III.   Biological Systems (PSYBIO)

Neuron, or Nerve, is the name given to a genus of highly specialized electrochemical sensory cells possessing the skills of networking with other cells, storage and retrieval of complex computational information, the orchestration of cellular activities and change within the body of the organism enabling it to function by departments, as well as a whole.

The word Nerve comes from the Latin word nervus meaning “sinew, string, fetter, strength, vigor or energy”.  The word Neuron comes from the Greek word νεuρον (neuron), meaning “nerve”. Therefore, the words Nerve and Neuron means one (1) and the same thing.

Neuron,or Nerve cells are found throughout the body of complex life forms such as mammals. Apart from the prevalence of certain types of Neurons within different sections of the body, there is no valid claim in asserting the “head” as the exclusive site of neurons and the “body” as the exclusive site for nerves.

All Neurons share a number of characteristics that distinguish them from other cells, namely:

(i) Axon - an axon is a distinctive outgrowth peculiar to one  (1)main class of Neurons. It is distinguished by extremely long bundles of microtubules extending from the body of the Neuron cell; and

(ii) Dendrites - Almost all Neurons possess multiple dendrites with branched projections emanating from the main cell body that act to receive, collect and transmit into the body of the cell the neurotransmitter and electrical stimulation received through a synaptic connection to a synapse as a branch of an axon; and

(iii) Large nucleus - All Neurons possess relatively large nucleus compared to other cells for the substantial production of Messenger RNA which may act as the carriers of both chemical messages and Messenger RNA to other cells; and

(iv) Large organelles - All Neurons possess large organelles for the production of small sized hormones called neurotransmitters which may act as the carriers of both chemical messages and Messenger RNA to other cells; and

(v) Large quantities of mineral pools especially calcium, potassium and sodium are used as catalysts for electrical potential and reaction.

(vi) Strong polarization and sensitivity to electrical stimulation - all Neurons possess strong polarization along the microtubules present in their dendrites and axon and remain highly sensitive to the presence of electrical stimulation; and

All Neurons may be classified into five (5) classes being Neuroglia, Unipolar, Bipolar, Multipolar and Ultrapolar:

(i) Neuroglia possess multiple dendrite connection with the cell body with the absence of any axon, as exhibited by astrocyte cells; and

(ii) Unipolar Neurons possess only one (1) connection between the cell body, an axon and absence of dendrites as demonstrated by sensory neurons; and

(iii) Bipolar Neurons possess one (1) dendrite and one (1) axon connection between the cell body, as demonstrated by neurons of the retina and inner ear; and

(iv) Multipolar Neurons possess multiple dendrite connections to the cell body as well one (1) axon connection, as demonstrated by motor neurons and interneurons within the cerebrum; and

(v) Ultrapolar Neurons are highly developed multipolar neurons whereby the dendrites as well as axon may extend significant distances as demonstrated by pyramidal neurons.

Neurotransmitters are stored by neurons in the axon terminals. There are principally two (2) classes of neurotransmitters:

(i) "Peptide" - that degrade and ultimately wither after usage; and

(ii) "Classical" - neurotransmitters that are recycled and reused (such as acetylcholine and catecholamine).