Exam #1: Development--Self Study Flashcards
What is neurulation?
Process by which the trilaminar embryo internalizes its developing nervous system (ectoderm)
Describe the process of neurulation.
Gastrulation= formation of the trilaminar disc
Neurulation=
1) Mesoderm forms the notochord
2) Notochord induces the overlying ectoderm to proliferate & become the neural plate
3) Induction causes the neural plate to fold & become a central neural groove/ lateral & raised neural folds
4) Neural folds approximate & fuse, forming the neural tube
What is the embryological defect that causes spina bifida?
Incomplete fusion of the neural tube (opening into the ectoderm)
What are the three sources of nervous tissue in the body?
1) Neural tube
2) Neural crest cells
3) Ectodermal placodes
What tissue & cell types are derived from the neural tube?
CNS
Somatic motoneurons
Preganglionic ANS neurons
Where do most neural crest cell migrate?
Pharyngeal arches of the developing head & neck
What tissue & cell types are derived from ectodermal placodes?
Lens of the eye
Inner ear
Pituitary gland
Some somatic sensory ganglia of cranial nerves
What are neural crest cells?
- A narrow strip of cells at either edge of the neural plate
- Do NOT fuse with the neural tube; instead, lie ontop of it forming “neural crest”
What are the derivatives of neural crest cells? Specifically, what are the neural crest derivates of the head/ neck & body?
Head & Neck
- Bones, cartilage, & muscles in the head / neck
- Neurons of sensory ganglia in CN: V, VII, VIII, IX, X
- Odontoblasts
- Parafollicular cells of the thyroid gland
- Cells of aortic & carotid bodies
- PNS ganglia of CN
Body
- Ganglia (ANS & DRG)
- Schwann cells
- Adrenal medulla
- Melanocytes)
During early development, what are the three divisions of the neural tube?
1) Prosencephalon (forebrain)
2) Mesencephalon (midbrain & cerebral aqueduct of Sylvius)
3) Rhombencephalon (hindbrain)
When in gestation are the three major division of the neural tube further divided?
Week 5
Which of the three major divisions further divide?
Prosencephalon
Rhombencephalon
What does the prosencephalon divide into?
Telencephalon–>cerebral hemispheres & lateral ventricles
Diencephalon–>thalami & 3rd ventricle
What does the Rhombencephalon divide into?
Metencephalon= pons & cerebellum/ upper 4th ventricle Mylencephalon= medulla oblongata/ lower 4th ventricle
What are the three flexures in the brain?
1) Cephalic flexure
2) Cervical flexure
3) Pontine flexure
What is the Cephalic Flexure?
Bend in the region of the mesencephalon
What is the Cervical Flexure?
Bend between the Rhombencephalon & future spinal cord
What is the Pontine Flexure?
Bend in the Rhombencephalon that forms the two distinct:
- Metencephalon (pons & cerebellum)
- Myelencephalon (medulla oblongata)
What are CNS neurons & neuroglia derived from?
Neuroepithelium of the neural tube
What is the neuroepithelium?
Cells of the neural tube that form three distinct layers:
1) Ventricular
2) Intermediate/ Mantle
3) Marginal
Describe the formation of neurons in the CNS.
During weeks 4-20:
1) G1 ventricular
2) Migration to marginal & S-phase
3) Return to ventricular G2
4) Mitosis in ventricular
5) Migration to mantle & differentiation into neurons
6) Axon growth into the marginal layer
*****Migratory neurons that establish synaptic contacts remain; those that don’t undergo apoptosis
Describe the formation of neuroglia in the CNS.
Following the same general process as neuroblasts, glioblasts migrate into the marginal layer
How do the three zones of the neural tube translate into the mature spinal cord?
Ventricular= ependymal cells that line the ventricles Mantle= gray matter Marginal= white matter
How do microglia differ from other glial cells in the CNS?
Derived from bone marrow i.e. hematopoietic stem cells that migrate to the CNS; these are the macrophages of the CNS
How does the development of the PNS differ from the CNS?
All PNS cells are derived from neural crest cells i.e. neurons & neuroglia of the PNS are neural crest in origin
How do the meninges differ in their development?
Pia & arachnoid mater= neural crest
Dura= mesoderm
Describe the process of myelination. Specifically address: start & end/ cell types.
- Myelination begins at 16 weeks gestation
- Ends 3 years, except frontal lobes that continue till 20s
- CNS= oligodendrocytes
- PNS= Schwann cells
What is Spina Bifida Occulta?
- Incomplete closure of the neural tube in 1st month of gestation
- Overlying bone (L5/ S1) will have subtle defects
- Mildest form that is typically asymptomatic–maybe tuft of hair on skin in lumbar region
What is Spina Bifida Cystica?
- Incomplete closure of the neural tube in 1st month of gestation
- Herniate of nervous tissue through the bony defect causes a visible cyst-like structure in the individuals back i.e. “cystica”
- Two subtypes:
1) Meningocele
2) Meningomyelocele
What is Spina Bifida Meningocele?
- Herniation of meninges through body defect
- Spinal cord intact in spinal canal
What is Spina Bifida Meningomyelocele?
Herniation of meninges & spinal cord through defect
What is Spina Bifida Myeloschisis?
This is the most severe form of Spina Bifida that involves an externally open & flattened spinal cord
What supplement in early pregnancy can reduce the risk of Spina Bifida?
Folic acid
