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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 1 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). 2 MCQ The hypothalamus is involved in regulation of: a) b) c) d) Food consumption Body heat Water intake All of above 3 MCQ The cingulate gyrus a) Is a medial structure of the cortex. b) Is located in the brainstem c) Is located in the cerebellum d) Is a lateral structure of the cortex 4 Cingulate Gyrus 5 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 6 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 7 Colliculi = Corpora Quadrigemina 8 MCQ Which is part of the cortical spinal tract? a) Internal Capsule b) Lateral Geniculate Nucleus c) Dura mater d) Cerebellum 9 Internal Capsule 10 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 11 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 12 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 13 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 14 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 15 Blastocyst Embryoblast Blastocyst Trophoblast 16 Blastocyst Uterine stroma Trophoblast cells Embryoblast Blastocyst cavity 17 The first week 18 The second week: Bilaminar Embryo Embryo has two primary layers: Epiblast & Hypoblast Cytotrophoblast Amniotic Cavity Epiblast Hypoblast Primary Yolk Sac Exocoelomic Membrane 19 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 20 Third week: Trilaminar Embryo Develops 21 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 22 Week 3 Primitive Streak Forms dorsally Forms neural tube, notochord (cartilaginous rod, future spine) and neural crest cells 23 Presomite Embryo – 18 days Cut edge of amnion Neural plate Primitive pit Primitive streak (mesoderm) 24 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 25 Presomite Embryo – 20 days Cut edge of amnion Neural groove Somite Primitive streak 26 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 27 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 28 Human Embryo – 23 days Cranial neuropore Pericardial bulge Caudal neuropore 29 Week 5 Prosencephalon Develops – Telencephalon (cortex) – Diencephalon (thalamus, hypothalamus) Mesencephalon Develops (mid brain) Rhombencephalon – Metencephalon (pons, cerebellum) – Myelencephalon (medulla) 30 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 31 Third Trimester All structures present at birth All structures become more distinct in Third Trimester Commissures develop 32 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 33 Seven Steps of CNS Development 1. 2. 3. 4. 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) 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 34 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. 35 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 36 Rate of Myelination Varies Spinal tract completed by 9th month Major motor tracts by 2 years Cerebrum and Cerebellum into the teens 37 Abnormal Development Anencephaly Anencephalic – Cerebral Hemispheres reduced or missing – More common in Females Cranial Bifidum – Bone fusion presented by brain or spinal cord protruding through skull 38 Anencephalic Newborn 39 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 40 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 41 Causes of hydrocephalus 42 Hydrocephalus Treatment Many adults had developmental hydrocephalus with no problems Others need urgent surgery 43 Microcephaly Brain and Skull cap are small Face is normal Mental Retardation 44