Systemic Embryology: Muscular System

Question 1

Nearly all the muscles in the body develop from which germ layer?

Answer 1

mesoderm

Question 2

Which muscles DO NOT develop from mesoderm? And from which germ layer do they develop?

Answer 2

Muscles of the iris
Arrector pili of skin
Myoepithelial cells of glands

all come from ectoderm

Question 3

What is specific mesodermal origin of skeletal, smooth, and cardiac muscle?

Answer 3

Skeletal - paraxial mesoderm

Smooth & Cardiac - splanchnic mesoderm

Question 4

Differentiate the development of the 3 types of muscle tissue in the body.

Answer 4

Myoblasts of skeletal muscle fuse & form true syncytium while those of cardiac and smooth muscle do not. Cardiac myoblasts do make connections, but those persis as intercalated disks. Smooth muscle myoblasts do not give off branches.

Contractile elements of smooth muscle (unlike for cardiac and skeletal) do not develop in a sarcomeric arrangement

Question 5

What Purkinje fibers and how do they form?

Answer 5

Bundles of cells that activate the left and right ventricles of the heart.
Develop late in embryonic period when some myoblasts develop into cardiac cells that have relatively fewer myofibrils and relatively larger diameters

Question 6

Skeletal muscles of the trunk derived from epimere are innervated by which rami of spinal nerves? How about those derived from hypomere?

Answer 6

From epimere get dorsal rami (since epimere is dorsally located)
From hypomere get ventral rami (since it is anteriorly located)

Question 7

Which skeletal muscles form from the epimere?

Answer 7

Extensor muscles of vertebral column

Question 8

Which skeletal muscles does the hypomere give rise to?

Answer 8

In thorax; intercostal muscles + rectus sternalis
In abdomen; external + internal oblique, transversus abdominis, and rectus abdominis
In neck; flexors (longus capitis and colli, scalene muscles) + infrahyoid muscles (sternohyoid, omohyoid superior belly, sternothyroid, thyrohyoid)