muscular system development

endochondral ossification forms by

replacing the hyaline cartilage into bone cells

intramembranous ossification develops from

fibrous membrane and forms flat bones

intramembranous ossification replaces mesenchymal connective tissue with

osseous tissue

first step in endochondral ossification

mesenchymal cells condense

second step in endochondral ossification

cells differentiate into chondrocytes that form a cartilaginous model of the bone

third step in endochondral ossification

blood vessels invade center of cartilaginous model bringing in osteoblasts, restricting chondrocyte proliferation to ends of bones

fourth step endochondral ossification

chondrocytes in diaphysis die off as bone is deposited. later blood vessels invade epiphyses forming secondary ossification centers

fifth step in endocondral ossification

bone growth is maintained by proliferating chondrocytes in growth plates

somitomeres begin in the

cephalic region and proceed cephalocaudally

ventral and medial cells of somites become

sclerotomes

dorsomedial and ventrolateral somites form

myotomes

cells in upper region of somite form

dermatone and ventrolateral and dorsomedial lips

VLL and DML migrate and proliferate to form

dermomyotome

cells from VLL migrate into adjacent parietal layer of lateral plate mesoderm to form

infrahyoid, abdominal wall and limb muscles

VLL and DML remaining cells form

muscles of back, shoulder girdle and intercostal muscles

border between each somite and parietal lateral plate mesoderm

lateral somitic frontier

lateral somitic frontier separates into

primaxial domain and abaxial domain

primaxial domain

comprises the region around the neural tube and contains only somite derived paraxial mesoderm cells

abaxial domain

consists of parietal layer of lateral plate mesoderm with somite cells from paraxial mesoderm that migrated across the lateral somitic frontier

abaxial receives their signals from

lateral plate mesoderm

primaxial receives signals from the

neural tube and notochord

each myotome receives its innervation from

spinal nerves derived from same segment as muscle cells

cardiac muscle develops from

visceral mesoderm

smooth muscle of aorta and large arteries is derived from

lateral plate mesoderm and neural crest cells

smooth muscles in gut is from

splanchnic lateral plate mesoderm

region between two developing bones

interzone

limb muscles develop from

paraxial mesoderm

upper limb somites

C4-T2

Lower limb somites

L2-S2

muscles of the limb innervated by

ventral primary rami

spinal nerves provide

sensory and autonomic innervation

sensory and sympathetic nerves are derived from

neural crest cells