The structure and development of the nervous system

Question 1

Neurolation

Answer 1

Neurulation refers to the folding process in vertebrate embryos, which includes the transformation of the neural plate into the neural tube. The embryo at this stage is termed the neurula.

Question 2

Neuroectoderm

Answer 2

The portion of the outermost embryonic germ layer (the ectoderm) that based upon its proximity to the mesodermally derived notochord differentiates into a field of multipotent neural stem cells that give rise to the entire nervous system (CNS and PNS).

Question 3

Notochord

Answer 3

A transient, cylindrical structure of mesodermal cells underlying the neural plate (and later the neural tube) in vertebrate embryos. Source of important inductive signals for neural development.

Question 4

Neural plate

Answer 4

The thickened region of the dorsal ectoderm of a neurula/vertebrate embryo that gives rise to the neural tube.

Question 5

Ectoderm

Answer 5

The most superficial of the three embryonic germ layers; gives rise to the nervous system and epidermis.

Question 6

Mesoderm

Answer 6

The middle of the three embryonic germ layers; gives rise to muscle, connective tissue, skeleton, and other structures.

Question 7

Neural tube

Answer 7

The primordium of the brain and spinal cord; de- rived from the neural ectoderm.

Question 8

A primordium

Answer 8

in embryology, is an organ or tissue in its earliest recognizable stage of development.[1] Cells of the primordium are called primordial cells.

Question 9

Neural induction

Answer 9

The mechanism by which ectodermal cells, in response to local signals available in the embryo, acquire neural stem cell identity.

Question 10

Gastrulation

Answer 10

Gastrulation begins as the local invagination of a subset of cells in the very early embryo (which starts out as a single sheet of cells). By the time invagination is complete, the embryo consists of three layers of cells called the germ layers: an outer ectoderm; a middle mesoderm (these cells initiate the invagination that defines gastrulation); and an inner endoderm

Question 11

Answer 11

During late gastrulation and early neurulation, the notochord forms by invagination of the mesoderm in the region of the primitive streak. The ectoderm overlying the notochord becomes defined as the neural plate.

Question 12

Answer 12

As neurulation proceeds, the neural plate begins to fold at the midline (adjacent to the notochord), forming the neural groove and, ultimately, the neural tube. The neural plate immediately above the notochord differentiates into the floorplate, whereas the neural crest emerges at the lateral margins of the neural plate (farthest from the notochord).

Question 13

Answer 13

Once the edges of the neural plate meet in the midline, the neural tube is complete. The mesoderm adjacent to the tube then thickens and subdivides into structures called somites—the precursors of the axial musculature and skeleton.

Question 14

Answer 14

As development continues, the neural tube adjacent to the somites becomes the rudimentary spinal cord, and the neural crest gives rise to sensory and autonomic ganglia (the major elements of the peripheral nervous system). Finally, the anterior ends of the neural plate (anterior neural folds) grow together at the midline and continue to expand, eventually giving rise to the brain.

Question 15

What are Somites

Answer 15

Somites are blocks of mesoderm that are located on either side of the neural tube in the developing vertebrate embryo. Somites are precursor populations of cells that give rise to important structures associated with the vertebrate body plan and will eventually differentiate into dermis, skeletal muscle, cartilage, tendons, and vertebrae. Somites also determine the migratory paths of neural crest cells and of the axons of spinal nerves.

Question 16

Spina bifida

Answer 16

Failure of the posterior neural tube to close completely.

Question 17

Spina Bifida remedy.

Answer 17

Folic acid to mothers reduce the risk with 50-70%.

Question 18

Neural crest

Answer 18

A transient region where the edges of the folded neural plate come together, at the dorsalmost limit of the neural tube. Gives rise to neural crest cells that migrate to become a variety of cells types and structures, including peripheral sensory neurons, enteric neurons, and glial cells as well as facial bones, teeth, and melanocytes in the skin.

Question 19

Neural crest cells

Answer 19

Cells that migrate to become a variety of cells types and structures, including peripheral sensory neu- rons, enteric neurons, and glial cells.

Question 20

Answer 20

Cross section through a developing mammalian embryo at a stage similar to that seen in Figure 22.1B. The neural crest cells are established based on their position at the boundary of the embryonic epidermis and neuroectoderm. Arrows indicate the initial migratory route of undifferentiated neural crest cells.

Question 21

Answer 21

Four distinct migratory paths lead to differentiation of neural crest cells into specific cell types and structures. Cells that follow pathways 1 and 2 give rise to sensory and autonomic ganglia, respectively. The precursors of adrenal neurosecretory cells migrate along pathway 3 and eventually aggregate around the dorsal portion of the kidney. Cells destined to become non-neural tissues (for example, melanocytes) migrate along pathway 4. Each pathway permits the migrating cells to interact with different kinds of cellular environments, from which they receive inductive signals.

Question 22

What happens to crest cells that follow pathways 1 and 2?

Answer 22

They give rise to sensory and autonomic ganglia, respectively.

Question 23

What happens to crest cells that follow pathway 3?

Answer 23

They are the precursors of adrenal neurosecretory cells and eventually aggregate around the dorsal portion of the kidney.

Question 24

What happens to crest cells that follow pathway 4?

Answer 24

They are cells destined to become non-neural tissues (for example, melanocytes).

Question 25

Cell types of the neural tube

Answer 25

Neural precursor cells (neural stem cells)

• neurons
• astrocytes
• oligodendroglia

Neuroepithelium

• Floorplate
• Roofplate

Neural crest cells

Question 26

Mitogenic effect

Answer 26

A mitogen is a peptide or small protein that induces a cell to begin cell division: mitosis. Mitogenesis is the induction (triggering) of mitosis, typically via a mitogen. The mechanism of action of a mitogen is that it triggers signal transduction pathways involving mitogen-activated protein kinase (MAPK), leading to mitosis.

Question 27

Bone morphogenetic proteins (BMPs)

Answer 27

Peptide hormones that play important roles in neural induction and differentiation.

Question 28

Retinoic acid (RA)

Answer 28

A derivative of vitamin A that acts as an inductive signal during early brain development.

Question 29

Sonic hedgehog (Shh)

Answer 29

An inductive signalling hormone essential for the development of the mammalian nervous system; believed to be particularly important for establishing the identity of neurons in the ventral portion of the developing spinal cord and hindbrain.

Question 30

Wnt

Answer 30

A large family of secreted ligands that regulate stem and precursor cell proliferation, transcriptional activation/ repression, and differentiation within and beyond the nervous system.

Question 31

Cell proliferation

Answer 31

Cell proliferation is the process by which a cell grows and divides to produce two daughter cells.

Question 32

Transcription

Answer 32

Transcription is the process of making an RNA copy of a gene sequence. This copy, called a messenger RNA (mRNA) molecule, leaves the cell nucleus and enters the cytoplasm, where it directs the synthesis of the protein, which it encodes.

Question 33

Transcriptional activator

Answer 33

A transcriptional activator is a protein (transcription factor) that increases transcription of a gene or set of genes.

Question 34

Transcriptional repressor

Answer 34

In molecular genetics, a repressor is a DNA- or RNA-binding protein that inhibits the expression of one or more genes by binding to the operator or associated silencers. A DNA-binding repressor blocks the attachment of RNA polymerase to the promoter, thus preventing transcription of the genes into messenger RNA.

Question 35

Cellular differentiation

Answer 35

Cell differentiation is the process through which a cell undergoes changes in gene expression to become a more specific type of cell. The process of cell differentiation allows multi-cellular organisms to create uniquely functional cell types and body plans.

Question 36

Notch signalling

Answer 36

1. Notch signalling is crucial for early proliferation/differentiation control and symmetric/asymmetric cell division
2. Notch represses the expression of pro-neuro (neurogenic) factors

Question 37

Neuronal polarization

Answer 37

Neuronal polarization establishes distinct molecular structures to generate a single axon and multiple dendrites.

Question 38

How does an axon find its target?

Answer 38

1. Ligands in environment (=axon guidance cues) stimulate receptors on growth cone
2. Intracellular signaling cascade that locally alters actin cytoskeleton in growth cone and changes behavior (ie. stops, turns etc)
3. Axon is directed to correct target