Embryology

Question 1

What is a placode?

Answer 1

A local thickening of the embryonic ectoderm layer that develops into a sensory organ or ganglion.

Question 2

Which week does the neural plate appear?

Answer 2

Third week

Question 3

What is the neural tube and how is it formed?

Answer 3

It begins as the neural plate, which is a placode. The lateral edges of the neural plate elevate and start approaching each other. When the neural folds fuse, they create the neural tube.

Question 4

Where does fusion of the neural tube first occur?

Answer 4

In the cervical region, and then it moves in a cephalic and caudal direction.

Question 5

When does the neuropores close?

Answer 5

At the 18- to 20-somite stage, which is around day 25, the cranial neuropore close, and the caudal one close 3 days later.

Question 6

What are the first three dilations visible on the neural tube (the primary brain vesicles)? And which flexures can be seen?

Answer 6

• prosencephalon (forebrain)
• mesencephalon (midbrain)
• rhombencephalon (hindbrain)
• cervical flexure (junction of hindbrain and spinal cord)
• cephalic flexure (midbrain region)

Question 7

What are the secondary brain vesicles, and which primary vesicles do they develop from?

Answer 7

Prosencephalon -> telencephalon and diencephalon
Mesencephalon -> remains the same
Rhombencephalon -> metencephalon and myelencephalon

Question 8

What is the rhombencephalic isthmus?

Answer 8

It separates the mesencephalon from the metencephalon

Question 9

What is the pontine flexure?

Answer 9

The boundary between metencephalon and myelencephalon

Question 10

What is/are the derivatives of the telencephalon?

Answer 10

Cerebral hemispheres

Question 11

What is/are the derivatives of the diencephalon?

Answer 11

Optic vesicle, thalamus, hypothalamus, pituitary

Question 12

What is/are the derivatives of the mesencephalon?

Answer 12

Anterior (visual) and posterior (auditory) colliculi

Question 13

What is/are the derivatives of the metencephalon?

Answer 13

Cerebellum and pons

Question 14

What is/are the derivatives of the myelencephalon?

Answer 14

Medulla oblongata

Question 15

What brain vesicle does the fourth ventricle develop from?

Answer 15

Rhombencephalon

Question 16

What brain vesicle does the third ventricle develop from?

Answer 16

Diencephalon

Question 17

Where does the cerebral aqueduct (aqueduct of Sylvius) develop from?

Answer 17

Mesencephalon

Question 18

From where does the lateral ventricles develop?

Answer 18

Telencephalon

Question 19

What is the neuroepithelium?

Answer 19

The neuroepithelium is the epithelium lining the wall of the closed neural tube. It is a pseudostratified epithelium that divide rapidly. They give rise to the primitive nerve cells (neuroblasts).

Question 20

What is the mantle layer?

Answer 20

The mantle layer is a zone around the neuroepithelial layer consisting of neuroblasts. It gives rise to the gray matter of the spinal cord.

Question 21

What is the marginal layer in the spinal cord?

Answer 21

The marginal layer is the zone around the mantle layer consisting of the nerve fibers arising from the neuroblasts bodies lying in the mantle layer. It will become the white matter of the spinal cord.

Question 22

What are the basal plates of the spinal cord?

Answer 22

The ventral thickenings of the spinal cord that will form the motor area

Question 23

What is the alar plate of the spinal cord?

Answer 23

The alar plate is the dorsal thickenings of the spinal cord that will give rise to the sensory areas.

Question 24

In which sections of the spinal cord does the intermediate horn exist?

Answer 24

Contains the neurons of the sympathetic portion of the autonomic nervous system (ANS). Present at thoracic levels (T1-T12) and upper lumbar levels (L2 or L3).