Embryonic Brain Development and Nervous System Structure

Question 1

the germ layers

Answer 1

*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

Question 2

Gastrulation:

Answer 2

rearrangement of cells in the developing organism to form the germ layers
Forming the three layers

Question 3

Neurulation:

Answer 3

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.

Question 4

Gastrulation and Neurulation

• date of notochord formation?
• how does the neural plate come to be?

Answer 4

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

Question 5

Gastrulation, and the formation of the mesoderm, is the single most important event in your development

Answer 5

No gastrulation –> No mesoderm –> No notochord –> No molecular signals to support the formation of neural tissue

Question 6

Mammalian Neurulation cont

Neural plate, Primitive streak, Neural crest

Answer 6

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

Question 7

Neural Crest Cells

-location

Answer 7

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

Question 8

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 ___

Answer 8

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

Question 9

does the Anterior neuropore (at brain end) or the Posterior neuropore close first

Answer 9

the anterior neuropore

Question 10

Anencephaly:

Answer 10

a failure to develop a brain
Often a result of the anterior neuropore not closing
Fatal
(Anterior novel cord closer)

Question 11

Iniencephaly:

Answer 11

also an anterior neural tube defect; regions of skull and cervical spine fail to develop along with brain structures
Fatal

Question 12

Encephalocele:

Answer 12

brain bulges through sac-like opening in skull
Also an anterior neural tube defect
Almost always fatal

Question 13

Craniorachischisis:

Answer 13

exposed brain and spinal cord
The tube does not pinch close… instead stays open
Fatal
Extremely incomplete closure of neural tube

Question 14

Spina Bifida

-day #?

Answer 14

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)

Question 15

Myelomeningocele:

Answer 15

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.

Question 16

Meningocele:

Answer 16

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

Question 17

Spina Bifida Occulta:

Answer 17

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

Question 18

the multipotent cells

Answer 18

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

Question 19

Progressive Regional Specification of the Nervous System

Answer 19

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

Question 20

Things That Can Go Wrong during neurosystem development ***

Answer 20

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

Question 21

Telencephalon- adult brain derivatives ***

Answer 21

Cerebral cortex, hippocampus, amygdala, and basal ganglia

Question 22

Diencephalon

Answer 22

Thalamus, hypothalamus, epithalamus

Question 23

Brainstem

Answer 23

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)

Question 24

Mesencephalon –> Midbrain

Answer 24

Dorsal surface: tectum
Ventral surface: tegmentum

Tectum: superior and inferior colliculus
Important for vision and hearing
Tegmentum: substantia nigra and red nucleus
Control movement

Question 25

Rhombencephalon–>

Answer 25

Metencephalon and Myelencephalon

Question 26

Metencephalon –>

Answer 26

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

Question 27

Myelencephalon –>

Answer 27

Medulla Oblongata

Relays somatic and autonomic sensory information
Contains important motor nuclei that keep you alive

Question 28

spinal cord

Answer 28

Gray matter= cell bodies (central)
White matter= axons (external)

Dorsal= mostly sensory information
Ventral= motor neurons

Question 29

*Ectoderm: skin (epidermis) and nervous system

Answer 29

• 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

Question 30

which germ layer will condense to form the notochord?

-day?

Answer 30

Mesoderm:
(–> mostly muscle and connective tissues)
-Middle germ layer

Will condense to form the notochord by 16-18 days post-fertilization

Question 31

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

Answer 31

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

Question 32

Neurulation: formation of neural ____ and then neural ____

Answer 32

Neurulation‐ formation of neural plate and then neural tube

Question 33

Neurulation

Answer 33

Neurulation refers to the folding process in vertebrate embryos, which includes the transformation of the neural plate into the neural tube.

Question 34

What makes the neural plate the neural plate? **

Answer 34

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

Question 35

what region is the the neural tube being formed from

Answer 35

the neural plate which arose from the ectoderm:

- due to the signals coming from the mesoderm / notochord that tells them to neurally fated

Question 36

Neural plate:

Answer 36

ectodermal cells that overly the notochord; receive molecular signal to become neurally fated
- Involute to form the neural tube

Question 37

neural crest cells

Answer 37

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.

Question 38

folic acid and birth defects / neural tube

Answer 38

folic acid can help prevent these ??

Question 39

Note the splitting of the ____ into two hemispheres

Answer 39

Note the splitting of the telencephalon into two hemispheres

Question 40

Holoprosencephaly: ***

Answer 40

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

Question 41

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

Answer 41

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

Question 42

formation of the notochord timeline

Answer 42

the mesoderm cells migrate to along the midline and condense to form the notochord by 16-18 days post-fertilization

Question 43

where does the neural tube start closing? where does it extend?

Answer 43

The neural tube closes starting in the middle and extends to the anterior and posterior

Question 44

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.

Answer 44

Myelomeningocele

Question 45

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

Answer 45

Spina Bifida Occulta:

Question 46

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

Answer 46

Meningocele:

Question 47

folic acid helps prevent…

Answer 47

Folic acid can help reduce the risk for certain birth defects, such as spina bifida and anencephaly