Porth's Essentials of Pathophysiology, 4e
831
Organization and Control of Neural Function
C h a p t e r 3 4
POSTERIOR Dorsal view
Future neural crest
Neural plate Somites
ANTERIOR
1
Neural plate
Ectoderm
Neural folds
Notochord
Endoderm
Rostral neuropore
Mesoderm
Neural groove
Neural folds
1
Cut edge of amnion
Neural crest
Ectoderm
2 3
2
Neural tube Yolk sac wall Neural groove Neural folds
Somites (mesoderm)
Mesoderm Endoderm
Notochord
Neural groove
Caudal neuropore
Neural tube
Neural crest
Mesoderm
Neural plate
Ectoderm
3
POSTERIOR Dorsal view
A
B
Notochord
Endoderm
Transverse sections
FIGURE 34-5. Folding of the neural tube. (A) Dorsal view of a six-somite embryo (22 to 23 days) showing the neural folds, neural groove, and fused neural tube.The anterior neuropore closes at about day 25 and the posterior neuropore at about day 27. (B) Three cross-sections taken at the levels indicated in A.The sections indicate where the neural tube is just beginning to form.
Segmental Organization Developmentally, the basic organizational pattern of the nervous system is that of a longitudinal series of segments, each repeating the same fundamental pattern that is retained in postnatal life. The CNS and its associated peripheral nerves consist of approximately 43 segments,
CSF-filled cavities, the first and second (lateral) ven- tricles. The remaining diencephalic portion of the neu- ral tube develops into the thalamus and hypothalamus. The neurohypophysis (posterior pituitary) grows as a midline ventral outgrowth at the junctions of segments 1 and 2. A dorsal outgrowth, the pineal body, develops between segments 2 and 3.
Mesencephalon (Midbrain)
Prosencephalon (Forebrain) Optic vesicle
Rhombencephalon (Hindbrain)
(developing eye)
Prosencephalon (Forebrain)
Developing heart
Mesencephalon (Midbrain)
Rhombencephalon (Hindbrain)
FIGURE 34-6. Frontal and lateral views of a 5-week-old embryo showing the brain vesicles and three embryonic divisions of the brain and brain stem.
Spinal cord
Frontal view
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