Embryology Intro

Question 1

The cephalic flexure occurs between which two parts of the brain, and at what angle?

Answer 1

80 degree bend between the midbrain and the diencephalon

Question 2

Ventral =
Rostral =
Dorsal =
Caudal =

Answer 2

ventral - towards the stomach
rostral - towards the nose
dorsal - towards the back
caudal - towards the feet

Question 3

Which end of the blastocyst becomes the caudal end (probably?)

Answer 3

The side that contacts the uterine wall, due to signalling gradients established at implantation.

Question 4

The primitive streak forms at the caudal/rostral end?

Answer 4

Caudal

Question 5

CNS components are derived from endo/ecto/mesoderm?

Answer 5

Ectoderm

Question 6

Differentiate primary vs secondary neurulation

Answer 6

Primary neurulation: Anterior end of NT closes at 23-25 daysProceeds from both directions
From the rhombencephalon caudally
From the future optic chiasm cranially
Site of final closure is the commissural plate which is immediately anterior to the lamina terminalis at the site of the future anterior commissure
Failure → anencephaly
posterior end at 26-27 days
Proceeds craniocaudally
Site of closure is roughly opposite somites 30/31 (~S2 level) more caudal segments formed by different process (secondary neurulation)
Failure → myelomeningocele

Secondary neurulation - (text from ppt comments) Primitive streak has regressed, and forms a pluripotent mass of cells called the caudal eminence or end bud Formation of caudal NT (lower sacral and coccygeal segments) occurs by sequential canalization (4-7gw) and retrogressive differentiation (7wks - birth+) At 28-32 days, aggregate of undifferentiated cells at caudal end (caudal cell mass) develop vacuoles - enlarge - coalesce - make contact with central canal; accessory lumina may remain
Remaining structures are ventriculus terminalis (in the conus) and filum terminale

Question 7

Cauda equina -

Answer 7

These nerves connect the spinal cord segment (eg s2) to the dorsal root ganglion, which resides down near the corresponding vertebral segment.

Question 8

Proliferation occurs near the ventricular surface (near the lumen of the neural tube). Radial migration outward forms the six layers of cerebral cortex.

Answer 8

x

Question 9

Dorsoventral patterning in the spinal cord. What two “plates” form dorsally/ventrally and what end structures do they contribute to?

Answer 9

Basal plate = efferent

Alar plate = afferent (DRG, sensory inputs)