Explanation Of Nervous System Biology Essay



Nervous system is communication network of the organism which consists of specialised cells controlling all the activities of the organism. Nervous system is divided in two sections, Peripheral Nervous System (PNS) and Central Nervous System (CNS). The major anatomical divisions of the CNS are the cerebrum, the cerebellum, the brain stem and the spinal cord. Functionally, it consists of billions of neurons organised to form several neuronal systems with nuclei and their tracks, each concerned with certain specialised function such as motor activity, perceptions and regulations of various body functions[1] (Cohen 2008). It is also likely that one area may modify or control more than one function. The CNS is not only concerned with the regulation of specialised functions like circulation, digestion and respiration but it also modifies the psychic reactions such as feeling, attitude, thoughts and memory.

Both the CNS and autonomic nervous system can be considered as analogous to an elaborate system of telegraphy wherein numerous wire connections in the form of neurons bring in information from both internal and external environment. This information is received, ‘decoded', decisions are made by various centres in CNS and instructions are sent out to various peripheral tissues to produce appropriate responses (Edmunds 2006). The reaction pattern could be: (Brick & Erickson 1998)

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Psychic- manifested by changes in emotions, thoughts and attitude

Somatic- demonstrated by various types of body movements

Autonomic- indicated by changes in respiration, circulation and visceral functions

As communication within the mammalian nervous system is almost exclusively through chemical messengers, nerosecretion is a fundamental property of all neurones. The chemicals released into the synaptic left are called: (Hefti 2005)

It is generally accepted that the CNS has excitatory and inhibitory chemical transmitters. The neurotransmitters[2] are of three types: Amines, Amino acids and Peptides. The transmitters like dopamine, Gamma amino butyric acid (GABA) and glycine have been considered as inhibitory transmitter substances (Kamienski & Keogh 2006). Many drugs which modify the functions of CNS affect the concentration of one or more of such substances in the central as well as peripheral nervous system. Apart from the neurochemicals, several endogenous peptides have been discovered in the brain. These include angiotensin, encephalin, endorphins and vasopressin (Kamienski & Keogh 2006).

Various pharmaceutical agents affect the CNS in different ways. They may act directly on neurons and modify their function or act reflexly by sending afferent impulses to the CNS via the chemoreceptors and peripheral nerves, there by eliciting psychic, somatic or visceral responses. They can even affect the nutrition and oxygen supply of the CNS by altering its blood supply or affecting its metabolism.

It is extremely difficult to define what constitutes psyche or mind which is supposed to carry three functions: (Tierney, Krupp, Mcphee, Chatton, & Papadakis 1999)

Very little is known about the neurophysiological differences between normal individuals and mentally ill patients as well as the definite biochemical basis for various psychiatric disorders. The exact site and mode of action of various psychotherapeutic agents, therefore, remain largely unidentified (Myers 2005).


Drugs were initially developed for medical reasons.

In pharmacology, a drug is "a chemical substance used in the treatment, cure, prevention, or diagnosis of disease or used to otherwise enhance physical or mental well-being."[4]

P Drugs are chemical substances that affect the central nervous system, such as heroins and cocain.

Depending on the primary use of the drug, psychoactive drugs may be grouped into-

Antipsychotic group

They are useful in all types of functional psychosis, especially schizophrenia. They reduce apomorphine induced hyperactivity, inhibit conditioned avoidance responses and cause some ataxia are likely to be useful as antipsychotic agents.

Antianxiety group

They are mainly used for anxiety and phobic states. They act by reducing aggressiveness but increase the exploratory activity in maze without causing ataxia.

Antidepressants group

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They are commonly used for minor as well as major depression illness, phobic states, obsessive compulsive behaviour and certain anxiety disorders.

Antimaniac group

This group of agents are used to control mania and to break into cyclic affective disorders. The mechanism is not well known.

Psycho- mimetic group

They are seldom used therapeutically but produce psychosis like states. Majority are drugs of abuse. They alter the mood, behaviour, thought and perception in a manner similar to that seen in psychosis. They are not widely prescribed.


PD or recreation drugs reduce irrational behaviour, agitation and aggressiveness and controls psychotic symptomatology in psychotic patient. However, in normal individuals it produces indifference to surroundings, paucity of thoughts and reduction in initiatives by its effect on dopamine receptors in brain.

Psychoactive drugs usually have their effect by interfering with the functioning of neurotransmitters and neuromodulators in the brain. Heroin and cocaine are no exceptions.

Heroin and cocaine are two examples of drugs that were originally developed for medical purposes, but were soon widely used, illegally, as recreational drugs. In UK law, they are both ‘Class A' drugs, i.e., they are thought to be extremely harmful. Surprisingly, they are both still sometimes legally used as painkillers - heroin (a.k.a. diacetyl morphine or diamorphine) for controlling extreme pain, and cocaine as an anaesthetic for ear, nose and throat operations.

Both heroin and cocaine are synthetic drugs, derived from plants – heroin from the opium poppy and cocaine from the coca plant. In both cases, the synthetic compound turns out to be highly addictive – even more than the original plant material. Users experience a powerful compulsion to take more of the drug. Both also have a tolerance effect – the more you use, over time, the more you need to get the same ‘high'. And in both cases, when you stop taking the drug, withdrawal effects are highly unpleasant. In other words, users typically experience both psychological and physical dependance on the drug.

Heroin belongs to a family of drugs called ‘opiates' (meaning, substances derived from opium). Other examples are morphine, and codeine. All of these drugs have an analgesic effect – they reduce pain. Heroin and other opiates are also referred to as narcotics, meaning that they have a numbing, sedative effect. Heroin is especially powerful though. At first, it produces feelings of euphoria and then a general feeling of well-being that can last for several hours. For physically dependent users, however, the withdrawal effects can be extreme – including severe pain, nausea, diarrhoea, sweating, anxiety and depression.

Heroin is really just a fast delivery mechanism for morphine. When injected into the bloodstream, it gets into the brain more quickly than pure morphine does – and once there, it quickly breaks down into monoacetylmorphine and morphine.

Morphine is an endorphin agonist, since it mimics the body's natural endorphins and binding with endorphin receptors in the brain. Endorphins have the function of controlling pain, so this explains the analgesia which results from heroin use. Stimulation of the endorphin receptors also inhibits the production of GABA (gamma-Aminobutyric acid), a neurotransmitter which normally inhibits production of dopamine. Dopamine is an important neuromodulator which has many functions, including increasing pleasure. By inhibiting GABA, morphine has the effect of increasing the level of dopamine in the brain. This explains the euphoria resulting from heroin use.

Unfortunately, the body reacts to regular doses of heroin by reducing production of natural endorphins. This means that when you don't take heroin, endorphins are too low and painful withdrawal symptoms take place.

Initiation and perpetuation of the abuse of heroin and other psycho stimulants are determined by a complex interaction between the pharmacologic properties and relative availability of each drug, the personality and expectations of the user, and the environmental context in which the drug is used (Cohen 2008). Some forms of poly-drug abuse, such as the combined use of heroin and cocaine intravenously, are especially dangerous and remain a major problem in hospital emergency rooms. Sometimes one drug is used to enhance the effects of another, as with the combined use of benzodiazepines and methadone, or cocaine and heroin (Myers 2005).

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Chronic heroin and other psycho stimulant abuse may cause a number of adverse health consequences, ranging from pulmonary disease to reproductive dysfunction. The adverse health consequences of drug abuse are further complicated by increased vulnerability to infections (Myers 2005). This suggest that such group of drug should be taken only after confirmation in diagnosis or while other options are not available. In addition to that strict medical monitoring is required.


Laboratory studies of how recreational drugs affect neurotransmitters can tell us a lot about how these drugs work – why they are addictive, and why they affect mood and behaviour in the way they do, and why they are particular withdrawal symptoms when you stop taking them.

However, the explanations given in this article only scratch the surface. In reality, the effects of these drugs on the nervous system is probably much more complicated. Also, drug addicts often use more than one powerful drug at the same time – for example, heroin, cocaine and alcohol – complicating things much more.

Finally, as I said before, an explanation of the primary effects of a drug on the nervous system doesn't necessarily explain the long term effects of abuse – especially when the drug is illegal, and other factors besides the drug itself can come into play.


Cohen, B., (2008).Medical Terminology. Baltimore: Wolters Kluwer Health / Lippincott Williams & Williams.

Edmunds, M., (2006).Introduction to Clinical Pharmacology. St. Louis: Elsevier Mosby.

Brick, J., & Erickson, C. (1998).Drugs, the Brain, and Behavior. New York: The Haworth Medical Press.

Hefti, F., (2005).Drug Discovery for Nervous System Diseases. London: J. Wiley.

Kamienski, M., & Keogh, J. (2006).Pharmacology Demystified. New York: McGraw-Hill.

Tierney, L., Krupp, M., Mcphee, S., Chatton, M., & Papadakis, M. (1999).Current Medical Diagnosis & Treatment. Los Altos: Lange Medical Publications.

Myers, D., (2005).Exploring Psychology. New York: Worth Publishers.

Hanson, G., & Venturelli, P., (2006).Drugs and Society. Boston: Jones and Bartlett Publishers.

[1] (Cohen 2008)

[2] Neurotansmitters: stimulate or inhibit post synaptic neurones