1 CNS Development

7/31/2019 1 CNS Development

1/43

The Nervous System

SMS 1084

Dr. Mohanad R. Alwan

1


2/43

The Nervous System

SMS 1084

Dr. Mohanad R. Alwan

12 June 2007 CNS1.ppt 2


3/43

Stages and Time Frames

Ovum

Zygote

Morula

Blastocyst Embryo

Fetus

(Oh, Zee my baby eats fast)


4/43

Stages of fertilization

(1) 12-30 hours first cell division

(2) 3 days division continues until a solid ball is formed

(3) 5 days continue to divide, but cells move toward

outer edge of blastocyst(4) 6 days cells begin to move inward

(5) 8 days beginning of embryonic disc & zygote

becomes attached to the uterus

(6) 14 days zygote is completely attached to the uterus

and embryonic disc is fully formed


5/43


6/43

Begins at the full formation of embryonic disc:

i. Mesoderm: contains chemical signals for various areasof nervous system; directs formation

ii. Endoderm: forms everything else

iii. Ectoderm: forms nervous system (brain), fingernails,hair, and skin. Changes:

1. Thickens in the middle (neural plate)

2. Groove starts to form (neural groove)

3. Groove closes to form tube (neural tube)a. At the top of canal is neural crest, forms PNS

Embryonic stage (14 days 8 weeks):


7/43

Similar in all "Amniotes"

Blastoderm over yolk sac

three "germ layers"

Ectoderm ("outside skin")

Mesoderm ("middle skin")

Endoderm ("inner skin")

7

Development of the CNS


8/43

Nervous System Development

1) At 18 days after conception the embryo begins to

implant in the uterine wall. It consists of 3 layers of

cells: endoderm, mesoderm, and ectoderm.

Thickening of the ectoderm leads to thedevelopment of the neural plate (inserts).

2) The neural groove begins to develop at 20 days.

8


9/43


Develops from Ectoderm

Rising of neural folds

Sinking of neural plate

forms neural groove Folds fuse to complete

neural tube

9


10/43


Again

Neural tube forms CNS

(esp. spinal cord)

Expands anteriorly to formbrain

Peripheral nerves develop

from lateral "neural crest"

cells

10


11/43


3. At 22 days the neural groove closes along the

length of the embryo making a tube.

4.A few days later 4 major divisions of the brain are

observable the: Telencephalon,

Diencephalon,

Mesencephalon, and

Rhombencephalon.

11


12/43

Nervous System Development in the Human

Embryo


13/43


14/43


15/43

Expansion of Brain

Primary

Forebrain

Midbrain

Hindbrain

15


16/43

Expansion of Brain

Secondary

Forebrain

Telencephalon

Diencephalon

Midbrain

remains just midbrain

Hindbrain Cerebellum

Brain stem

16


17/43

Then further differentiation into 5 secondary vesicles:


18/43


19/43

Expansion of Brain

Final development

Telencephalon = cerebrum

Diencephalon = thalamus + hypothalamus

Cerebellum

Brain stem = Midbrain + pons + medulla

oblongata

19


20/43


21/43

Expansion of Brain


22/43


23/43

Expansion of Brain


24/43


25/43

24-hr Chick22-23 days pf Human

Expansion of Brain


26/43

23-26 days of Human


27/43


28/43

Differentiation of the Neural Tube

Histological changes

1. Neural tube initially a single layer of cells: germinal

epithelium

2. Cells are called neural stem cells Neurons

Glial Cells: Myelin sheath


29/43

Origin of PNS Cells

From neural tube: All motor neurons of somatic nervous system

Preganglionic neurons of autonomic system

From neural crest:

Sensory nerves and associated ganglia

Postganglionic neurons of autonomic system


30/43


31/43

Neural Crest Cells

Induced by organizing cells of notochord Main functional groups:

Cranial neural crest:

Bones and connective tissue of face

Tooth primordia

Thymus, parathyroid, thyroid glands

Sensory cranial neurons

Parasympathetic ganglia and nerves Parts of the heart (cardiac neural crest)


32/43

Neural Crest Cells

Main functional groups: Trunk neural crest:

Melanocytes

Sensory neurons

Sympathetic ganglia and nerves

Medulla of adrenal glands


33/43

Differentiation of Neurons

Within nerve tube: Dorsal Interneurons

VentralMotor neurons


34/43

Differentiation of Neurons

Motor neurons:

Tissues they innervate depends on:

Anterior-posterior location along the nerve tube

When the cells were born


35/43

Fetal Period: Two Months to Birth (38 weeks)


36/43

Fetal Period

Foundation for the entire CNS is set

6 stages of CNS development complete the

prenatal process

Si S f S l


37/43

Six Stages of Nervous System Development


38/43

1. Mitosis (cell division) or Neurogenesis in theventricular zone, One cell division can lead to a daughter

cell, will divide again forming an immature neuron

2. Migration: cells move from VZ to their destination; thismigration is aided by glial cells, abnormal migration found

in a number of disorders

Abnormalities in migration are presentin people withlearning disabilities, schizophrenia and autism (more onthis in a little while)


39/43

3. Differentiation: The Process which gives rise tospecific neurons and glial cells

4. Synaptogenesis: Neuronal maturation

1. Elongation of axons (w/growth cones)

2. Establish terminals

3. Elongation of dendrites

4. Expression of NT

Neurotrophic factors

stimulate cell growth, i.e.nerve growth, factor helps neuron to mature.


40/43

5. Normal cell death (more on this later)

- Apotosisactive cell death duringdevelopment

- Necrosis passive cell death due to injury

6. Synaptic rearrangement: dependent onapotosis and experience!!!!


41/43

Cellular Development of the Postnatal Brain

Cells of the Cerebral Cortex


42/43

Brain Development Occurs in Waves through

Age 21

Temporal

Parietal

Limbic Frontal


43/43

Documents

1 CNS Development