1. Embryonic Development of the Human Neurological System Chapter 4

2. Embryonic Development of the Human Neurological System (pp. 66-76 in W&A) OVERVIEW Neural plate, which is part of the ectoderm, folds in on itself (neural fold, neural groove), to form the neural tube (Fig 3-25) with the neural crest dorsal to it Neural plate, which is part of the ectoderm, folds in on itself (neural fold, neural groove), to form the neural tube (Fig 3-25) with the neural crest dorsal to it Neural crest (dorsal to neural tube) splits laterally to form ganglia of the PNS, e.g. dorsal root ganglia (Figs 3-28 and 3-34) Neural crest (dorsal to neural tube) splits laterally to form ganglia of the PNS, e.g. dorsal root ganglia (Figs 3-28 and 3-34) Lateral walls of the neural tube thicken to form: Lateral walls of the neural tube thicken to form: –alar plate (dorsal, sensory) and basal plate (ventral, motor) Alar and basal plates (together) develop into Alar and basal plates (together) develop into –central gray matter of spinal cord (Fig 3-29-A) –Nuclei of brainstem (Fig 3-29-B) Neural tube flexes (bends) as the brain develops Neural tube flexes (bends) as the brain develops –Sections separated by flexures develop into different brain structures

3. Embryo, and its early stages of development Embryo: Beginning of third week after conception to end of eighth week after conception Embryo: Beginning of third week after conception to end of eighth week after conception –Beginning of 3 rd week: 3 germ cell layers form Ectoderm (outer) Ectoderm (outer) Endoderm (inner) Endoderm (inner) Mesoderm (between the other two) Mesoderm (between the other two) –Later: Germ cell layers expand and develop to give rise to: Epidermis (of skin) and nervous system (ectoderm) Epidermis (of skin) and nervous system (ectoderm) Linings of digestive and respiratory system (endoderm) Linings of digestive and respiratory system (endoderm) Everything else, ie.., muscles, bone, blood vessels, connective tissue, etc. (mesoderm) Everything else, ie.., muscles, bone, blood vessels, connective tissue, etc. (mesoderm) We’ll focus on ECTODERM

4. Ectoderm, Mesoderm,Endoderm (18 days): Focus on ECTODERM and formation of NEURAL PLATE Neural plate develops in midline portions of ectoderm (neurulation) ( Signals that start neurulation come from notocord)

5. Neural plate FOLDS IN ON ITSELF to begin formation of the neural tube Note neural groove with neural folds along each side, and neural crest dorsally Neural folds move together and begin to fuse to form neural tube Fusion occurs first in the middle, then progresses cranially and caudally

6. Neural plate FOLDS IN ON ITSELF to form neural tube Fusion occurs first in the middle, then progresses cranially and caudally Neural tube and the dorsal neural crest separate from the surface ectoderm. Central canal gives rise to ventricular system of brain, and the central canal of the spinal cord. Somites become muscle, bone.

7. Neural plate FOLDS IN ON ITSELF to form neural tube Fusion occurs first in the middle, then progresses cranially and caudally. Neural tube fully closed at both ends by end of fourth week. (NOTE: spinal bifida and anencehpaly….) Neural crest separates laterally to form sensory ganglia of PNS, which will later send out axonal processes to connect to CNS

8. Lateral walls of the neural tube thicken to form alar plate and basal plate. alar plate (dorsal, sensory) basal plate (ventral, motor) The ganglia send axonal processes to the CNS, and the ventral CNS sends axons to the muscles Note again how neural crest has split to form future (sensory) ganglia of PNS.

9. Alar and basal plates (alar sensory, basal motor) will develop into –central gray matter of spinal cord (Fig 3-29-A) –nuclei of brainstem (Fig 3-29-B)

10. Neural tube flexes (bends) and expands as the brain develops Neural tube flexes (bends) and expands as the brain develops –At the rostral end of the tube, sections separated by flexures develop into different brain structures

11. PRIMARY BRAIN VESICLES (5 th week) SECONDARY BRAIN VESICLES (7 th week) MATURE BRAIN Rhombencephalon (hindbrain) MyelencephalonMedulla oblongata MetencephalonPons and cerebellum Mesencephalon (midbrain) MesencephalonMidbrain Prosencephalon (forebrain) DiencephalonThalamus, epithalamus, hypothalamus, subthalamus TelencephalonCerebral hemispheres, including olfactory system; cortex; basal ganglia

12. Embryonic Development of the Human Neurological System (pp. 66-76 in W&A) OVERVIEW Neural plate, which is part of the ectoderm, folds in on itself (neural fold, neural groove), to form the neural tube (Fig 3-25) with the neural crest dorsal to it Neural plate, which is part of the ectoderm, folds in on itself (neural fold, neural groove), to form the neural tube (Fig 3-25) with the neural crest dorsal to it Neural crest (dorsal to neural tube) splits laterally to form ganglia of the PNS, e.g. dorsal root ganglia (Figs 3-28 and 3-34) Neural crest (dorsal to neural tube) splits laterally to form ganglia of the PNS, e.g. dorsal root ganglia (Figs 3-28 and 3-34) Lateral walls of the neural tube thicken to form: Lateral walls of the neural tube thicken to form: –alar plate (dorsal, sensory) and basal plate (ventral, motor) Alar and basal plates (together) develop into Alar and basal plates (together) develop into –central gray matter of spinal cord (Fig 3-29-A) –Nuclei of brainstem (Fig 3-29-B) Neural tube flexes (bends) as the brain develops Neural tube flexes (bends) as the brain develops –Sections separated by flexures develop into different brain structures