for class XII

Muscular tissue
Mesodermal in origin, except the ciliary muscle iridial muscle ectodermal)
639 types of muscle in human body.
Properties
o excitability – can excited by nerve impulse of stimulus of specific strength called threshold stimulus.
o Conductivity - can conduct waves of contraction along their length at the rate of 3-5 mitre/sec.
o All or none rule – muscle fibre can not be stimulated by sub threshold stimuli, single muscle twitch a muscle fibre contracts only once when stimulated
o Refractory period - undergoes refractory period of 0.005 second during which it recovers itself.
General structure
 A muscle cells are highly elongated and contractile called muscle fibres.
 Always contract along their longitudinal axis and can contract up to one third or one half of their length.
 Cytoplasm of muscle fibres – sacroplasm is highly conctractile, mitochondria collectively called sarcosomes, a network of modified SER sarcoplasmic reticulum and numerous glycogen granules to provide energy for its contraction and relaxation. Sarcoplasm contains large no. of fine longitudinal and contractile proteinaceous threads called myofibrils, each myofibril 1-2 um in diameter.
 Highly specialized for movement and locomotion, so no power of division and regeneration.
 Do not secrete intercellular subs almost no intercellular space, held together by connective tissue.
Functions
1. responsible for movements in hands, legs eye
2. equilibrium
3. prevents escape of food
4. helps in collecting information about changes in environment
5. brings about movement of food in digestive tract, urine in ureters, sperms in vasa diffrentia , ovum in fallopian tube, production of sound, beating of heart, respiratory movements .
6. provide support to skeletal structure.
7. locomotion of living organisms, which help protection from predators, to locate food and water, to find mating partner, to reach favorable area for egg laying or rearing the youngs.
8. also control facial expression and gesture.

In vertebrates, three kinds of muscular tissue are recognized.
1. smooth or unstriated or involuntary muscle
2. striated or voluntary muscle
3. cardiac muscle
smooth muscle - spindle shaped, rounded or polygonal in cross section, contain centrally placed oval or rod shaped nucleus, length of cell 1/20th of mm , width 1/60th of a mm. cytoplasm or sarcoplasm contain fine longitudinally arranged thread like elements known as myofibrils, found in visceral structure, part of digestive tube, blood vessels urinary bladder or ducts.
Striated muscle - because of their appearance, these are called striated or striped and because of their physiology, these are voluntary. Each striated muscle is composed of very large no. of long and cylindrical fibres measuring 100 microns in diameter and about 40 mm in length. These fibres are much wider, non tapering and their cells boundaries can not be clearly distinguished. The muscle fibres are coenocytic( multinucleate) with many elongated peripheral nuclei. The cytoplasm of each fibre contains large no. of myofibrils and sarcostyles which are relatively course and therefore not difficult to see under the microscope in a profusely stained preparation. Myofibrils are tightly packed. Each fibre has extensive sheath of sarcolemma which encloses contractile myofibrils. Just beneath the sarcolemma of each fibre occur in the sarcoplasm several elongated nuclei at regular intervals. When examined under the microscope each muscle fibre appears to be divided into an alternating dark and light bands which appear as such due to fact that each myofibril itself is formed of number of alternating light and dark sections . the dark bands or A discs are separated from one another by light band or I discs.
Stiated muscle fibres are united in parallel bundles. These muscles have power of contracting rapidly and strongly, are liable to fatigue and get their nerve supply from ventral roots of spinal cord. The striated muscles work in pair. A flexor causing bending at joint and extensor muscle causes straightening. Striated muscle is generally found attached to the bones except some of the muscle of tongue.
Cardiac muscle - cardiac muscles are characterized by branching and anastomosing fibres, central nuclei, transeverse striations and intercalated discs. Adult cardiac muscle consists of muscle fibres joined into a intricate network. Myofibrils appear to be similar to those of striated muscle. They usually present a staircase appearance. Cardiac muscle has as extremely rich blood supply. It contracts automatically and rhythmically. Cardiac muscles are found in walls of heart.

Nervous tissue

It consists of neurons, nerve fibers and neuroglia. Neurons are highly specialized cells. Neuroglia are more or less undifferentiated supporting cells which form packing around neurons.

Properties
Excitability - neurons have pre existing potential difference across their membrane called membrane potential. A stimulus of adequate strength called threshold stimulus can cause depolarization of neuron locally and initiates the nerve impulse. On stimulation, potential difference undergoes change and cell is said to be excited. The cell then transmits this change as a wave along the membrane.
Conductivity - message is transmitted along axon is called nerve impulse. It is conducted in the form of electric impulse. It always travels from cell body towards axon.

Structure of neuron
It possesses two distinct regions
1. cell body, perikaryon or soma
2. cytoplasmic extensions

Cell body contains nucleus, abundant granular cytoplasm. Cell organelles like mitochondria, golgi apparatus, rough endoplasmic reticulum and neurofibrils are present.
Cytoplasm contains conical, angular or rhomboidal granules called Nissl’s granule rich in RNA. These are concerned with protein synthesis. These are absent in axon.

Cytoplasmic extensions extend from the cell body. They are of two kinds.
o Dendron or dendrite - small wide processes that break up into numerous fine branches. They convey impulses toward cell body.
o Axon or nerve fibre - it is a long process, several meters long. It carries nerve impulse away from cell body. Terminal ends are swollen. These are neurosecretory. They release acetylcholine, adrenaline. They communicate with neuron through synapse.

Types of neuron
Neurons are of three types
o Unipolar neurons - they have just one process arising from cyton. These neurons have only axon. This type of neurons is found in the embryonic condition only. In the adult, there is presence of pseudo unipolar neurons. In pseudo unipolar neuron, the single process divides into two branches. They have axon at one branch and dendron at another branch.
o Bipolar neurons - these neurons have two processes arising from opposite poles of cyton. On one process there is dendron and on the other process there is axon. These are found in the retina of eye, nasal chamber etc.
o Multipolar neurons - they have many processes arising at different points of cyton. There are many dendrons and one axon. They are found in developed organisms.

Types of nerve fibres based on the presence or absence of myelin sheath
o Myelinated or medullated nerve fiber - in this, the nerve fiber is covered by myelinated sheath. They are white in color. These are found in white matter of Brain and spinal cord. They are involved in quick conduction of nerve impulse.
o Non myelinated or medullated nerve fiber - these nerve fibers are without myelin sheath. These are grey in color. They are found in the grey matter of brain and spinal cord. They conduct nerve impulse slowly.

Types of neurons on the basis of their functions
o Sensory or afferent - these neurons take impulses from the sensory organs to the brain or spinal cord. Some of the cranial nerves like optic nerve, auditory nerve are sensory in function.
o Motor or efferent - these neurons take information from brain to the target organ or muscles. Some of the cranial nerves like oculomotor nerve, trochlear nerve are motor in function.
o Mixed nerve - some are mixed in nature. They are both sensory and motor in function. The spinal nerves are all mixed in nature.

Neuroglia cells or glial cells
These are non nervous in nature. These are about 10 times more than the nerve cells. These are capable of division. These are cells from the connective tissue.
Functions
o Form packing between nerve fibres.
o Help in wear and tear.
o Insulate adjoining nerurons, prevent lateral transmission of nerve impulse.
o Provide nutrition.
o Act as phagocyte.
o Help in memory.

Types
o microglial or microgliocytes - these are small spindle shaped, make reticulo endothelial system.
o Astrocytes – large sized, highly branched and present around blood vessel.
o Oligodendrocytes – large sized, few branched processes, form insulating covering of nerve fibre.

Ependymal cells
These are also non nervous in nature. These are found in the central canal of spinal cord. These are ciliated and help in spreading of cerebrospinal fluid.
Neurosecretory cells
These are also non nervous in nature. These are found in hypothalamus of brain. These are special cells of endocrine nature. They secrete the neurohormones like Adreno cortico tropic hormone ACTH, thyroid stimulating hormone TSH etc.











Biotechnology
It is the new discipline of science. It is an application of scientific principles to the processing of materials using biological agents to provide goods and services. It is defined as “any technique that uses living organisms to make or modify products to improve plants and animals or to develop microorganisms for specific uses.

Antibiotics
These are chemical substances produced synthetically b micro organisms. It inhibits the growth of bacteria and other micro organisms and even destroy them.

First antibiotic - Penicillin
It was discovered by British Bacteriologist Alexander Flemming in 1928. Once he was working with Staphylococcus. It happened that some spores of mould floated in his laboratory. He threw them from window. Luckily these spores landed on one of his Staphylococcus colony. He observed that bacteria were quickly killed or destroyed. Later the mould was identified as Penicillium notatum. Due to this reason, the active substance which killed bacteria was named as Penicillin.

Commonly used antibiotics
Penicillin- prepared from Penicillium notatum and Penicillium chrysegenum. It is proved to be effective for treatment of bacterial infection such as pneumonia, meningitis, tetanus etc since 1940. It has saved millions of lives.

Streptomycin - it is obtained from mould Streptomyces griseus. It is effective for treatment of TB, Typhoid.

Tetracycline - it is broad spectrum, made up of group of antibiotics. It is effective for treatment of bacterial and viral infections.

Actions
Bacteriostatic (inhibiting the growth of microorganisms in the body. Later the immune system of body will kill the microorganism)
Bacteriocides (killing pathogenic microorganism directly)

Catogories
Broad spectrum - destroy several pathogen species eg Penicillin, Streptomycin
Specific antibiotics - have limited action.

Application
1. medicinal use – control no. of infectious diseases human and animal
2. food preservation – especially meat, fish, poultry
3. supplement in animal feed, some antibiotics have been used to enhance growth of animals




Vaccines
These are preparations of killed or living microorganisms which produce immunity when administered into body.
Dr Edward Jenner an Eighteenth century physician made an important observation in 1790. Small Pox was most dreadful disease in those days. Dr Jenner noticed that milkmaids and diary workers did not get the disease. He found that these people contacted cow pox from animal at some time earlier during life which appeared in the form of pustule on hand and left scar and nothing serious happened.
Dr Jenner experimented with the boy Philips and infected with first cow pox and later with small pox (after six month). To his surprise, the boy did not get small pox an survived the attack showing he was immunized to small pox. Jenner gave the term vaccine . vacca in Latin means cow ) to the fluid he inoculated.

Types of immunity
1. natural or inborn - it is present at birth. Some antibodies pass through placenta to foetus. It gives passive immunity for short time. However protects from no. of diseases like Polio, measles till body’s own immune system develops.
2. acquired immunity - it is developed after birth.
active - produced by injecting small quantity of antigen called vaccine into body. The process is called vaccination or immunization. Then body manufactures antibodies. It lasts for long time. When body is exposed to antigen, it contacts disease. The body not only produce antibodies also memory cells. When same antigen strikes for second time, memory cells produce large amount of antibodies and body does not contact disease. This is why some childhood disease like mumps, chicken pox occur only once in life.
Passive - body does not produce antibodies, instead readymade antibodies from some other organism is introduced

Types of vaccine

1. killed vaccine - it is prepared from killed pathogenic organism by heat or UV light or alcohol, formalin of phenol. Example Typhoid vaccine, cholera vaccine
2. toxoid - it is prepared by destroying toxic property of toxin retaining antigenic property. Example TT tetanus toxoid
3. attenuated living vaccines - pathogen weakened to make non virulent. Example oral Polio vaccine, BCG
4. antibodies as vaccine - serum used after a person or animal has been exposed to infection. Serum contains antibodies against pathogen. Example anti tetanus serum (ATS)
5. mild strain of virus - non pathogenic strain of virus. Vaccine developed through recombinant DNA Technology used to clone the gene for protective antigen protein. Example Hepatitis B, influenza, foot and mouth disease(FMD)



Tissue and organ transplantation

It is the process of removing tissue or organ from animal and planted to the other or from one individual to another. It is a process applied to replace injured or diseased tissue or organ with natural or artificial ones.

Tissue transplantation
Skin or part of bone -- highly successful.

Types
• autograft - from one part to another
• isograft – between genetically identicals - twins
• allograft - between different members of same species
• heterograft - between different species. Monkey to man

Organ transparent

Best known and successful one is cornea transplant.
Others include kidney, liver, heart etc.
Draw back - the transplanted organ contains about 40 antigens which can trigger the production of antibodies. The recipient recognizes the transplanted organ as foreign body. Does not accept, immune system activated and causes destruction or reject
Drugs used to force accept the transplanted organ.
Radiation to suppress immune system.
So usually between siblings
Cryopreservation - it is the preservation of organ at very low temp.
This technique involves the use of tissue taken form human and other animal for the purpose of reconstructive surgery.

The transplant of cornea is called keratoplasty. The credit of keratoplasty goes to Russian Dr Filotov.
The first heart transplant was done by Christian Bernard in 1967 in the USA
The first lung transplant was performed by JD Hardy in 1964.
The science of transplantation is new one and represent one of the major frontiers. Research and experimental transplant are done and attempted with all parts of human organs.

Benefit of organ and tissue plantation
• Millions of blind people can see the this beautiful world due to cornea transplant.
• Can give life to those patients where the hope of treatment has been given up.
• Skin transplantation, a successful one for those who have met accidents.








Amniocentesis

When a pregnant women is known to have chance of bearing a child with a genetic defect, it may be desirable to diagnose the condition of fetus. This can be done by taking some cells from the fetus by drawing about 10 cc of amniotic fluid with the help of hypodermic needle. This technique is called the amniocentesis. This is usually performed at 15th week of pregnancy to allow enough time for safe abortion if recommend . more than 30 genetic diseases have been detected.

Karyotype analysis - fetal cell analysis- useful for detection of chromosomal abnormalities.

Biochemical test – presence of absence of certain enzymes detection of prenatal disease

Termination of pregnancy is advised if there is serious congenital defect.
This technique has been misused to know the sex of the growing child and abort the normal female fetus. So it is banned.



Test tube baby

For those unable to conceive and give birth to a child normally. Fertilization not possible. Unfertilized ovum taken out , kept under sterile or septic condition. Fertilization carried out by the sperm from her husband out side body. Zygote developed in vitro up to 32 cells stage. Put into reproductive tract. The mother then can give birth to child in a normal way.

It is a great achievement of medical science. The first attempt was made by Italian scientist Dr Petrucci in 1959. He removed an ovum from a patient and put it in a glass tube among swarming millions of spermatozoa. One of which met and fertilized the egg. The embryo grew and survived for 29 days. It is credited to Gynecologist Patric Steptoe and physiologist Robert Edwards of England. The first test tube baby born on July 25, 1978 named Louse Joy Brown, a female child. Mrs. Brown gave birth at 28 weeks and 5 days.
This technique can help those female with obstruction in oviduct to carry down the ovum. In males, it can help if the sperm count is less. In some rare cases, a surrogate or substitute mother has been used to bring up in vitro fertilized ovum to maturity. In reality, ovum does not belong to substituted mother but she delivers the child. It has created ethical and legal problems such as right over child. In case of male infertility, sperms can be used from the sperm bank.

In Nepal, Om Hospital with the technical support of Assisted Reproductive Technology(ART) has started the technology of Test tube baby. The first test tube baby is Om mani Tamang born in 2005 March 3 at 8.52 am in Kathmandu, belonged to Mr Rajendra Tamang and Mrs. Sandhya Syanbo. Since then hundreds of test tube babies have been born.