Chapter 4 Embryological Development of CNS

1. 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

2. The parasympathetic system: Conserves and restores energy Facilitates digestion and absorption of nutrients Facilitates excretion of waste products All of the above 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).

3. The hypothalamus is involved in regulation of: Food consumption Body heat Water intake All of above MCQ

4. 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 MCQ

5. Cingulate Gyrus

6. 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 MCQ

7. 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 MCQ

8. Colliculi = Corpora Quadrigemina

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

10. Internal Capsule

11. 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

12. 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

13. 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

14. 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

15. 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

16. Blastocyst • Embryoblast • Blastocyst • Trophoblast

17. Blastocyst Uterine stroma Trophoblast cells Embryoblast Blastocyst cavity

18. The first week

19. The second week: Bilaminar Embryo • Embryo has two primary layers: Epiblast & Hypoblast Cytotrophoblast Amniotic Cavity Epiblast Hypoblast Primary Yolk Sac Exocoelomic Membrane

20. 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

21. Third week: Trilaminar Embryo Develops

22. 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

23. Week 3 • Primitive Streak Forms dorsally • Forms neural tube, notochord (cartilaginous rod, future spine) and neural crest cells

24. Presomite Embryo – 18 days Cut edge of amnion Neural plate Primitive pit Primitive streak (mesoderm)

25. 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

26. Presomite Embryo – 20 days Cut edge of amnion Neural groove Somite Primitive streak

27. 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

28. 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

29. Human Embryo – 23 days Cranial neuropore Pericardial bulge Caudal neuropore

30. Week 5 • Prosencephalon Develops • Telencephalon (cortex) • Diencephalon (thalamus, hypothalamus) • Mesencephalon Develops (mid brain) • Rhombencephalon • Metencephalon (pons, cerebellum) • Myelencephalon (medulla)

31. 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

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

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

34. Seven Steps of CNS Development • Production of initial neurons and glial cells • Migration of cells to definitive location • Selective gathering of cells to functional group • Cytodifferentiation (axon, dendrite, synaptic patterns) • Selective death of some cells in groups (Apoptosis) • Outgrowth of axons to specific target cells and establishment of connections • Elimination of certain connections and functional stabilization of others

35. 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.

36. 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

37. Rate of Myelination Varies • Spinal tract completed by 9th month • Major motor tracts by 2 years • Cerebrum and Cerebellum into the teens

38. 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

39. Anencephalic Newborn

40. 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

41. 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

42. Causes of hydrocephalus

43. Hydrocephalus Treatment • Many adults had developmental hydrocephalus with no problems • Others need urgent surgery

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