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Chapter 9

BGYB30 Chapter 9 textbook notes

Biological Sciences
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Chapter 9 the central nervous system
Affective Behaviours:Behaviours that have to do with feelings and emotions
Cognitive Behaviours: Behaviours related to thinking
The CNS consists of the brain and the spinal cord
Early Development
In the very early embryo, the cells that become the CNS lay flatted on a region called the
neural plate. At about 20 days old, the neural plate starts migrating towards the midline to
form a hollow neural tube. By 23 days the neural tube is almost complete.
The neural tube remains hollow and eventually will become the CNS. The cells in the inside
of the tube either become ependyma (connective tissue that separates fluids) or
undifferentiated stem cells. The cells on the outside become the neurons and the glial cells.
The neural crest cells become the neurons of the PNS.
By 4 weeks, 3 distinct divisions of the CNS are obvious: the forebrain, the midbrain, and the
hindbrain. At this point, the forebrain is no bigger than the other parts

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By week 6, growth of the forebrain outpaces the other regions and the embryo has
developed all 7 regions of the CNS present at birth: the cerebrum, the diencephalon, the
midbrain, the cerebellum, the Pons, the medulla oblongata, and the spinal cord
Also by week 6, ventricles form and the neural tube becomes the central canal of the CNS
By week 11, the cerebrum is much more developed than the other regions and is the most
obvious structure when the infant is born
Grey & White Matter
The tissue of the CNS are divided into 2 groups: white matter and grey matter
Grey Matter:Grey matter consists of unmyelinated nerve cell bodies, dendrites and
axons terminals. They usually form layers over certain parts of the
brain or form clusters of neurons with the same function (called
White Matter:White matter is made up mostly of myelinated axons and contains
very few cell bodies. The white colour comes from the myelin (bundles
of axons that connect to different regions of the CNS are known at
tracts. Tracts = nerves in the PNS)
Bone and Connective Tissue Support of the CNS
The brain is encased in a bony skull/cranium and the spinal cord is protected and runs

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through the vertebral column (many vertebrae separated by disks of connective tissue)
There are 3 layers of connective tissue in between the spinal cord and the vertebral column:
the Dura Mater, the Arachnoid Membrane, and the Pia Mater (together are called the
From the bone to the spinal cord, the order is:
1. The Dura Mater:a thick durable layer that is associated with veins that drain
blood from the brain via vessels called sinuses
2. Arachnoid Membrane:A thin cobweb like membrane found between the Dura mater
and the Pia mater
3. Pia Mater:The layer directly on top of the spinal cord, it is associated with
the supply of blood to the brain via different arteries
Extracellular fluid helps cushion the delicate neural tissue. The cranium has about 1.4L of
extracellular fluid. Of the 1.4L, about 1L goes to the neurons, 100-150mL goes t the blood,
and 250-300 goes to the cerebrospinal fluid and interstitial fluid
Interstitial fluid is found inside the Pia Mater; cerebrospinal fluid is found between the Pia
Mater and the Arachnoid Membrane
Cerebrospinal fluid is a salty solution that is secreted by the choroid plexus (found on the
walls of the ventricles). From there it is pumped into the subarachnoid space (between the
Arachnoid Membrane and the Pia Mater) where it flows around the neural network until it
is reabsorbed by villa
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