Embryology, lecture 1.pdf

Development of Spinal Cord & Vertebral Column Color Code: Important Done Doctors Notes Extra explanation OBJECTIVES: Describe the development of the spinal cord from the neural tube....

Development of Spinal Cord & Vertebral Column Color Code: Important Done Doctors Notes Extra explanation OBJECTIVES: Describe the development of the spinal cord from the neural tube. List the layers of the spinal cord and its contents. List subdivisions of mantle & marginal zones. List meningeal layers and describe positional changes of spinal cord. Describe development of vertebral column from sclerotomic portion of paraxial mesoderm. Describe chondrification & ossification stages in vertebral development. Describe spina bifida and its types. The Three Germ Layers: Ectoderm, Mesoderm, Endoderm The Neural Tube is a derivative of the ectoderm.Neural tube gives rise to Spinal Cord and Brain Notochord stimulates neural tube formation which in turn stimulates development of the vertebral column. Notochord acts as an axis which will be formed around it the Vertebral column. It helps in vertebral column development Development of Neural Tube: 1. Ectodermal cells dorsal to notochord thicken to form the neural plate. 2. A longitudinal groove, neural groove, develops in the neural plate. 3. The margins of the neural plate (neural folds) approach to each other and fuse to form the neural tube. neural plate ‫ ﻋﻠﻰ أﻧﮭﺎ ﺗﺗﻛﺛف وﺗﻛون ﻟﻲ ﺷﻛل ﻣﺳطﺢ اﻟﻠﻲ ھو‬ectoderm ‫ ﺑﺗﺣﻔز اﻟـ‬notochord ‫اﻟـ‬ neural groove ‫ ﺑﯾﺑدأ ﯾﺳوي ﻟﻲ ﺷﻛل زﺑدﯾﺔ وھو ﻧﺳﻣﯾﮫ‬neural plate ‫ﺑﻌد ﻛذا ھذا اﻟـ‬ ‫ اﻟﻠﻲ راح ﯾﻠﺗﺣم ﻣﻊ ﺑﻌض وﯾﺗﺳﻛر ﻋﻠﺷﺎن‬neural fold ‫ ﻓﯾﮫ طﯾﺎت ﻧﺳﻣﯾﮭﺎ‬neural groove ‫ﻧﮭﺎﯾﺔ ھذا اﻟـ‬ neural tube ‫ﯾﺳوي ﻟﻲ‬ Development of the Spinal Cord: brain ‫اﻟﺛﻠث اﻷول ﯾﺗﻛون ﻣﻧﮫ ال‬ The spinal cord develops from the caudal 2/3 of the neural tube. The cells of the neural tube are arranged in three layers: ventricular zone mantle zone marginal zone Inner Middle Outer undifferentiated cell bodies of nerve fibers or cells neurons (future grey axons of neurons matter) (future white matter).‫ أول طﺑﻘﺔ )اﻟداﺧﻠﯾﺔ( ﻣﻛوﻧﺔ ﻣن ﺧﻼﯾﺎ ﻏﯾر ﻣﻌروﻓﺔ‬،‫ ﻣﻛون ﻣن ﺛﻼث طﺑﻘﺎت‬neural tube ‫ھﻧﺎ اﻟـ‬ ‫ﻣﺳﺗﻘﺑﻼ‬ ً White matter ‫ واﻟطﺑﻘﺔ اﻷﺧﯾرة )اﻟﺧﺎرﺟﯾﺔ( ﺑﺗﻛون‬،‫ﻣﺳﺗﻘﺑﻼ‬ ً Grey matter ‫اﻟطﺑﻘﺔ اﻟﺛﺎﻧﯾﺔ )اﻟوﺳطﻰ( ﺑﺗﻛون‬ :‫ ﻟذﻟك ﺑﺗﻧﻘﺳم إﻟﻰ ﻗﺳﻣﯾن‬،‫ﻣﺳﺗﻘﺑﻼ‬ ً grey matter ‫ﻣﺛل ﻣﺎ ﻗﻠﻧﺎ اﻟطﺑﻘﺔ اﻟوﺳطﻰ راح ﺗﻛون‬ ‫ﻣﺳﺗﻘﺑﻼ‬ ً Dorsal horn ‫( اﻟﻠﻲ راح ﯾﻛون‬Dorsal alar plate) ‫ اﻟﻘﺳم اﻟﺧﻠﻔﻲ‬-1 Ventral horn ‫( اﻟﻠﻲ راح ﯾﻛون‬Ventral basal plate) ‫ اﻟﻘﺳم اﻷﻣﺎﻣﻲ‬-2 Mantle Layer of Spinal Cord: ‫ﻣﺳﺗﻘﺑﻼ‬ ً Neurons of mantle layer (future grey matter) differentiate into : Dorsal alar plate Ventral basal plate future dorsal horn future ventral horn containing sensory neurons containing motor neurons The 2 areas are separated by a longitudinal groove (sulcus limitans).  Ventral basal plate ‫ واﻟـ‬Dorsal alar plate ‫ﺗﺑدأ اﻟﺧﻼﯾﺎ اﻟﻣوﺟودة ﻓﻲ‬ ‫ ھذا اﻟﺗﻘﺎرب ﺑﯾﺻﯾر ﻟﮫ ﻧﺗﺎﺋﺞ‬،‫ﺗﺗﻛﺎﺛر وﺗﺗﻛﺛف إﻟﻰ ان ﺗﻘﺗرب اﻟﻣﻧطﻘﺗﯾن ﻣن ﺑﻌض‬ Proliferation and bulging of both alar & basal plates result in: Formation of dorsal median septum. Formation of ventral median fissure. Narrowing of the lumen of the neural tube to form a small central canal. The marginal layer (future white matter): increases in size due to addition of ascending, descending & intersegmental nerve fibers and it is divided into : dorsal, lateral and ventral funiculi (white column) Myelination of nerve fibers starts at 4th month & continues during the 1st postnatal year. Motor fibers myelinate before sensory fibers. So, After a nerve injury, both motor and sensory axons have the ability to regenerate and, given a proper pathway. Motor fibers myelination is faster than sensory fibers Meninges: These Are 3 Membranes covering the neural tube: Outer thick dura mater Middle arachnoid mater Inner thin pia mater MESODERMAL in origin ECTODERMAL in origin A cavity appears between the arachnoid & the pia mater (subarachnoid space) becomes filled with cerebrospinal fluid (CSF)..‫ ﻣﺳﺎوي ﻟطول ﻓﻘرات اﻟظﮭر‬spinal cord ‫ﻓﻲ اﻟﺑداﯾﺔ ﯾﻛون طول اﻟـ‬ Positional Changes of Spinal Cord: spinal cord ‫ﻟﻛن ﺑﻌد ﻣﺎ ﺗﺑدأ ﺗﻧﻣو ﻓﻘرات اﻟظﮭر ﺗﺻﯾر أطول ﻣن اﻟـ‬ 1. Initially, the spinal cord occupies the whole length of the vertebral canal. 2. As a result a faster growth of vertebral column, the caudal end of spinal cord (conus medullaris) shifts gradually to a higher level Prenatal periods is consistent of two periods: 1- embryonic period: since fertilization to the end of 8th week 2- fetal period: beginning of 9th week to birth End of embryonic period: Spinal cord at the end of vertebral Shift upward: column Spinal cord at S1 Spinal cord at L3 Spinal cord at L1-L2 Development of the Vertebral Column: The vertebral column develops from the ventromedial parts (sclerotomes) of the somites. The somites develop from the para-axial mesoderm..notochord ‫ ﺗﻘﺳم إﻟﻰ ﺛﻼث أﻗﺳﺎم ﻣن اﻟﯾﻣﯾن واﻟﯾﺳﺎر وﯾﻔﺻل ﺑﯾن اﻟﯾﻣﯾن واﻟﯾﺳﺎر اﻟـ‬mesoderm ‫طﺑﻘﺔ اﻟـ‬ :‫ وھذا اﻟﻘﺳم ﯾﻘﺳم إﻟﻰ ﺛﻼث أﺟزاء‬para-axial mesoderm ‫أول ﻗﺳم ھو اﻟـ‬ Intraembryonic Mesoderm: ‫ ﯾﺗﻛون ﻟﻧﺎ ﻋظﺎم ﻓﻘرات اﻟظﮭر‬Sclerotome ‫ ﻣن اﻟـ‬.. Sclerotome, Dermatome, Myotome Located between Ectoderm & Endoderm EXCEPT in the central axis of embryo where NOTOCHORD is found. Differentiates into 3 parts: 1. Paraxial mesoderm 2. Intermediate mesoderm 3. Lateral mesoderm Paraxial mesoderm divides into segments called ‘somites’. Each somite divides into 3 parts: 1. Dermatome Future skin 2. Myotome Future muscles 3. Sclerotome Future bones DEVELOPMENT OF VERTEBRA: 1. Sclerotome around neural tube: forms vertebral (neural) arch. 2. Sclerotome around notochord: forms body of vertebra. 3. Sclerotome in body wall near to neural tube and notochord: forms costal process ( gives ribs in thoracic region only ). Formation of Body of Vertebra: At 4th week, each sclerotome becomes subdivided into two parts : an cranial part, consisting of loosely arranged cells. a caudal part, of more condensed tissue. The Caudal Part Of each somite fuses with the cranial part of the consecutive somite, around the notochord to form the body of the vertebra, called the centrum. Thus each centrum develops from 2 adjacent sclerotomes. Fate of Notochord: In the region of the bodies of vertebrae: It degenerates Between bodies of vertebrae: It forms the central part, ’nucleus pulposus’ of the intervertebral discs. Annulus fibrosus part of the intervertebral discs is formed by the mesoderm surrounding the notochord. The fused sclerotomes grow dorsally around the neural tube and form the vertebral (neural) arch. Ventrolaterally, costal processes develop that give rise to ribs in thoracic region. Nucleus pulposus developed from the remnants of notochord Annulus fibrosus developed from mesoderm surrounding the notochord Vertebral Development: This picture represents the changes that occurs into 2 stages : chondrification stage and ossification stage. - The chondrification centers appears at 6th week ‫ﺗﻛون اﻟﻌظﺎم ﺑﻧﮭﺎﯾﺔ‬ embryonic period (cartilage):(Pic.B) - And by the (at the end of 8th week) the 3 primary ossification Primary Ossification Stage centers appears (bone): (Pic.c) Mesenchymal Stage Chondrification Stage - And The 5 secondary ossification centers appear at puberty. Fusion of bony halves of vertebral arch occurs at 3-5 years (pic.D). and Fusion of centrum with vertebral arch occurs at 4-6 years (pic.D). All centers unite around 25 years. SO, Ossification starts at the end of embryonic period ( end of 8th week) and ends at adult age 25 years. Stage of fusion Dr.sanaa Notes ( 435 team ) Stage of Secondary Ossification Curvatures of Vertebral Column: Primary curvatures : (concave Secondary curvatures: (convex anterior) anterior) develop prenatally develop postnatally ‫ﻗﺑل اﻟوﻻدة‬ ‫ﺑﻌد اﻟوﻻدة‬ 1.Thoracic 1.Cervical: as a result of lifting 2.Pelvic or Sacral the head 2.Lumbar: as a result of walking Vertebral column is concave anterior during the prenatal period The it convex in 2 areas Cervical - as results when baby is lifting his head Thoracic - as result when the baby walks Spina Bifida Cause: Failure of fusion of the halves of vertebral arches Incidence: 0.04-0.15% Meningo = meninges Sex: more frequent in females myelo = spinal cord ocoele = sac contains fluid or cysist schisis= opening Types: 1.Spina bifida occulta (20%) 2.Spina bifida cystica (80%) Better prognosis The closed type The open type Only one vertebra is affected No clinical symptoms Cystica is the most severe and complex form of Skin overlying it is intact. spina bifida. Sometimes covered by a tuft of hair. It usually involves serious or fatal neurological Usually Doesn't Involve underlying neural problems. tissue. A portion of the nerves and the spinal cord are exposed outside the body Neurological symptoms are present Subdivided into: 1. Spina bifida with meningocoele 2. Spina bifida with meningomyelocoele ‫ھﻧﺎ ﻓﻘط اﻟﻔﻘرة ھﻲ اﻟﻠﻲ ﺗﺄﺛرت وﻣﺎﻓﻲ أي ﺷﻲء طﺎﻟﻊ ﻣن اﻟﺳﺑﺎﯾﻧل ﻛورد‬ 3. Spina bifida with myeloschisis 1.Spina bifida with meningocoele 2.Spina bifida with 3.Spina bifida with myeloschisis meningomyelocoele protrusion of sac containing protrusion of sac containing spinal cord is open due to failure of meninges and cerebrospinal meninges with spinal cord fusion of neural folds. fluid. and/or nerve roots. Failure in development of neural tube and neural fold ‫ھﻧﺎ اﻟﻔﻘرة ﺗﺄﺛرت وطﺎﻟﻊ زي اﻟﻛﯾس داﺧﻠﮫ‬ ‫ھﻧﺎ اﻟﻔﻘرة ﺗﺄﺛرت وطﺎﻟﻊ زي اﻟﻛﯾس داﺧﻠﮫ‬ ‫ھﻧﺎ اﻟﻔﻘرة ﺗﺄﺛرت واﻟﺳﺑﺎﯾﻧل ﻛورد طﺎﻟﻊ وﻣﺎﻓﻲ أي‬ Meninges and CSF Meninges and spinal cord ‫ﺷﻲء ﯾﻐطﯾﮫ‬  Summary Structure Origin Neural tube Ectoderm Spinal cord Caudal 2\3 of the neural tube. Grey matter Mantle layer. White matter Marginal layer. arachnoid mater and pia mater Ectoderm Dura matter mesoderm Vertebral column ventromedial parts (sclerotomes)of the somites. Somaits Para-axial mesoderm. nucleus pulposus Notochord between the bodies of vertebrae. Annulus fibrosus Mesoderm Time Changes 3rd week (early) Three germ cell layers 4th week Each sclerotome becomes subdivided into cranial and caudal part. 6th week Chondrification centers appear. End of 8th week 3 primary ossification centers appear. 4th month Starting of myelination of nerve fibers. During 1st postnatal year Continuation of the myelination of nerve fibers. 3-5 years Fusion occurs (fusion of 2 vertebral arches) 4-6 years Fusion of centrum with vertebral arch. At puberty 5 secondary ossification centers appear. 25 years All centers unite. During development the end of spinal cord shifts its position: at (level of S1), at birth (level of L3), adult position (level of L1-L2).  Questions 1. spina bifida with............. Is a protrusion of sac 2. Mantle zone is a future........... and marginal is zone is containing meninges with spinal cord: a future............ A. Spina Bifida Occulta A. Grey Matter–white matter B. Spina bifida with meningomyelocoele B. Central canal – grey matter C. Spina bifida with meningocele C. White matter – grey matter D. Spina bifida with myeloschisis D. White Matter–central canal 3. 16-Which one of the following regions of spinal cord 4. As a result of fast growth of vertebral column, which contains cell bodies of sensory neurons? part of spinal cord shifts gradually up? A. Alar plate A. Cauda Equina B. Ventricular zone B. Conus Medullaris C. Basal plate C. Clarke's column D. Dorsal funiculus D. Central canal 5. The dorsal alar plate and ventral basal plate are 6. which one of the following periods of life fusion separated by: between vertebral arch & body of vertebra occurs? A. Marginal layer A. 8th week B. Ventricular layer B. Puberty C. Sulcus limitans C. 4-6 years D. Ventral Media Fissure D. Around 25 Years 7. 14-Regarding spina bifida which one of the following 8. Myelination of nerve fibers continues after birth statements is correct? during: A. The Closed Type Is More Frequent Than The A. First 2 Months Open type B. The closed type presents with clinical symptoms. B. First 4 Months C. Spina bifida is due to failure of fusion between C. First 8 Months the halves of vertebral arch. D. In cases of spina bifida with meningocoele, the D. First 12 Months spinal cord is open. Q 1 2 3 4 5 6 7 8 Answers B A A B C C C D  ‫ﷲُ ِﺑﻣَﺎ ﺗَﻌْ َﻣﻠُونَ ﺧَ ﺑِﯾر (‬ ‫ت َو ﱠ‬ ‫ﷲُ ا ﱠﻟذِﯾنَ آ َﻣﻧُوا ﻣِﻧ ُﻛ ْم َوا ﱠﻟذِﯾنَ أ ُوﺗُوا ا ْﻟ ِﻌ ْﻠ َم دَ رَ ﺟَ ﺎ ٍ‬ ‫) ﯾَرْ ﻓَﻊِ ﱠ‬ ‫‪Team leaders‬‬ ‫ﻣﯾﻌﺎد اﻟﻧﻔﯾﻌﻲ ‪ -‬ﻓﮭد اﻟﻧﮭﺎﺑﻲ‬ ‫‪Team members‬‬ ‫ﻏﺎدة اﻟﻘرﻧﻲ ‪ -‬ﺳﺎره اﻟﺑﻠﯾﮭد ‪ -‬ﻋﮭد اﻟﻘرﯾن ‪ -‬ﺑﻠﻘﯾس اﻟراﺟﺣﻲ ‪ -‬ﻟﯾﻠﻰ اﻟﺻّﺑﺎغ‬ ‫‪[email protected]‬‬ ‫‪@embryology437‬‬ ‫‪Your feedback‬‬ ‫‪Editing file‬‬