Introduction• Nervous Tissue is four of major class of tissue.• Neuron.• Supporting Cells.
Neuron• Neuron is an electrically excitable cell that processes and transmits information by electrical and chemical signaling.• A nerve is made up of many nerve cell fibers (neurons) bound together by connective tissue.• Epineurium (Connective Tissue of Nerve).• Perineurium ( Connective Tissue of Bundle of Nerve Fibers).• Endoneurium (Connective Tissue of Nerve Fiber)
Structure of Neuron• Cell body (soma). -> Nucleus. ->Perikaryon (Cytoplasm). ->Neurolema (Plasma Membrane).• Dendrites.• Axon.• Synapse.
Cell Body (Soma)• The neuronal cell body is the site where almost all of the metabolic and biosynthetic machinery is located.• Mostly in C.N.S.• 4 to 100 micrometers in diameter.• The soma is the central part of the neuron. It contains the nucleus and Organells of the cell, and therefore is where most protein synthesis occurs.• The nucleus ranges from 3 to 18 micrometers in diameter.
Dendrites• A branched protoplasmic extension of a nerve cell that conducts nerve impulses from adjacent cells inward toward the cell body; a single nerve may possess many dendrites; typically dendrites are relative short.
Axon• An axon is a special cellular extension that arises from the cell body at a site called the axon hillock.• Some axons are enveloped by Schwan Cells which provide structural and metabolic support.• These are classified on Basis of Presence/Absence of Myeline Sheath. -> Myelinated ( Concentric Layers of Schwan Cells) E.g Longer Axons -> Non-Myelinated ( No Concentration).
Myelin• Myelin is a fatty covering which envelops many axons and permits action potentials to be propagated at a much greater velocity.
Myelination• A Schwann cell is illustrated with brown cytoplasm.• The blue oval is the Schwann cells nucleus.• Observe that as the growing Schwann cell spirals inward around the axon, it wraps its membrane into layers of myelin.
Axon (Continued)• Many neurons have only one axon, but this axon may—and usually will—undergo extensive branching, enabling communication with many target cells.• The part of the axon where it emerges from the soma is called the axon hillock.• Axon Hillock the most easily-excited part of the neuron and the spike initiation zone for the axon.
Difference b/w Axon & Dendrites.Feature Axon DendriteShape Circular/ Constant Radius TaperLength Large SmallFunction Output Input All Rules above has Exception.....
Synapse• A site where two neurons join and intercommunicate......• The axon terminal contains synapses, specialized structures where neurotransmitter chemicals are released to communicate with target neurons.
Nodes of Ranvier• Nodes of Ranvier are short fragments of unmyelinated segments of the axon, which are found periodically in between the cells of the myelin sheath. These nodes are areas where the action potential is amplified using a high density of sodium (Na+) ions and is subsequently passed along the axon.• The points between segments of myelin are called nodes of Ranvier.
Support Cells• Schwann cells• Glial cells• Oligodendroglia• Astroglia or astrocytes• Microglia