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Flashcards in L19 Early Emb Dev Deck (7)
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1

LO3: desc format of coelom.

-see diag.
-mesod organise v rap- lot cell div, form cells.
Paraaxial mesod- organise arnd axis (notochord and neural tube) either side axis clumps.
Intermed mesod btw axis and edge.
Lat plate mesod 2 lays:
Somat mesod- boys struc, somat innervat-skel musc, dermis etc.
Splanchnic mesod- int with/surr viscera.
Intraemb coelom- sp btw lays conv to sp inside emb.

2

LO4: desc diff of somite to dermatome, myotome, sclerot, and fate of these.

-somites- org of paraaxial mesod to segms.
1st pair at 20d in occipital reg- more in cranio caudal seq at 3 pair/d until 42-44 pairs by wk 5. Some disapp=31 tot.
Ridge=neural tube. Blocks either side paraaxial mesod becomes org to somites blocks of tiss. Occs craniocaudally=segmentat.
Somites app as regul block of mesod cells arr arnd small cov- beginn to diff. Foll by org degen- vent wall of somite breakd=sclerot one=hard tiss. Lose block struc but derivs maint affil to ori somite.
Furth org of dorsal portion= comb dermomyotome- contrib to form skin and musc. Myotome prolif and miss and dermatome disperses. Myotome precurs rem affil to par somite. Dermatome disperses deep to form dermis.
-somite derivs-
Dermatome- skin section=dermis.
Myotome-muscles.
Sclerot one- hard tiss sec=bones. (See diag).
-implics of segm-
Org mesod to somites= rep strucs. Verteb, ribs, intercostal musc, SC segm. Also guides innerv. SC nerves grow into somites and innerv all derivs. Epimerise innerv by dorsal be of spinal nerve for that segm. Hypo mere by ventral. 31 somites to 31 emb segms to 31 pairs spinal nerves.
-dermatome and myotome-
Dev- for given bod segm- dermatome is the part of somite gives rise to dermis. Myotome=muscles.
Clinic:

3

LO5: expl use of dermatome and myot in desc innerv skin and musc in ad.

-dermatome is strip of skin supp by 1 spinal nerve.
Myotome is musc/grp of supp by 1 spinal nerve.
Can be exam clinic.
No overlap but territs of SNS, patt distorted by growth. As myotome mig, brings innerv corresp to that func segm SC.

4

LO6: list derivs of each reg of mesod.

-notochord.
Paraaxial- axial skel (vert col and ribs), dermis, muscs of AL bod wall, some limb musc.
Lat plane- somat leaf= CT of limbs, AL bod will, diaph and limb muscs. Splanchnic leaf=smooth musc, CT and vasc of gut, musc of heart and visc. Coelom btw=bod cavs.
-cardiogenic area (fut heart) devs as neural tube format and segm- is furth cranial than buccophar mem (fut mouth) at this pt. changed by trilam disc folding.

5

LO7: desc format of head, tail and Lat bod folds.

-neural tube is dev in endod. Gets thick= mech face on endod=curl under at cranial and caudal end=cephalocaudal fold=head and tail folds.
Also Lat fold driven by size of dev somite punch down at edges disc. =inside and outside. Pocket 1 opening to umb. Endod inside= eg lining GIT and gls.
See diag so.
-res of folding: draws togeth disc margins=vent bod wall, active proc, needs to close. Pulls amn mem arnd disc=emb susp in amn sac. Pulls connec stalk ventrally-modif into umb cord. Also=primordium of gut from YS, puts heart and primord of diaph in corr pl. and= new cav in emb for dev sys. Begin see bod form.

6

Summ

-end wk 4- NS started. Segms assign tasks to cells-dermis, myot, skel. Emb fold= ev corr pl and intraemb cav.
-bott line- neurulation- neural pl and NT only. Format of primord of NS. Org of mesod- derivs of mesod regs- somites. Segm.
-Fold closes off emb from YS. Folded edges close along vent aspect, leave umb open for YS stalk and umb vess.
At same time, neural plate on dorsal aspect of emb folds to neural tube=neurulation. Emb now has all cell types req in basic bod plan- much is segm from somites. Somites change= patt outgrowth of spin nerve roots from SC, format vert col, and innerv musc and skin. Each somite seps to dermatome, myot, and sclerotome (vert and ribs). SN roots growing out NT ent and innerv derm and myot. Sclerot rearr to lie btw nerve roots and become vert. Myot become musc of thoracic and abdo walls. In limbs bone and musc arise in situ not from somites, but init nerves grow into them in segm patt.
Dermatome and myot clinic def area of skin/musc supp from 1 SN root. SC desc as segms, each give rise to a nerve root.

7

LO1: desc diff mesod to notochord, somites, intermed mesod, Lat plate.
LO2: desc form and fate of neural plate. NP=oval thickening above notochord= ori of NS. Wide ant end to brain post to SC.

-notochord- neurulation. Notoc driven induc of ectod=NS. Diffus lim sigs act close. Neural plate- wk 4 fold=neural tube- brain and SC. tube key in norm dev CNS, defec eg spina bifida, anencephaly.
-notochord in neurulation- notochord formed dur gastrulation- sol rod cells down midline along length ectod, imp sig role. Diffis lim sigs reach close ectod cells. Notochord direct convers of overly ectod to neuroectod.
-notoc sigs=ectod thicken= slipper shaped neural plate. Wider cranial end. Edges elev out of plane as grow faster and curl tow each other=neural tube. Ectod close over top.