7. Neurulasi

8/9/2019 7. Neurulasi

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28 hr


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Gerakan morfogenetik Kelompok sel-sel yg berjauhan letaknya

pd saat blastula berdekatan --> terbentuk3 lapisan lembaga (tripoblastik)

Sel-sel yg berdekatan --> interaksiinduktif --> perkembangan embrio normalterjadi

Perk.embrio setelah stadium gastrula diawali dg induksi primerantara chordamesoderm (notochord) dg ektoderm diatasnya -->bakal SSP

Respon awal ektoderm terinduksi adalah menebalnya sel-sel -->neural plate --> neural groove --> nerual tube

Sealan dg pembentukan neural tube! lapisan mesoderm kedua sisinorochord membagi menadi bagian-bagian (massa) spt bata kearah memanang --> somit


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Induksi Primer

Selama gastrulasi akhir! chordamesoderm berinvolusi

sekitar bibir dorsal blastoporus am"ibi

Pada aves dan mammalia tonjolannoto!hord yg terbentuk dr sel-sel yg

melalui nodus "ensen terdorong ke arah!ranial di ba#ah ektoderm

Sementara teradi pembentukan notochord! sel-sel chorda

menginduksi ektoderm di atasnyapenebalannerual

plate

aksi tsb.induksi primer (induktor # chordamesoderm

(bkl. notochord$ aringan kompeten # ektoderm)


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Induksi terjadi bila1. Induktor dan jaringan responden pd tempat dan waktu yg

tepat

2. Ektoderm di atas notochord memiliki kompetensi untukmerespons rangsang induksi

c/: tanpa notochord di bwhnya, ektoderm neural ektodermkulit

selama gastrulasi pd amfbi ektodermdorsal dan ventral memiliki kompetensi untukmembentuk jar.sara bila dipengaruhiinduktor

akhir perioda gastrulasi, ektoderm paling jauh dr

notrochord mulai kehilangan kompetensi untuk meresponinduktor saraf

pd sta.neurula sbgan bsr. Ektoderm non-neural kehilangan kompetensi untuk menjadi

jar.saraf


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Neurulasi pd Amfbi

o

khir gastrulasi !!" penyempurnaan gerakan !!"pembentukan primiti#e gut, blastoporusmenciut tajam. Induksi primer dimulai !!"ekotderm menebal !!" neural plate

o $ekitar ektoderm sekarang mrpknlap.mesoderm yg sempurna. %d dorsal!tengahtubuh !!" notochord nampak spt batang

o %d kedua tepi notochord, lap.mesoderm dorsal&epimer' mulai menebal dan secara bersamaan

!!" agregasi !!" somito (esoderm yg lain &hipomer' mengisi bagian

lateral dan #entral embrio !!" pelat mesodermlateral


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Middle neurulation -

amphibia


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Neurulasi pd ayam : 24 jam

Section 7 of 240 through head fold and subcephalic space

In this more caudal section, the continuity of the neural folds are evident. Theouter layer of the head fold (also called the head process) is composed of

ectoderm. Below the head fold note the subcephalic space, a layer of

ectoderm, and a layer of endoderm.


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24 jam

The formation of the foregut occurs concomitant with the formation of the head

fold. The anterior tip of the preoral gut can be seen as a mass of endodermal cells

located below the neural folds. The preoral gut is the portion of the foregut that is

located anterior to the oral plate and lie the foregut is composed of endoderm.


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24 jam

Section 27 of 240 through head fold, foregut, and notochord!t this level, sectioning has now reached the notochord. The notochord is evident ventral to the neural

folds. "entral to the notochord, the foregut appears as a smile#shaped cavity delimited by thin

endodermally derived walls. $ote that the mid portion of the floor of the foregut is slightly thicened.

Below this region is a region of slightly thicened ectoderm. This region is the oral plate which will

become perforated at a later date to form the mouth. Below the head fold is the subcephalic space and

e%traembryonic germ layers. $ote the proamnion (ectoderm and endoderm) below the head fold. &ateral

to the proamnion, layers of mesoderm are visible between the ectoderm and endoderm. The cavity that is

evident between the layers of mesoderm is the coelom.


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24 jam

Section 35 of 240 through posterior limit of head fold, foregut, and

notochord

This section is approaching the end of the head fold and subcephalic space. $ote

the continuity of the head ectoderm with the e%traembryonic ectoderm on the right

hand side of the section.


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24 jam

Section 51 of 240 through region posterior to head fold'ectioning has now past the head fold of the embryo. $ote the absence of the subcephalic space. The

portions of the specimen that will become part of the body of the embryo are continuous with the portions thatwill form the e%traembryonic membranes. $ote the neural folds, notochord, and foregut. %amine the germ

layers and trace their continuities. The coelom is clearly apparent at this level of sectioning. The layer of

mesoderm closest to the ectoderm is the somatic mesoderm and the layer of mesoderm closest to the

endoderm is the splanchnic mesoderm. ne of the main differences in the developmental fates of these two

layers of mesoderm is that the splanchnic mesoderm will form the heart, blood vessels, and part of the yol

sac and allantois while the somatic mesoderm forms the dermis, musculature of the body wall, and part of the

amnion and serosa.


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24 jam

Section 51 of 240 through region posterior to head fold

'ectioning has now past the head fold of the embryo. $ote the absence of the subcephalic space. Theportions of the specimen that will become part of the body of the embryo are continuous with the portions

that will form the e%traembryonic membranes. $ote the neural folds, notochord, and foregut. %amine the

germ layers and trace their continuities. The coelom is clearly apparent at this level of sectioning. The

layer of mesoderm closest to the ectoderm is the somatic mesoderm and the layer of mesoderm closest

to the endoderm is the splanchnic mesoderm. ne of the main differences in the developmental fates of

these two layers of mesoderm is that the splanchnic mesoderm will form the heart, blood vessels, and

part of the yol sac and allantois while the somatic mesoderm forms the dermis, musculature of the body

wall, and part of the amnion and serosa.


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24 jam

Section 57 of 240 through anterior intestinal portalIn this section, note that the neural folds have come together to form the neural

tube. This section is also at the level of the open foregut. $ote that the endoderm

of the foregut is continuous with the rest of the endoderm. The opening of the

closed foregut is called the anterior intestinal portal. %amine the thicened,

splanchnic mesoderm on each side of the anterior intestinal portal. This region of

thicened, splanchnic mesoderm is prospective cardiac mesoderm.


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24 jam

Section 61 of 240 through anterior intestinal portal

In this more caudal section through the anterior intestinal portal, review the germlayers. $ote the mesenchyme on each side of the neural tube.


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24 jam

Section 71 of 240 through midgut

The middle part of the gut that has the yol for the floor of its cavity is called themidgut. In the section, find the endoderm and the midgut. *eep in mind that the

embryo was removed from the yol for fi%ation and sectioning. If the yol was

present in the section it would fill the bottom part of the photograph.


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24 jam

Section 95 of 240 through somites

In this section through a pair of somites, the neural folds have not yet closed together.The somites developed from dorsal mesoderm (+) and are located on each side of the

neural folds and notochord. &ateral and adacent to the somites is a small region of

mesoderm nown as the intermediate mesoderm (I). The intermediate mesoderm will

develop into the idneys. &ateral to the intermediate mesoderm, is the lateral plate

mesoderm (&) which will delaminate to form the somatic and splanchnic mesodermal

layers.


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7. Neurulasi