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Nervous Histology
16.2--Histology of Nervous Tissue
| Term | Definition |
|---|---|
| Neurons | Electrical excitability -- ability to respond to stimulus and convert it to nerve impulse |
| Nerve Impulse | Action Potential propagates along surface of neuron due to movement of ions between neuron and interstrital fluuid |
| Cell Body | Nucleus + cytoplasm. Typical organelles + Nissl Bodies |
| Nissl Bodies | Clusters of RER, important for protein synth and repair, transmission of nerve impulses and reception |
| Neurofibrils | Intermediate filament bundles; support cell shape |
| Microtubules | Movement of materials between cell body and axon |
| Lipofuscin | Pigment, yellow brownish granules |
| Somatic Gemmules (Spines) | Bumps on plasma membrane; increase surface area for nerve cell interactions |
| Initial segment | Part of axon closest to hillock; location of nerve impulse arisal -- trigger zone (free of Nissl Bodies). |
| Axon Collaterals | Side branches |
| Axon Terminal Arborizations | Division of axon into terminal branches |
| Axosomatic | Axon end to Somatic cell body |
| Axoaxonic | Pre axon end to post axon |
| Electrical Synapse | Gap junctions via connexins; rapid, uniform, coordinated movement (ex. heart, stomach) |
| Multipolar Neurons | Multiple Dendrites, one axon |
| Bipolar Neuron | One dendrite, one axon |
| Unipolar | Sensory; Split into peripheral process and central process. Cell body branches off between axon and dentrite. |
| Neuroglia | Constitute about 1/2 volume of CNS. Don't carry nerve impulse, Have ability to divide |
| CNS--Astrocyte | Protoplasmic (short branches) in gray matter; fibrous (long unbranched) in white matter. Support neurons via microfilaments, create blood brain barrier, secrete growth chemicals in embryo, maintain chemicals of nerve impulse, learning and memory |
| CNS--Oligodendrocytes | Smaller astrocytes. Form and maintain protective covering around CNS axons |
| Pia Matter | Thin membrane around brain and spinal cord. |
| CNS--Microglia | Slender processes with spinelike projections. Originate in red bone marrow and migrate. Phagocytes. Remove cellular debris, microbes, and damaged tissue |
| CNS--Ependymal Cells | Cuboidal to columnar cells -- single layer. Line ventricles of brain and central canal of spinal cord. Assist and circulate cerebrospinal fluid. |
| PNS--Schwann Cells | Flat cells--encircle axons. Form myelin sheath. 1:1 ratio of cell to axon portion. |
| PNS--Satellite Cells | Surround cell bodies of neurons of PNS ganglia. Structural support + exchange of materials between neuronal cell bodies and interstitial fluid. |
| White Matter | Aggregations of myelinated and unmyelinated axons of many neurons. |
| Gray Matter | Neuronal cell bodies, dendrites, unmyelinated axons, axon terminals, and neuroglia. |
| Nucleus (CNS) | Cluster of nerve cell bodies ~to Ganglion in PNS |
| Tract (CNS) | Cluster of axons and nerve fibers; connect spinal cord up and down the brain |
| 2 Reasons of Lack of Neurogeneration | inhibitory influence from neuroglia (oligodendrocytes--myelin); absence of growth stimulating cues |
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