THE GLYCOSIDIC BOND

 

INTRODUCTION: Glycosidic In chemistry, a glycosidic bond or glycosidic linkage is a type of covalent bond that joins a carbohydrate also known as a sugar molecule to another group, which may or may not be another carbohydrate. A glycosidic bond is formed between the hemiacetal or hemiketal group of a saccharide, or a molecule derived from a saccharide, and the hydroxyl group of some compound such as an alcohol.  

A substance containing a glycosidic bond is a glycoside. A glycoside is a molecule in which a sugar is bound to another functional group via a glycosidic bond. Glycosides play numerous important roles in living organisms. Many plants store chemicals in the form of inactive glycosides. These can be activated by enzyme hydrolysis, which causes the sugar part to be broken off, making the chemical available for use. Many such plant glycosides are used as medications.  

In animals and humans, poisons are often bound to sugar molecules as part of their elimination from the body. In formal terms, a glycoside is any molecule in which a sugar group is bonded through its anomeric carbon to another group via a glycosidic bond. Glycosides can be linked by an O- (an O-glycoside), N- (a glycosylamine), S-(a thioglycoside), or C- (a C-glycoside) glycosidic bond. Glycosylation Sugars are commonly attached to proteins in a process called glycosylation. Typically the attachment is to a hydroxyl or other functional group. The majority of proteins synthesized in the endoplasmic reticulum are glycosylated.

RELATED;

1.  DISACCHARIDES

2.  POLYSACCHARIDES

3.  THE FORCES THAT INTERACT WITH BIOLOGICAL MOLECULES

VIRULENCE FACTORS OF MICROORGANISMS

 

Introduction: The virulence factors may be broadly subdivided into two categories;  

Invasiveness: This is the ability to enter host tissues, multiply there, and spread. This in otherwise means, the organism will be able to bypass the body’s defense system and if possible, enter immunity surveillance free environments. Take an example of infection from Mycobacteria tuberculosis, antaemeba histolytica.  

Toxigenicity: This is the ability to produce toxic substances to the human cells. In this case, the chemicals produced by such organisms will not only be strange and new to the host cell, but also dangerous or able to cause toxicity. For example tetanus toxin produced by Clostridium tetani.  In addition, microorganisms adopt many strategies to circumvent the defenses of the host. Different microbes possess these attributes in varying degrees depending on the specific strain. Most pathogens have many such factors and although some have been identified, it is still not known in all cases precisely how each factor functions in the production of disease. The nature and mode of action of some of the known virulence attributes in pathogenesis is described here.  

Invasiveness and the role of Adhesin:  Most infections actually begin on the mucous membranes of the respiratory, gastrointestinal or urogenital tracts. In these environments, the potential pathogen must first adhere to the host cell. Adherence prevents the microorganism from being flushed away in mucus secretions and renders it less susceptible to the effects of enzymes and secretory IgA.  If disease is to result from the effects of a toxin, close adherence of the bacterium assures that the toxin will be delivered in high concentrations directly to the host cell. Adherence must occur before penetration of host cells (invasion) is possible for example in case if HIV.  

RELATED;

1.  BACTERIOLOGY

2.  VIROLOGY

3.  IMMUNITY

4.  SEPSIS AND SEPTIC SHOCK

CAFFEINE

INTRODUCTION: Caffeine is a central nervous system (CNS) stimulant of the methylxanthine class. It is the world's most widely consumed psychoactive drug, but unlike many other psychoactive substances, it is legal and unregulated in nearly all parts of the world.  Although there maybe many sources of caffeine in different parts of the World, coffee beans are the most known abundant source in many countries. 

PHARMACODYNAMICS:  There are several known mechanisms of action to explain the effects of caffeine. The most prominent is that it reversibly blocks the action of adenosine on its receptor and consequently prevents the onset of drowsiness induced by adenosine. Caffeine also stimulates certain portions of the autonomic nervous system. 

EFFECTS OF CAFFEINE IN THE BODY:  Caffeine can have both positive and negative health effects. It can be used to treat bronchopulmonary dysplasia of prematurity, and to prevent apnea of prematurity: caffeine citrate was placed on the WHO Model List of Essential Medicines in 2007.  It may confer a modest protective effect against some diseases, including Parkinson's disease and certain types of cancer. One meta-analysis concluded that cardiovascular disease such as coronary artery disease and stroke is less likely with 3–5 cups of non-decaffeinated coffee per day but more likely with over 5 cups per day. 

Some people experience insomnia or sleep disruption if they consume caffeine, especially during the evening hours, but others show little disturbance. 

Evidence of a risk during pregnancy is equivocal. Some authorities recommend that pregnant women limit consumption to the equivalent of two cups of coffee per day or less.

TOLERANCE AND DEPENCE TO CAFFEINE:  Caffeine can produce a mild form of drug dependence associated with withdrawal symptoms such as sleepiness, headache, and irritability when an individual stops using caffeine after repeated daily intake. Tolerance to the autonomic effects of increased blood pressure and heart rate, and increased urine output, develops with chronic use.  Caffeine is classified by the Food and Drug Administration as "generally recognized as safe" (GRAS). 

TOXICITY DUE TO CAFFEINE:  Toxic doses, over 10 grams per day for an adult, are much higher than typical dose of under 500 milligrams per day. A cup of coffee contains 80–175 mg of caffeine, depending on what "bean" (seed) is used and how it is prepared. Thus it requires roughly 50–100 ordinary cups of coffee to reach a lethal dose. However pure powdered caffeine, which is available as a dietary supplement, can be lethal in tablespoon-sized amounts.

RELATED;

1.  DOPAMINE
2.  DRUG DEPENDENCE

3.  SEDATIVE-HYPNOTICS

4.  PARKINSON'S DISEASE

BLOOD CLOTTING AND IT'S PREVENTION

 

INTRODUCTION: Clotting should take place to stop bleeding, but too much clotting would obstruct vessels and interfere with normal circulation of blood. Clots do not usually form in intact vessels because the endothelium is very smooth and repels the platelets and clotting factors. If the lining becomes roughened, as happens with the lipid deposits of atherosclerosis, a clot will form.

HEPARIN AND BLOOD COAGULATION: Heparin, produced by basophils, is a natural anticoagulant that inhibits the clotting process. The liver produces a globulin called antithrombin, which combines with and inactivates excess thrombin. Excess thrombin would exert a positive feedback effect on the clotting cascade, and result in the splitting of more prothrombin to thrombin, more clotting, more thrombin formed, and so on. Antithrombin helps to prevent this, as does the fibrin of the clot, which adsorbs excess thrombin and renders it inactive. All of these factors are the external brake for this positive feedback mechanism.  Together they usually limit the fibrin formed to what is needed to create a useful clot but not an obstructive one.

THROMBOSIS: Thrombosis refers to clotting in an intact vessel; the clot itself is called a thrombus. Coronary thrombosis, for example, is abnormal clotting in a coronary artery, which will decrease the blood (oxygen) supply to part of the heart muscle. An embolism is a clot or other tissue transported from elsewhere that lodges in and obstructs a vessel.

DISSOLVING CLOTS: Abnormal clots may cause serious problems in coronary arteries, pulmonary arteries, cerebral vessels, and even veins in the legs. However, if clots can be dissolved before they cause death of tissue, normal circulation and tissue functioning may be restored. One of the first substances used to dissolve clots in coronary arteries was streptokinase, which is actually a bacterial toxin produced by some members of the genus Streptococcus. Streptococcus

Streptokinase did indeed dissolve clots, but its use created the possibility of clot destruction throughout the body, with serious hemorrhage a potential consequence. Safer chemicals called third-generation thrombolytics are now used. In a case of coronary thrombosis, if a thrombolytic can be administered within a few hours, the clot may be dissolved and permanent heart damage prevented. The same procedure is also used to prevent permanent brain damage after strokes (CVAs) caused by blood clots.

RELATED;

1. STROKE  

2. STREPTOKINASE  

3. THE COAGULATION CASCADE

REFERENCES

EATING DISORDERS

BULIMIA: Bulimia nervosa and anorexia nervosa are potentially devastating disorders. Bulimia is characterized by episodic intake of large amounts of food also known as binges, followed by ritualistic purging through emesis, the use of laxatives, or other methods. Medical complications of the purging, such as hypokalemia, are common and dangerous.

ANOREXIA: Anorexia is a disorder in which reduced food intake results in a loss of weight of 15% or more of ideal body weight, and the person has a morbid fear of gaining weight and a highly distorted body image. Anorexia is often chronic and may be fatal in 10% or more of cases.

PHARMACOTHERAPY: Antidepressants appear to be helpful in the treatment of bulimia but not anorexia. Fluoxetine was approved for the treatment of bulimia in 1996, and other antidepressants have shown benefit in reducing the binge-purge cycle. The primary treatment for anorexia at this time is refeeding, family therapy, and cognitive behavioral therapy. Bupropion may have some benefits in treating obesity. Non-depressed, obese patients treated with bupropion were able to lose somewhat more weight and maintain the loss relative to a similar population treated with placebo. However, the weight loss was not robust, and there appear to be more effective options for weight loss.

RELATED;

1.  TREATMENT OF ANXIETY AND INSOMNIA

REFERENCES

BETA-LACTAMASE INHIBITORS (CLAVULANIC ACID, SULBACTAM, & TAZOBACTAM)

Introduction: These substances resemble β-lactam molecules, but they have very weak antibacterial action and therefore we are not classifying them as antibiotics in nature. They are potent inhibitors of many but not all bacterial β-lactamases and can protect hydrolyzable penicillins from inactivation by these enzymes. Beta-lactamase inhibitors are most active against Ambler class A β-lactamases (plasmid-encoded transposable element [TEM] β-lactamases in particular), such as those produced by staphylococci, H. influenzae, N. gonorrhoeae, salmonella, shigella, E. coli , and K. pneumoniae.

Spectrum of activity: They are not good inhibitors of class C β-lactamases, which typically are chromosomally encoded and inducible, produced by Enterobacter sp, Citrobacter sp, S. marcescens , and P. aeruginosa , but they do inhibit chromosomal β-lactamases of B. fragilis and M. catarrhalis . The three inhibitors differ slightly with respect to pharmacology, stability, potency, and activity, but these differences usually are of little therapeutic significance.

Formulations: Beta-lactamase inhibitors are available only in fixed combinations with specific penicillins. The antibacterial spectrum of the combination is determined by the companion penicillin, not the β-lactamase inhibitor. An inhibitor extends the spectrum of a penicillin provided that the inactivity of the penicillin is due to destruction by β-lactamase and that the inhibitor is active against the β-lactamase that is produced. Thus, ampicillin-sulbactam is active against β-lactamase-producing S. aureus and H. influenzae but not against serratia, which produces a β lactamase that is not inhibited by sulbactam.

Similarly, if a strain of P. aeruginosa is resistant to piperacillin, it is also resistant to piperacillin-tazobactam because tazobactam does not inhibit the chromosomal β-lactamase produced by P. aeruginosa. The indications for penicillin-β-lactamase inhibitor combinations are empirical therapy for infections caused by a wide range of potential pathogens in both immunocompromised and immunocompetent patients and treatment of mixed aerobic and anaerobic infections, such as intra-abdominal infections.

RELATED;

1.  PENICILLINS

2.  CEPHALOSPORINS

3.  PHARMACOLOGY AND THERAPEUTICS

REFERENCES

ANALYSIS AND PRESENTATION OF DATA

OBJECTIVES OF THE DISCUSSION

By the end of this discussion, the learner/medical student/reader will be able to;

1.  Explain the meaning of data analysis

2.  Explain the ways data can be presented

3.  List some of the tools that can be used in data analysis

INTRODUCTION: So much we have discussed about data, the types of data, analysis of data and presentation of data. For a medical scientist whether a biostatician or a medical researcher, the way data is analysed and presented matter a lot. For it gives the exact understanding and a broad picture before conclusions are made. 

In most cases some readers will have hard time reading through the written work of the data analysed however, it may be easier for them to understand the graphical presentation of data.  I too find it very easy to understand the work presented in form of graphs and pie chart compared to the written documents of the same work.  In our discussion here, we are going to see the different techniques data can be presented and analyzed.

DATA ANALYSIS:  Now we are taking it that you have finished collecting your data and compiled it to make sure everything is in your data pack including consent forms and the questionnaires in case you used them.  The next step will be data analysis and here, it is up to the researcher to decide using electronic software or manual methods to analyze their data.  I can not discourage either the manual or the electronic method but what I can say, for an undergraduate not very well experiences with electronic data systems, the manual method will save time and minimize on the possible mistakes.  In my discussion here therefore, I am going to rely on manual methods of data analysis, and then we shall be able to look at the electronic  methods later.  For those interested in the electronic data analysis using tools, follow the link below for some of the most frequently used data tools.

Download PAST v4 for electronic data analysis

Before starting the process of data analysis, it important to know the types of data you are analyzing whether it is qualitative data or quantitative data.  For both types of data are analysed differently.  If you are not well versed with the difference between qualitative and quantitative research, click on the links below, to continue with our discussion.

The qualitative study design

The quantitative study design

Analysing data for qualitative studies

Analysis of data for quantitative studies

RELATED;

1.  HOW TO WRITE A RESEARCH REPORT

2.  VIDEO DEMONSTRATION ON DATA ANALYSIS USING TOOLS

3.  RESEARCH METHODOLOGY

4.  DATA COLLECTION

CARBON DIOXIDE

 

Introduction: Carbon dioxide (chemical formula CO₂) is a colorless and odorless gas vital to life on Earth. This naturally occurring chemical compound is composed of a carbon atom covalently double-bonded to two oxygen atoms. Carbon dioxide exists in Earth's atmosphere as a trace gas at a concentration of about 0.04 percent (400 ppm) by volume.

Sources of carbondioxide: Natural sources include volcanoes, hot springs and geysers, and it is freed from carbonate rocks by dissolution in water and acids. Because carbon dioxide is soluble in water, it occurs naturally in groundwater, rivers and lakes, in ice caps and glaciers and also in seawater. It is present in deposits of petroleum and natural gas. Atmospheric carbon dioxide is the primary source of carbon in life on Earth and its concentration in Earth's pre-industrial atmosphere since late in the Precambrian was regulated by photosynthetic organisms and geological phenomena.

As part of the carbon cycle, plants, algae, and cyanobacteria use light energy to photosynthesize carbohydrate from carbon dioxide and water, with oxygen produced as a waste product. [Carbohydrates] [Water, the universal solvent]

Carbon dioxide (CO2) is produced by all aerobic organisms when they metabolize carbohydrate and lipids to produce energy by respiration. It is returned to water via the gills of fish and to the air via the lungs of air-breathing land animals, including humans. Carbon dioxide is produced during the processes of decay of organic materials and the fermentation of sugars in bread, beer and wine-making. It is produced by combustion of wood, carbohydrates and fossil fuels such as coal, peat, petroleum and natural gas.

RELATED;

1.  OXYGEN

2.  NITRIC OXIDE

3.  BIOCHEMISTRY

[references]

CARBOHYDRATES

 

Functions of Carbohydrates

Carbohydrates are the main sources of energy in the body. Brain cells and RBCs are almost wholly dependent on carbohydrates as the energy source.  2)  Storage form of energy (starch and glycogen).  3)  Excess carbohydrate is converted to fat.  4)  Glycoproteins and glycolipids are components of cell membranes and receptors.  5)  Structural basis of many organisms: Cellulose of plants; exoskeleton of insects, cell wall of microorganisms, mucopolysaccharides as ground substance in higher organisms.  The general molecular formula of carbohydrate is C_n(H₂O)_n. For example, glucose has the molecular formula C₆H₁₂O₆. Carbohydrates are polyhydroxy aldehydes or ketones or compounds which yield these on hydrolysis.

NOMENCLATURE: Molecules having only one actual or potential sugar group are called monosaccharides. They cannot be further hydrolysed into smaller units. When two monosaccharides are combined together with elimination of a water molecule, it is called a disaccharide. Trisaccharides contain three sugar groups. Further addition of sugar groups will correspondingly produce tetrasaccharides, pentasaccharides and so on, commonly known as oligosaccharides. When more than 10 sugar units are combined, they are generally named as polysaccharides. Polysaccharides having only one type of monosaccharide units are called homopolysaccharides and those having different monosaccharide units are heteropolysaccharides. Sugars having aldehyde group are called aldoses and sugars with keto group are ketoses. Depending on the number of carbon atoms, the monosaccharides are named as triose (C3), tetrose (C4), pentose (C5), hexose (C6), heptose (C7) and so on.  

STEREOISOMERS: Compounds having same structural formula, but differing in spatial configuration are known as stereoisomers. While writing the molecular formula of monosaccharides, the spatial arrangements of -H and -OH groups are important, since they contain asymmetric carbon atoms. Asymmetric carbon means that four different groups are attached to the same carbon. The reference molecule is glyceraldehyde (glycerose) which has a single asymmetric carbon atom.  

RELATED;

1.  DIGESTION OF LIPIDS

2.  BIOCHEMISTRY

[REFERENCES]

CELLULAR EVENTS OF INFLAMMATION

 

INTRODUCTION: At the beginning of the inflammatory process, cells move out of the vessels into the area of inflammation recruited by chemotactic agents. Inflammatory cells become activated and then can phagocytized offending materials, in a process that occur in steps as follows.

MARGINATION AND ROLLING OF WBCS: Moving from axial flow to the margin of the vessels is called margination. Marginated leukocytes begin to roll on the endothelial surface by forming transient adhesion molecules via the selectin family of proteins: In that respect, E-selectin on endothelial cells, P-selectin on endothelial cells and platelets and L-selectin on leukocytes. Selectins bind oligosaccharides that decorate mucin-like glycoproteins. Adhesion to endothelium occurs via selectins and integrins.

MIGRATION OF LEUCOCYTES: Passage of the cells across the wall of blood vessels, and moved to reach the site of inflammation by the effect of chemical mediators gradient (chemotaxis). Chemotaxis is a process resulting from certain products of WBCs, platelets, and microorganisms, which attracts WBCs towards the inflammation area according to the high concentration of that substance.  

[THEPROCESS OF INFLAMMATION]

PHAGOCYTOSIS: This is defined as the engulfment and internalization of foreign bodies which maybe bacteria, viruses and others, in the phagosome and digestion of this substance. Phagocytosis is a process whereby cells ingest solid particles. The first step in phagocytosis is adhesion of the particle to be phagocytesed to the cell surface. Then the phagocyte ingests the attached particle by sending out pseudopodia around it. Then met and fused so that the particle lies in a phagocytic vacuole (called a phagosome) then bounded to small bodies containing enzymatic compounds called lysosomes, to form phagolysosomes. In which intracellular killing of microorganisms occurs. Phagocytic cells include neutrophils, polymorph nuclear cells, eosinophils, and monocytes.

RELATED; 

1.  CHRONIC INFLAMMATION

[REFERENCES]

TREATMENT OF ANXIETY AND INSOMNIA

Introduction:  Antidepressants are frequently used to treat symptoms of anxiety. These drugs have an ability to reduce anxiety symptoms by altering levels of two important neurotransmitters in the brain, norepinephrine and serotonin. Restoration of normal neurotransmitter balance helps to reduce symptoms associated with depression, panic, obsessive–compulsive behavior, and phobia.  Typical antidepressants include tricyclic antidepressants (TCAs), selective serotonin reuptake inhibitors (SSRIs), and monoamine oxidase inhibitors (MAOIs). Atypical antidepressants are more diverse. 

CNS depressants used for anxiety and sleep disorders are categorized into two major classes, the benzodiazepines and barbiturates. Benzodiazepines:  Barbiturates

A third class consists of miscellaneous drugs that are chemically unrelated to the benzodiazepines or barbiturates but have similar therapeutic uses. Other CNS depressants that have a calming effect in the body include the opioids and ethyl alcohol.  Opioid analgesics

CNS depression should be viewed as a continuum ranging from relaxation, to sedation, to the induction of sleep and anesthesia. Coma and death are the end stages of CNS depression. Some drug classes are capable of producing the full range of CNS depression from calming to anesthesia, whereas others are less efficacious. Medications that depress the CNS are sometimes called sedatives because of their ability to sedate or relax a patient. At higher doses, some of these drugs are called hypnotics because of their ability to induce sleep. Thus, the term sedative–hypnotic is often used to describe a drug with the ability to produce a calming effect at lower doses and the ability to induce sleep at higher doses. Sedative-hypnotics

Tranquilizer is an older term that is sometimes used to describe a drug that produces a calm or tranquil feeling. Many CNS depressants can cause physical and psychological dependence. The withdrawal syndrome for some CNS depressants can cause life-threatening neurologic reactions, including fever, psychosis, and seizures. Other withdrawal symptoms include increased heart rate and lowered blood pressure; loss of appetite; muscle cramps; impairment of memory, concentration, and orientation; abnormal sounds in the ears and blurred vision; and insomnia, agitation, anxiety, and panic. Obvious withdrawal symptoms typically last from 2 to 4 weeks. Subtle ones can last months.

RELATED;

1.  Sedative-hypnotics  

2.  Zolpidem

3.  Depression

REFERENCES

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RELATED;

1.  UGANDAN GOSPEL MUSIC DOWNLOAD

2.  GOSPEL MUSIC DOWNLOADS

3.  GOSPEL MUSIC BY CHRIS TOMLIN

CHAPTER THREE: METHODOLOGY

OBJECTIVES OF THE DISCUSSION:  By the end of this discussion, the reader will be able to;

1.  List the components of chapter three of the research proposal

2.  

CHAPTER THREE:  RESEARCH METHODOLOGY:  Chapter three is one of the backbone of a research proposal and research report.  For it fully describes the methods and the way they will be employed in the process of research.  In addition, this section also looks at the research ethics that will be employed in the research project and at the end of this chapter, the research student is expected to be approved to continue with their data collection as the next step.  In this article, we are listing the components of Chapter three and where needed, the details will also be redirected.

3.0  Introduction:  In this section, the student is expected to write a list of all the components expected in the chapter such that it gives a reader few question to ask if any.  This should of course be in form of a paragraph.

3.1  Study settings:  In the study settings, you are expected to tell the place you wish to conduct your research study from.  Depending on the type of study you are conducting, it may require you to outline some social and economic activities carried out in the study setting and the distance of the place from the nearby most recognized location.  To read more about the research study settings click here.

3.2  Study design:  The study design is one of the most important and core parts of any research projects.  In all dimensions, the research study design will elaborate the way a study will behave and the most predictable outcomes.  To continue reading about the various study designs, click here.

3.3  Study population:  The study population are the individuals from which you as the researcher is intending to collect data.  The study population the broad way of looking at the sources of data and the number projected will be higher than the anticipated sample size.  To read about the details of study population and how to precisely choose a reliable study population, click here.

3.4  Sample size determination:  Sample size determination is one other very crucial step in conducting a research study that follows prediction of the study design.  Usually the first question will be; 

How will I chose the sample from which to collect data?  

And then the answer to the question will be, determine the appropriate study design.  The next question then will be;

From how many respondents will I be able to collect sufficient data?

And the answer will be;  Predetermine the sample size in relation to your study.  in one of my previous discussions I have already talked about the criteria to determine the sample and if you have not been following me, click here for the link.

RELATED;

1.  CHAPTER FOUR OF THE RESEARCH REPORT

2.  DATA COLLECTION

3.  INITIAL PAGES OF A RESEARCH PROPOSAL AND RESEARCH REPORT

4.  HOW TO WRITE A RESEARCH PROPOSAL

5.  STRATEGIES FOR DETRMINATION OF SAMPLE SIZE

THE NERVOUS SYSTEM AND NERVE IMPULSE PROPAGATION

 

Introduction: The nervous system is conventionally divided into the central nervous system (CNS) which consists of the brain and spinal cord, and the peripheral nervous system (PNS) that consists of neuronal tissues outside the CNS.

Roles of the different parts of the nervous system: The motor (efferent) portion of the nervous system can be divided into two major subdivisions: autonomic and somatic. The autonomic nervous system (ANS) is largely independent (autonomous) in that its activities are not under direct conscious control. It is concerned primarily with visceral functions such as cardiac output, blood flow to various organs, and digestion, which are necessary for life. Evidence is accumulating that the Autonomic Nervous System, especially the vagus nerve, also influences immune function and some Central Nervous System functions such as seizure discharge.

On the other hand, the somatic subdivision is largely concerned with consciously controlled functions such as movement, respiration, and posture. Both systems have important afferent (sensory) inputs that provide information regarding the internal and external environments and modify motor output through reflex arcs of varying size and complexity. 

The nervous system has several properties in common with the endocrine system, which is the other major system for control of human body function. These include high-level integration in the brain, the ability to influence processes in distant regions of the body, and extensive use of negative feedback.

Both systems use chemicals for the transmission of information. 

In the nervous system, chemical transmission occurs between nerve cells and between nerve cells and their effector cells. Chemical transmission takes place through the release of small amounts of transmitter substances from the nerve terminals into the synaptic cleft. The transmitter crosses the cleft by diffusion and activates or inhibits the postsynaptic cell by binding to a specialized receptor molecule. In a few cases, retrograde transmission may occur from the postsynaptic cell to the presynaptic neuron terminal and modify its subsequent activity. By using drugs that mimic or block the actions of chemical transmitters, we can selectively modify many autonomic functions. 

RELATED;

1.  THE ENTERIC NERVOUS SYSTEM  

2.  DRUGS THAT ACT ON CNS

3.  ANATOMY AND PHYSIOLOGY

REFERENCES