14.5 Smooth musculature

• Origin of the smooth musculature
  
• Histological aspects
  
• The internal eye muscles

Origin of the smooth musculature

The smooth musculature of the viscera, trachea and bronchia, the blood vessels and of glandular tissue, stems from mesoderm cells that immigrate via the primitive streak directly into the vicinity where these organs arise. Initially an animated proliferation phase of the myoblasts begins. Then the cells lengthen; the typical muscle filaments actin and myosin are synthesized and elongated, tapering muscle fibers arise

Histological aspects

Fig. 26
Smooth musculature of the intestines 500x (longitudinal)

The internal eye muscles

The internal eye muscles (sphincter and dilator muscles of the pupil) are derivatives of the external layer of the optic cup in the region of the pars iridica retinae. They thus stem from the neural ectoderm. The ciliary muscle possibly stems from material of the neural crest (12th week).