Chapter 4 Embryological Development of CNS

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Chapter 4 Embryological Development of CNS

• Chris Rorden
• University of South Carolina
• Norman J. Arnold School of Public Health
• Department of Communication Sciences and
  Disorders
• University of South Carolina

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MCQ
The sympathetic division typically functions in
actions requiring quick responses. The
parasympathetic division functions with actions
that do not require immediate reaction. The main
actions of the parasympathetic nervous system are
summarized by the phrase rest and digest" (in
contrast to the "fight-or-flight" of the
sympathetic nervous system). A useful acronym
used to summarize the functions of the
parasympathetic nervous system is SLUDD
(salivation, lacrimation production of tears,
urination, digestion and defecation).

• The parasympathetic system
• Conserves and restores energy
• Facilitates digestion and absorption of nutrients
• Facilitates excretion of waste products
• All of the above

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MCQ

• The hypothalamus is involved in regulation of
• Food consumption
• Body heat
• Water intake
• All of above

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MCQ

• The cingulate gyrus
• Is a medial structure of the cortex.
• Is located in the brain-stem
• Is located in the cerebellum
• Is a lateral structure of the cortex

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Cingulate Gyrus
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MCQ

• Functions of the brainstem include
• Swallowing, respiration, and blood pressure
  regulation
• Vision, language, and muscle coordination
• Emotional memory, executive function, and visual
  processing
• Calculation, reading, and writing

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MCQ

• The Colliculi
• Are located on the anterior brainstem
• Are located on the posterior brainstem
• Are located on the ventral frontal lobe
• Are located in the insula

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Colliculi Corpora Quadrigemina
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MCQ

• Which is part of the cortical spinal tract?
• Internal Capsule
• Lateral Geniculate Nucleus
• Dura mater
• Cerebellum

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Internal Capsule
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Chromosomes and genes

• Humans have 46 Chromosomes
• Roundworm 2
• Chimps 48
• Amoeba 50
• Butterflies 380
• 22 pairs are alike in both sexes
• 1 pair determines sex
• X (female) or Y (male)
• Genome is all DNA in all chromosomes
• A Gene is the sequence of DNA required for a
  product to be expressed (proteins, enzymes)

Chromosome during division
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Types of Division

• Mitosis
• For general body growth and function
• Regularly occurring for much of our body during
  our entire life
• Meiosis
• Special division during reproduction

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Gametogenesis (involves meiosis)

• Meiosis cell division where number of pairs is
  cut in half
• Process of forming reproductive units
• Gametes
• Male Spermatozoa
• From puberty through adult life
• Female Ovum
• Completed prior to birth 2 million
• Oocyte germ cell

Chris Rorden Oocyte like oah in noah Meiosis
like my
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Zygote (fertilized egg)

• Produced from combination of male and female
  parent chromosomes
• Mitotic Division Begins
• New Cells called Blastomeres which form a Morula

Two-cell Stage
Four-cell Stage
Morula 3 days
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Morula

• Morula develops central cavity called Blastocyst
• Blastocyst attaches to uterine wall
• One week from fertilization to implantation in
  uterine wall
• Allows blastocyst to get nutrients and excrete
  waste products

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Blastocyst

• Embryoblast
• Blastocyst
• Trophoblast

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Blastocyst
Uterine stroma
Trophoblast cells
Embryoblast
Blastocyst cavity
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The first week
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The second week Bilaminar Embryo

• Embryo has two primary layers Epiblast
  Hypoblast

Cytotrophoblast
Amniotic Cavity
Epiblast
Hypoblast
Primary Yolk Sac
Exocoelomic Membrane
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When does life begin?

• British Warnock Committee (1984) suggested
  experimentation on the human embryo within the
  first 14 days of its development.
• Because before this time implantation in the
  uterus is not complete
• Because only after this time do the embryo cells
  lose their so-called totipotency Because after
  the 14th day there no longer exists the
  possibility that monozygotic twins could be
  formed from a single embryo.
• Appearance of primitive streak considered as
  the sign of a new human subject

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Third week Trilaminar Embryo Develops
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Week 3

• Embryo Trilaminar three layers between amniotic
  cavity and yolk sac
• Ectoderm future covering (skin, nails, hair,
  but also CNS)
• Mesoderm future muscles, bones, heart
• Endoderm future digestive tract

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Week 3

• Primitive Streak Forms dorsally
• Forms neural tube, notochord (cartilaginous rod,
  future spine) and neural crest cells

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Presomite Embryo 18 days
Cut edge of amnion
Neural plate
Primitive pit
Primitive streak (mesoderm)
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Early Highlights

• Day 18 - Neural plate invaginates (encloses) to
  form neural groove
• Day 22 - Neural Tube Forms
• Becomes brain and spinal cord
• About the same time, Neural Crest Forms
• Becomes cranial and spinal nerve ganglia

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Presomite Embryo 20 days
Cut edge of amnion
Neural groove
Somite
Primitive streak
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Neural Tube

• Anterior 2/3 will form brain
• Caudal 1/3 will form spinal cord
• Day 25 - Cranial opening closes
• Brain has 3 sections
• Prosencephalon
• Mesencephalon
• Rhombencephalon
• Day 27 - Caudal end closes
• Problems cause neural tube defects

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Human Embryo 22 days
Neural fold
somites are masses of mesoderm that will
eventually become skin, skeletal muscle , and
vertebrae.
Optic placode
Somite
Cut edge of amnion
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Human Embryo 23 days
Cranial neuropore
Pericardial bulge
Caudal neuropore
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Week 5

• Prosencephalon Develops
• Telencephalon (cortex)
• Diencephalon (thalamus, hypothalamus)
• Mesencephalon Develops (mid brain)
• Rhombencephalon
• Metencephalon (pons, cerebellum)
• Myelencephalon (medulla)

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Telencephalon

• Optic Vessels - retinae, optic nerve
• Cerebral Hemispheres - Lateral Ventricle
• Medial Connection Corpus Callosum
• Olfactory Lobe
• Corpus Striatum
• (Caudate N. Lenticular N.)
• Cerebral Cortex
• Very primitive though 20 weeks

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Third Trimester

• All structures present at birth
• All structures become more distinct in Third
  Trimester
• Commissures develop

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MCQ

• What is abnormal in this image?
• No gray matter
• No Cerebral Spinal Fluid
• Subcortical band of gray matter
• Looks like a normal brain

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Seven Steps of CNS Development

1. Production of initial neurons and glial cells
2. Migration of cells to definitive location
3. Selective gathering of cells to functional group
4. Cytodifferentiation (axon, dendrite, synaptic
   patterns)
5. Selective death of some cells in groups
   (Apoptosis)
6. Outgrowth of axons to specific target cells and
   establishment of connections
7. Elimination of certain connections and functional
   stabilization of others

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Maturation of CNS

• At birth, all neurons you will ever have present.
• Only a few exceptions (neurons involved w smell)
• Process of myelination signals onset of mature
  function
• Slow process
• Partially completed completed by age 7
• Axons and dendrites not until teens
• Some areas continue to age 70
• Some cells have programmed cell death (Apoptosis)
• tadpoles lose their tails and pigeons' feet
  become unwebbed. Crucial in brain
• Note not all developmental language disorders
  present at birth.

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Myelin Sheaths

• Short Gaps (Nodes of Ranvier) on Axons
• Speed up neural activity
• In CNS, formed by Oligodendrocytes
• Type of Glial Cell
• In PNS, formed by Neurilemmal or Schwann cells

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Rate of Myelination Varies

• Spinal tract completed by 9th month
• Major motor tracts by 2 years
• Cerebrum and Cerebellum into the teens

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Abnormal Development

• Anencephaly
• Cerebral Hemispheres reduced or missing
• More common in Females
• Cranial Bifidum
• Bone fusion presented by brain or spinal cord
  protruding through skull

Anencephalic
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Anencephalic Newborn
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Spinal Bifida

• Spinal Bifida Cystica
• Portions of the meninges or neural tissues not
  enclosed by posterior vertebral arches
• Spina Bifida Occulta
• Dimple on spinal column on top of an opening in
  between vertebrae

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Other Developmental Conditions

• Hydrocephaly
• Enlarged head, brain atrophy mental deficiency
• Excessive production of CSF or obstruction of
  drainage pathways
• http//neurosurgery.seattlechildrens.org/condition
  s_treated/hydrocephalus.asp

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Causes of hydrocephalus
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Hydrocephalus Treatment

• Many adults had developmental hydrocephalus with
  no problems
• Others need urgent surgery

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Microcephaly

• Brain and Skull cap are small
• Face is normal
• Mental Retardation