Download Neuronal Development

Neuronal Development
• Dr. Donald Allen
Learning Objectives
1. Describe the normal development of the
nervous system.
2. Describe the pathology of the following
developmental disorders
1.
2.
3.
4.
Neural tube defects
Prenatal exposure to drugs
Cerebral palsy
Abnormal location of cells
3. Describe the changes that occur in the
nervous system during infancy
4. Define and give an example of a critical
period
Three Stages of Human
Development in utero
1. Pre-embryonic
2. Embryonic
3. Fetal
Pre-embryonic
• Fertilization
• Cell Division
• Two groups of cells
– Inner cell mass
– Outer cell mass
Nature|Genetics 2001
Inner cell mass
• Two layers form first
–
–
• Third layer forms in
middle
–
Embryonic stage
• Organogenesis
– Ectoderm
– Mesoderm
– Endoderm
Fetal Stage
• Further development
• Myelination
Development of the Nervous
System
• Occurs during embryonic stage
• Two phases
– Formation of neural tube
– Formation of brain
Day 18 (after fertilization)
• Neural plate – thickening of ectoderm
• Extends from head to tail region
• A groove forms in center of neural plate,
with folds on either side
Neural Plate
Day 22
• The folds grow up and toward each other
– Form neural groove
• When the folds touch, they form the neural
tube
• Neural tube formation starts in the future
cervical region
– The groove closes rostrally and caudally
Neural Crest
• Some cells adjacent to the neural tube
separate from the tube and the ectoderm
• Brown cells on previous slide
Neuropores
•
•
•
•
Open ends of the neural tube
Rostral neuropore closes by day 24
Caudal neuropore closes by day 26
If the neuropores do not close correctly,
there will be neurological problems
Neuropores
More Day 26
• The neural tube divides into two layers
– Mantle layer
– Marginal layer
Neural tube
• Forms almost all of nervous system
• The inside space in the tube
–
• 4 weeks post-fertilization
– Sulcus limitans
– Alar plate (Association plate)
– Basal plate (Motor plate)
Organization of brainstem
• Level of medulla and pons
– Neural tube opens at top
• Same organization of cranial nerve regions
as in spinal cord (somatic/visceral,
sensory/motor)
Sacral Spinal Cord
• Secondary neurulation
Neural Crest Cells
• Cells that separate during formation of
neural tube
• Cells migrate
• Form many different types of cells
– Neurons
– Glia
– Non-neuronal cells
Neuronal and glial derivatives of
neural crest cells
• Sensory neurons of somatic nervous system
– Where are the cell bodies?
• Sensory neurons of some cranial nerves
• Schwann cells of PNS
• Postganglionic neurons of autonomic
nervous system