Chapter 9 notes

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20 Jun 2011
Chapter 9- The Central Nervous System
-in flatworms hard to distinct between central nervous system and peripheral nervous
othere is a cluster of nerve cell bodies concentrated in the head (cephalic) region
o2 large nerves called nerve cords come off the brain and lead to a nerve network
which innervates distal regions of the flatworm body
o(higher animal) Annelids (earthworms) clusters aren’t restricted to head, they
occur in pairs called ganglia along a nerve cord
oSince each segment of the worm contains a ganglion, simple reflexes can be
integrated within a segment without input from the brain
oReflexes which don’t require integration in the brain also occur in higher animals
and are called spinal reflexes in humans and other vertebrates
oAnnelids and aplysia (shell less mollusk) used for research because their neurons
are 10 times larger than in human brain neurons, and have identical number or
neurons from animal to animal
-brain evolve because they are first to be in contact with the environment
-as the brain evolved it became associated with specialized cephalic receptors; eyes for
vision and chemoreceptor for smell and taste
-in higher arthropods like insects specific regions of brain associated with particular
function (complex brain therefore complex behaviour can form colonies, divide labour)
-octopus has most sophisticated brain therefore most sophisticated brain development
-brain evolution change seen in forebrain region; includes cerebrum
oin human brain; cerebrum is what makes the brain; this part allows reasoning and
oin birds and rodents; part of the forebrain ahs enlarged into a cerebrum
oin fish; small buldge dedicated to processing olfactory information about odours
in the environment
-change in cerebellum; part of hindbrain
oimportant for coordinating movement and balance
oidentifiable like cerebrum by grooves and folds
Anatomy of the Central Nervous System
-in vertebrate nervous system the CNS consists of layers of neural tissue surrounding a
fluid filled central cavity which is lined with epithelium
-The CNS develops from a hollow tube
oIn early embryo the cells that become nervous system lie in a flattened region
called neural plate
oAt 20th day of human development neural plate cells along the edge migrate
towards the midline
oBy 23rd day the neural plate cells fuse with each other creating neural tube
oNeural crest cells from lateral edges of neural plate now lie dorsal to neural tube
oLumen of the neural tube remains hollow and becomes the central cavity of CNS
oCells lining the neural tube will either differentiate into epithelial ependyma or
remain undifferentiated neural stem cells
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oOuter cell layers of neural tube will become neurons and glia of CNS.
oNeural crest cells will become sensory and motor neurons of PNS
oWeek 4; anterior part of neural tube begins to specialize into regions of the brain;
forebrain mid brain and hindbrain. Tube posterior to hindbrain will become spinal
cord (at this point cerebrum is not larger than other regions of the brain)
oWeek 6; CNS forms 7 major divisions present at birth; [cerebrum, diencephalon]
forebrain, midbrain [cerebellum and pons, the medulla oblongaga] hindbrain, and
the spinal cord.
oWeek 6; central cavity (Lumen) of neural tube begun to enlarge into hollow
ventricles. 2 lateral ventricles and 2 descending ventricles. Central cavity becomes
central canal of spinal cord
oWeek 11; cerebrum enlarged and most obvious structure at birth. Surround
diencephalon midbrain and pons only visible parts below it is cerebellum and
medulla oblongata
-The CNS is divided into Gray Matter and White Matter
oComposed of neurons and supportive glial cells
oTissues divided into gray and white matter
oGray matter; consists of unmyelinated nerve cell bodies, dendrites, and axon
oCell bodies form layer in some part of brain and form cluster into groups of
neurons which have similar function
oClusters in cell bodies known as nuclei which have specific names ex. Lateral
geniculate nucleus
oWhite matter; made of myelinated axons contain very few cell bodies. Pale
because of myelin sheath.
oTracts; bundles of axons that connect different regions of CNS. Tracts equivalent
to nerves in PNS
oIndividual neurons and glial cells have organized internal cytoskeletons which
maintain cell shape and orientation
oNeural tissue has minimal extracellular matrix and relies on external support;
support comes from outer casing of bone, 3 layers of connective tissue and fluid
between membranes
-Bone and Connective Tissue Support the CNS
oSpinal cord runs through canal in vertebral column, brain encased in skull or
oSingle vertebra can be stacked on top of each other and separated by disks of
connective tissue
oNerves of PNS enter and leave spinal cord through notches between the stacked
o3 layers of membrane called meninges lie between bones and tissues of CNS
oMembranes help stabilize the neural tissue and protect it from bruising against
bones of skeleton
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