland include: Animal Hormone 1 – Pituitary Hormones secreted by the Pituitary gland Name of Hormone Initials Function Oversecretion Undersecretion Anterior Pituitary Gland Hormones Follicle-stimulating FSH Causes or Primary Ovary Infertility hormone stimulates the Insufficiency (gonadotropins) ovary to produce mature eggs and the testis to produce sperms. Luteinizing hormone LH Causes the release Increased sexual Decreased sexual (Interstitial-cell (ICSH) of mature egg urge urge stimulating (ovulation into hormone) fallopian tube and secretion of testosterone in the testes. Adrenocorticotropic ACTH Stimulates the hormone adrenal cortex to secrete corticosteroids Thyroid-stimulating TSH Stimulates the Exophthalmic goiter Simple goitre hormones thyroid gland to G v ’s d s s produce its hormone called thyroxine. Prolactin Stimulates the insufficient milk secretion of milk being produced by the mammary after giving birth gland. Growth hormone Stimulates the Gigantism Dwarfism (somatotropin) growth of long In adult - bones and ACROMEGALY a increases situation leading to metabolic rate in increase in size of the cells. Growth head, hand, body, hormones are legs thick lips. produced during childhood and adolescence. Posterior Lobe of the Pituitary Gland Hormones Anti-diuretic ADH It raises blood Excessive retention Too much water hormone pressure by of water by the excretion constriction of the body. (diabetes arterioles and insipidus) increasing the reabsorption of Biology Department, Mount Olive College, Anambra State.  water in the kidney tubules. Oxytocin Stimulates the contraction of the uterine wall and dilation of the cervix during parturition and milk letdown from the nipples. Animal Hormone 2 - Thyroid hormones from the Thyroid Gland The thyroid gland is located in the region close to the larynx (the neck region). It produces three main hormones, the most important of which is thyroxine (others are triiodothyronine and calcitonin). Hormone Functions or Oversecretion Undersecretion Description Calcitonin Help regulate Medullary thyroid cancer may increase a person's calcium levels in (MTC) risk of bone degradation your blood by and osteopenia, a decreasing it. condition that occurs Achieves thsi by when the rate in which opposing the the body reabsorbs old actions of the bone exceeds the rate in parathyroid which it produces new hormone, which is a bone. hormone that increases your blood calcium levels. Triiodothyronine Plays vital roles Exophthalmic goitre Simple goitre in the body's metabolic rate, heart and digestive functions, muscle control, brain development and function, and the maintenance of bones. Thyroxine It regulates the (Hyperthyroidism) (hypothyroidism) (formed from growth and produces exophthalmic produces three amino acid and development of all goitre. This condition conditions iodine) body cells by causes marked increase in Simple goitre. increasing basal the metabolic rate, rapid Enlargement of thyroid metabolic rate. It heartbeat, shortness of visible as a swelling in increases the rate at breath and the eyes the neck. It is caused which glucose is protrude out together with due to iodine deficiency oxidized in the body goitre in the neck. in food as iodine is cells and increases needed for production heat production as of thyroid hormones. Biology Department, Mount Olive College, Anambra State.  well. Cretinism: poor body growth (dwarfism) and mental retardation Myxoedema: Swelling of the face and hands. General sluggishness. Animal Hormone 3 - Parathyroid Hormones from the Parathyroid Glands The parathyroid glands are small pea-sized glands located in the neck just behind the butterfly- shaped thyroid gland. Most people have four parathyroid glands, with two parathyroid glands lying behind each 'wing' of the thyroid gland. The secretion produced by this gland is called PARATHORMONE which raises the level of calcium in the blood by stimulating calcium release through: 1. Releasing calcium from bone 2. Increasing calcium absorption in the gut. 3. Reducing calcium excretion by the kidney. Over secretion of parathormone causes the bones to become fragile, soft and prone to fracture while under secretion causes muscle spasms. Animal Hormone 4 – Panreatic Hormones from the Pancreatic Glands (Pancreas) The gland is located in the loop of duodenum and doubles as both an endocrine and exocrine gland. As a result of this, the pancreas is an organ that produces both enzymes and hormones which serve digestive and regulatory functions respectively. Pancreas has special groups of cells scattered all over it called the Islets of Langerhans, which consists of three kinds of cells:  Alpha cells producing the hormone glucagon,  beta cells producing the hormone insulin and  Gamma cells producing the hormone somatostatin. Hormones Description and Undersecretion Oversecretion Function Insulin Lowers the blood Causes diabetes mellitus Causes a fall in blood glucose level by i. e. in which excess sugar level and stimulating the blood sugar cannot be hypoglycemia (low liver cells to converted to glycogen blood sugar). The brain convert excess leading to may enter a state of glucose to hyperglycemia, meaning coma if the level of glycogen for ‘ h nn sug sugar in blood becomes storage in the n b d’; ss , too low. liver and muscles. great thirst and incessant hunger. Glucagon Raises the blood Diabetes high blood sugar, a skin glucose level by rash called necrotizing stimulating the migratory erythema, liver to reconvert weight loss, mild stored glycogen diabetes, anemia, an to glucose. inflamed and sore mouth (stomatitis) and a swollen tongue Somatostatin Inhibits secretion Alzheimer disease Biology Department, Mount Olive College, Anambra State.  Growth Hormone- of insulin as well Inhibiting Hormone as glucagon. (GHIH) Diabetic Patients suffer from the following complications:  has higher glucose in blood;  excretes a great deal of urine loaded with sugar;  feels thirsty because of loss of water through too much urination;  Loses weight and becomes weak. In some cases, the patient even loses the eyesight. Adrenal hormones from the Adrenal glands The Adrenal Glands The adrenals (ad: adjacent, renal; kidney) are a pair of glands situated like caps one above each kidney. Each adrenal consists of two parts - an outer adrenal cortex and inner adrenal medulla. They produce two distinct groups of hormones. The adrenal cortex produces corticoids (glucorticoids and mineralcorticoids) while adrenal medulla produces adrenaline and noradrenaline (the emergency hormones). Hormones Description and Undersecretion Oversecretion Functions Location: Adrenal Cortex Corticoids: Glucorticoids e.g. which raise blood Fatigue, dizziness Immunosuppression, muscle Cortisol glucose level (especially upon atrophy, central adiposity, during stress standing), weight loss, hepatosteatosis, muscle weakness, osteoporosis, insulin mood changes and the resistance, hypertension, darkening of regions of depression and insomnia. the skin. Regulate the levels Increased retention of excessive hydrogen ion of sodium and H+ and metabolic (H+) loss and metabolic Mineralcorticoids potassium ions in acidosis. alkalosis like Aldosterone body fluids e.g. aldosterone increases sodium ions absorption. Location: Adrenal Medulla Adrenaline and Emergency it brings about slow nc s s c n nd noradrenalin hormones which response to emergency anxiety prepare the body it leads to low Increases blood pressure for immediate heartbeat and heart beat action in time of it leads to low blood It leads to profuse fright, danger and pressure sweating. anger. A ds u d n. Biology Department, Mount Olive College, Anambra State. Reproductive hormones Certain cells in the reproductive organs produce hormones. Testes in males possess two kinds of cells: the sperm-producing germinal cells and the hormone-producing interstitial cells. The hormones produced are called androgens and the commonest one among them is testosterone. The ovaries produce 2 kinds of hormones namely oestrogen and progesterone. Sex hormone production begins at puberty (a period in late childhood, between 10 and 14 years of age), then the production of sex hormones is greatly increased, causing the body to grow rapidly and change into a sexually mature form. This continues well into old age. The production of sex hormones is stimulated by the gonadotropic hormones secreted by the pituitary gland. Hormones Description and Function Undersecretion Oversecretion Testosterone 1. Stimulates the growth and I ds und Abn ug maturation of the penis, development of sexual for sex in males testes and accessory sex organs I ds glands plus organs. It leads to low urge excessive 2. Stimulates the for sex in males. development of development of male sex sexual organ characteristics such as muscular body, growth of hair in the pubic region, armpit, chest and the face and deepening of the voice. Oestrogen Initiates the development of I ds Abn ug n (secreted from the secondary sexual development of sex in females follicles of the characteristics such as the reproductive system. E u f ovary) enlargement of the breasts, Th s s d d secondary sexual growth of hair in the pubic secondary sexual characteristics region and armpit, widening maturity. of hip and fats distribution. 2. Regulates the reproductive or menstrual cycle. Progesterone 1. inhibits egg production Results in poor excessive secreted by the (ovulation) during pregnancy development of development of corpus luteum 2. prepares and maintain the secondary sexual sexual organs and (follicle left after lining of the uterus characters, sexual abnormal urge for the release of 3. aids implantation and organs and low urge sex ovum) development of the embryo for sex. in the uterus Human maintains the activity of chorionic corpus luteum in secreting gonadotropin progesterone continuously, (HCG), when a women becomes Produced by the pregnant. placenta THE FEEDBACK MECHANISM (CONTROL OF HORMONAL SECRETION) The amount of hormone released by an endocrine gland is determined by the bod ’s n d f h particular hormone at any given time. The product of the target tissue exerts an effect on the Biology Department, Mount Olive College, Anambra State.  s c v nd c n g nd. Th s ff c b s v (‘s c ’ n g v (‘s c n ’ ‘s w d wn’. Th s c n b n d by taking the example of thyroid gland. Feedback mechanism of thyroid activity (Figure below).  Hypothalamus releases a hormone TSH-RH (TSH- Releasing Hormone) which instructs the anterior pituitary to release TSH (thyroid stimulating hormone).  The TSH stimulates thyroid to release thyroxine.  If the level of thyroxine in blood increases, the pituitary stops the release of TSH.  When the level of thyroxine falls in the blood, the thyroid gets stimulated to secrete more of it.  In feedback mechanism the starting point of an activity receives back the information whether to continue or increase, or to slow down or even stop. Plant hormones Co-ordination in plants is simpler than in animals. It is ensured and regulated to a great extent by chemicals known as plant hormones (phytohormones). These Plant hormones stimulate or inhibit growth in the target tissues in response to external stimuli such as light, temperature, gravity and touch. Though they are usually called plants growth hormones, they affect other activities such as fruit formation, root development and leaf fall. In essence, overall plant development is made possible by chemical substances influencing the plant internally while factors such as light temperature water and gravity influence the plant externally. Plant hormones are produced or manufactured in the apical meristem of shoots and roots, young growing leaves, developing seeds and fruits and diffuse to other parts to produce some special effects. One of the most important groups of plants hormones is auxins. Other groups include gibberellins, cytokinins, abscisic acid and ethene (ethylene). Similarities between Plant Differences between Plant and Animal Hormones and Animal Hormones Animal Hormones Plant Hormones 1. Only needed in a small produced in specific glands not produced in specialized amount to bring about their tissues effects. bring about a response in effects are also more general 2. Produced in one part of specific target organs varying with concentration and Biology Department, types of organs the body and transported to Mount Olive College, Anambra State. Faster response in comparison plant hormones are usually another part where they to plants much slower than most exert their effects. animals Types of Plant Hormones Auxins The most important naturally occurring auxin is indoleacetic acid (IAA). It is produced at the actively growing and developing parts of the plant namely the apices of shoots and roots, developing leaves, flowers and fruits. It is transported in one direction away from the tip moving across short distances by diffusion and longer distances through the phloem. Auxin influences cell division, elongation and differentiation. Other functions include:  Influences the growth of stem towards the light (positive phototropism) and roots away from it (negative phototropism). Similarly, it causes the growth of roots towards the force of gravity (geotropism).  Stimulates the development of lateral and adventitious roots for increased water and mineral absorption.  Causes apical dominance by inhibiting the growth of lateral buds  Promotes the development of fruits.  breaks dormancy in seeds ensuring early germination  delays leaf fall  Prevent formation of abscissic layer - the presence of auxin at the base of flower stalk will help to fruit to reach ripening stage. A reduction of auxin at the base of petiole will allow formation of abscission layer which will allow shedding of leaves Auxins have been created artificially and exhibit qualities similar to auxins Examples include: 2,4-Dichlorophenoxyacetic acid (2-4-D); Indole-3-Propionic Acid, alpha-Naphthalene Acetic Acid (NAA), and 2,4,5-T (2,4,5-Trichlorophenoxy Acetic acid). MODERN APPLICATION OF AUXIN IN AGRICULTURE  The synthetic auxin commonly known as 2,4-D is used as a selective weed killer (herbicide) to control weeds.  Naphthalene acetic acid (NAA) is a synthetic auxin is used to stimulate fruit production in flowering fruit trees. In some species it causes the flower to produce fruit without fertilization, a phenomenon called pathenocarpy.  Yam and potatoes have preserved for a long time by the application of auxin to tubers.  Synthetic auxin is used to seal up cut area of plant after grafting by inducing new tissues formation  Auxins are used as rooting powders which are applied to the ends if cutting to induce root formation. GIBBERELLINS They are produced in young foliage leaves and roots, apices of roots and stems as well as in embryo. They promote growth by stimulating both cell elongation and cell division. They also stimulate growth in dwarf varieties. Other effects of gibberellins include  Inducing dormant seeds to germinate  It increases resistance of some plants to harmful effects such as viral infection, radiation and low temperature.  Causing dormant auxiliary buds to grow  Increasing fruit size. Biology Department, Mount Olive College, Anambra State.   It stimulates mitosis in meristematic and in embryo during germination. Cytokinins These are hormones produced in the roots, embryo and fruits that are actively undergoing growth. Cytokinins are also growth promoting hormones like auxins and gibberellins. Together with auxins, they stimulate cell division so that stems and roots grow normally. Unlike auxins, they stimulate the lateral buds to grow into branches. Furthermore, they delay ageing in plants. Abscisic acid This hormone is produced in mature green leaves, fruits and root caps. It is a growth inhibitor whose effects generally oppose both auxins and gibberellins. It:  Suppresses the growth of bud.  induces dormancy  brings about ageing in leaves hence leaf and fruit fall  Controls the opening and closing of stomata.  The effects of abscisic acid enable the plants to withstand severe environmental condition. Ethylene (Ethene) The hormone produces a simple hydrocarbon in young shoots and fruit as well as leaves and stems. The hormone stimulates the ripening of fruits and suppresses the development of internal buds when activated by auxin. General Applications of hormones in agriculture As indicated in the Auxin section above, Natural plant hormones and synthetic ones are used in horticulture and agriculture. The uses are:  Artificial vegetative propagation: Auxins are used in rooting powders which are applied at the end of cutting to induce root formation. Synthetic auxins are used to knit together parts of plants after grafting by inducing wound tissue formation.  Weed control: The synthetic auxin is used as a selective weed killer (herbicide) e. g. 2, 4 –D  Harvesting: Auxins are used to ensure a longer stay of fruits on the plants.  Parthenocarpy: Auxin and gibberellins causes flowers to develop into fruits without fertilization  Preservation: Cytokinins used in storing vegetables prevent yellowing.  Growth inhibitors (abscisic acid) are used to prevent onions and potatoes in stores from sprouting. UNIT 3 COORDINATION AND RESPONSE Introduction Coordination is the process by which all actions of different parts of the body of an organism are harmonized to achieve various definitive objectives. All metabolic processes in the body of an organism do not function individually but are closely linked and dependent on each other for effective function. The two communication systems that bring about coordination in organisms are the:  Endocrine system  Nervous system. Biology Department, Mount Olive College, Anambra State. We have studied the Endocrine system earlier in the series. We will now look at the nervous system and how they combine with the endocrine system in some ways to bring about total coordination in Man. The Nervous System The nervous and hormonal systems co-ordinate various biological activities in the body of multicellular animals. The basic structural unit of the nervous system is the nerve cell called a neurone. It consists of a dense, cell body and protoplasmic processes called nerve fibres. A bundle of the long nerve fibre is called a nerve. The main mechanism of information transfer is electric impulses known as nerve impulses along the nerve fibres. All the nervous systems in complex animals have the following: 1. The central processing region (the brain) 2. The nerves bringing impulses from receptors to the brain. 3. Nerves carrying information from the brain to the effectors. A typical sequence of a nervous response to incoming information is outlined below:  Sensory receptors which are often found in sense organs detect stimuli from the external and internal environment and so act as information collectors.  The brain receives impulses from these sensory receptors and interprets processes and analyzes the information before forwarding them to the effectors.  Effectors include muscles and glands that go into action on receiving nerve impulses from the brain. Such actions include muscular contraction, enzymes production, hormone secretion etc. Biology Department, Mount Olive College, Anambra State. Bringing you up to speed Some basic terms Before you learn about the various aspects of the nervous system, get familiar with the following related terms.  Stimulus: an agent or a sudden change of the external or the internal environment That results in a change in the activities of the organism.  Impulse: a wave of electrical disturbance that travels accross the nerve cell and its fibre.  Response: a change in the activity of the organism caused due to stimulus.  Receptors: The nerve cells which on receiving the stimulus, set up wave of impulses towards the central nervous system (brain and spinal cord).  Effectors: muscles or glands, which on receiving the impulse from the brain or spinal cord contract or secrete substances.  Nerve: A bundle of axons (nerve fibres) of separate neurons connecting the central nervous system with other parts of the body.  Sensory (afferent) nerve or the cell: bringing the impulse from the receptor (sensory organ) to the main nervous system.  Motor (efferent) nerve or the cell: Carrying the impulse from the main nervous system towards a muscle or a gland. Biology Department, Mount Olive College, Anambra State. The nervous system of a mammal is made up of two parts  The central nervous system (CNS)  The peripheral nervous system (PNS) CENTRAL NERVOUS SYSTEM The central nervous system (CNS) consists of the brain which is enclosed protectively in the cranium or brain box and spinal cord which runs down the centre of vertebral column (backbone). The CNS, in coordinating biological activities, receives a constant input of impulses which keep nf d f ch ng s n h n ’s n n nd n nv n n. Impulses to the CNS from receptors are transmitted along sensory nerves and are therefore known as sensory impulses. Those impulses from the CNS to the effectors are known as motor impulses since they are transmitted along motor nerves. Summarily, the central nervous system of humans includes a highly developed brain and spinal cord. The Brain The brain is the most specialized organ of human body. An average-sized brain for an adult weight is 1.2 – 1.4kg. The brain consists of millions of nerve cells (neurones) enclosed in the skull and covered by three-layered membranes i. e. meninges (meninx: membrane):  An outer tough duramater (dura: tough; mater: mother),  A thin delicate web-like middle arachnoid (arachnae: spider),  And the innermost piamater (pia: tender) richly supplied with blood vessels. The space between the layers of the meninges is filled with a fluid called the cerebrospinal fluid. Th b n c nsu s b u 25 c n f h b d ’s g n su. The brain has three regions, the forebrain, middle brain and hindbrain. Regions of the Brain Part of the Brain Location Components Forebrain or Rostral (forward- cerebrum, olfactory lobes, thalamus and prosencephalon most) portion of the hypothalamus (diencephalon is a collective Biology Department, Mount Olive College, Anambra State.  brain. name for thalamus and hypothalamus) Midbrain or small tubular part Optic lobes, pineal body and pituitary gland. mesencephalon between the fore and the hindbrain Hindbrain or the lower back part of Cerebellum, pons, and medulla oblongata. rhombencephalon the brain Forebrain This is the most predominant part of the brain, connected with intelligence and speech. It comprises of three major parts; cerebrum, olfactory lobes, thalamus and hypothalamus. Cerebrum This is the largest part of the brain and occurs in two halves, connected together through a band of fibres called the corpus callosum and separated by a deep furrow called the median fissure. The halves are called the cerebral hemispheres - each hemisphere is made up of four indistinct lobes which are frontal, parietal, temporal and occipital.  The most active region of the cerebrum is the outer layer called cerebral cortex which is made up of grey matter outside as a result of the colour of unsheathed nerve cell, while the inner part of the cerebrum is called white matter because the nerves cells are sheathed.  The cortex is highly convoluted and deeply folded in an irregular pattern for increased surface area. The more convoluted the cortex, the more the cerebral capacity.  The cerebrum carries out its functions with each area specializing in a particular activity.  Left side of the cerebrum controls the right side of the body and vice-versa. The cerebral cortex has three main functions: - It controls and initiates voluntary muscle contractions. - It receives and processes information from the sense organs, like eyes, ear, nose etc. processes it and sends the response through the motor neurones to the effectors. - It is the seat of consciousness and thus carries out mental activities of thinking, reasoning, planning, memorizing and judgement. Olfactory Lobes These are two small structures placed anteriorly on the cerebrum that is at the front of the brain. The olfactory lobe is concerned with the sense of odour (olfaction, or smell). They are prominent in dogfish and animals depending on animal senses. Thalamus These are two ovoid structures attached to the back of the fore brain. It contains masses of grey matter. The thalamus is the body's information relay station. All information from the body's senses (except smell) must be processed through the thalamus before being sent to the brain's cerebral cortex for interpretation. Functions - It is the center for sensation of pains, touch and anger - It is the seat of consciousness or awareness - It receives impulses from mid brain, hind brain and spinal cord. Hypothalamus It lies below the thalamus and is connected to the pituitary gland. It contains reflex centre linked to the autonomic system. It plays an important role in homeostasis Functions - It controls sleep and alertness. Biology Department, Mount Olive College, Anambra State.  - It controls motivated behaviour like appetite, feeling or sex. - It acts mainly in the body homeostasis and osmoregulation e.g. controls body temperature, water balance and blood pressure. - It controls the secretion of hormones from the pituitary gland. - It is the seat of emotion like aggression, fright, joy and anger. The Mid Brain The mid brain is narrow and short with thick walls portion which connects the hind brain and fore brain together. It consists of optic lobes, pineal body and pituitary gland. Function - The optic lobes are the seat of sight or vision. - It connects the fore brain and hind brain thereby assisting transmission of impulses. - Controls reflexes connected with sight and hearing. HIND BRAIN The hind brain consists of three parts namely cerebellum, medulla oblongata and Pons varolli. Cerebellum It is located below the back of the cerebrum, oval in shape and consists of two lateral cerebellar hemispheres connected to a central part through the pons varolli.  It is less convoluted than cerebrum.  The surface is covered with grey matter while the inner side is composed of white matter.  It is connected to the semi-circular canals of the ears. Its main functions are. - Controls body posture - Coordinate muscular activities and movement to maintain body balance - it receives impulses from auditory organs and skin Pons Varolli It connects the two halves of the cerebellum and cerebrum to the medulla oblongata. It is made up of thick bundles of nerve fibres. Functions - Contains nuclei that relay signals from the forebrain to the cerebellum, along with nuclei that deal primarily with sleep, respiration, swallowing, bladder control, hearing, equilibrium, taste, eye movement, facial expressions, facial sensation, and posture. Medulla oblongata This is the posterior end of the brain which continues into the spinal cord. The medulla oblongata connects the cerebellum to the spinal cord.  Unlike the cerebellum and cerebrum, the medulla oblongata has an inner grey matter as well as an outer white matter.  Additionally, It is in the medulla oblongata that right and left motor fibres from the brain cross over each other, so that the left hemisphere controls the right side and the right hemisphere controls the left side of the body. Functions - Controls all involuntary actions e.g. yawning, blinking of the eye, breathing, swallowing etc. - Controls the involuntary movement of the body especially those involved in respiration, heartbeat and digestion. - Regulates the blood pressure by controlling dilation and constriction of blood vessels. The Spinal cord Biology Department, Mount Olive College, Anambra State. The spinal cord extends from the medulla of the brain downward almost the whole length of the neural canal of the backbone which serves to protect it. It is also wrapped in the same three meninges as the brain namely dura mater (outer layer), arachnoids mater (middle layer) and pia mater (inner layer) and the space between them contains the same cerebrospinal fluid which acts as protective cushions.  The transverse section shows that the arrangement of white and grey mater is reversed in it. The inner greyish region called the grey matter is surrounded by a outer lighter region called the white matter.  The inner grey matter is composed, practically of all the cell bodies of the neurones in the spinal cord. Since the cell bodies are dense and granular, they give this region its typical greyish appearance.  The outer white matter consists of the nerve fibres of these cell bodies. Some of these fibres run along the spinal cord to the brain connecting both together. Other fibres leave the spinal cord to form the spinal nerves. Functions - Carry out reflexes below the neck, coordinating simple reflex actions like knee jerk and automatic reflexes such as sweating. - Conducts sensory impulses from the skin and muscles to the brain. - Conducts motor responses from the brain to the trunk and limbs. PERIPHERAL NERVOUS SYSTEM The peripheral nervous system (PNS) consists of all nerves outside the brain and spinal cord. Overall, it consists of two kinds of pathways: the afferent (receiving) sensory pathways and efferent (carrying away) motor pathways. These are made up of a sensory system having sensory nerves which arise from all parts of the body to the central nervous system and the motor system having motor nerves running from the CNS to all parts of the body.  The peripheral nervous system receives signals or changes from the environment registered by the receptors or sense organs and send them to the central nervous system which integrates the information. It receives and sends appropriate messages to the effectors accordingly. Biology Department, Mount Olive College, Anambra State.   The PNS consists of twelve (12) pairs of cranial nerves (connecting the brain to the head and neck region) and thirty one (31) pairs of spinal nerves (connecting the spinal cord to the thorax, abdomen and limbs).  The peripheral nervous system is subdivided into two systems. These are; 1. Somatic nervous 2. Automatic nervous system. SOMATIC NERVOUS SYSTEM The somatic nervous system consists of nerves without synapses leading from the brain through the spinal cord to skeletal muscles. They deal mainly with external stimuli and their responses.  The sensory nerves transmit impulses from the external stimuli to the central nervous system and relay responses through the motor neurons or the body causing the body movement.  The motor neurones stimulate the effectors i.e. muscles and glands hence the somatic nervous system controls activities that are mainly voluntary. Summarily, the SNS consists of motor (efferent) neurones that connect the CNS to each skeletal muscle. It serves the parts of the body which take part in responses to external stimuli and all voluntary actions. AUTONOMIC NERVOUS SYSTEM (ANS) The autonomic nervous system is the part of the peripheral nervous system which controls the involuntary actions inside the body such as the rate of heart, sweating, and peristaltic contractions of the intestine.  The ANS consists of motor (efferent) neurones that connect the CNS to glands, smooth muscles and cardiac muscles (involuntary muscles of internal organs). Summarily, the autonomic nervous system comprises of sensory and motor neurones arising from the central nervous system and is connected to different internal organs. The autonomic nervous system consists of two parts namely i. Sympathetic nervous system ii. Parasympathetic nervous system. These two systems work in opposition to each other helping to regulate the vital internal organs such heart, eye, lungs, kidney etc. maintaining a system of check and balances. Sympathetic nervous system prepares the body for facing emergency situations and the parasympathetic nervous system re-establishes the normal conditions once the emergency is over. The Sympathetic Nervous System (SNS) It is made up of nerves which connect internal organs to the thoracic and lumbar areas of the spinal cord.  The effect of this nervous system dominates in times of danger, emergency and exertion.  It regulates homeostatic mechanisms such as vasodilation, vasoconstriction and secretion by sweat gland etc. Para-sympathetic Nervous System This consists of nerves which connect internal organs to several cranial nerves and spinal nerves of the sacral region of the same organ as sympathetic nervous system but its action is opposite or antagonistic to sympathetic nervous system. The effect of this nervous system dominates during normal relaxed periods. Effects of the Autonomic Nervous System Organ Effect of Sympathetic Effect of Para-sympathetic Biology Department, Mount Olive College, Anambra State.  Activity activity Heart Accelerates heart beat Slows down the heart beat Eye pupil Dilated iris Constructs iris Blood vessels on skin Constricts arteries Dilates arteries Gut movement Slows gut movement Speeds up gut movement Urinary bladder Muscles relax Muscles contract Salivary secretion Stops Increased Tear glands Activated Slowed down Erector muscles of skin Stimulated (hair raised) Relaxed (hair flattened) hair Intestine Peristalsis decreased Peristalsis increased Stomach glands Decreased secretion Increased secretion The autonomic nervous system is strongly influenced by emotions such as grief, anger, fear, sexual stimulation, etc. THE NEURONES A neurone or nerve cell is defined as the basic structural and functional unit of the nervous system which is responsible for the transmission of impulses within the body. The neurons are found in the brain, spinal cord or nerve fibres of animals which are responsible for receiving and transmitting impulses. STRUCTURE OF A NEURONE A neuron consists of three major parts. Each neurone is composed of some basic parts namely:  A cell body (soma)  One or more short extensions or processes called DENDRONS each of which branches to form many DENDRITES.  A long process called axons which branch at the free end and terminate at the synaptic knobs. Biology Department, Mount Olive College, Anambra State. Summarily, the three parts are the cell body (soma), Dendron /dendrite and axon, Descriptions of Parts of the Neurone The Cell body (soma) They may be oval, polygonal or star-shaped and consists of a large nucleus plus organelles in a dense granulated cytoplasm which gives it its greyish colour. - It relays impulses it receives from the dendrons to the axon. The Dendron They are projections from the cell body which each dendron branches to form many fine dendrites. - The dendrites carry impulses towards the cell body. - The dendrites are the main receptive regions of the neurones and may be stimulated by sensory receptors and other neurones carrying impulses. - There may be as many as 200 dendrites in a single neuron allowing as many connections with the axon endings of other neurones. The Axon The axon is made up of a single, long fibre which transmits electric impulses away from the cell bodies to the proper destination usually some distance away. The axon of a motor neurone going to a skeletal muscle may be several metres long. It may also divide into several branches so that impulses from one neurone go to several places. - Sometimes, a fatty sheath known as myelin sheath surrounds the axon. The myelin is interrupted at intervals by constrictions known as nodes of Ranvier. - Myelin sheath acts as an electrical insulator. It also increases the speed at which impulses travel along the axon. Neurones are joined end to end in a special away to form a nerve. The axon of one neurone forms a junction with the dendrite of the next neurone and where the two meet is a nerve junction called synapse (Synapse is the point of communication between one nerve cell and another or between nerve cell and a muscle). Classification of Neurons There are three types of neurons these are: 1. Sensory Neurone 2. Motor Neurone 3. Relay Neurone Sensory (afferent) Neurones  These neurones which transmit impulses from sensory cell or receptors towards the central nervous system and spinal cords. The dendrites are connected to other neurons. Motor (efferent) Neurones  These are neurones that transmit impulses away from the central nervous system to the effector organs e.g muscles and gland. The dendrites are connected to the intermediate neuron while the axon is connected to an effectors Relay (association or intermediate) Neurones  They are neurons that join the sensory neurone with motor neurone connecting both the pathways of sensory and motor impulses. In order words, it transmits impulses from one neurone to the other within the central nervous system and both their dendrites plus axons are connected to other neurones. Biology Department, Mount Olive College, Anambra State. CONDUCTION OF NERVE IMPULSE ALONG THE NEURON ANDOVER THE SYNAPSE Recall that neurones are usually interlocked with other neurones through their dendrites and axons to form a nerve fibre. Secondly, a synapse is the point of communication between one nerve cell and another or between nerve cell and a muscle The conduction of nerve impulses along a neurone or through the nerve fibre is electrical in nature while the one through the synapse is chemical in nature. Transmission of impulse along a neurone Transmission of impulse along the nerves or transmission of nervous impulse is a wave of electrical activity travelling along the neurones. The transmission of nerve impulse is partially electric and chemical (electrochemical). Though it is said to be electrical however it can be likened to the flow of electrons like an electric current in a wire but travels as a wave of depolarization.  A neurone that is not transmitting an impulse is known as a resting neurone. A resting neurone is actually actively generating electricity. It does this by pumping sodium ions (Na+) out of the cell through the cell membrane, leaving behind chloride ions (cl-).  In normal resting condition, the outside of the nerve fibre carries a positive (+) charge. In this condition, the nerve fibre is said to be polarized. The polarization is due to the Presence of more Na+ ions outside the cell membrane. Such state is maintained due to the sodium ions being continuously pumped out by means of the sodium potassium pump and operated by active transport using ATP for energy. The changes when a stimulus arrives at the nerve fibre are as follows:  The axon membrane at that spot becomes more permeable to Na+ ions, which moves inward and brings about depolarization or localised change of charge from positive to negative (see diagram) on that spot.  This point of depolarization itself becomes the stimulus for the adjoining area of the membrane, which in turn becomes depolarized.  Meanwhile, the previous area becomes repolarised due to active movement of the sodium ions to the outside of the membrane by means of what is called ‘s d u u ’.  And now the fibre is ready for the next wave of depolarization. Biology Department, Mount Olive College, Anambra State.   Thus a nerve impulse is a self- propagating wave of depolarization and repolarization Sodium potassium pump is a carrier protein on the plasma membrane which transports sodium and potassium ions across the membrane. Normally ions move from the region of their high concentration to the region of their low concentration. Transmission of nerve impulses Transmission of impulses along a neurone is by electrical (through a nerve fibre) and chemical (across a synapse) means. Three phases involved include: 1. Resting-state: A state when a neurone is not transmitting an impulse. In this state, the nerve fibre is electrically polarized with excess sodium ions (Na) outside the cell and excess potassium (K) inside the cell. Therefore the cell becomes positively charged outside and negatively charged inside. 2. Action state: When the dendrites of a neurone receive impulses, the neurone becomes depolarized and the cell membrane suddenly permits the inflow of sodium ions and outflow of potassium ions. The cell body then transmits the impulse to its axon. 3. Transmission between neurons: Transmission here is by chemical means. When an impulse reaches the synapse, it stimulates the secretion of a chemical substance called acetylcholine which transmits the impulse to another neurone or muscle fibres. Over the Synapse – Chemical Signalling Biology Department, Mount Olive College, Anambra State. The impulse travelling through a nerve fibre may reach either its destination. (muscle or gland) for action or the dendrites of another neurone for further transmission. The meeting place is called synapse. The transmission over a synapse is a chemical process. The detail of this process is enumerated below:  Neurones never touch each other  The junctions (gaps) in between them are called synapses  The electrical impulse travels along the first axon  This triggers the nerve-ending of the presynaptic neurone to release chemical messengers called neurotransmitters from vesicles which fuse with the presynaptic membrane  The neurotransmitters (acetylcholine) diffuse across the synaptic gap (or cleft) and bind with receptor molecules on the membrane of the second neurone (known as the postsynaptic membrane).  This stimulates the second neurone to generate an electrical impulse that travels down the second axon. This is known as firing the second neuron.  The neurotransmitters (acetylcholine) are then destroyed to prevent continued stimulation of the second neurone which would cause repeated impulses to be sent. (The neurochemical is quickly destroyed by an enzyme called Chlorine terase which render the acetylcholine inactive thereby preventing it from accumulating at the synaptic gap)  N u ch c c n n v f h n’s s n c knob to the target cell membrane, so impulses are always transmitted in one direction only. Synapses ensure that impulses only travel in one direction, avoiding confusion within the nervous system if impulses were travelling in both directions. In case the axon endings are branched and in contact with the dendrites of other neurones, the impulse will travel through all of them. NB: As this is the only part of the nervous system where messages are chemical as opposed to electrical, it is the only place where drugs can act to affect the nervous system - eg. This is where heroin works All or none’ principle: If the stimulus is strong enough (with a minimum threshold) to produce the impulse, the impulse will set up and travel at its own speed. Threshold is the minimum strength of a stimulus that can initiate an impulse. Increasing the intensity of the stimulus cannot raise the speed of transmission. Reflex and voluntary actions Actions are responses to stimuli. These actions are grouped into two: involuntary (reflex) and voluntary actions. A reflex action or involuntary action is a fast automatic response to a stimulus of an organ or a system organ, the action which is not initiated by the brain. Protective actions guarding us from dangerous stimuli and helping us to maintain posture and balance such as sneezing, yawning, knee jerk, blinking of the eyes, breathing action are actions that are not initiated by the brain but by muscle receptor cells. Summarily, involuntary (or reflex) responses:  Does not involve the brain as the coordinator of the reaction and you are not aware you have completed it until after you have carried it out.  Is an automatic and rapid response to a stimulus such as touching something sharp or hot.  As it does not involve the brain, a reflex response is quicker than any other type of nervous response. Biology Department, Mount Olive College, Anambra State.   This helps to minimise the damage to the body The reflex arc represents the series of neurons which impulses have to pass in order to bring about a reflex response. The events that occur during a reflex action when a person suddenly touches a hot object can be outlined as follows: I. The pin (the stimulus) is detected by a pain/pressure/touch receptors or nerve ending in the skin. II. Sensory neurone sends electrical impulses through the dorsal root ganglion into the spinal cord (the coordinator). A ganglion is a complex set of synapses. III. Electrical impulse is passed on to relay neurone in the spinal cord. IV. Relay neurone connects to motor neurone and passes the impulse on. V. Motor neurone carries impulse to a muscle in the leg (the effector). VI. The muscle will contract and pull the hand or foot up and away from the sharp object causing the painful stimulus (the response). The reflex arc The reflex arc involves the following: 1. The sensory receptors that receive the stimulus. 2. The sensory neurones along which the sensory impulse travels 3. The relay or intermediate neurone through which the sensory impulse is passed on. 4. The motor (efferent) neurones along which the response is transmitted. 5. The effectors (muscles and glands) which the motor impulses trigger to bring about an appropriate response. Biology Department, Mount Olive College, Anambra State. Reflex actions can be: 1. Spinal reflex involving the spinal cord e.g knee jerk 2. Cranial or cerebral reflexes involving the brain e.g closing of the pupil in the presence of bright light. Voluntary Responses A voluntary response is one where you make a conscious decision to carry out a particular action therefore it starts with your brain. These are actions initiated and controlled by the conscious part of the brain, which involves thoughts before a performance. For examples writing, walking, running, reading, talking, driving, swimming, typing, dancing and climbing and reaching out to pick up a cup of coffee Voluntary actions They involve: 1. The conscious parts of the cerebrum 2. Most of the reflex arc components 3. Ascending and descending fibres in the spinal cord. Reflex Actions Voluntary Actions Biology Department, Mount Olive College, Anambra State. Actions does not involve the higher centre of Actions involve the higher centre of the brain the brain (unconscious) (conscious) It is inborn It can be learnt Response is rapid and automatic Response is neither fast nor automatic Nerve impulse do not reach brain Nerve impulse always reach the brain Response is stereotyped Response varies with circumstances It occurs unconsciously It occurs consciously Reflex action Source of stimulus Response Sneezing Irritation of nasal mucous Quick and violent contraction of the membrane abdominal muscle Contraction of iris Variation in height intensity Increase or decrease in the pupil of the muscle eye. Knee jerk Tap on the tendon which Muscle flexes and the lower leg is raised. causes the muscle to stretch Coughing Irritation or the throat by Contraction of the abdominal muscle foreign body Resulting in the closure of the epiglottis. Conditioned Reflex A reflex action may be instinctive (does not have to be learned) e. g. sucking behaviour of a newly born baby or a conditioned reflex (learned responses or behaviour that can be performed without thinking about it) e. g. walking, riding a bicycle, writing, driving, swimming, typing. Therefore, conditioned reflexes are those behaviou s’ wh ch are acquired through learning. Such actions can be repeated without thinking about it. Most of our behaviours are conditioned reflexes. A famous Russian biologist, Ivan Pavlon demonstrates what is meant by conditioned reflex using a puppy and associating its food time with the sound of a bell. Summary of Ivan Pavlov's work in 1902 on Classical Conditioning  Ivan Pavlov was a Russian scientist conducted experiments on conditioned reflexes.  He discovered that dogs produced extra saliva when they were offered food.  Pavlov noticed that they also did the same when the person who fed them came into the room, even if the person had not brought any food.  Pavlov went on to ring a bell at the start of feeding time.  Eventually, the dogs produced extra saliva when they heard the bell, before any food was brought.  A dog salivating when it hears a bell is not a natural response.  They would not do this without being conditioned to do so.  The behaviour has been learned. It is called a conditioned response. Roles or Functions of conditioned Reflex on behaviour i. It helps individuals to acquire new skills through the learning of such habit. ii. It helps to develop certain behaviours which are not originally shown in the individual. iii. The principles were used by a Russian biologist Ivan Pavlov in 1902 in the training of dogs for their role in crime detection and for security. iv. Unhealthy behaviour like smoking, drinking, and drug taking may become bad habit when acquired through conditioned reflex be difficult to stop. Reflex action Conditioned Response It is an inborn behaviour It is learnt behaviour It takes a short time It takes a longer time Biology Department, Mount Olive College, Anambra State. Action starts by muscle Action starts in the brain cells receptor Property Nervous Coordination Hormonal Coordination Nature of signal Messages are passed mainly as Messages are passed as electrical impulses along chemical substances. nerves. (Chemical signalling only occurs in the synapses). Speed of signal Rapid. Between 0.7 metres