Anatomy L12 - Embryo L04 - Development of the Nervous System

Question 1

Describe the process of neurulation.

Answer 1

Ectoderm –> Neuroectoderm –> Neural Plate (folds into) –> Neural Crest (closes into) –> Neural Tube

Question 2

What layer gives rise to most of the peripheral nervous system?

Answer 2

Neural crest cells

Question 3

What degenerates and only persists as the nucleus pulposus of the intervertebral discs?

Answer 3

Notochord

Question 4

What structure separates the dorsal from the ventral aspects of the early spinal cord?

Answer 4

Sulcus limitans

Question 5

What are the embryological terms for dorsal and ventral?

Answer 5

Dorsal = Alar; Ventral = Basal

Question 6

What are bipotential progenitor cells?

Answer 6

Bipotential Progenitor Cells are a population of cells arising from cellular division and maturation in the neural tube that will give rise to either neuronal progenitor cells or glial progenitor cells.

Question 7

What is the neuronal progenitor cell lineage?

Answer 7

The neuronal progenitor cells give rise to cells that make up the functional aspect of the nervous system, that is, the neurons.

Question 8

What is the glial progenitor cell lineage?

Answer 8

The glial progenitor cell lineage gives rise to cells that make up the support network of the nervous center, that is, the neuroglia.

Question 9

What is the ventricular layer in the developing spinal cord?

Answer 9

The ventricular layer is the layer immediately surrounding the central canal in the developing spinal cord. Bipotential progenitor cells and ependymal cells are located in the Ventricular Layer.

Question 10

What is the mantle layer in the developing spinal cord?

Answer 10

The mantle layer is the layer inbetween the ventricular layer and the marginal layer that will eventually become the inner spinal grey matter that contains neuronal cell bodies and neuroglia.Postmitotic neurons and glioblasts migrate outward to form the Mantle Layer.

Question 11

What is the marginal layer in the developing spinal cord?

Answer 11

The marginal layer in the developing spinal cord is the outermost layer of the developing spinal cord that will eventually become the spinal white matter. Neuronal processes migrate to surround the developing grey matter and form the marginal layer.

Question 12

What is the function of BMP4 and 7?

Answer 12

BMP4 and 7 act to differentiate the developing spinal cord into the roof plate. BMP4 upregulates a cascade of TGF-Beta proteins, including dorsalin, that establish the roof plate.

Question 13

What is the function of SHH?

Answer 13

SHH is secreted in the notochord and establishes additional signalling in the floor plate. It is the overlapping gradient between SHH and BMP4 that determines dorsal/ventral segmentation of the spinal cord in cross section.

Question 14

What is the paraxial mesoderm?

Answer 14

The paraxial mesoderm is made up of the longitudinal blocks of tissue on either side of the notochord and it condenses to form somites that give rise to the axial skeleton and all skeletal muscle (and somitomeres in the head that we shall blissfully ignore).

Question 15

What is the Intermediate mesoderm?

Answer 15

The intermediate mesoderm lies between the paraxial mesoderm and lateral plate mesoderm and gives rise to the urogential system.

Question 16

What is the lateral plate mesoderm?

Answer 16

The lateral plate mesoderm give rise to connective tissue and appendicular skeleton, as well as smooth muscle and connective tissue of the viscera and blood vessels.

Question 17

What is the transverse mesoderm?

Answer 17

The transverse mesoderm is the most cranial aspect of the developing embryo where the heart develops.

Question 18

What are Hox genes?

Answer 18

Hox genes are genes that regulate growth and differentiation in the head. Hox genes track neural development and segmentation of mesoderm into somitomeres. They are responsible for the longitudinal segmentation of animals.Hox genes are remarkably conserved. Differences in segmentation are the result of different patterns of oscillations of the same (homologous) Hox genes.

Question 19

What are oscillation?

Answer 19

Oscillations are pulses of gene expression that control segmentation. The on and off burst of Hox protein expression is responsible for the longitudinal segmentation of mammals.

Question 20

What is the Notch signaling pathway?

Answer 20

The Notch signaling pathway is a highly evolutionarily conserved intercellular signaling pathway that regulates interactions between physically adjacent cells and is extremely essential to proper segmentation. Notch protein accumulates in presomitic mesoderm destined to form the next somite and then decreases as that somite is established. The increase in Notch protein activates other segment-patterning genes that establish the somite.

Question 21

What is the relationshipe between Notch and Retinoic Acid?

Answer 21

Notch signals that the somite is complete and Retinoic Acid induces segmentation by acting as a “cleaver.” Retinoic Acid is expressed at high concentrations cranially and decreases in concentration cuadally, while FGF8 and WNT3a are inversely expressed to establish a gradient. This gradient controls the segmentation clock and activity of the NOTCH pathway.

Question 22

What determines the number of somites generated in an animal?

Answer 22

The clock component oscillations. In snakes, the clock components seem to “tick” around four times faster (relative to growth rate) than in shorter-bodied animals, leading to many more, though smaller, somites.

Question 23

What are the divisions of the somite?

Answer 23

The somite can be divided into three parts: the Sclerotome, the Dermatome, and the Myotome. The Dermatome and the Myotome are collectively referred to as one division known as the dermamyotome.

Question 24

What is the sclerotome?

Answer 24

The sclerotome is the ventromedial division of the somite closest to the notochord and will give rise to cartilage that will then further be ossified (i.e. that part of the somite that gives rise to the skeleton). The sclerotome will completely surround the notochord and turn into the vertebrae. The notochord will remain as the nucleus pulposus of the intervertebral disc.

Question 25

What is the Dermatome?

Answer 25

The Dermatome is a division of the dermamyotome, which is a division of the somite, that gives rise to the dermis (i.e that part of the somite that gives rise to the connective tissue of the dermis). The skin (epidermis) is derived from surface ectoderm, not somite.

Question 26

What is the myotome?

Answer 26

The myotome is a division of the dermamyotome, which is a division of the somite, that gives rise to the muscles.

Question 27

What is resegmentation?

Answer 27

Resegmentation, or second segmentation, is a process that takes place only in the sclerotome (a division of the somite) whereby the rostral and caudal halves of a somite segregate, and re-fuse with their neighboring halves to form vertebrae.

Question 28

What are MyoD and MYF5?

Answer 28

MyoD and MYF5 are members of a family of transcription factors called myogenic regulatory factors that regulate the development of muscle. They are themselves regulated by different signals. MYF5 is responsible for differentiating EPAXIAL muscles (of the deep back).MyoD is responsible for differentiating HYPAXIAL muscles.

Question 29

What is the somatopleure?

Answer 29

The somatopleure is a layer of tissue in a vertebrate embryo comprising the ectoderm and the outer layer of mesoderm, and giving rise to the amnion, the chorion, and part of the body wall. It is the outer aspect of the lateral plate mesoderm that gives rise to somatic structures. It faces inwards, and is located just deep to the surface ectoderm.

Question 30

What is the splanchnopleure?

Answer 30

The splanchnopleure is the interior aspect of the lateral plate mesoderm that gives rise to the splanchnic, or visceral, structures of the body. These include internal organs and other structures innervated by the autonomic nervous system. The splanchnopleure wraps around the gut tube.