SDL-4 Neuroembryology (1) Flashcards
What does the ectoderm become?
Skin, sweat glands, hair, teeth, eye & ear, and pituitary
What does the mesoderm become?
Most organs, connective tissue, DURA MATER
What does the endoderm become?
Epithelial linings (GI, lung, bladder), parenchyma of 4 throat structures (Tonsils, Thyroid, paraThyroid, Thymus), liver and pancreas
Describe primary neuralation.
Induction of the ectoderm to form the neural plate until ectoderm fusion over neural tube
What genes are important in primary neurulation?
- Sonic hedggehog (Shh)
- FGF8
- BMP4
- TGFb
What is formed in primary neurulation?
C1-S2 segments
What are some defects associated with primary neurulation?
Craniorachischisis totalis, anencephaly, myeloschisis, encephalocele, myelomeningocele
What is Sonic hedgehog (Shh)?
- Protein that induces overlying ectoderm to differentiate into neuroectoderm,
- Signals for cell differentiation into VENTRAL spinal cord
- Basal plate under influence of Shh
- Opposes BMP gradient (promotes dorsoventral differntiation)
What is Bone Morphogenic Protein (BMP)?
- Protein that signals for cell differentiation into DORSAL spinal cord
- Alar plate under influence of BMPs
- Opposes Shh gradient (promotes dorsoventral differntiation)
What are Homeobox genes (Hox genes)?
- A set of genes that are variably expressed at different levels of the spinal cord and determines head-to-toe development
- Important for anterior-posterior axis development and secondary neurulation
What is the cause of Craniorachischisis totalis?
- Complete failure of neurulation - exposed tissue dies.
- Incompatible with life
What is the cause of Myeloschisis?
Posterior neuropore not closed, neural plate caudal to NECK is open
What is the cause of Myelomeningocele?
Partial failure of posterior neuropore closure
What is dysjunction?
Separation of neural tube from surface ectoderm
Describe neural crest cells.
Transition from epithelial to mesenchymal, migrating away from neuroectoderm to mesoderm
What do neural crest cells become?
Nerve ganglia, autonomic ganglia, meninges, PNS glial/schwann cells (and connective tissues, melanocytes, & thyroid)
Describe secondary neurulation.
Mesenchymal cells around “posterior” neural tube (caudal mass region) form a tube and fuses with neural tube
What is formed in secondary neurulation?
S3-Coccyx innervations
What are some defects associated with secondary neurulation?
Diastematomyelia, tethered spinal cord, caudal regression syndrome
What is Tethered spinal cord?
Fixed caudal end of spinal cord (filum terminale anchors spinal cord, rendering it inflexible)
What is Diastematomyelia?
Split spinal cord due to persistence of neuroenteric canal
What is Caudal Regression Syndrome?
Sacral hypoplasia/hypoplasic femurs
What is Spina Bifida Meningocele?
Fluid-filled sac of meninges protrudes outwards
Neurological symptoms present
Spina Bifida Myelomeningocele (neural tissue included in fluid filled sac)
What is Spina Bifida Cystica?
Meninges or neural tissues protrude outwards
What is Spina Bifida Occulta?
Defective vertebral arches, asymptomatic (except little patch of hair over unclosed space)
Failure of sclerotome cells to migrate into the region dorsal to the neural tube leading to the absence of vertebral arches in that region
What are the layers of the neural tube?
- Proliferative
- Mantle
- Marginal
Describe the proliferative layer of the neural tube.
Neuroepithelial cells, innermost of the layers, give rise to intrinsic cells of the CNS and ependymal cells along the spinal cord lumen (neurocele)
Describe the Mantle layer of the neural tube.
Neuroblasts, the “grey matter” of the spinal cord
Describe the Marginal layer of the neural tube.
Nerve fibers of neuroblasts, the “white matter” of the spinal cord
What is the sulcus limitans?
Groove between alar (dorsal) and basal (ventral) plates
What are primary vesicles?
Earliest differentiation (week 4) of the rostral neural tube
- Prosencephalon (Forebrain)
- Mesencephalon (Midbrain)
- Rhombencephalon (Hindbrain)
What do primary vesicles become?
Forebrain, midbrain, hindbrain
What are secondary vesicles?
Week 6 differentiation of rostral neural tube
- Prosencephalon (primary)
- Diencephalon (secondary)
- Telencephalon (secondary)
- Mesencephalon (primary)
- Rhombencephalon (primary)
- Metencephalon (secondary)
- Myelencephalon (secondary)
What are the flexures of the primary vesicles?
- Cephalic
- Cervical
What are the flexures of secondary vesicles?
Pontine
What do secondary vesicles become?
Diencephalon, telencephalon, mesencephalon, metencephalon, myelencephalon
What is the Prosencephalon?
Forebrain
What is the Mesencephalon?
Midbrain
What is this image?
Mesencephalon
What is the Rhombencephalon?
Hindbrain
What does the Diencephalon become?
- Thalamus/hypothalamus (two alar plates)
- No basal motor plates
What is this image?
Diencephalon
What does the Telencephalon become?
- Cerebral hemispheres (lateral outpocketings)
- Lamina terminalis (most rostral part of brain)
What is this image?
Telencephalon
What does the Metencephalon become?
- Pons
- Cerebellum
What is this image?
Metencephalon
What does the Myelencephalon become?
Medulla
What is this image?
Myelencephalon
What is the casue of Holoprosencephaly?
Cerebral hemisphere fails to cleave
Ventral inductive defect (mutation in Shh)
Alcohol
Maternal diabetes
How does Holoprosencephaly present?
Malformation of brain and face, facial defects (i.e. cyclops eye)
What is the cause of Schizencephaly?
Failure of gyri to form in specific areas
Results in “Cleft Brain”, cognitive impairment, paralysis, seizures
What is the cause of Lissencephaly?
Failure of gyri to form
Results in “Smooth Brain” (few gyri)
What is the cause of Pachygyri?
Failure of narrow gyri (fine-sized) gyri to form
Results in broad gyri, too few gyri
What is the cause of Polygyri?
Failure of broad gyri to form
Results in small gyri
What does the forebrain consist of?
Diencephalon (midline)
Telencephalon (lateral)
What is the organization of the Mesencephalon?
Basal plate (two functionally distint groups of motor nerurons):
- Somatic efferent
- General visceral efferent
Alar plate
- Two sperate colliculi
- Visual and auditory
Central canal
Marginal layer enlarges to form crus cerebri
What is the organization of the Myelencephalon?
Lateral walls everted
Alar plate (sensory groups; columns of neurons)
- Somatic afferent (pain, touch, temp)
- Special visceral afferent
- General visceral afferent
Basal plate (motor groups; columns of neurons)
- General visceral efferent
- Special visceral efferent
- Somatic efferent
What are risk factors for neural tube defects?
- Alcoholism
- Nutritional deficiency
How are neural tube defects diagnosed?
- Ultrasound
- Maternal alpha-fetal protein levels
What is Fibroblast Growth Factor (FGF)?
Protein secreted to maintain immaturity of neural progenitor cells, secreted from caudal mesoderm to form a caudal(high)-to-rostral(low) gradient (So, neural tube develops ROSTRAL TO CAUDAL)
