Introduction to Nerve Cells and Nervous Systems
The essence of nervous system function is control by means of communication. Unicellular (acellular) organisms, such as Amoeba or Paramecium, can perform every function necessary to sustain their lives. They can take in nutrients from their external environment, organize their metabolic reactions, excrete waste products and move towards or away from objects in their external environment; that is, they can perform simple behavioural adjustments. These actions are performed without the aid of a nervous system as such. In multicellular organisms more complex than sponges the constituent cells have become specialised into organs and tissues for carrying out specific functions, such as digestion and assimilation of foodstuffs, respiration, circulation of the blood to carry oxygen, metabolites and hormones to and from the tissues, reproduction and so on. In these organisms the nervous system and the endocrine system together carry out the function of control and communication, between the various organs and tissues of the body and between the organisms and its external environment.
KeywordsPermeability Dioxide Glycine Respiration Serotonin
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