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The lower group of chordate animals do not have a developed organ like brain and therefore their functions are autonomous silvitra 120 mg without a prescription. The brain rests securely inside the skull and is covered by three membranes to protect against friction cheap silvitra 120mg overnight delivery. It extends right from the centre of the brain to the spinal cord, as well as in the outer membranes of the brain and spinal cord. F range from assisting the metabolism of the brain to the prevention of friction: As the cells of the brain perform complex functions, they need extra nourishment and oxygen. If the supply of blood and oxygen to the cortex stops completely for more than five minutes, the cortex stops functioning permanently, resulting in death. Cerebellum is located in the posterior region of the skull and is divided into two - left and right - parts. The brain stem, which joins the two sides of the brain, consists of mid-brain, pons and medulla oblongata, which truncate into the spinal cord. The frontal lobe is basically responsible for the movements of the limbs, the personality and the behavior of an individual. The temporal lobe and the limbic system are associated with memory as well as basic instincts, and according to some it can be the seat of special powers like the sixth sense, etc. The left side of the brain of a right handed person (who uses his right hand for writing, eating, throwing etc. However, others believe that the mana may exist either in the temporal lobe, in the limbic circuit, or in the pineal gland of the brain. It is actually a complex biochemical and electromagnetic process and it is the limitation of our science and brain that we do not have the proper understanding of this subject. Similarly, Hypothalamus is an important centre and is the final control point of the sympathetic and the parasympathetic nervous system. It is associated with functions of our involuntary muscles, as well as physical processes like stress. This type of nervous system autonomously controls the extremely important functions of the heart, intestines, eyeballs, blood pressure, respiration etc. We have thus studied the anatomy of the brain, but brain has some amazingly unique features also, which make man superior to all living beings. There is a kind of electrical impulse emanating from the cells of the brain, which is rhythmic and constant. This electrical impulse travels chemically across one nerve cell to the other through neurotransmitters and receptors which form an amazing network and can transmit information from one part to another in a 1000th fraction of a second. Transmission of messages from one person’s minds to the other, as in telepathy can be called an electronic process. Moreover, the human brain is endowed with developed features like thinking, intelligence, the power to differentiate between good and bad, memory, creativity, etc. Though anatomically the heart is situated in the chest, the way poets have described the emotional heart it appears that in fact they are referring to the mind. The amazing thing is that we ourselves can think about our own brain, analyze it; but the one, who has created us, has discreetly left us in the dark about him. The electrical impulse generated by the posterior part of the brain during waking with eyes closed is known as alpha wave. In the past few decades, mental maladies have come to be recognized as problems of the brain, and antidotes have emerged as the treatment of choice. Regardless of how one feels about the biological basis of psychiatry today, two facts must be acknowledged. The essence of who we are is encoded in our brain, and brain changes account for the alterations of thought, mood, and behavior that occur in mental illness. It is instead the nature of the neural changes that underlie mental problems, and the manner in which treatment should proceed. These sections provide a broad framework of the basic concepts and terms necessary to understand the fundamental processes underlying brain function. Basic unit - a neuron & neural organisation As mentioned earlier, the Nervous System comprises of the brain, the spinal cord, the nerves emanating from them and their innervations of muscle fibres (i. Although that extraordinary number is of the same order of magnitude as the number of stars in the Milky Way, it alone cannot account for the complexity of the brain. A major part of the complexity arises from the rich diversity of nerve cells, or neurons, which the famous neuroanatomist Ramon y Cajal described as “the mysterious butterflies of the soul”. A neuron has three main parts - a cell body containing the nucleus, dendrites which are specialized branches for receiving information from other neurons, and axons which are specialized branches for sending out information to other neurons. A neuron that has been excited conveys information to other neurons by generating electrical impulse known as action potentials. These signals propagate like waves down the length of the cell’s single axon and are converted to chemical signals at synapses, the contact point between neurons. When the impulse reaches the axon terminals of the presynaptic neuron, it induces the release of neurotransmitter molecules. Such binding leads to the opening of ion channels and often, in turn, to the generation of action potentials in the postsynaptic neuron.
The forces that attract the drug to its receptor are termed chemical bonds and they are (a) hydrogen bond (b) ionic bond (c) covalent bond (d) Vander waals force discount silvitra 120mg amex. Covalent bond is the strongest bond and the drug-receptor complex is usually irreversible purchase 120mg silvitra overnight delivery. Dose Response relationship The exact relationship between the dose and the response depends on the biological object under observation and the drug employed. When a logarithm of dose as abscissa and responses as ordinate are constructed graphically, the “S” shaped or sigmoid type curve is obtained. The lowest concentration of a drug that elicits a response is minimal dose, and the largest concentration after which further increase in concentration will not change the response is the maximal dose. Graded dose effect: As the dose administered to a single subject or tissue increases, the pharmacological response also increases in graded fashion up to ceiling effect. Quantal dose effect: It is all or none response, the sensitive objects give response to small doses of a drug while some will be resistant and need very large doses. The quantal dose- effect curve is often characterized by stating the median effective dose and the median lethal dose. Penicillin has a very high therapeutic index, while it is much smaller for the digitalis preparation. Structural activity relationship The activity of a drug is intimately related to its chemical structure. Knowledge about the chemical structure of a drug is useful for: (i) Synthesis of new compounds with more specific actions and fewer adverse reactions (ii) Synthesis of competitive antagonist and (iii) Understanding the mechanism of drug action. Slight modification of structure of the compound can change the effect completely. Pharmacokinetics Pharmacokinetics deals with the absorption, distribution, metabolism and excretion drugs in the body. Biotransport of drug: It is translocation of a solute from one side of the biological barrier to the other. Structure of biological membrane: The outer surface of the cell covered by a very thin structure known as plasma membrane. The 5 membrane proteins have many functions like (a) contributing structure to the membrane (b) acting as enzyme (c) acting as carrier for transport of substances (d) acting as receptors. The plasma membrane is a semipermeable membrane allowing certain chemical substances to pass freely e. Drug absorption: Absorption is the process by which the drug enters in to the systemic circulation from the site of administration through biological barrier. In case of intravenous or intra-arterial administration the drug bypasses absorption processes and it enters into the circulation directly. Routes of drug administration: a) From the alimentary tract: (i) Buccal cavity: e. Disadvantages of oral route: Onset of drug action is slow, irritant drugs cannot be administered and it is not useful in vomiting and severe diarrhea, gastric acid and digestive enzymes may destroy some drugs, and water soluble drugs are absorbed poorly. Disadvantages: Pain at local site of injection, the volume of injection should not exceed 10 ml. Advantages: It can be given in large volumes, production of desired blood concentration can be obtained with a well designed dose. Disadvantages: Drug effect cannot be halted if once the drug is injected, expertise is needed to give injection. Bioavailability: It is the rate and amount of drug that is absorbed from a given dosage form and reaches the systemic circulation following non-vascular administration. The route of administration largely determines the latent period between administration and onset of action. Drugs given by mouth may be inactive for the following reasons: a) Enzymatic degradation of polypeptides within the lumen of the gastrointestinal tract e. Factors affecting drug absorption and bioavailability: a) Physico-chemical properties of drug b) Nature of the dosage form c) Physiological factors d) Pharmacogenetic factors e) Disease states. However at the cell surface, the lipid soluble drugs penetrate into the cell more rapidly than the water soluble drugs. Unlike inorganic compounds, the organic drugs are not completely ionized in the fluid. Unionized component is predominantly lipid soluble and is absorbed rapidly and an ionized is often water soluble component which is absorbed poorly. T is impermeable to the ionized form of a weak organic acid or a weak organic base. Disintegration time: The rate of break up of the tablet or capsule into the drug granules. Fillers may not be totally inert but may affect the absorption as well as stability of the medicament.