Differentiation of the mesoderm. Muscular system

BLUE ectoderm - WHITE amnion YELLOW - endoderm

parallel happenings!

RED - mesoderm

GASTRULATION

The extraembryonic central mesoderm - somatopleura (parietal mesoderm) - splanchnopleura (visceral mesoderm) becomes continuous with the newly formed intraembryonic mesoderm axial mesoderm (notochord) paraaxial mesoderm

lateral plate mesoderm

dorsal aorta

cavity between the layers

intraembryonic coelomic cavity

paraaxial mesoderm intermediate mesoderm SAME lateral plate, NAMES!!! somatopleura lateral plate,

splanchnopleura

PARAAXIAL MESODERM - SEGMENTS beginning of 3rd week - somitomeres in cephalic region - somites (from day 20) - Occ 4 -C8 - T 12 -L5 -S5 - Coc 8-10 (...41-43) day 21 - 4-7 day 25 - 17-20 day 30 - 34-35 Based on the number of somites we can compare different creatures!

intraembryonic mesoderm

axial mesoderm paraxial mesoderm intermediate mesoderm lateral mesoderm somatopleura splanchnopleura

mesoderm

extraembryonic mesoderm

central mesoderm somatopleura splanchnopleura

connecting stalk- mesoderm chorion mesoderm (peripheral mesoderm)

ectoderm removed

1. dermatome 2. myotome dermomyotome (each has its own segmental nerve!)

3. sclerotome later

PARAAXIAL MESODERM earlier

intermediate mesoderm “gononephrotome”: ( .. later pro-, meso-, and metanephros...)

- cervical, upper thoracic segmented (nephrotomes) - caudally unsegmented nephrogenic cord

LATERAL PLATE parietal mesoderm (somatopleura): serous membrane and c.t. of body wall (overlying ectoderm will give epidermis)

visceral mesoderm (splanchnopleura): serous membrane, c.t., and smooth muscle of gut (endoderm will give epithelium and glands)

Beginning of 3rd week: wall of yolk sac, chorion, connecting stalk: angioblasts - endothelial cells - blood cells (later also within the embryo → fusion, → placental circulation)

Muscular system from mesodermal germ layer -paraaxial mesoderm - skeletal -splanchnic mesoderm - smooth - cardiac - somatopleura - m. arrector pili

Skeletal muscle: Myotome cells

myoblasts

fusion

Somitomeres + 4 occipital somites: muscles for the head (eye, jaw, larynx, tongue - cranial nerves!!)

Somites: limbs and trunk (axial muscles, body wall)

MYOTOME epimere (dorsal rami of spinal nerves) hypomere (ventral rami)

upper: C4 – T2 lower: L2 – S2

muscle in limb bud

motor and sensory innervation of myotomes and dermotomes

5th week

7th week

neural tube

VERTEBRAL COLUMN

sclerotome notochord

spinal nerve segmental - myotome - nerve

nucleus pulposus in intervertebral disk

notochord

* V

V 1 2

3

* S

S

S

ectodermal - epidermis and its appendices - neural crest, placodes - central and peripheral nervous system

mesodermal

- c.t. and supportive tissue - all muscles - heart, blood, lymph vessels, spleen - urogenital tract (most) - cortex of suprarenal gland

endodermal

- lining of intestinal and respiratory tract - parenchyma of thyroid, parathyroids, liver, pancreas - lining of urethra and bladder - lining of tympanic cavity and auditory tube