Nervous tissue embryology
Neural Tube Formation
1. Primary Induction:
• Begins with the formation of a thickened ectodermal neural plate overlying the notochord.
• BMP-4, produced by dorsal ectoderm, inhibits neural tissue differentiation.
• Notochord-secreted noggin and chordin counteract BMP-4, allowing neural tissue formation.
2. Stages:
• Neural Plate: The initial step where the ectoderm thickens.
• Neural Groove: Formation of a midline ventral depression flanked by neural folds.
• Neural Tube: The groove deepens and folds merge, forming a tube, precursor to the CNS.
Key Structures Derived from Ectoderm
1. Surface Ectoderm: Epidermis, hair, nails, sebaceous glands, lens
and cornea of the eye, anterior pituitary, tooth enamel.
2. Neural Tube: Brain and spinal cord.
3. Neural Crest: Schwann cells, adrenal medulla cells, melanocytes,
odontoblasts, neuroglial cells.
Brain Development
1. Primary Brain Vesicles:
• Forebrain (Prosencephalon): Divides into the telencephalon and
diencephalon.
• Midbrain (Mesencephalon): Remains undivided.
• Hindbrain (Rhombencephalon): Divides into metencephalon and
myelencephalon.
2. Closure of Neural Tube:
• Occurs cranially and caudally, with cranial closure at 24 days and
caudal closure at 26 days.
• Key regions like the forebrain, midbrain, and hindbrain become
Signaling Pathways
distinguishable.
1. Sonic Hedgehog (Shh):
• Induces floor plate formation and motoneuron development in the ventral neural tube.
2. BMP-4 and BMP-7:
• Induce dorsal structures and maintain dorsal gene expression.
• Counteracted by Shh in ventral regions.
Defects and Disorders
1. Spina Bifida: Incomplete closure of the spinal column, potentially exposing the spinal cord and meninges.
2. Anencephaly: Failure of anterior neuropore closure, leading to poor brain development and cranial vault absence.
3. Epilepsy: Can result from abnormal cortical cell migration, disrupting interneuronal function.
Neural Tube Formation
1. Primary Induction:
• Begins with the formation of a thickened ectodermal neural plate overlying the notochord.
• BMP-4, produced by dorsal ectoderm, inhibits neural tissue differentiation.
• Notochord-secreted noggin and chordin counteract BMP-4, allowing neural tissue formation.
2. Stages:
• Neural Plate: The initial step where the ectoderm thickens.
• Neural Groove: Formation of a midline ventral depression flanked by neural folds.
• Neural Tube: The groove deepens and folds merge, forming a tube, precursor to the CNS.
Key Structures Derived from Ectoderm
1. Surface Ectoderm: Epidermis, hair, nails, sebaceous glands, lens
and cornea of the eye, anterior pituitary, tooth enamel.
2. Neural Tube: Brain and spinal cord.
3. Neural Crest: Schwann cells, adrenal medulla cells, melanocytes,
odontoblasts, neuroglial cells.
Brain Development
1. Primary Brain Vesicles:
• Forebrain (Prosencephalon): Divides into the telencephalon and
diencephalon.
• Midbrain (Mesencephalon): Remains undivided.
• Hindbrain (Rhombencephalon): Divides into metencephalon and
myelencephalon.
2. Closure of Neural Tube:
• Occurs cranially and caudally, with cranial closure at 24 days and
caudal closure at 26 days.
• Key regions like the forebrain, midbrain, and hindbrain become
Signaling Pathways
distinguishable.
1. Sonic Hedgehog (Shh):
• Induces floor plate formation and motoneuron development in the ventral neural tube.
2. BMP-4 and BMP-7:
• Induce dorsal structures and maintain dorsal gene expression.
• Counteracted by Shh in ventral regions.
Defects and Disorders
1. Spina Bifida: Incomplete closure of the spinal column, potentially exposing the spinal cord and meninges.
2. Anencephaly: Failure of anterior neuropore closure, leading to poor brain development and cranial vault absence.
3. Epilepsy: Can result from abnormal cortical cell migration, disrupting interneuronal function.
