<p></p><h2><a name="_Toc28940476">Blood Supply</a></h2><p>&nbsp;The blood supply to the brain takes up to 20% of the total oxygen consumption of the body. A lack of oxygen to the brain results in ischemia, hypoxia (partial restriction of oxygen) and anoxia (total deprivation of oxygen to the brain). In the image of the arterial supply of blood to the central nervous system are the larger pair of the left and right carotid artery and the smaller pair of the vertebral arteries.</p><p style="text-align: center;"><span style="font-size: 1rem;">&nbsp;</span><img src="@@PLUGINFILE@@/Vertebral%20Arteries.png" alt="Vertebral Arteries" width="600" height="352" class="atto_image_button_middle" style="font-size: 1rem; text-align: center;"><br><span style="font-size: 1rem; text-align: left;"><br></span></p><p style="text-align: left;"><span style="font-size: 1rem;">This is a great video on blood flow in the brain:</span></p><p></p><p></p><p style="text-align: center;"><a href="https://www.youtube.com/watch?v=Pl2tYwx7o5w">Blood Flow</a><br></p><p style="text-align: center;">And here is a video on the up-close dynamics of blood flow in the brain:&nbsp;<a href="https://www.youtube.com/watch?v=9hhfM7rQHiM">Blood Flow Part 2</a></p><p></p><p style="text-align: left;">The left and right carotid
arteries bifurcate at the fourth vertebrae and form the internal
carotid &nbsp;arteries,
entering the brain through
the carotid canal of the temporal bone. These internal&nbsp;<span style="font-size: 1rem;">carotid &nbsp;arteries form the circle
of Willis, as well as the ophthalmic arteries (supplies
the structures of the orbit), the posterior communicating artery (the "connecting vessel: in
the circle of willis), the anterior choroidal
artery (supplies the areas of the brain
important for&nbsp;</span><span style="font-size: 1rem;">motor &nbsp;control and vision, and the anterior &nbsp;cerebral artery (which supplies
the cerebrum).</span></p><p style="text-align: left;"><br></p><p></p><h3 style="text-align: left;">Carotid Canal</h3><p></p><p style="text-align: center; ">&nbsp;<img src="@@PLUGINFILE@@/Carotid%20Canal.png" alt="Carotid Canal" width="474" height="398" style="text-align: center; " class="img-responsive atto_image_button_middle"></p><h2 style="text-align: center; "><br></h2><h2 style="text-align: left;"><a name="_Toc28940477" style="color: rgb(55, 71, 79); font-size: 2.143rem; background-color: rgb(255, 255, 255);">Glia</a><br></h2>

<p style="text-align: left;">Other than neurons,
the other major
cells of the central nervous
system are glia, in fact, glial cells
are the most abundant cells in the central nervous
system. Glia is Latin for "glue/'&nbsp; and glia
surround the neurons and provide support and insulation for them. The extensive brain vessel
system needs the support&nbsp; of glial cells because glia feed neurons
and the brain is supplied
by the highest density of blood vessels
in the entire body.</p>

<p style="text-align: left;">Glia can be divided into two classes, macroglia and microglia.&nbsp;</p><p style="text-align: left;">1) Microglia are glial cells that are scavengers of the central nervous
system, removing pathogens, debris, bacteira, damaged cells, and other
foreign substances.&nbsp; They have a spider-like shape.</p><p style="text-align: left;">The other types of glial cells are macroglia, including:</p><p style="text-align: left;">1) <b>Astrocytes</b>, which are involved in supportive
&nbsp;structural and metabolic &nbsp;events, as well as repairing damaged
cells, regulating neuronal communication and maintaining the blood-brain barrier (keeping blood from entering the brain).&nbsp;</p><p style="text-align: left;"><ul><li><span style="font-size: 1rem;">They are the most abundant&nbsp;</span></li><li><span style="font-size: 1rem;">Numerous star-shaped projections that anchor
neurons to their
capillaries (nutrient supply)&nbsp;</span></li><li><span style="font-size: 1rem;">Form a living barrier
(blood-brain barrier) between
capillaries and neurons
to protect against
harmful substances in
the blood.&nbsp;</span></li><li><span style="font-size: 1rem;">Help control the
chemical environment</span><span style="font-size: 1rem;">&nbsp;</span></li></ul><span style="font-size: 1rem;">2) <b>Oligodendrocytes,</b> which are responsible for the formation
and maintenance &nbsp;of the <span><u>myelin sheath</u></span> that ensheaths
the axons, allowing for efficient communication
between &nbsp;neurons,&nbsp;</span></p><p style="text-align: left;"><span style="font-size: 1rem;">3) <b>Schwann cells</b>,
which are the myelinating glia of the spinal
cord and peripheral nervous system,&nbsp;</span></p><p style="text-align: left;"><span style="font-size: 1rem;">4) <b>Ependymal cells</b>, which are found in the walls of the ventricles,
where they produce
cerebrospinal fluid; their cilia circulates the CSF around the brain removing waste products, washing
it over at night, and protecting the brain from injury&nbsp;</span></p><p style="text-align: left;"><span style="font-size: 1rem;">5) <b>Satellite cells</b>, which are also part of the peripheral nervous system and playing
both a supportive and protective role of regulating the neural environmental for the peripheral nerves and 6) radial glia, which are fundamental for neurogenesis and neural migration (the movement of
new neurons through the brain).</span><br></p><p style="text-align: left;"><br></p><h3 style="text-align: left;">Types of Glia</h3><p></p><p style="text-align: center; ">&nbsp;<img src="@@PLUGINFILE@@/Glia.png" alt="Glia" width="474" height="374" style="text-align: center; " class="img-responsive atto_image_button_middle"></p><p style="text-align: center;"><br></p><p style="text-align: center; "><br></p><p style="text-align: center; ">In his book, "The Other Brain," R. Douglas Fields talks all about glia. It's a pretty fascinating read, surprisingly.&nbsp; I recommend it.</p><p style="text-align: center; ">&nbsp;<img src="@@PLUGINFILE@@/The%20Other%20Brain.jpg" alt="The Other Brain" width="300" height="453" style="text-align: center; " class="img-responsive atto_image_button_middle"></p><p style="text-align: center;"><br></p><p></p><p style="text-align: center; "><br></p><p style="text-align: left;"><br></p><div><h2 style="text-align: left;"><a name="_Toc28940478">Ventricles</a></h2>

<p style="text-align: center; ">&nbsp;<img src="@@PLUGINFILE@@/ventricles.png" alt="ventricles" width="549" height="331" class="img-responsive atto_image_button_text-bottom"></p>

<p style="text-align: left;">The ventricles are a network of cavities that are filled with cerebrospinal fluid. The main role
&nbsp;of the &nbsp;ventricles is
the creation and circulation of the cerebrospinal fluid; this clear, colorless liquid surrounds and
protects the brain, suspending it in fluid. This fluid removes toxins
&nbsp;and washes over the brain. There are the two C-shaped lateral ventricles, the third ventricle,
which &nbsp;is formed when the &nbsp;diencephalon is formed in
the first &nbsp;5 weeks of life, the cerebral aqueduct (which connects the third and the fourth ventricles), the intraventricular foramen and the fourth ventricle. In the third ventricle is a connection of the thalami, called the interthalamic
adhesion. The fourth ventricle&nbsp; is shaped like a tent &nbsp;and lives between
the brainstem and the cerebellum. The cerebrospinal fluid leaves the brain through
&nbsp;the fourth ventricle &nbsp;and moves into the cerebral aqueduct
into the central
canal, which travels
the spinal cord. The ventricles
are surrounded by the choroid
&nbsp;plexus, which is composed
of glial cells, called ependymal
cells</p>

<p style="text-align: left;">(it is these cells that secrete
cerebrospinal fluid throughout the ventricles and around the
brain).</p>

</div><p style="text-align: left;"><span style="font-size: 1rem;">Watch a little video about ventricles here:&nbsp;</span></p><p style="text-align: center;"><a href="https://www.youtube.com/watch?v=9e9Lo0OPON4" style="font-size: 1rem;">Ventricles</a></p><p></p>