NERVOUS SYSTEMI. Nervous Tissueare conductile tissues capable of transmitting or conveying nerve impulses orelectrochemical Impulses from one part of the body to another, thus exhibit two physiologicproperties of irritability and conductivity.Irritabilityis the ability of nervous tissue to respond to the changes of the environmentConductivityis the ability of the nervous to transmit or convey nerve impulses from onepart of the body to another.Structurally, nervous tissue is made up of just two principal cell populations: neuron andsupporting cells also called as neuroglia or glial cells.II. Neurons or Nerve CellsNeurons are the structural and functional units of the nervous tissue. They arespecialized to transmit messages (nerve impulses) from one part of the body to another.Neurons differ structurally, but they have many features in common.All neurons have a cell body from which slender processes or fibers or neurites extend.Neuron cell bodies are typically found in the CNS in clusters called nuclei, sometimesthey reside in ganglia (clusters of neuron cell bodies outside the CNS). They make up thegray matter of the nervous system.The neuron cell body contains a large round nucleus surrounded by cytoplasm.The cytoplasm is riddled with neurofibrils, cytoskeletal elements of the neurons, whichhave a support and intracellular transport function, and an elaborate rough endoplasmicreticulum called Nissl bodies.Neuron processes or neurites are running through the CNS form tracts of white matter.In the PNS they form the peripheral nerves.There are two neuritesaxonanddendrites.These differ structurally and functionally.The neuron processes that conduct electrical currents toward cell body are calleddendrites, and those carry impulses away from nerve cell body are called axons.Neurons have only one axon (which may branch into collaterals) but may have manydendrites, depending on the neuron type.BASIC DIFFERENCE BETWEEN AXON AND DENDRITESAxonBASISAXONDENDRITE1.No. per neuronSingleNumerous2.Presence ofbranchesUnbranched except theterminal end and collateralbranchesHighly branched3. FunctionConvey messages away fromthe soma or bodyConvey messages towards thesoma or body4.Size and LengthLarger and longerSmaller and shorter
III. Classification of NeuronsA. Functional classification:1. Afferent neurons or sensory neurons are carrying impulses from the sensory receptors(internal organs and skin) to the CNS whose cell bodies are always found in the gangliaoutside the CNS.- sensory receptors are the distal ends dendrites that are activated by specific changesoccurring nearby2. Efferent neurons or motor neurons are neurons carrying impulses from the CNS to theviscera and/or muscles glands whose cell bodies are always located in the CNS.