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INTRODUCTION ·  Human body is exposed, at all times, to a variety of disease-causing organisms - pathogens. Pathogenic organisms are- bacteria, viruses, fungi and parasites. ·  Pathogenic organisms enter the body through the air we breathe, the fluids we drink, through body contact and ingested food items. Many of these organisms, if they manage to reach the deeper tissues, can produce diseases. ·  Body possesses several mechanisms that combat these pathogens all the time and enable us to lead a normal life. ·  Infectious diseases are the result of the absence or breakdown of these defence mechanisms. ·  The defence mechanisms of the body provide us with resistance against the invading pathogenic organism. ·  The ability of the body to withstand the harmful effects of pathogens is termed immunity and the defence mechanisms together constitute the immune system. ·  The immune system is a collection of organs, cells and molecules whose complex interactio...

COMPONENTS OF LIMBIC SYSTEM ·  The limbic system consists of the phylogenetically old limbic lobe and the related subcortical structures. ·  The limbic lobe forms a rim (limbus) around the hilum of the cerebral hemispheres. ·  It includes the subcallosal gyrus, cingulate gyrus, the parahippocampal gyrus with the underlying hippocampus and the dentate gyrus. ·  The limbic lobe is well preserved throughout the animal kingdom and is associated with the sense of olfaction. ·  The subcortical structures that are related to the limbic lobe are the amygdala, the septum, hypothalamus, the habenula, anterior thalamic nucleus and parts of the basal ganglia (ventral striatum). ·  The limbic lobe and the associated subcortical structures forming the limbic system are concerned with emotions through their role in visceral regulation. CONNECTIONS ·  The important tracts of the limbic system are: (1) median forebrain bundle, (2) fornix & (3) stria terminalis. · ...

·  The structural and functional unit of the nervous system is Neuron. ·  Nervous system is derived from embryonic Ectoderm. ·  Nerve cells do not divide because they do not have Centrosome. ·  Neurons are the longest cell of the human body and have the least power of regeneration. ·  Nissl’s granules are the irregular masses of the ribosomes and RER and are the sites of protein synthesis. ·  Cell body of neurons is called Perikaryon or soma or Cyton. ·  Axons are of two types: myelinated and non-myelinated. ·  The myelinated or medullated nerve fibres are enveloped with Schwann cells which form or medullary sheath around the axon. ·  The gaps of two myelin sheaths are called Nodes of Ranvier. ·  Unmyelinated or non-medullated nerve fibres are enclosed by the Schwann cell that does not form a myelin sheath around the axon. ·  Myelinated nerve fibres appear white and non-myelinated grey. ·  The immediate covering of a neuron is...