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Neural Embryology
Embryology
Question | Answer |
---|---|
Carnegie Stages | Used to characterize embryo development (weeks 2-9). A Carnegie Stage between 1 and 23 is assigned to an embryo based on external features. |
Carnegie Stage 5 | Implantation is complete and planetal circulation begins. The structure is two layers. Outer layer is embryo and amniotic cavity. The inner layer is the egg yolk. |
Carnegie Stages 7-9 | The beginning of neural tube formation. |
Dorsal Induction | A differentiation in the ectoderm which leads to a longitudinal groove forming in the neural plate. |
Ectoderm | Made up of 3 distinct layers: 1) External ectoderm 2) Neural tube 3) Neural crest. |
Neural Crest | The neural crest lies between the external ectoderm and the neural tube. It contains the predecessors of neurons and glial cells. |
Neuropores | Fusion of the neural tube begins in what is to be the cervical region of the spine and begins to spread both caudally and rostrally. The rostral neuropore fuses first, and then the caudal. |
Carnegie Stage 11 | Several things here: 1) Rostral neuropore is closed 2) 2 pharyngeal arches appear 3) Optic vesicle appears 4) 15-20 pairs of somites are present. |
Sulcus limitans | Two lateral longitudinal grooves that appear in the walls of the neural tube. They differentiate alar and basal plates. Alar plate derivatives will eventually be associated with sensory processing. Basal plates will be associated with motor processing. |
Carnegie Stage 13 | Rostral differentiation leads to 5 vesicles. Prosencephalon-telencephalon and diencephalon, mesencephalon, and rhombencephalon-metencephalon and myelencephalon. |
Telencephalon | Forms the cerebral hemispheres |
Diencephalon | Forms the thalamus/hypothalamus. |
Cephalic Flexure | Occurs between the prosencephalon and the mesencephalon, and allows the prosencephalon to bend down and eventually swallow up the mesencephalon. |
Pontine flexure | Occurs between the metencephalon and the myelencephalon, at the location of the future pons. Is implicated in caudal brainstem formation. |
Stage 13 | Four limb buds. A primitive mouth emerges at this point. Additionally, brain begins to differentiate into the three parts. |
Defective closure of the neural tube | Leads to spinal cord defects. |
Carnegie Stage 14 | The pharyngeal arches emerge at this time. |
Pharyngeal Arches | The future basis for cranial nerves. Form on the ventrolateral surface of the embryo |
First pharyngeal arch | Forms much of the face |
Second pharyngeal arch | Forms the hyoid bone. |
Carnegie Stages 17-19 | The telencephalon (cerebral hemispheres), grows rapidly, forming the insula and surrounding it. |
Ventricular System of the CNS | What was formerly the empty cavity of the neural tube, now a continuous series of fluid filled spaces in all major components of the CNS. |
The lateral ventricles | Contained in the cerebral hemispheres |
3rd ventricle | Found in diencephalon |
4th ventricle | Found in the pons and rostral medulla |
5th and 6th months of fetal development | The speech processing regions of the brain begin to slow their growth. Additionally, at this point the baby can now hear sounds! |
Synaptogenesis | Babies are born with only rudimentary cerebral connections between hemispheres. Synaptogenesis comes with learned skills. |