Development of The Nervous System Flashcards
What are the three utero development stages in humans?
- Pre-embryonic: conception to day 14
- Embryonic: day 15 to the end of week 8
- Fetal: week 8 to birth
What occurs during the pre-embryonic stage?
Lasts from conception to approximately day 14.
A single cell begins division as it moves down the uterine tube and into the cavity of the uterus.
During implantation, the inner cell mass develops into the embryonic disk.
What happens during the embryonic stage?
From day 15 to the end of the eighth week, organs begin formation and three primary germ layers form.
What are the three primary germ layers and their developments?
- Ectoderm: develops into sensory organs, epidermis, and nervous system.
- Mesoderm: develops into dermis, muscles, skeleton, excretory and circulatory systems, connective tissue, and mesenchyme.
- Endoderm: develops into lining and glands of the digestive system and lining of the respiratory system.
What characterizes the fetal stage?
Lasts from the end of the eighth week until birth;
organ systems continue growth and development into functional systems. The nervous system develops more fully, and myelination begins.
What are the phases of nervous system formation?
- Neural tube formation (days 18 to 26)
- Brain formation (begins on day 28)
What determines the mature structure of the CNS?
- Cell proliferation
- Folding of expanded tissue sheets
- Migration of individual cells
- Growth of long fiber tracts
From what does the nervous system develop?
The nervous system develops from ectoderm, now called neuroectoderm to distinguish it from other ectoderm.
How is the neural plate made?
Some ectoderm thickens into the neural plate, which develops a neural groove with neural folds on either side.
What forms the neural tube?
The neural folds fuse to form the neural tube (day 18-26—week 4).
What does the neural crest form?
The neural crest will form: 1. Spinal ganglia (DRG)
2. Ganglia of the autonomic nervous system
3. Schwann cells of the PNS
4. Many others (pia mater, arachnoid mater)
What are the cranial and caudal neuropores?
The neural tube remains open at the cranial and caudal ends as the cranial and caudal neuropore; these close during the fourth week: Cranial by day 27, Caudal by day 30.
What develops from the cranial end of the neurotube?
The brain forms from the cranial end of the neurotube, while the rest develops into the spinal cord.
What occurs as the neural tube closes?
Adjacent mesoderm develops into somites.
What are the three derivatives of somites?
- Dermatome: develops into dermis of skin
- Sclerotome: develops into axial skeleton
- Myotome: develops into skeletal muscle
What is the neural canal?
The hollow lumen of the neural tube.
What does the neural canal ultimately form?
The brain ventricles and the central canal of the spinal cord.
What lines the walls of the neural tube?
Neuroepithelium.
What do neuroepithelial cells differentiate into?
Neuroblasts and glioblasts.
What do neuroblast cells develop into?
Neurons.
What do glioblast cells develop into?
Glia (macroglia).
What is the mantle layer?
A new region formed by neuroblasts surrounding the neural canal that will become the gray matter of the spinal cord and brainstem.
What will the cells in the marginal layer become?
The white matter that surrounds the central gray matter.
What are the two layers formed by day 26?
Mantle and marginal layers.
