Developmental Biology: Neural Tube and CNS

Ectoderm Neurulation

• Ectoderm gives rise to the epidermis, nervous system, sense organs, and other cell types.
• Endoderm forms tissues lining the digestive tract and related organs (liver, pancreas, lungs).
• Mesoderm develops into skeletal, muscle, circulatory, excretory, and reproductive systems.

Spemann-Mangold Organizer

• The Spemann-Mangold organizer is a cluster of cells in amphibian embryos.
• It induces the development of the central nervous system.
• Induction is the process where one group of cells influences the development of others.

The Spemann-Mangold Organizer Experiment

• The experiment involves transplanting cells from one part of an embryo to another.
• Cells in the dorsal lip of the blastopore are crucial.
• These transplanted cells induce the formation of a new central nervous system in the recipient area.

Neurulation

• Neurulation is the embryonic process forming the neural tube.
• This tube develops into the central nervous system.
• It involves a primary and secondary neurulation process.

Primary Neurulation

• Formation of the neural plate begins the process.
• The plate bends and folds into a groove.
• Eventually, the neural groove closes to form the neural tube.
• Underlying mesoderm signals the ectodermal cells to elongate.
• Intrinsic movement within epidermal and neural plate regions affects shaping.

Primary Neurulation Steps

• Formation of the neural plate
• Shaping of the neural plate
• Bending of the neural plate -- neural groove (neural fold)
• Closure of the neural groove -- neural tube

Primary Neurulation of the Neural Plate

• The neural plate forms during primary neurulation stages.
• Its medial hinge point (MHP) and dorsolateral hinge points (DLHP) play essential roles.
• The shape changes.

Closure of the Neural Tube

• Paired folds are brought together at the dorsal midline.
• A neuropore forms where ectoderm closes around the neural tube.
• Genes like Pax3, Sonic hedgehog (Shh), and open brain (opb) are involved.
• Dietary folic acid (Vitamin B12) and cholesterol are important.

Differentiation of the Neural Tube

• The neural tube's lumen bulges, and constricts, forming brain and spinal cord chambers.
• Cell populations rearrange within the neural tube to form different CNS regions.
• Neuroepithelial cells differentiate into neurons and glial cells.

Neurulation in Humans

• The stages display the developmental changes at specific time points.
• Events include neural plate formation, neural fold formation, closure of the neural tube.
• Important structures such as neuropores are visible.

Differentiation of the Neural Tube: Cranial Vesiculation

• Developmental processes (vesiculation) lead to primary (forebrain, midbrain, hindbrain) and secondary brain vesicles.
• Vesicles become distinctive areas in the mature brain (e.g., telencephalon).

Derivatives of Three Primary Vesicles

• Forebrain (Prosencephalon) develops into the cerebrum, thalamus, and hypothalamus.
• Midbrain (Mesencephalon) forms the midbrain.
• Hindbrain (Rhombencephalon) gives rise to the pons, cerebellum, and medulla oblongata.

Neurogenesis

• Neural stem cells differentiate into neurons and glial cells.
• Neurons migrate and develop axons and dendrites, forming synapses.

Neuronal Formation

• There are 10¹¹ neurons and 10¹² glial cells in the nervous system.
• Oligodendrocytes are CNS glial cells, and Schwann cells are PNS glial cells.

Spinal Cord

• The spinal cord develops from the caudal end.
• Cells form the alar plate (dorsal horn) and basal plate (ventral horn).

Neural Crest

• Cells along neural plate edges form the neural crest.
• These cells break away from the neural tube and migrate.
• They differentiate into diverse cell types.
• Derivatives include cranial, circumpharyngeal, and trunk neural crest cells.

Neural Crest Derivatives

• Neural crest cells differentiate into neurons, glia, sensory, autonomic, and enteric ganglia.
• They contribute to adrenal medulla, melanocytes, cartilage, and bone.
• They respond to signals for their fate.

Neural Crest: Endocrine and Paraendocrine Derivatives

• The neural crest cells are crucial for adrenal medulla, smooth dermal muscles and paraendocrine tissue formation.

Neural Crest: Other Derivatives

• Pigment cells, anterior facial cartilage, connective tissue components are derived from neural crest cells.
• The neural crest is a crucial part of the nervous system.
• These include the cornea, tooth papillae, salivary glands, lacrimal glands, thymus, thyroid, pituitary, as well as adipose tissue.