CNS Development Flashcards
Identify the sources for central and peripheral nervous system.
The central nervous system begins to form in the 3rd week as the neural plate, which will become the neural tube and eventually the brain and spinal cord.
The peripheral nervous system is derived from 3 sources:
1) Neural Crest Cells
2) Neural Tube
3) Mesoderm
Discuss the process of closure of the neural tube.
The neural tube does not close like a zipper, rather there are multiple closure sites along the length of the tube. there are small areas of the tube that remain open on either end. The anterior neuropore closes on day 25 and becomes lamina terminalis. The posterior (caudal) neuropore closes on day 27
Describe the formation of the meninges.
There is mesenchyme surrounding the neural tube, which condenses to form primordial meninges. The external layer thickens to form dura mater. The internal layer is called the leptomeninges and is derived from neural crest cells. It will form the pia and arachnoid mater. Fluid filled spaces form in the leptomeninges and coalesce to form the subarachnoid space where CSF will form in the 5th week.
Discuss the positional changes of the spinal cord during its embryological development.
Week 8- Spinal cord extends the entire length of the vertebral column, but the vertebral column and spinal meninges grow faster than the spinal cord.
Month 6- Caudal end of the spinal cord ends at S-1.
Newborn-2nd or 3rd lumbar vertebra
3rd Post-natal Week- Inferior border of L1 vertebra (range from T12-L3)
Describe the embryological development of the three primary brain vesicles and the further division into the five secondary brain vesicles.
In the 4th week, just before closure of the anterior neuropore, the anterior end of the neural tube begins to expand forming 3 primary brain vesicles:
1) Prosencephalon
- Diencehpalon
- Telencephalon
2) Mesencephalon
3) Rhombencephalon
- Myelencephalon
- Metencephalon
Discuss the embryological derivatives of the myelencephalon.
Myelencephalon is a subdivision of the hindbrain or rhombencephalon. It will become the medulla oblongata.
Describe the embryological evolution and name the adult derivatives of the mesencephalon.
The mesencephalon undergoes less change than any other portion of the developing brain except the caudal part of the hindbrain. It has well defined basal and alar plates. The neural canal in the midbrain narrows and becomes the cerebral aqueduct, which connects the 3rd and 4th ventricles.
Discuss the embryological derivatives of the diencephalon.
The diencephalon is a subdivision of the prosencephalon or the forebrain. It will form the subcortical areas and the third ventricle and the posterior part of the pituitary gland.
Describe the embryological development of the pituitary gland.
The pituitary gland is ectodermal in origin and develops from two sources:
1) Anterior lobe (adenohypophysis)- Develops from upgrowth of ectodermal roof of the stomodeum (hypophysial diverticulum; Rathke’s pouch)
2) Posterior lobe & stalk (neurohypophysis)- downgrowth from neuroectoderm of the diencephalon (infundibulum).
Describe the embryological development of the choroid plexuses and the secretion of cerebrospinal fluid.
Tufts of capillaries invaginate into roof plates of the forebrain and hindbrain. They form eventual choroid plexuses. The thin roofs of all the ventricles and pia mater = tela choroidea, which will invaginate into ventricles and differentiate into choroid plexus. The choroid process secretes ventricular fluid, which becomes CSF when additions are made to it from the surfaces of the brain and spinal cord and from pia-arachnoid layers of the meninges.
Describe the developmental processes that continue in the brain after birth.
- Production of new neurons limited
-Myelination of sensory pathways, then motor pathways, then association areas. (some do not fully myelinate until adolescence.
-Brain size reaches 90 % of adult size by age 6.
There are a number of regressive events:
1) glial apoptosis
2) synaptic pruning
3)cortical thinning- marker of cortical maturation in healthy kids. Associated with development of fine motor skills and phonological processing skills. First occurs in sensorimotor areas, then association areas, then higher-order cortical areas.
Describe the process of neurulation. (When does it start? What structure induces neurulation?)
- Neurulation refers to the entire process of forming and then closing off the neural tube. It begins ~day 22.
- The notochord starts the whole process by inducing the overlying ectoderm to differentiate into neuroectoderm and form the neural plate.
- The neural plate will fold with some cells differentiating into neural crest cells & others into the neural tube. (Cranial 2/3 of neural tube = brain; Caudal 1/3 = spinal cord)
Describe the layers of the early neural tube, with their embryological development and derivatives.
neural tube is (3) layers of cells:
- Ventricular Zone = most internal. Single layer of cells lining future central canal of spinal cord and ventricular system. Neuroblasts FORM here and migrate to Intermediate zone.
- Intermediate zone: Basal + Alar plates. Migrated neuroblasts will form neurons and glial cells = Gray matter of spinal cord/brain.
- Marginal zone = outer. Axons of nerve fibers here = White matter of spinal cord/brain
Describe the embryological development of the spinal cord. (What 2 structures combine?)
Spinal cord develops from Neural tube + Caudal eminence:
Expl: Most of spinal cord comes from Neural tube. But the neural tube stops at level of 2nd sacral somites. So, the sacral and coccygeal segments come from Caudal eminence, which arises from the primitive streak, canalizes, and blends w/ neural tube.
What is the basal plate? What are its derivatives?
Basal plate = Motor = Ventral horn (ventral roots)
The basal plate is a ventrolateral thickening of the intermediate zone of the neural tube. It gives rise to motor neuroblasts of the ventral and lateral horns. It will become the Ventral Horn of the spinal cord.
*This basal plate will send out axons that exit the spinal cord and will become the Ventral Roots.
