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Nervous Tissue (Myelination (CNS (Formed by processes of oligodendrocytes,…

- - - - Neuron cell body (perikaryon or soma)
        
        Biosynthetic center of neuron: synthesizes proteins, membranes, chemicals while the rough ER (chromatophilic substance or Nissl bodies) (?)
        
        Contain spherical nucleus with nucleolus
        
        In most, plasma membranes are part of the receptive region that receives input info from other neurons
        
        Some contain pigments
        
        Most neuron cell bodies are located in CNS: Nuclei (clusters of neuron cell bodies in CNS) and Ganglia (clusters of neuron cell bodies in PNS)
      - Neuron processes
        
        Tracts: bundles of neuron processes in CNS
        
        Nerves: bundles of neuron processes in PNS
        
        Armlike processes that extend from cell body: CNS contains both neuron cell bodies and their processes, PNS contains chiefly neuron processes
        
        Two types of processes
        
        Dendrites: frequent, short, tapering diffusely branched processes, receptive (input) region of neuron, convey incoming messages toward cell body as graded potentials (short distance signals). Finer dendrites are highly specialized to collect info (contain dendritic spines or appendages with bulbous or spiky ends)
        
        Axon
        
        Structure: Each neuron has one axon that starts at cone-shaped area called axon hillock, can be short or absent or comprise entire length of cell, long axons are called nerve fibers (can be over 1 meter long!), have occasional branches called axon collaterals, branch profusely (as many as 10,000 terminal branches!) at their end (terminus), distal endings are called axon terminals or terminal boutons
        
        Functional characteristics: Conducting region of neuron, generates nerve impulses and transmits them along axolemma (neuron cell membrane) to axon terminal (can excite or inhibit neurons it contacts, terminal=region that secretes neurotransmitters, which are released into extracellular space), carries on many conversations with different neurons at same time, rely on cell bodies to renew proteins and membranes, quickly decay if cut or damaged, have efficient internal transport mechanisms (molecules and organelles are moved along axons by motor proteins and cytoskeletal elements), movement in both directions (anterograde (away from cell body i.e. enzymes, mitochondria, cytoskeletal elements) vs retrograde (toward cell body i.e.signal molecules, viruses, bacterial toxins))
  - - - Ependymal: range in shape from squamous to columnar, may be ciliated (cilia beat to circulate cerebrospinal fluid (CSF)), line the central cavities of the brain and spinal column, form permeable barrier between CSF in cavities and tissue fluid bathing CNS cells
      - Astrocytes: most abundant, versatile, and highly branched glial cells, cling to neurons, synaptic endings and capillaries. Functions include supporting and bracing neurons, assisting in exchanges between capillaries and neurons, guiding migration of young neurons, controlling chemical environment around neurons, responding to nerve impulses and neurotransmitters, influencing neuronal functioning and participating in information processing in the brain
      - Oligodendrocytes: branched cells, processes wrap CNS nerve fibers, forming insulating myelin sheaths in thicker nerve fibers
      - Microglial: small, ovoid cells with thorny processes that touch and monitor neurons, migrate toward injured neurons and can transform to phagocytize microorganisms and neuronal debris
    - - Satellite cells: surround neuron cell bodies in PNS, function similar to astrocytes of CNS
      - Schwann cells (neurolemmocytes): surround all peripheral nerve fibers and form myelin sheaths in thicker nerve fibers (similar function to oligodendrocytes), vital to regeneration of damaged peripheral nerve fibers