VPHY 3100 Lecture Notes - Lecture 12: Myelin, Schwann Cell, Ependyma
27 Apr 2018
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VPHY3100 / Wells / Spring 2018
CHAPTER 7 LECTURE
Slides #8-17: Structure & Function of Glial Cells
Slide #8: Lecture Outline
This portion of lecture will focus on glial cells, which are the support cells of the nervous system.
In the simplest sense, these cells ensure that neurons can thrive and perform their needed
functions. The importance of glia can be inferred by the large number of glial cells found in the
adult brain. There are typically ~100 billion neurons in the adult brain, but about 3-5x that
number of glial cells (so 300-500 billion support cells).
Slide #9: Supporting Cells: Glia
This cartoon shows us the major glial cells of the CNS (central nervous system): astrocytes,
oligodendrocytes, ependymal cells, and microglia. Astrocytes have many functions; regulation
of the extracellular environment and support functions for neurons are two primary examples.
Oligodendrocytes are responsible for myelinating the axons of CNS neurons. Ependymal cells
are specialized epithelial cells that line the ventricles (in the brain) and the central canal (in the
spinal cord). Microglia are the major immune cell found within the interstitial fluid of the brain;
they have an anti-inflammatory and scavenging role.
Slide #10: Predominant Glia of Vertebrates
The three predominant glial cell types, found within our nervous systems, are astrocytes,
oligodendrocytes, and Schwann cells. Astrocytes are the most abundant glial cell. They have
numerous functions, mediated via the numerous processes that extend from their cell bodies.
Each process terminates with an “end-foot” that makes physical contact with either a capillary
or with a neuron.
Slide #11: Astrocytic Functions
Here we can see some of the many functions of astrocytes. A primary function is to provide
neurons with an energy supply. Thanks to those end-feet that make contact with capillaries,
astrocytes take up glucose from the blood supply, convert that glucose into lactate, and then
deliver that lactate to neighboring neurons. The nerve cells will then use the lactate as an energy
source. Astrocytes are also important for “cleaning up” the extracellular space around active
synaptic connections. The two cells on the right (in yellow) are two neurons communicating
with one another via a synaptic connection. Periods of active neuronal communication result in
elevated levels of both potassium (K+) and neurotransmitter (glutamate is shown here) in the
extracellular space around that synapse. Astrocytes are critical for sopping up that excess
potassium as well as the glutamate; within the astrocyte, enzymes convert the glutamate to
glutamine and then deliver that glutamine back to the neurons. The neurons can then
regenerate neurotransmitter (glutamate) from the imported glutamine. Astrocytes are also
essential for proper brain and nervous system development – synaptogenesis (the creation of
new synapses) and neurogenesis (the creation of new neurons) in particular. And finally,
astrocytes are key to creating & maintaining the blood-brain barrier – this is a very tight &
highly regulated interface between the blood supply and the nervous system.
Slide #12: Predominant Glia of Vertebrates
The other two major types of glial cells are oligodendrocytes and Schwann cells. These two cells
serve the same kind of function, but in different places and through different means. Both of
these cells are responsible for creating & maintaining the myelin sheath that exists around many
axons. Oligodendrocytes do this in the CNS; Schwann cells do this in the PNS. In either case,
Document Summary
Slides #8-17: structure & function of glial cells. This portion of lecture will focus on glial cells, which are the support cells of the nervous system. In the simplest sense, these cells ensure that neurons can thrive and perform their needed functions. The importance of glia can be inferred by the large number of glial cells found in the adult brain. There are typically ~100 billion neurons in the adult brain, but about 3-5x that number of glial cells (so 300-500 billion support cells). This cartoon shows us the major glial cells of the cns (central nervous system): astrocytes, oligodendrocytes, ependymal cells, and microglia. Astrocytes have many functions; regulation of the extracellular environment and support functions for neurons are two primary examples. Oligodendrocytes are responsible for myelinating the axons of cns neurons. Ependymal cells are specialized epithelial cells that line the ventricles (in the brain) and the central canal (in the spinal cord).
