Neuronal Support Cells

Snapshot

• A 26-year-old male presents with bilateral gradual hearing loss mostly of his left ear. He reports having difficulty hearing conversations when the phone is on his left side. Family history is significant for neurological disease in his father, but he cannot recall the name. He does state that his father complains of headaches and has to be followed every 3-5 years with an MRI of his brain and spine. Weber and Rinne testing suggest a sensorineural hearing loss mostly affective the left ear. Skin examination is shown on the right.

Introduction

• Glial cells play a supportive role for neurons
  • outnumber the amount of neurons in the central nervous system (CNS)
• Glial cells can be divided into macroglia and microglia
  • macroglia
    • three main types: oligodendrocytes, astrocytes, Schwann cells
  • microglia
    • cells of the immune system for the CNS

Neuroglial Cells

Glial Cell (and Its Origin)	Function	Clinical Correlate
Astrocytes  (neuroectoderm)	GFAP (+)Foot processes envelope neurons and capillariesmantain blood-brain barrierInvolved in neurotransmitter metabolism (e.g., GABA, glutamate)Uptake excess K+ in the extracellular space, acting as a K+ bufferthus maintain neuronal signaling efficiencyNeuronal injury → reactive gliosis (glial scar)Contain glycogen granulescan provide glucose to neurons	Glioblastoma multiforme (grade IV astrocytoma) primary brain tumor that is highly malignantability to cross the corpus callosum → “butterfly glioma”pseudopalisades on histology associated with necrosis
Oligodendrocytes (neuroectoderm)	Myelinates neurons in the CNS~ 30 CNS axons↑ speed of conductionvia saltatory conductionFried egg-appearance on histology	Oligodendrogliomaclassic histology findings of “fried egg” appearance with “chicken wire loop” capillaries Multiple sclerosisloss of oligodendrocytes can be histologically seen in white matter plaquesProgressive Multifocal Leukoencephalopathy (PML)secondary to reactivation of JC virus infection in the immunocompromised → lytic damage to oligodendrocytes
Microglia (mesoderm)	CNS scavenger cellsphagocytic cell that has the ability to present antigens to lymphocytestissue damage (e.g., stroke, neurodegeneration, infection) leads to its activation	Microglia infected with HIV → multinucleated giant cells in CNS
Ependymal cells (neuroectoderm)	Cililated cells that line the central canal and ventricles of the CNSaids in moving cerebrospinal fluid (CSF) throughout the ventricular systemAt certain places in the CNS, the ependymal cells are continuous with the choroid plexusleads to CSF production	Ependymomacommonly found in 4th ventriclerisk of leading to hydrocephalusperivascular rosettes on histology
Schwann cells (neural crest)	Myelinates axons in the peripheral nervous system (PNS)Each cell myelinates 1 PNS axon↑ speed of conductionvia saltatory conduction Involved in nerve regeneration Can act as phagocytes to remove debri post neuronal damage	Guillain-Barré syndrome (GBS)respiratory or gastrointestinal illness → acute inflammatory reaction to peripheral nerves (may affect Schwann cells)e.g., Campylobacter jejuni (classic), Mycoplasma pneumoniaeacute inflammatory demyelinating polyradiculopathy (most common subtype of GBS)Vestibular schwannoma (acoustic neuroma)commonly affects vestibular portion of cranial nerve VIIIcan expand to the cerebellopontine angle after it fills the internal auditory meatus bilateral acoustic neuroma is a characteristic feature of neurofibromatosis type 2 (NF2)mutation in merlin protein on chromosome 22