Nervous System Cells

• Neurons' dendrites receive input and synthesize neurotransmitters.
• Neurons' cell bodies/axons send output.
• Cell bodies and dendrites stain, but axons do not, when using Nissl staining.
• Neurons are permanent, in contrast to astrocytes which divide after injury.
• Neuron markers include neurofilament protein and synaptophysin.
• Astrocytes contain Glial Fibrillary Acidic Protein (GFAP), an astrocyte marker that increases in response to injury.
• Astrocytes, the largest and most abundant glial cell in the CNS, provide physical support, repair, remove excess neurotransmitters, are components of the blood-brain barrier and act as a glycogen fuel reserve buffer.
• Reactive Gliosis is a response to injury characterized by hypertrophy and hyperplasia of astrocytes.
• Specialized ependymal cells (choroid plexus) produce CSF.
• Cilia circulate CSF, and microvilli help with CSF absorption, on the apical surfaces of ependymal cells.
• Ciliated simple columnar glial cells line ventricles and the central canal of the spinal cord.
• Oligodendrocytes are functioning (CN2).
• Oligodendrocytes myelinate axons of neurons in the CNS.
• Each oligodendrocyte can myelinate around 30 axons.
• Oligodendrocytes are the predominant glial cell type in white matter.
• "Fried egg" appearance indicates a histology of dark chromatin.

Pathology Associations of Oligodendrocytes

• Multiple sclerosis
• Progressive multifocal leukoencephalopathy (PML)
• Leukodystrophies
• Schwann cells are developed from the neural crest, PNS glial cells.
• Schwann cells are function (CN3 - CN12).
• Schwann cells myelinate neuron axons in the peripheral nervous system (PNS).
• Schwann cells promote axonal regeneration after injury.

Pathology Associations of Schwann Cells

• Guillain-Barré syndrome
• Peripheral neuropathies
• Schwann cell marker: S100
• Microglia develops from the mesoderm and are CNS glial cells.
• Microglia function as phagocytic scavenger cells in the CNS.
• Microglia activate in response to tissue damage by releasing inflammatory mediators.

HIV Associated Dementia

• Not readily discernible by Nissl stain.
• HIV-infected microglia fuse to form multinucleated giant cells in CNS.
• Myelin is synthesized from oligodendrocytes in the CNS.
• Myelin is synthesized from Schwann cells in the PNS.
• Myelin insulation of axons increases conduction velocity of signals via "jumps" from one node of Ranvier.
• Myelin wraps and insulates axons.
• Decreases membrane capacitance (ability to store electric charge), decreases time constant, and increases membrane resistance.
• Increases space (length) constant where travel distance voltage passively spread along the axon.