6 - CNS Development Flashcards
CNS development is all about __________, except for the notochord, which originates from _________.
CNS development all about the ectoderm, except the notochord, which originates as mesoderm, induces neurulation, and becomes intervertebral disks.
What does the ectoderm become?
All things that help us interact with the environment such as the epidermis, nails, hair and nails.
What do neural crest cells become?
They come off of the neural tube and carry peripheral nerves to their final effectors.
They make all ganglia in the PNS such as the sympathetic chain and ganglia in the head and neck (COPs)
When does the primitive streak appear and what happens to it?
Week 3, appears as a groove in the epiblast which establishes the longitudinal axis and bilateral symmetry of the embryo.
At the head end is the elevation called the primitive node which surrounds the primitive pit thats confluent with the primitive groove.
What does the notochordal process and adjacent mesoderm induce?
It induces the overlying embryonic ectroderm to form the neural plate, the origina of the central NS.
Describe the process of neural crest formation and neurulation?
Surface ectoderm bulges up and rises due to growth of surface ectoderm; they get thrown up into waves and at the crest of the waves are neural crest cells that are exteriorized in the neural tube and fuse to make the neural tube that will eventually make the brain and spinal cord.
-Crest cells get pushed out and become peripheral nerves
How does neurulation occur sequentially?
As the neural tube closes off, it starts in the thoracic regoin and then ZIPS cranially and caudually to eventually close at anterior and posterior ends.
When is neurulation complete?
Around the fourth week of development, neurulation is complete and you have a neural tube that’s closed at both ends.
What is diagnostic for a neural tube defect?
Alpha-fetoprotein in the amniotic fluid is diagnostic for a neural tube problem because it’s usually what’s secreted into a CLOSED neural tube and shouldn’t be in the amniotic fluid.
What nutritional and environmental factors play a role in the formation of neural tube defects (NTDs)? When do spinal cord defects normally occur?
Folic acid could prevent up to 75% of neural tube defects!
Most defects of the spinal cord result from abnormal closure of neural folds in the 3rd and 4th weeks of development.
What are the different types of neural tube defects in order from least to most severe?
Spina bifida occulta - tuft of hair at site of abnormality
Dermal sinus
Meningocele
Meningomyolocele
What is a meningocele? How prevalant is this?
Combo of a defect in the vertebral arch formation and a herniated meningial sac filled with CSF.
Can present anywhere along in the spine but are most common in lumbar region and arise in embryonic period.
1/1000 live births. Makes up 10% of spina bifida cystica cases.
What does it mean if someone has spina bifida cystica?
Cystica is a broad term used. Once you know more details, it will be categorized as either a meningocele or a meningomyelocele.
How does the CNS develop?
As the neural tube grows, the middle space gets smaller and the ventricle system forms.
You see optic vesicles near the rostral end.
What does the prosencephalon develop into?
The telencephalon and the diencephalon
What does the rhombencephalon (hindbrain) develop into?
Metencephalon adn the myelencephalon
How does the telencephalon arise? What does it become?
Arises as two lateral expansions, overgrows the diencephalon and becomes the cerebral hemispheres and lateral ventricles.
What does the diencephalon become?
It’s the more caudal part of the forebrain that becomes the thalami and 3rd ventricle.
What does the metencephalon become?
The cerebellum, pons, and upper part of the 4th ventricle.
What does the myelencephalon become?
This is the least developed part of the brain; it becomes the medulla oblongata and caudal part of the 4th ventricle.
What is hydrocephalus and what causes it? What are the places of obstructive hydrocephalus?
Build up of CSF in the brain, causing the ventricles to become enlarged and putting large amounts of pressure on the brain.
Lesion sites:
- Interventricular foramen of monroe
- Cerebral aqueduct
- Lateral apertures (of luschka)
- Median aperture (of magendie)
What is communicating hydrocephalus? What are the three main causes?
CSF freely communicates btween intracranial ventricular system and subarachnoid space behond the 4th ventricle outflow. Increased pressure caused by:
- Defective CSF reabsorption at arachnoid villi
- Excessive CSF production
- Inadequate cerebral venous drainage
What is non-communicating hydrocephalus?
An obstruction of CSF flow within the ventricular system or at its outlet to the subarachnoid space proximal to the level of the 4th ventricle outflow.
CSF cannot freely communicate with the SAS and ventricle fluid builds up and pressure infreases.
What are the most common causes of non-communicating hydrocephalus?
Either an intraventricular mass or extraventricular mass-occupying lesion that disrupts and/or occludes normal CSF flow.
