indentation that eventually formw cavity as the neural plate folds into itself, will form cerebral aqueduct/central canal/ventricles.

location of midline axis

portion of neural tube that will form brain/cephalic end, closes ast 26 days post fertilization

failure to close properly will lead to anencephaly 

portion of neural tube that will form the spinal cord, closes at 24 days post fertilization

failure to close will cause spina bifida

segmented collection of mesodermal cells adjacent to developing neural tube- will form skeleton/muscles/connective tissue 

segemented structures reflect our evolution from earlier organisms 

ONTOLOGY RECAPITULATES PHYLOGENY

beginning: thickening of neural plate

end: closure of neuropores

cells of the CNS including:

• multipolar preganglionic motor neurons of ANS (fight-or-flight)
• pseudo-unipolar sensory neurons
• all interneurons (in both sensory and motor processing)
• oligodendrocytes & astrocytes (may reside in pns or migrate to cns)

will become cell of PNS including:

• bipolar sensory neurons (vestibular & auditory systems)
• arachinoid/pia mater cells (meningial) 
• chromaffin cells of adrenal medulla
• pseudo-uniplor sensory neurons ( maj type in somatosensory system)
• microglia
• schwann cells
• multipolar postganglionic motor neurons of ans

Where do neurons develop from?

How do they find their final destination?

Neurons develop from the neuroepithelium in the ependymal layer of the neural tube,

ependymal layer in the lining of theneural tube surrounding central canal

They reach their destination with the help of radial glial cells  (which will differentiate into astrocytes) as a guiding scaffold

1. ependymal (lines ventricles/central canal)

2. mantle (generally becomes grey matter)

3. marginal (generally becomes white matter)

neuroblasts from neurepithelium in ependymal layer migrate to mantle layer (grey matter), where their somas will reside (including interneurons). Future motor neurons will send their axons through the marginal layer (white matter).

Future Sensory neurons (with somas outside spinal cord) will send their axons through the marginal layer and then into the mantle layer.

 white matter forms outside grey matter in spinal cord

neuroblasts from ependymal layer will migrate through mantle zone into marginal zone, marginal zone will further split into specific layer- somas will reside in outer portion of marginal layer while their axons will be sent into inner marginal layer. Mantle layer will disapear later in development.

Grey matter lies outside white in CNS

limiting groove in neural tube (4-6 weeks) that divides (dorsal) alar plate and (ventral) basal plate

this division continues up into the brainstem, but does not enter the diencephalon (there are no more motor neurons after this point)

replaced by the hypothalamic sulcus that continues into di- and telencephalon and divides dorsal structures (sensory) with ventral structures (motor)

dorsal portion of spinal cord that recieves input from axons of sensory neurons and contains somas of interneurons

remember: pseudo-unipolar sensory neuron somas lie outside cord and are derived from neural crest cells

dorsal=alar=sensory=afferent

central portion of  containing somas of motor neurons that receive input from interneuron axons (originating in alar plate) 

 -ends after mesencephalon where there are no more motor neurons

ventral=basal=motor=efferent

encephalization-->

3 major vesicles at 4 weeks

5 major vesicles at 5 weeks & what they will form

prosencephalon (telencephalon + diencephalon), mesencephalon, rhombencephalon (metencephalon + myelencephalon)

telencephalon = cortex + basal ganglia

diencephalon = thalamus + hypothalamus

mesencephalon = midbrain

metencephalon = pons + cerebellum

myelencephalon = medulla

lateral ventricles: telencephalon

3rd ventricle: diencephalon

cerebral aqueduct: mesencephalon

4th ventricle: metencephalon + myelencephalon

central canal: spinal cord

cervical: divides hindbrain and spinal cord

cephalic: between midbrain and hindbrain

pontine: within hindbrain

only cephalic remains in adult brain (causing curved longitudinal axis)