Lecture 8: Development of the Brain Flashcards
What induces the formation of the neural plate, neural groove, neural folds, and neural tube?
Notochord
As the neural folds migrate to the middle and zipper up and down you get the formation of a rostral neuropore and caudal neuropore, when do these close by?
Rostral neuropore: close by day 25
Caudal neuropore: close by day 27
Which 5 cells of the CNS arise from neuroectoderm?
1) Astrocytes: structural and support cells
2) Dendrites and Axons
3) Oligodendrocytes: myelinate axons in CNS
4) Ependyma cells
5) Epithelium of Choroid Plexus
Where are Microglial cells of the CNS derived from?
Mesoderm (mesenchyme)
Neural tube cranial to _______ somites becomes the brain?
4th
What are the 3 primary brain vesicles?
- Prosencephalon (forebrain)
- Mesencephalon (midbrain)
- Rhombencephalon (hindbrain)
What week does the forebrain and hindbrain divide and what are their divisions?
- 5th week
- Forebrain —> Telencephalon (cerebral hemisphere) and Diencephalon (thalamus, hypothalamus, and optic nerve)
- Hindbrain —> Metencephalon (pons/cerebellum) and Myelencephalon (medulla)
*The midbrain does NOT divide
The cervical flexure demarcates what?
Hindbrain from the spinal cord
The pontine flexure divides what?
Divides the hindbrain into Metencephalon (rostral) and Myelencephalon (caudal)
What 4 brain components arise from the Diencephalon?
1) Thalamus
2) Hypothalamus
3) Epithalamus
4) Eye (optic nerve)
What is Holoprosencephaly (HPE) and what other abnormalities is it commonly associated with?
- Incomplete separation of cerebral hemispheres
- Most associated w/ facial abnormalities due to reduction of FNP
Describe the embryological development of the Pituitary Gland; where does each lobe arise from?
- Upgrowth from roof of mouth (first arch ectoderm) forms Hypophysial diverticulum (Rathke’s pouch) = Anterior lobe
- Downgrowth from diencephalic floor (neuroectoderm) forms Neurohypophysial diverticulum = Posterior lobe
- Stalk of Rathke’s pouch regresses around week 6 and lobes fuse together
The spinal cord is formed by the neural tube caudal to the ______ pair of somites
4th
What is found in the Ventricular (zone 1), Intermediate (zone 2), and Marginal (zone 3) of the spinal cord?
1) Ventricular (Zone 1): neuroepithelial stem cells
2) Intermediate (Zone 2): neurons, astrocytes, microglia and/or glia
3) Marginal (Zone 3): oligodendrocytes, microglia, and axons that will eventually become myelinated (white matter)
Differentiation of the SC produces _____ walls, but _____ roof and floor plates
Thick walls, but thin roof and floor plates
The sulcus limitans is important for dividing?
- Alar plate (dorsal): sensory
- Basal plate (venral): motor
Where do the nucleus gracilis and nucleus cuneatus of the lower medulla develop from and what aspect of the medulla are they located on?
- In caudal Myelencephalon, neuroblasts in Alar plate from these nuclei
- Located on the Dorsal aspect of the medulla
What aspect of the medulla are the pyramids found on; which tract do they contain?
- Ventral aspect
- Contain CST
As the pontine flexure forms what affect does it have on the walls and roof plate of the medulla; what does it do to the alar and basal plates?
- Causes walls of medulla to move laterally
- Thins the roof plate
- Alar plates becomes lateral to the basal plates —> motor nuclei develop medially and sensory nuclei develop laterally
Cerebellum develops from what part of the alar plate and what must occur for its development?
- Dorsal parts of the Alar plates
- Rhombic lip (aka cerebral swelling) migrate and fuse midline
Which 4 nuclei develop from the basal plate of the Metencephalon?
1) Abducens nucleus
2) Facial motor nucleus
3) Trigeminal motor nucleus
4) Superior salivatory nucleus
Which CN’s are associated with GSE?
CN III, IV, VI, XII
Which CN’s are associated with GVE?
CN III, VII, IX, X
Which CN’s are associated with SVE; these innervate muscles derived from where?
CN V, VII, IX, X, XI
*Muscles derived from the pharyngeal arches
Which CN’s are associated with GSA?
CN V, VII, IX, X
Which CN’s are associated with GVA?
CN: IX, X
Which CN’s are associated with SSA?
CN II, VIII
Which CN’s are associated with SVA?
CN I, VII, IX, X
Which ventricle is located in the Telencephalon?
Lateral ventricles
Which ventricle is located in the Diencephalon?
Third ventricle
Which part of the ventricular system is located in the Mesencephalon?
Cerebral aqueduct
Which ventricle is located in both the Metencephalon and Myelencephalon?
Fourth ventricle
What other pathology is Syringomyelia highly associated with?
Type I Chiari malformations
What is Hyrdrocephalus and what causes it?
- Excess CSF in the ventricular system of brain
- Can be caused by obstruction in the ventricles, arachnoid villi, or overproduction by choroid plexus adenoma
What occurs in Chiari Type I malformation; highly associated with what other abnormality?
- Herniation of cerebellar tonsils through foramen magnum (defect in hindbrain)
- Usually no symptoms, but pressure on cerebellum can lead to decreased coordination
- Highly associated with Syringomyelia
What is Arnold-Chiari type II malformation; what other pathology is it highly associated with?
- Herniation of medulla and cerebellum through foramen magnum
- May lead to Hydrocephalus due to compression of medial and lateral foramina
- Highly associated with Spina Bifida (Myelomeningocele)
Which nuclei form from the Basal plates in the Mesencephalon?
- Red nucleus
- Edinger-Westphal nucleus
- Oculomotor nucleus
*Think motor, anything basal plate
What is formed by the Alar plates of the Mesencephalon?
1) Superior Colliculus
2) Inferior Colliculus
The 1st neurons from the Ventricular zone migrate up and form what?
Preplate
Axons from the preplate extend on the inner side, establishing which zone?
Intermediate zone
After formation of the intermediate zone the next set of neurons migrate into the middle of the preplate and split it producing what 3 things?
- Cortical plate, in between..
- Marginal zone (future lamina I) and…
- Subplate
Early neurons of the cortical plate will form which layers/laminae first?
- Deep layers
- Laminae VI and V
Late neurons migrate throuh which zones/lamina and form which layers/lamina
- Migrate through intermediate zone and subplate
- Passing through layers VI and VI (born first)
- Establishing layer IV —> III —> II (born last)
Neurons are able to migrate through the cortex using which cells?
Radial glial cells
Which laminae are born first and which are last?
Earliest: V and VI
Last: IV —> III —-> II
What causes Lissencephaly or Agyria (smooth brain); characterized by; patients later develop what problems?
- Incomplete neuronal migration to cerebral cortex during 12-24 wks
- Characterized by: enlarged ventricles, lack of gyri (smooth looking), complete/partial agenesis of corpus callosum
- Patients later develop seizures, mental retardation and mild spastic quadriplegia
What are the causes of Microcephaly?
- Genetic
- Prenatal and perinatal brain injury (Cytomegalovirus, Rubella toxoplasma gondii, Zika)
- Ionizing radiation
- Maternal alcohol abuse
Why is the cytodifferentiation of the cerebellum unique?
- Some cells migrate from inside out, giving rise to the purkinje fibers
- Some cells will migrate from ouside back in and give rise to the granular cells
All 4 types of spina bifida are a result of what failure?
Failure of the caudal neurpore to close at day 27
What is seen in Spina Bifida Oculta?
- Vertebral arches did not close correctly, skin remains intact
- Failure of fusion of the neural folds/caudal neuropore at day 27
- May have a tuft of hair on back
What is seen with Spina Bifida w/ Meningocele; do these patients have problems with motor and sensory?
- Vertebral arch did not form, and caudal neuropore late to close
- Cyst like structure covered with meninges extruded from back
- May or may not have problems with motor and sensory
What is Spina Bifida w/ Meningomyelocele; do these patients have problems with sensory and motor?
- Meninges and neural tissue are both inside the cyst
- Spinal cord in improper location
- These patients DO have motor and sensory defects
- Trouble walking, bladder/bowel control, and general sensory issues below location of lesion
What is Spina Bifida w/ myeloschisis (myelocele); do these patients have motor and sensory issues?
- Neural tube/caudal neuropore did not close at all!
- Open neural tissue on back, at high risk for infection
- These patients have motor and sensory issues
What is the root cause of Anencephaly, Encephalocele (w/ and w/o brain tissue)?
Failure of the rostal neuropore to close at day 25
