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Is the spinal cord part of the CNS or PNS?
CNS
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What embryologically forms the spinal cord?
neural tube
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The lateral walls of the neural tube thicken to form:
small lumen (central canal)
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How long is the central canal?
runs length of spinal cord
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What does the central canal become?
ventricular system of the brain
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What is the ventricular system of the brain filled with?
CSF
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The central canal and ventricular system are continuous at what level?
level of magnum foramen (at 4th ventricle)
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What is the sulcus limitans?
indentation of central canal
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What is the purpose of the central canal?
divide spinal cord (neural tube) into dorsal and ventral halves
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What is the alar plate?
lateral walls of the dorsal half of the spinal cord
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What does the alar plate develop into?
sensory structure/function (dorsal horn)
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What is the basal plate?
lateral wall of ventral half of the spinal cord
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What does the basal plate develop into?
motor structure/function (ventral horn)
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What are the 3 embryonic layers of the CNS?
- ventricular zone
- marginal zone
- mantle zone
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What is another name for the ventricular zone?
ependymal layer
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What is the first layer of the CNS to form?
ventricular zone
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What is the second layer of the CNS to form?
marginal zone
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What is the third layer of the CNS to form?
mantle zone
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What is the innermost embryonic layer of the CNS?
ventricular zone
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What is the middle embryonic layer of the CNS?
mantle zone
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What is the outermost embryonic layer of the CNS?
marginal zone
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What does the ventricular zone surround?
central canal
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What does the ventricular zone produce?
- neurons (motor or sensory)
- glial cells (astrocytes and oligodendrocytes)
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The marginal zone is formed as...
the outer layer of ventricular zone differentiates and the neuron is displaced laterally
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What does the marginal zone become?
white matter
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Are cellular processes in the marginal zone myelinated?
yes
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Is the marginal zone cellular or acellular?
acellular, contains axons and dendrites of cell w/in ventricular layer (does not contain neurons)
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The mantle zone is the product of what?
neuroblasts (immature neurons) that develop in the ventricular layer then migrate laterally into the mantle layer
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What does the mantle zone produce?
neurons of ventral and dorsal horn (motor, interneurons, projection neurons)
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What are the different spinal cord meninges?
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Where does dura mater come from?
(pachymenix) from mesoderm
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Where is the dura mater on the spinal cord?
outermost layer
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What are the leptomeninges a product of?
neural crest/ectoderm
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What are the two types of leptomeninges?
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What layer of the spinal cord is pia mater?
innermost layer
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How are neurons myelinated in the embryo?
insulates axons in concentric layers with phospoholipids
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When does myelination in the embryo begin?
4.5 months in gestation through 1st post natal year (SC)
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At birth, where does brain myelination occur?
it is limited to only a few areas of the brain
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When does the brain complete myelination?
25 years of age
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Where does myelination in the embryo begin?
- proceeds from back of cerebral cortex to ventral portion
- Myelination starts posteriorly and moves anteriorly; also begins inferiorly and works up superiorly
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What explains teenagers not so well thought-out behavior?
frontal lobe is not fully myelinated because it is the last to be myelinated
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Why is the brain myelinated in the order it is?
- primitive life sustaining areas are myelinated first
- Like the brain stem, it is important for life so it is good that it is myelinated first
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In general, aspects of CNS, fiber tracts (in brain or spinal cord) will become functional when...
myelination is complete
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Does the rostral end of the neural tube grow rapidly or slowly?
rapid
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What occur at 28 days of embryonic development?
- neural tube forms prosencephalon, mesencephalon, and rhombencephalon
- neural tube bends ventrally to form transitions
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What does the prosencephalon become?
forebrain
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What does the mesencephalon become?
midbrain
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What does the rhombencephalon become?
hindbrain
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What three transitions are formed at 28 days of embryonic development?
- midbrain flexure
- pontine flexure
- cervical flexure
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What is another name for the midbrain flexure?
cephalic flexure
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Where is the midbrain flexure?
between forebrain and midbrain
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Where is the pontine flexure?
between pons and hindbrain (medulla)
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Where is the cervical flexure?
the transition between hindbrain and spinal cord
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What occurs at 35 days of embryonic development?
the brain forms 5 vesicles
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How many vesicles does the forebrain form at 35 days of embryonic development?
2
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How many vesicles does the midbrain form at 35 days of embryonic development?
1
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How many vesicles does the hindbrain form at 35 days of embryonic development?
2
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What forms the forebrain?
prosencephalon
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What forms the midbrain?
mesencephalon
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What forms the hindbrain?
rhombencephalon
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What are the vesicles of the prosencephalon/forebrain?
- telencephalon
- diencephalon
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What is another name for the telencephalon?
endbrain
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What is another name for the diencephalon?
interbrain
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What does the telencephalon form?
cerebral hemisphere
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What does the diencephalon form?
thalamus structures
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What are the vesicles of the rhombencephalon/hindbrain?
- metencephalon
- myelencephalon
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What does the metencephalon become?
cerebellum and pons
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What does the myelencephalon become?
medula oblongata
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What occurs at 5 weeks of embryonic development?
- refinement and diversification of vesicles
- central canal develops into ventricular system
- telencephalon grows over diencephalon
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Embryonic origins of the PNS are made up of:
- 12 crainal nn
- 31 spinal nn
- sympathetic an dparasympathetic nn
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The majority of PNS comes from what embryonic structure?
- neural crest
- Exceptions:
- -lower motor neurons of PNS are in ventral horn of SC--from neural tube
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What does the neural crest form?
- all sensory neurons of the PNS
- schwann cells
- autonomic NS ganglia
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Where are the spinal nn and automatic sensory neurons cell bodies of the PNS located?
in the dorsal root ganglia
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Where are cranial nn cell bodies of the PNS located?
- in ganglia in the head and neck
- -cranial nn V, VII, VIII, IX, X associated w/ ganglia (sensory function)
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Which cranial nerves are outgrowths of the brain and not nerves?
olfactory (I) and optic (II) therefore, they are products of the neural tube
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What do schwann cells do?
myelinate neurons in peripheral nn (sensory and motor)
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Which pre and postganglionic neurons of the autonomic NS synapse?
both sympathetic and parasympathetic of ANS
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Where do preganglionic neurons come from?
CNS
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Where do preganglionic neurons synapse?
at a ganglia w/ post-ganglionic to go to a target structure
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What embryonic structure forms postganglionic fibers?
neural crest (motor neurons, efferent in nature)
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What embryonic structure forms preganglionic fibers?
mantle of neural tube
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All motor neurons of the PNS have their cell bodies located where?
in the ventral horns of the spinal cord and are products of the neural tube
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