Congenital Disease Associated with Central Nervous system Flashcards
What is Neurulation and at what stage will it occur ?
This is the process through which the neural tube forms and this occurs at around week 3/4
What does the neural tube form ?
The brain, spinal chord ,meninges ( membranous covering of brain and spinal chord ) and bones that surround them.
What are the three layers of the embryo ?
Ectoderm
Mesoderm
Endoderm
What is Gastrulation?
Gastrulation is the process during embryonic development that changes the embryo from a blastula with a single layer of cells to a gastrula containing multiple layers of cells.
What does the Ectoderm differentiate into?
This will form the outer component's of the body such as : Skin Hair Nervous system Mammary glands
What does the Mesoderm differentiate into ?
This will give rise to : skeletal muscles smooth muscle blood vessels bone cartilage joints connective tissue endocrine glands Kidney cortex Heart muscle urogenital organ uterus fallopian tube
What does the Endoderm differentiate into ?
The pharynx Oesophagus stomach Small intestine Colon Liver Pancreas Bladder Trachea bronchi lungs Thyroid Parathyroid
What is the notochord
This induces neurulation and will then form the nucleus pulposus
(soft gelatinous central portion of the intervertebral disk )
What is the somite ?
These are a set of bilaterally paired blocks of paraxial mesoderm that form the vertebrae, ribs and dermis of the dorsal skin, skeletal muscles of the back and the skeletal muscles of the body wall and limbs.
Describe process of Neuralation
By the end of week3 :
The lateral edges of the ectoderm will become more elevated and form the neural fold.
The depressed mid region is called the neural groove. The whole layer is referred to as the neural plate.
Neurulation will advance both cranially (brain /head) and caudally (Tail/ spinal chord)
The neural plate will form neural folds on either end forming the depression in the middle =the neural groove.
How does the neural tube form ?
The outer parts of the neural fold will fuse together forming the neural tube.
The outer section of the ectoderm will move and surround the endoderm and mesoderm.
Describe how the neural crest will form and what’s the function of this structure ?
Week 4
Some of the ectodermal cells will migrate forming several layers of cells called the neural crest.
This will give rise to structures that work closely with the nervous system
E.g- Peripheral nervous system spinal and cranial nerves +ganglia
Autonomic nervous system ganglia
Meninges
What are the different sections of the neural tubes ?
Prosencephalon-Cerebrum and thalamus
Mesencephalon -Mid brain
Rhombencephalon -Pons cerebellum and medulla
Spinal chord -Spine
What is an Anencephaly
Birth defect in which a baby is born without parts of the brain / skull.
Neural tube defect.
Opening is in anterior region
What is Craniorachischisis?
Occurs when the entire spinal chord and brain are exposed.
What is spina bifida ?
This is a birth defect that occurs when the spine and spinal chord do not form properly
This is in the caudal region .
Where does the closure of the neural tube begin?
In a mouse
This occurs at three different locations :
Closure 1-Craniorachischisis
(Located at the edge between hind brain and spinal chord)
Closure 2 -Anencephaly
(Edge between forebrain and mid brain )
Closure 3-Spina bifida
(Most rostral portion of forebrain-progresses posteriorly)
What are the additional closures found in humans and where are they located ?
Closure 4
More rosterly in hindbrain than closure 1
Closure 5
Very posterior portion of the neural plate and progresses anteriorly.
What are the two modes of neural tube closure?
Primary Neurulation -
Rolling up of the tube
Closure is by fold apposition then “zipping up”
Cranial and caudal neuropores
Secondary neurulation
Tunnelling or hollowing of tail bud
The primary and secondary neural tube becomes continuous
Region of fusion
Somities 30-31 in human (2nd sacral)
What is a neuropore ?
Caudal Neuropore
temporary opening at the extreme caudal end of the neural tube in early embryos
Cranial Neuropore
temporary opening at the extreme rostral (cephalic) end of the early embryonic
What are the steps of primary neurulation?
1.Shaping
It is originally broad in medial lateral axis and short along rostral caudal xis.It will narrow dbecome longer along the rostral caudal axis.
The first step is essential for neurulation
2.Folding
There are hinge points established. The first is the midline hinge point along the middle of neural plate.
3.Elevation
The folding of the lateral wings of neural plate.The edges become closer to each other along mid line
4.Convergence
The neural folds become further opposed to each other. There are more hinge points and more doral regions.
The two folds fuse and leads to a complete closure of neural tube
What are the two main processes which are essential to the folding of the neural plate into neural tube ?
- Shaping of the neural plate occurs by convergence/extensions
Tubing requires bending at hinge points
- Cell wedging at hinge points-Microtubules and actin filaments are remodelled -The process through which hinge points are created.
How are the two processes controlled
The Planar Cell polarity pathway
What is the process of convergence and extension?
This is the process of lengthening by narrowing which requires cells to become polarised in the plane of the cell layer.
The cells will intercalate within each other. Changing the shape of the cells. This leads to narrowing of the tissue. The tissue will elongate as we still require the same number of cells within the tissue.
