Development of the Central Nervous System Flashcards
Neural Plate
Surface Ectoderm that gives rise to the CNS
Neural Tube Formation
Invagination of the Neural Plate to form a Neural Groove with Neural Folds on either side.
Neural Crest
Forms from Surface Ectoderm while the Neural Tube is detaching from the Surface, giving rise to the Peripheral Nervous System
Neural Tube Progressive Development
WALLS (CRANIAL 2/3):Thicken to form the Brain
WALLS (CAUDAL 1/3): Thicken to form the Spinal Cord
LUMEN - Forms the Ventricular System of the Brain and Central Canal of the Spinal Cord
Dilations of Primordial Brain
Prosencephalon - Forebrain
Mesencephalon - Midbrain
Rhombencephalon - Hindbrain
Primordial Brain Structures, Associated Secondary Structures, and Adult Derivates of Walls and Cavities
Flexures of the Primordial Brain
- Cephalic (mesencephalic) flexure – forebrain rotates ventrally and posteriorly
- Cervical Flexure – Demarcates cervical S.C. & brainstem
- Pontine Flexure – Reverse dorsal flexion
Prosencephalon (Forebrain) Gives Rise To
Telencephalon (Endbrain) and two lateral outpocketings that from the Primitive Cerebral Hemispheres
Diencephalon (Outgrowth of the Optic Vesicles)
Rhombencephalic Isthmus
Separates the Mesencephalon from the Rhombencephalon
Pontine Flexure
Separates the Rhombencephalon into the Metencephalon and the Myelencephalon
Metencephalon
Forms the Pons and Cerebellum
Neuroepithelial Cell Differentiation Tree
Neuroepithelial Cells → Neuroblasts (1st) + Glioblasts (2nd) + Ependymal Cells (3rd)
Neuroblasts → Neurons
Glioblasts → Astroblasts (Fibrous and Protoplasmic) + Oligodendroblasts
(Ependymal) Ventricular, Mantle and Marginal Zones
VENTRICULAR (EPENDYMAL) - Innermost layer formed by Neuroepithelial Cells
MANTLE - A zone formed by Neuroblasts around the Epithelial layer that will give rise to the Gray Matter of the Spinal Cord
MARGINAL - Outermost layer of the Spinal Cord that contains the nerve fibers emerging from the Neuroblasts in the Mantle Layer
Glioblasts
Formed from differentiated Neuroblasts that migrate from the Ventricular Zone into the Mantle and Marginal Layers. Gives rise to Astroblasts and Oligodendroblasts
Astroblasts
Formed from the Glioblasts and found in the Mantle and Marginal layer. Will give rise to both Fibrous and Protoplasmic Astrocytes
Oligodendroblasts
Formed from the Glioblasts and found in the Marginal layer forming Myelin sheaths around the ascending and descending axons.
Ependymal Cells
Ependyma of the Ventricular Zone that line the Central Canal of the Spinal Cord.
These differentiate from Neuroepithelial cells once Neuroblasts and Glioblasts have ceased formation
____________ senses molecular markers that guide axons to the correct route
Growth cone
Guidance of Growth Cone
The axon travels through the Extracellular Matrix, guided by both Diffusible and Non-Diffusible signals
Netrins/DCC (Chemo-Attractant/ Chemo-Repellent)
Chemo-Attractants
Slit/Robo (Chemo-Attractant/ Chemo-Repellent)
Chemo-Repellents that prevent an axon from straying back over the midline once the axon has passed the midline in reponse to Netrin
Semaphorin/Plexin (Chemo-Attract/ Chemo-Repellent)
Chemo-Repellents that prevent the lateral extension of the nearby axons and cause lateral collapse of growth cones
Basal vs Alar Plates
BASAL - Ventral thickenings that contains the Ventral Motor Horn Cells (becomes the ventral horn)
ALAR - Dorsal thickenings that form the Sensory (Afferent) Areas (becomes the Dorsal Horn)
Sulcus Limitans
Marks the boundary between the Basal and Alar plates
Roof/Floor Plates
Midlines portions of the neural tube that do not contain Neuroblasts but serve as pathways for nerve fibers crossing from one side to the other
Metencephalon Derivatives
The Metencephalon will give rise to the Pons and Cerebellum
Cerebral Aqueduct
Forms form the narrowing of the Neural Canal and functions to connect the Third and Fourth Ventricles
Ectoderm
CNS, PNS, epidermis, sensory organs
Mesoderm
skeletal system, muscles, connective tissues, dermis, vascular region
Endoderm
Gut, lungs, liver
Phase I: Primary Neurulation
Neural crest cells:
Group of cells from crest of each neural fold “pinched off” during formation of neural tube
differentiating into:
• Ganglia of sensory neurons of spinal nerves (DRGs), and cranial nerves
• postganglionic neurons of Autonomic nervous system
(autonomic ganglia)
• Schwann cells and satellite cells of PNS.
• Endocrine organs (adrenal
medulla)
• Leptomeninges: pia & arachnoid connective tissue of CNS
Phase II: Neural Tube Differentiation
Secondary Neurulation
Closed neural tube separates into 2 distinct layers
( ~Day 26)
-Mantle layer: ‐ the inner ring
cell bodies grey matter
-Marginal layer: the outer ring
axons white matter
-Ependymal layer: the inner most ring
cells line ventricles, etc.
Midbrain fate
remains the midbrain
cavity becomes cerebral aqueduct connecting the 3rd and 4th ventricles within the midbrain region
Hindbrain (rhombencephalon) fate
Metencephalon
–becomes pons, medulla, cerebellum and part of 4th ventricle
Myelencephalon
–becomes lower medulla
part of 4th ventricle and part of central canal
What happens when cranial neural tube fails to fuse properly?
Anencephaly
Arnold-chairi Malformation
Developmental deformity of hindbrain
Types:
• Type I: herniation of cerebellar
tonsils through foramen magnum
into central canal; pons & medulla
smaller and malformed
• Type II: brainstem & cerebellum
malformed and pushes down into
foramen magnum
• Hydrocephalus requiring
shunting in ~ 90%
• Associated with spinal bifida
Meningocele
failed vertebral column formation resulting in sac-like protrusion of membrane- no neural tissue
myelomenigocele
Failed vertebral column formation resulting in sac‐like protrusion of membrane with protrusion of spinal cord and membrane
Thoughout the primitive streak and node, the cells that make up this area are prolifereating and migrate to different areas of the embryo. The ones that migrate through the primitive streak and node ___________ are important because they give rise to the notochord and the CNS.
Rostrally
How is right and left symmetry formed?
- The cells that form the notochord (mesoderm) go through the primitive node and go through a period where they fuse with the encoders (ectoderm) and become a rod that forms the axis that forms left and right symmetry.
- Basically the mesoderm-forming somites and the overlying ectoderm take to each other.
- They send signals that go back and forth to each other so that the NS forms in conjuction with the segmentation of the body.
What are the derivatives of the mesoderm? What does each derivative form? Where is each located in relation to the midline?
Paraxial Mesoderm
- Closest to midline (medial), thick
- Forms somitomeres which give rise to mesenchyme of head and organize into somites at occipital and caudal levels – vertebral column, limb, body wall musculature
Intermediate
•Urogenital system
Lateral Plate Mesoderm
- Thin, lateral
- line peritoneal, pleural and pericardial; thin membrane around each organ, vessels,etc.
The notochord has a ________ axis of formation.
Cranial-Caudal
The notochord is important in establishing the body’s ____________ axis.
Longitudinal