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Chapter 4 Embryological Development of CNS

Chris RordenUniversity of South CarolinaNorman J. Arnold School of Public HealthDepartment of Communication Sciences and DisordersUniversity of South Carolina

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MCQ

The parasympathetic system:

a) Conserves and restores energy

b) Facilitates digestion and absorption of nutrients

c) Facilitates excretion of waste products

d) All of the above

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).

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MCQ

The hypothalamus is involved in regulation of:

a) Food consumption

b) Body heat

c) Water intake

d) All of above

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MCQ

The cingulate gyrus a) Is a medial structure of

the cortex.

b) Is located in the brain-stem

c) Is located in the cerebellum

d) Is a lateral structure of the cortex

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Cingulate Gyrus

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MCQ

Functions of the brainstem include a) Swallowing, respiration, and blood pressure

regulation

b) Vision, language, and muscle coordination

c) Emotional memory, executive function, and visual processing

d) Calculation, reading, and writing

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MCQ

The Colliculi a) Are located on the

anterior brainstem

b) Are located on the posterior brainstem

c) Are located on the ventral frontal lobe

d) 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?

a) Internal Capsule

b) Lateral Geniculate Nucleus

c) Dura mater

d) 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 lifeMeiosis

– 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

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 BeginsNew 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 wallOne 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

Embryoblast

Blastocyst cavity

Uterine stroma

Trophoblast cells

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The first week

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The second week: Bilaminar Embryo

Cytotrophoblast

EpiblastHypoblast

Amniotic Cavity

Primary Yolk Sac

Exocoelomic Membrane

Embryo has two primary layers: Epiblast & Hypoblast

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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.

1. Because before this time implantation in the uterus is not complete;

2. 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.

3. 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 dorsallyForms neural tube, notochord (cartilaginous

rod, future spine) and neural crest cells

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Presomite Embryo – 18 days

Neural plate

Primitive pit

Primitive streak (mesoderm)

Cut edge of amnion

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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

Neural groove

Somite

Primitive streak

Cut edge of amnion

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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

Optic placode

Somite

Cut edge of amnion

Neural foldsomites are masses of mesoderm that will eventually become skin, skeletal muscle , and vertebrae.

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Human Embryo – 23 days

Pericardial bulge

Cranial neuropore

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 nerveCerebral Hemispheres - Lateral VentricleMedial Connection – Corpus CallosumOlfactory LobeCorpus Striatum

– (Caudate N. & Lenticular N.)Cerebral Cortex

– Very primitive though 20 weeks

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Third Trimester

All structures present at birthAll structures become more distinct in Third

TrimesterCommissures develop

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MCQ

What is abnormal in this image?

A. No gray matter

B. No Cerebral Spinal Fluid

C. Subcortical band of gray matter

D. Looks like a normal brain

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Seven Steps of CNS Development

1. Production of initial neurons and glial cells2. Migration of cells to definitive location3. Selective gathering of cells to functional group4. 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 connections7. 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 OligodendrocytesType of Glial Cell In PNS, formed by Neurilemmal or Schwann

cells

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Rate of Myelination Varies

Spinal tract completed by 9th monthMajor motor tracts by 2 yearsCerebrum 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/conditions_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 normalMental Retardation