Neuro Lab 5, Nervous System Development

What are the developmental stages in Utero?

1. Pre embryonic or germinal

2. Embryonic 

3. Fetal Stage 

What is Pre embryonic or germinal?

a developmental stage in utero

Lasts from conception to 2 weeks

Fertilization, Single Cell, Cell division Blastocyst formation

What is Embryonic

A developmental stage in Utero 

2-8 weeks formation of organs

Ectoderm, Mesoderm, Endoderm made 

What is the Ectoderm?

• Outer Cell Layer

gives rise to the nervous system (Spinal cord, brain, and peripheral nerves and sensory organs) and epidermis

What is the Mesoderm? 

• Middle Cell Layer

• Develops into the dermis, muscles, skeleton, excretory and circulatory system

What is the Endoderm?

• Inner Cell layer

• differentiates into gut, liver, pancreas, and respiratory system

What is the Fetal Stage?

part of the developmental stages in Utero

• Brain and cellular level development continues till birth to divide into a systematic nervous system, and also in the natal stages 

List the order of development of the embryo

1. egg

2. zygote'

3. 2 cell stage

4. 4 cell stage

5. morula

6. blastocyst

What is Gastrulation?

Formation of the trilaminar embryonic disk (ectoderm, mesoderm and endoderm) from bilayered (epiblast and hypoblast) embryo (during week 3)

What is Notochord?

Acellular rod that forms the primary axis skeleton of a three layered
embryo and provides cell signaling for the midline of the embryo (during week 3). '

Arises from the mesoderm

What is Neurulation?

Neural tube formation (during week 3 and 4)

What does Neurulation include?

Neural plate

Neural Groove

Neural Tube

Neuropores

Neural Crest

What is the Neural Plate? 

Longitudinal thickening of the ectoderm induced by the Notochord

What is the Neural Groove?

Invagination of neural plate flanked by neural folds becomes this groove

What is the Neural Tube?

Neural folds fuse to form this tube

• develops into the brain and spinal cord. The central
  The cavity of the neural tube develops
  into the ventricles of the brain and
  central canal of the spinal cord

What are Neuropores?

Open ends of the neural tube until closure

What is the Neural Crest? 

Some neural fold cells migrate laterally

• differentiate, and develop into sensory neurons, autonomic neurons,
  myelin cells, and some endocrine organs. In other words, it forms
  PNS with the exception of motor neuron axons.

The Cellular Nervous System Development includes: 

1. Neurogenesis 

2. Cell migration 

3. Cell differentiation: Neurons 

4. Process outgrowth and Synaptogenesis 

5. Neuronal Death and Synaptic rearrangement 

What is Neurogenesis?

Formation of neurons from undifferentiated stem cells or progenitor cells. Glial cells are also produced during neurogenesis

What is Cell Migration?

Migration of immature neurons to their destinations in the embryo. They send a process to the brain surface and lift them along the process or climbing along radical glia

What is Cell Differentiation: Neurons?

differentiate after reaching their final location. Function and appearance of
Neurons depend on the location of migration.

What is the process outgrowth and Synaptogenesis?

Growth of axons and dendrites. Growth cone, the forward end of an axon contacts its target cell and forms synapse.

What is Neuronal death and synaptic rearrangement?

Neurons failed to establish connections die during
development. Lifelong synaptic rearrangements occurs based on
activities.

What is the Brain Development?

The closing of the superior (Cranial) Neuropore marks the development of the future brain

• Neural tube expands to form three enlargements

What is the Forebrain?

Embryonic brain regions

• Telencephalon

• Diecephalon

Brain structures in a child and an adult

• Cerebrum

What is the Midbrain?

Embryonic brain regions

• Mesencephalon 

Brain structures in children and adult 

• Midbrain (part of the brainstem)

What is the hindbrain?

in Embryonic brain regions

• Metencephalon

• Myelencephalon

In brain structures in child and adult

• Pons

• Medulla Oblongata

What are Somites?

Part of Spinal Cord Development

• As the inferior neural tube closes (caudal neuropore), adjacent
  mesoderm divides into spherical cell clusters

three types-

• Sclerotome → becomes vertebrae and skull

• Myotome → becomes skeletal muscle

• Dermatome → Becomes dermis

also determine the migratory paths of neural crest
cells and of the axons of spinal nerves.

What is the Marginal Layer? 

• Outer wall 

• Contains processes of cell bodies present in mantle
  layer and becomes white matter in fetal stage containing axons and glial cells.

What is the Mantle Layer?

• Inner wall

• Contains cell bodies and becomes gray matter in fetal
  stage.

What is the Ependymal Layer?

Cells line the opening or lumen of the neural tube

What is the ventral section of developing spinal cord neurons?

Motor plate/ Basal plate (Ventral section)

• Gray matter derived from the basal plate in the mature spinal cord is called the ventral horn. Motor plate cells become motor neurons, which innervate skeletal muscle, and interneurons

What is the Dorsal section of developing spinal cord neurons?

Association plate/ Alar plate (Dorsal section):

Gray matter derived from the association plate in the mature spinal
cord is called the dorsal horn. Association plate cells become interneurons and projection neurons.

Neurons in the dorsal region of the neural tube process sensory information while neurons in the ventral region process
motor information.

What is Anencephaly? 

The formation of a rudimentary brainstem without forming the
cerebral and cerebellar hemispheres

Occurs when the cranial end (cranial neuropore) of the neural tube
remains open, and the forebrain does not develop

The skull does not form over the incomplete brain leaving the
malformed brainstem and meninges exposed

What is Arnold-Chiari Malformation?

Developmental deformity of the hindbrain

• Type I: This type is not associated with defect of lower neural tubes.
  Consists of herniation of the cerebellar tonsils through the
  foramen magnum

Type II: This type is associated with lower neural tube defects.
Consists of a malformation of the brainstem and cerebellum leading
to the extension of the medulla and cerebellum through the foramen magnum

What is Spina Bifida?

Neural tube defect that results when the caudal (inferior)
neuropore does not close properly. The developing vertebrae do not
close around an incomplete neural tube, resulting in a bony defect that
may allow spinal cord and/or meninges to protrude.
• There are four types of spina bifida

What is Spina Bifida Occulta? 

In this condition neuronal tissue does not protrude through the bony defect. Mildest form of spinal bifida (hidden). Spinal cord function is normal.

What is Spina Bifida Meningocele? 

Protrusion of meninges through the bony defect. In some cases, a meningocele may be asymptomatic. In other cases, the spinal cord function is impaired

What is Spina Bifida Meningomyelocele?

Neural tissue with the The meninges protrudes outside the body. This results in abnormal growth of the spinal cord and some degree of
lower extremity dysfunction, often bowel and bladder
control is impaired

What is Spina Bifida with Myeloschisis? 

The most severe defect consists of a malformed spinal cord exposed to the surface of the body; it occurs when the neural folds fail to close