Embryonic Brain Development and Nervous System Structure Flashcards
the germ layers
*Ectoderm: skin (epidermis) and nervous system
-Outer germ layer
-from this layer getting the skin and the nervous system so getting a shared lineage
-“outside”: nerve endings are towards the outside
*Mesoderm: mostly muscle and connective tissues
-Middle germ layer
-Will condense to form the notochord
Important for development of nervous system: provide a lot of signals to tell where and when to make a nervous system
*Endoderm: all the other good stuff, like most of your organs
-Inner germ layer
Gastrulation:
rearrangement of cells in the developing organism to form the germ layers
Forming the three layers
Neurulation:
the process by which the region of the ectoderm that will become the nervous system involutes
Neurulation refers to the folding process in vertebrate embryos, which includes the transformation of the neural plate into the neural tube. The embryo at this stage is termed the neurula.
Gastrulation and Neurulation
- date of notochord formation?
- how does the neural plate come to be?
First, the cells that will become the mesoderm move to the inside of the embryo
Will condense to form the notochord by 16-18 days post-fertilization
Next, the region of ectoderm overlaying the mesoderm (the neural plate) will involute to form the neural tube
Neural tube is the major indicator that…? What has happened
What makes the neural plate the neural plate?
Signals from the underlying mesoderm/notochord act on this region of tissue to specify it to be neurally-fated and not epidermally-fated like the rest of the ectoderm
Gastrulation, and the formation of the mesoderm, is the single most important event in your development
No gastrulation –> No mesoderm –> No notochord –> No molecular signals to support the formation of neural tissue
Mammalian Neurulation cont
Neural plate, Primitive streak, Neural crest
Primitive streak: groove along midline where cells migrate through
- Mesodermal cells migrate in first –> condense to form the notochord inside along the midline
Neural plate: ectodermal cells that overly the notochord; receive molecular signal to become neurally fated
- Involute to form the neural tube
- Neural crest: cells at the very border between the neural plate and the rest of the ectoderm
- Break away from the ectoderm and neural tube
- Will eventually form many things including sensory/peripheral neurons and some glia
Neural Crest Cells
-location
becoming lots of different things because of different environments…
-do a lot of migrating around. ultimately contributing to the peripheral nervous system
- Neural crest: cells at the very border between the neural plate and the rest of the ectoderm
- Break away from the ectoderm and neural tube
- Will eventually form many things including sensory/peripheral neurons and some glia
The neural tube closes starting in the middle and extends to the anterior and posterior
Anterior neuropore: at brain end; should close by __
Posterior neuropore: at the tail end; should close by ___
The neural tube closes starting in the middle and extends to the anterior and posterior
Anterior neuropore: at brain end; should close by Day 26
Posterior neuropore: at the tail end; should close by Day 28
does the Anterior neuropore (at brain end) or the Posterior neuropore close first
the anterior neuropore
Anencephaly:
a failure to develop a brain
Often a result of the anterior neuropore not closing
Fatal
(Anterior novel cord closer)
Iniencephaly:
also an anterior neural tube defect; regions of skull and cervical spine fail to develop along with brain structures
Fatal
Encephalocele:
brain bulges through sac-like opening in skull
Also an anterior neural tube defect
Almost always fatal
Craniorachischisis:
exposed brain and spinal cord
The tube does not pinch close… instead stays open
Fatal
Extremely incomplete closure of neural tube
Spina Bifida
-day #?
Incomplete closing of the backbone and membranes around the spinal cord
28th day of gestation (posterior neuropore)
The most common location is the lower back, but it can occur in the middle back or neck (See previous slide)
Myelomeningocele:
Most serious type of spina bifida.
A sac of fluid comes through an opening in the baby’s back.
Part of the spinal cord and nerves are in this sac and are damaged
This type of spina bifida causes moderate to severe disabilities, such as problems affecting how the person goes to the bathroom, loss of feeling in the person’s legs or feet, and not being able to move the legs.
Meningocele:
A sac of fluid comes through an opening in the baby’s back, but the spinal cord is not in this sac.
There is usually little or no nerve damage. This type of spina bifida can cause minor disabilities.
Better long term prognosis
Spina Bifida Occulta:
Mildest type of spina bifida.
Sometimes called “hidden” spina bifida.
With it, there is a small gap in the spine, but no opening or sac on the back.
The spinal cord and the nerves usually are normal.
Not usually doing a surgery
Doesn’t really cause problems
the multipotent cells
They are restricted in that they must become some type of neural cell, but they are still open to becoming any type of neural cell
Early on, most are progenitors who will give rise to more progenitors, neurons, and glia
Expand the nervous system
As development progresses, their fates will become restricted
Progressive Regional Specification of the Nervous System
First, make big segments
Then continue to subdivide and subdivide the cells into different regions/structures/sub-structures
Note the splitting of the telencephalon into two hemispheres
-pretty sure this continues until reach puberty
Things That Can Go Wrong during neurosystem development ***
Holoprosencephaly: failure of the prosencephalon to develop into two hemispheres; sometimes the result of Sonic Hedgehog (Shh) defects
-result is a blob rather than the two distinct hemisphere
Retinoic Acid Exposure: retinoic acid is anti-anterior/anti-brain; too much retinoic acid during the wrong part of development can lead to loss of forebrain structures
Medulloblastoma: progenitors keep dividing after they should stop; leads to uncontrolled granule cell proliferation; often a result of a Shh defect
Telencephalon- adult brain derivatives ***
Cerebral cortex, hippocampus, amygdala, and basal ganglia
Diencephalon
Thalamus, hypothalamus, epithalamus
Brainstem
In humans, includes the midbrain, pons, and medulla
Midbrain includes substantia nigra, colliculi, red nucleus, VTA…
This is why I generally call the brainstem “the midbrain and stuff”
Home of 10 pairs of cranial nerves
We know it for role as motor and sensory information highway
We love it for role in cardiac and respiratory function
(12 cranial nerves total)
Mesencephalon –> Midbrain
Dorsal surface: tectum
Ventral surface: tegmentum
Tectum: superior and inferior colliculus
Important for vision and hearing
Tegmentum: substantia nigra and red nucleus
Control movement
Rhombencephalon–>
Metencephalon and Myelencephalon
Metencephalon –>
Cerebellum and Pons
Rhombic lip of the rhombencephalon gives rise to the cerebellum
Pons develops alongside the cerebellum
Motor signals from the cortex pass go to the pons and the pons sends the information on to the cerebellum
Myelencephalon –>
Medulla Oblongata
Relays somatic and autonomic sensory information
Contains important motor nuclei that keep you alive
spinal cord
Gray matter= cell bodies (central)
White matter= axons (external)
Dorsal= mostly sensory information Ventral= motor neurons
*Ectoderm: skin (epidermis) and nervous system
- Outer germ layer
- from this layer getting the skin and the nervous system so getting a shared lineage
- “outside”: nerve endings are towards the outside
which germ layer will condense to form the notochord?
-day?
Mesoderm:
(–> mostly muscle and connective tissues)
-Middle germ layer
Will condense to form the notochord by 16-18 days post-fertilization
which comes first:
the region of ectoderm overlaying the mesoderm (the neural plate) will involute to form the neural tube
the cells that will become the mesoderm move to the inside of the embryo
First, the cells that will become the mesoderm move to the inside of the embryo
Will condense to form the notochord by 16-18 days post-fertilization
Next, the region of ectoderm overlaying the mesoderm (the neural plate) will involute to form the neural tube
Neurulation: formation of neural ____ and then neural ____
Neurulation‐ formation of neural plate and then neural tube
Neurulation
Neurulation refers to the folding process in vertebrate embryos, which includes the transformation of the neural plate into the neural tube.
What makes the neural plate the neural plate? **
Signals from the underlying mesoderm/notochord act on this region of tissue to specify it to be neurally-fated and not epidermally-fated like the rest of the ectoderm
what region is the the neural tube being formed from
the neural plate which arose from the ectoderm:
- due to the signals coming from the mesoderm / notochord that tells them to neurally fated
Neural plate:
ectodermal cells that overly the notochord; receive molecular signal to become neurally fated
- Involute to form the neural tube
neural crest cells
Neural crest cells: are considered multipoint
Neural crest cells can become many different cells. Neural crest cells originate at the very border between the neural plate and the rest of the ectoderm (the orange in that one image). They break away from the ectoderm and neural tube and take distinct migratory routes. Each route will have the neural crest cells exposed to different chemical cues (different cellular environments/ different inductive factors) which will control the types of cells they differentiate into.
neural crest cells can become 1)sensory neurons 2) autonomic ganglia 3) schwann cells 4) pigment cells (non-neural tissues (for example, melanocytes= a skin cell)
5) smooth muscle (precursors of adrenal neurosecretory cells that will aggregate around the dorsal portion of the kidney)
- note I think there are 5 different inductive factors but 4 paths? not entirely sure.
- so basically neural crest cells can become a lot of things, including neural and non-neural cells.
folic acid and birth defects / neural tube
folic acid can help prevent these ??
Note the splitting of the ____ into two hemispheres
Note the splitting of the telencephalon into two hemispheres
Holoprosencephaly: ***
Holoprosencephaly: failure of the prosencephalon to develop into two hemispheres; sometimes the result of Sonic Hedgehog (Shh) defects
-result is a blob rather than the two distinct hemisphere
Primitive streak: groove along midline where cells migrate through
- indent on top- during gastrulation?
- Mesodermal cells migrate in first –> condense to form the notochord inside along the midline
Primitive streak: groove along midline where cells migrate through
- indent on top- during gastrulation?
- Mesodermal cells migrate in first condense to form the notochord inside along the midline
formation of the notochord timeline
the mesoderm cells migrate to along the midline and condense to form the notochord by 16-18 days post-fertilization
where does the neural tube start closing? where does it extend?
The neural tube closes starting in the middle and extends to the anterior and posterior
Most serious type of spina bifida.
A sac of fluid comes through an opening in the baby’s back.
Part of the spinal cord and nerves are in this sac and are damaged
This type of spina bifida causes moderate to severe disabilities, such as problems affecting how the person goes to the bathroom, loss of feeling in the person’s legs or feet, and not being able to move the legs.
Myelomeningocele
Mildest type of spina bifida.
Sometimes called “hidden” spina bifida.
With it, there is a small gap in the spine, but no opening or sac on the back.
The spinal cord and the nerves usually are normal.
Not usually doing a surgery
Doesn’t really cause problems
Spina Bifida Occulta:
A sac of fluid comes through an opening in the baby’s back, but the spinal cord is not in this sac.
There is usually little or no nerve damage. This type of spina bifida can cause minor disabilities.
Better long term prognosis
Meningocele:
folic acid helps prevent…
Folic acid can help reduce the risk for certain birth defects, such as spina bifida and anencephaly
