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54 Cards in this Set

  • Front
  • Back
BASAL PLATE
The ventral part of the neural tube that becomes the motor part of the nervous system.
ALAR PLATE
The dorsal part of the neural tube that becomes the sensory part of the nervous system
FLOOR PLATE
The ventralmost part of the neural tube.
TGF- beta
The embryonic structure immediately ventral to the neural tube.
NOGGIN AND CHORDIN
Secreted by the basal plate and notocord. These inhibit BMP to allow the neural tube to form and also promote the development of the basal plate
of the neural tube.
NOTCH AND NUMB
Numb antagonizes notch effect on gene transcription. As long as notch is suppressed, the cell keeps replicating. When notch dominates, the cell stops dividing.
NOTCH AND DELTA
Delta, expressed on a cell surface interacts with notch on the adjacent
cell, which inhibits delta expression in that cell. This results in adjacent cells
having high levels of notch and delta. High notch results in a glioblast, high delta
results in a neuroblast. Therefore, glia and neurons are intermixed.
BASIC HELIX- LOOP-HELIX GENES
Activation of these genes contributes to development of a neuron.
GROWTH CONE
Activation of these genes contributes to development of a neuron.
LAMELLOPODIA
Flattened part of the growth cone.
FILOPODIA
“Fingers” extending from the growth cone, sampling the environment.
LAMININ
Extracellular matrix protein that interacts with integrins in the filopodia.
INTEGRIN
Cell surface protein that interacts with extracellular matrix (especially laminin)
and also with intracellular signaling molecules to promote outgrowth.
CELL ADHESION MOLECULE (CAM)
Many splice isoforms thainteration (in this case, between growing neuritis).
CADHERIN
Calcium dependent interaction molecules for direct cell-to-cell interaction.
CHEMOATTRACTANT
A molecule that results in attraction of a growing axon.
CHEMOREPELLENT
A molecule that results in repulsion of a growing axon.
PINOEER AXON
The first-arriving axon, which other axons in the pathway follow.
FASCICULATION
The guidance of growth of adjacent nerve processes along the course of adjacent ones (through cell adhesion molecules)
NETRINS
Chemoattractive for growing axons that express Netrin receptors.
SLIT
A repulsive factor on a growing axon (works by interacting with a receptor, Robo.
EPHRINS
A family of proteins that interacts with receptors (eph) on a growing fiber. Eph
contains a tyrosine kinase function and can be attractive or repellent.
SEMAPHORIN 3A
Diffusible protein manufactured by cells in cortical layer I that attracts dendrites of pyramidal cells and repels their axons.
AGRIN
Protein secreted by growing motor axon that interacts with muscle-specific kinase (MuSK) in muscle membrane. This results in activation of rapsyn, which causes expression of acetylcholine receptors.
NEUROGLIN
Made by the axon terminal at the neuromuscular junction. This results in increased expression of acetylcholine receptors.
NOGO
Prevents neurite outgrowth. Is at least one factor inhibiting repair of CNS axons.
NERVE GROWTH FACTORS
A family of proteins that work to switch off cell death program
(i.e., prevent apoptosis) via interaction with trk (tyrosine kinase) receptors.
What are the 3 germ layers and what do they form?
1) ECTODERM
skin, skin appendages, hair, lens, iris, cornea and inner ear
Neural plate - neuroectoderm
Will form the neural tube

2) MESODERM
connective tissue, muscle (all kinds), blood vessels, blood and urogenital system

3) ENDODERM
digestive and respiratory systems
What 8 things occur in NEURULATION?

A) What different tissues thicken? (2)

B) When do the neural folds fuse to form the tube?

C) What does the lumen become? (2)
A)
1) Thickening of ectoderm (neuorectoderm) forms neural plate

2) Thicken and form a pseudostratified columnar epithelium

B) Edges have increased growth and form folds

This leads to groove (neural groove)

Folds fuse to form tube (fusion begins at day 21) and it starts at 4th somite and goes rostrally and caudally

Anterior and posterior neuropores

C) Lumen becomes the ventricle system and central canal of spinal cord.
What is SPINA BIFIDA?
This is a deficit in the structures covering the inferior portion of the spinal cord and cauda equina

If there is just deficient mesoderm covering the dorsal aspect then can get spinabifida occulta
When do you get a MENINGOCELE?
If neural crest tissues are deficient
When do you get a RACHISCHISIS?
If neural tube doesn't close (in posterior neuropore)
Where are the NEURAL CREST CELLS in relation to the NEURAL TUBE?
They are the cells at lip of neural tube as it closes
What are the two types of cells that NC develop into?
NEURONAL

NON NEURONAL
What are the NEURONAL developments? (4)
1) Dorsal root (spinal) ganglia and all sensory nerve fibers

2) Ganglia of cranial nerves

3) Autonomic gangli

4) Adrenal medulla
What are the NON NEURONAL developments? (3)
1) Schwann cells and satellite cells

2) Leptomeninges (pia/arachnoid)

3) Bone and connective tissues of the face and skull base
BRAIN VESICLES:

What are the PRIMARY BRAIN VESICLES? (3)

A) When do they start to develop?

B) What do each of the vesicles develop into?
A) Begin to develop after the neuropore closes at day 25

B)

1) RHOMBENCEPHALON- most caudal
a) MYLENCEPHALON- medulla
b) METENCEPHALON- pons and cerebellum

2) MESENCEPHALON
a) MIDBRAIN

3) PROSENCEPHALON
a) DIENCEPHALON- thalamus
b) TELENCEPHALON- cerebral cortex and basal ganglia
What are teh 3 BRAIN FLEXURES and where are they located?
1) Cervical flexure
Spinal cord - rhombencephalon
juncture

2) Pontine flexure
Dorsal fold at mylencephalon/ metencephalon junction

3) Cephalic flexure
At mesencephalon
HISTOGENESIS:

A) What is the cell structure of the NEURAL TUBE?

B) Where does cell nuclei move frokm?

C) Where does DNA synthesis occur?

D) Where does NUCLEUS migrate towards?
A) Neural tube initially pseudostratified columnar

B) Cell nuclei move from near internal limiting membrane to external limiting
membrane

C) DNA synthesis occurs when nucleus near external limiting membrane

D) Nucleus migrates toward internal membrane and cell divides
Eventually no longer synthesize DNA (postmitotic)

NOTE: We now know that some neurons maintain the ability to divide later in life but it
is not known how important or functional these neurons are
MIGRATION:

A) What are the 3 layers of the CNS?

B) Where do NEUROBLASTS migrate from?

C) What does the MANTLE ZONE become?

D) What does the MARGINAL WHITE ZONE become?

E) Where do GLIOBLASTS migrate and whta do they become?
A) Ventricular zone, intermediate (mantle) zone and marginal zone

B) Neuroblasts migrate from the ventricular zone to mantle zone

C) Neuroblasts send axons into the marginal zone

D) Mantle zone becomes gray matter and marginal zone white matter

E) Glioblasts migrate and become astrocytes or oligodendrocytes
What are RADIAL GLIA and what is their function?
Early in development, some glial cells maintain connection with the internal and external limiting membrane

These provide guidance to migration
A) What is the CEREBRAL CORTEX?

B) What is the OLDEST/ YOUNGEST layer?

C) What is SEMAPHORIN A?
A) Successive waves of migration from ventricles to reach Layer I (the oldest layer)

B) Therefore, layer VI is next oldest and layer II is the youngest layer
The thalamic connections grow into the cortex and determine what kind of cortex
it will become (sensory, motor, association, etc).

C) SEMAPHORIN A is diffusible molecule created in Layer I. This attracts dendrites of
pyramidal cells and repels the axon (leads to charpyramidal cells)
What are MICROGLIAL CELLS?
These are mesodermal

Migrate into neural tube are derived from macrophages
What are GLIOBLASTS?
These differentiate quite late (oligodendroglia last – myelination is a late process)
What are EPENDYMAL CELLS?
Glial cells that do not migrate from ventricular zone

Line the lumen of the tube
FACTORS DETERMINING CELL AND NEURONAL FATE:

A) Where are FACTORS that determine if a NERUAL TUBE will develop located?

B) What do factors DIFFERENTIATE?

C) What do DIFFUSIBLE compounds determine?
A) Factors determine if a neural tube will develop from ectoderm
Must inhibit BMPs by presence of noggin and chordin

B) Factors differentiate ventral from dorsal part of the neural tube
Sonic hedgehog ventrally, TGF betas dorsally (BMP, dorsalin, vit A)

C) Diffusible compounds determine level of the brain stem that will develop from a
particular part of the neural tube
What is RETINOIC ACID an example of?
* see notes
What factors determine whether a cell will become a NEURON or GLIAL CELL?
1) Notch (interacting with delta) will prevent cells from becoming neuroblasts.

2) Basic Helix-Loop-Helix genes activated in neuroblasts

*NOTE: There are factors that determine the fate of a cell as it develops.

Cells are affected by the milieu through which they migrate.
What are the 3 important factors in wiring of the brain?
1) PATHWAY SELECTION

2) TARGET SELECTION

3) ADDRESS SELECTION
1) PATHWAY SELECTION
• Fundamentally, there are forces on growth cone. This cone puts out filopodia
from the lamellopodia.

• Attractants result in polymerization of actin and later of tubulin.

• Repellents result in depolymerization of actin.

• There are chemoattractive and repulsive soluble compounds. There are receptors
for these compounds that are linked to intracellular mechanisms that result in the
stabilization or destabilization of processes.

• A classic example is the decussation of spinothalamic tract. Growth cone makes
netrin receptors that are attracted by netrin in the floorplate. The axon grows to
the floorplate where the high concentration of netrin causes upregulation of Robo receptors (and downregulation of netrin receptors). There is also high concentration of slit in the floorplate that is chemorepulsive to axons containing
Robo. Therefore, the axons do not recross.

• The decussation of nasal, but not temporal fibers at the optic chiasm results from
expression of eph receptors on the temporal optic nerve fibers that are repelled by
the particular ephrin made by glial cells of the optic chiasm.

• Axons are guided along pioneer fibers by interaction with adjacent fibers through
cell adhesion molecules. These result in “fasciculation” (i.e., the tendency of
fibers to clump together in tracts).
2) TARGET SELECTION

What does it involve?
• It involves specific recognition molecules and “directions” in the environment

• Gradient of ephrins (interacting with eph receptors on the growing axons) are important in topographic termination of visual inputs to frog superior colliculus
3) ADDRESS SELECTION

What does this result in?

What is AGRIN?

What promotes ACH receptor expresssion?
• ADDRESS SELECTION of synapses result from interactions between the growing axon and its target.

• This is most well known for the neuromuscular junction.

• Agrin is a protein secreted by growing motor axon. This interacts with muscle-
specific kinase (MuSK) in muscle membrane, resulting in activation of rapsyn.
This causes aggregation of acetylcholine receptors in the muscle membrane.
Acetylcholine receptor expression is promoted by neureglin, which is also made by the axon terminal.
ADDRESS SELECTION CONT...

How are neurons prevented from undergoing PROGRAMMED CELL DEATH?
•This occurs through interaction between nerve growth factors (many varieties) and tyrosine kinase (trk) receptors.
What is the significance of ACTIVITY- DEPENDENT PLASTICITY?
• Both the amount and the quality of the synaptic input can result in stabilization of
a synapse. The precise signals are not known, but appear to involve metabotropic
receptors (through second messenger mechanisms) and calcium-dependent
mechanisms at the level of the synapse.

• There are critical periods in which this happens in most pathways (best shown inthe visual system).