arizona state university bio 467 neuro exam 1 latest 2021 correct study guide
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NEUROBIOLOGY – EXAM 1 NOTES
NERVOUS SYSTEM DEVELOPMENT
Early Development
Embryogenesis – development of the embryo (the earliest form of the organism)
o Includes Fertilizations, cleavage, morula, and blastocyst stages
o Represents the period of time up to the implantation of the early embryo into the uterine wall by
the syntrophoblast
Takes ~8 days until the embryo is implanted into the uterus (posterior uterine wall)
o Being to see different areas of development
Inner cell mass – superior pole of the blastocyst; site of development of embryonic cell
layers (polarity)
o Problems with early stage/implantation
Oocyte can be fertilized too high and become ectopic pregnancy
Fertilization/cleavage
o Zygote undergoes division
o Inner cell mass forms superiorly and a cystic chamber forms below that’s supportive of embryo
Syncytiotrophoblast – offshoot of the cytotrophoblast and stimulates lacunae formation
(vascular supportive tissues)
What contains the inner cell mass and trophoblast
Basically placenta formation
Inner cell mass becomes more defined
o Embryonic disk – distinct early division of embryonic cell layers in the inner cell mass; consists
of 2 things
Primary ectoderm – forms the roof of the primary yolk-sac
Embryonic endoderm – closely applied to its outer surface facing the amniotic cavity
Happens ~16 days
o Extraembryonic Coelom – body cavity that develops around day 12 (space that’s not inner cell
mass)
Shrinks down ~ day 13 to help anchor the embryo (connecting stalk)
Becomes a well-developed vascular bed
Formation of the Primitive Streak – extensive polarization of cells around day 16
o Primitive Streak – (16 days) stream/indentation of cellular activity moving from the narrower
posterior portion of the embryonic disk to the wider anterior portion (back to front)
Causes blastocyst to become bilaminar
Epiblast – ectodermal
Hypoblast – endodermal
Primitive (Henson’s) Node – small cellular bump at anterior end of primitive streak
Primitive Pit – opening of the neuroenteric canal at the center of Henson’s node
Cells of hypoblast and epiblast mix – creates mesoderm
o Neural ectoderm – surface ectoderm
o Notochord – anterior midline (dorsal-tubular) structure; forms from
primitive pit mixing (day 18)
Nucleus pulposis in intervertebral disks
Notochord triggers rapid proliferation of surface ectoderm to
invaginate and begin to make nervous system
Notochordal Accessory Structures
o Somites – (21-24 days) layed down alongside notochordal axis; give rise to PNS structures
Cause 2 membranous regions form
Prochordal Plate – at front of primitive node; becomes anterior aspect
(stomadeum/mouth)
, Cloacal Membrane – at back of primitive node; becomes posterior aspect
(hindgut/urogenital)
o Neurotubular epithelium – gives rise to CNS stuctures
o Pericardial bulge – where the thorax and cardiac region develop (22 days)
Neurulation – at 28 days formation of the nervous system (dorsal tubular nervous system)
Rapid proliferation of neuroectoderm leads to invagination of nervous sytem
o Neural tube – open tubular structure formed by proliferation from front to back
Openings: anterior and posterior neuropores
Neural crest cells – lateral borders of evolving neural tube; develop into neuron
populations that are associated with the PNS (ex: dorsal root ganglia)
α-fetoprotein – released into spaces because CSF is forming which causes tubes to close; prevents too
much pressure on the developing brain
can be seen in a mom’s blood test
o High levels – increase risk of Spina Bifida or hydrocephalis/anacephalis
Inhibits fusion of posterior vertebral column
o Low levels – increased risk of Down’s Syndrome
Neural tube closes (lots of problems form because of this) from middle to outside; so anterior and
posterior aspects need to close
o Primary Vesicle – closing of both ends of neural tube; basically the CNS
Most anterior aspect – prosencephalon (forebrain)
Behind that – mesencephalon (midbrain)
Behind the mesencephalon – rhombencephalon (hindbrain)
Last – spinal cord
o Secondary Vesicle – further growth/differentiation of primary vesicle by transverse
segmentation (4 regions versus six regions)
Forebrain
Telencephalon – very important because it leads
to cerebral hemispheres and lateral ventricles
Diencephalon – thalami (third ventricle)
Mesencephalon – grows at constant rate and leads to
midbrain and aqueduct of sylvius
Rhombencephalon
Metencephalon – into pons and cerebellum
Myelencephalon – into medulla
Spinal cord
Evagination – folding/flexion of neural tissue is small developing skull
o Telencephalon evaginates off very quickly
Orbits grow and optic capsule grows and need to beat the orbital walls
Pituitary is growing down and up (rathke’s and infundibulum)
Auditory vesibular apparatus is growing as well
o So it has to fold on itself to fit in the skull
Flexion of developing brain
Cervical flexure – at the junction of the rhombencephalon and the spinal cord
Cephalic flexure – at the region of the mesencephalon
Pontine flexure – between the metencephalon and myelencephalon
Derivations of the Embryonic Brain *****
o Telencephalon (part of prosencephalon)
Cerebral cortex
Basal nuclei
Olfactory bulbs/tracts
, Lateral ventricles
o Diencephalon (part of prosencephalon)
Optic chiam/tracts/nerves
Thalamus
Hypothalamus
Third Ventricle
o Mesencephalon
Mid-brain nuclei
Cerebral aqueduct
o Metencephalon (part of Rhombencephalon)
Pons
Cerebellum
Fourth ventricle
o Myelencephalon (part of Rhombencephalon)
Medulla oblongata
Fourth ventricle
NERVOUS SYSTEM OVERVIEW
Anatomical Definitions
CNS – brain, brainstem, spinal cord
o Dorsal tubular nervous system – from neurotubular epithelium
o Site of perception and integration of sensory info
o Initation and coordination of motor activity
PNS – cranial nn., spinal nn. (ANS)
o From neural crest cells
o Conveys neural impulses to CNS form sensory receptors and from CNS as output to muscles and
glands
o 2 parts
Somatic Nervous System
Afferent neurons – cell bodies in posterior dorsal root ganglia
Efferent neurons – located in anterior brainstem or spinal cord grey matter
Visceral Nervous System
Afferent neurons – from viscera
ANS – efferent to SM, cardiac muscle, and glands (2nd order cells)
Cranial nerves
12 pairs
Can have CNS components with nuclei in the brain or brainstem
Have PNS component with sensory or motor cell bodies in peripheral ganglia
Spinal Cord and nerves
In general
o Extends from base of skull to coccygeal area of the vertebral canal
o 32-33 spinal nn. designated by region – come out below vertebra #
8 cervical (first one comes out above 1st vertebra), 12 thoracic, 5 lumbar, 5 sacral, 2-4
coccygeal
o Ends at L2 to form conus medullaris
o Lumbosacral Cistern – meningeal encased cerebrospinal fluid filled space that lumbar/sacral
spinal nerves travel through
Core of spinal cord
o White matter – outer shell of cord, consists of myelinated fibers
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