Embryology of the Muscular System

Question 1

What embryonic tissue type do muscles come from?

Answer 1

All from mesoderm except for the dilator pupillae and iris sphincter, which develop from neuroectoderm

Question 2

Discuss development of muscle from myotomes

Answer 2

Mesenchymal cells in the myotome areas of the somites differentiate into myoblasts that then elongate and fuse into tubular structures called myotubes.

Fibroblasts and external laminae that form around the muscle tubules encase the muscle in a fibrous sheath during its development. Myofilaments, myofibrils, and other muscle-specific organelles develop early. Skeletal muscle starts to grow as myotubes fuse together.

After the first year, the increase in myofilaments leads to muscle growth.

Question 3

Discuss the two myotomes of the head

Answer 3

• Preoptic myotomes give rise to extraocular muscles

- Occipital myotomes give rise to the tongue muscles

Question 4

Each myotome of each somite of the trunk region divides into two parts, ______ and _____ from the ________ and ______ sides of the myotome, respectively.

Answer 4

Each myotome of each somite of the trunk region divides into two parts, an epaxial myotome and a hypaxial division from the dorsal and ventral sides of the myotome, respectively.

Question 5

Epaxial myotomes lead to:

Answer 5

Intrinsic back muscles and extensors of the neck and vertebrae

Question 6

Hypaxial myotomes lead to:

Answer 6

Limb, abdominal, and intercostal muscles

Question 7

Divide up the 4 myotome types of the hypaxial division and describe what they give off

Answer 7

Cervical - Prevertebral, geniohyoid, infrahyoid, and scalene muscles
Thoracic - Flexor muscles of the vertebrae
Lumbar - Quadratus lumborum muscle
Sacrococcygeal - Pelvic diaphragm muscles

Question 8

Several Parts Build the Diaphragm

What are they?

Answer 8

Several Parts Build the Diaphragm
S - Septum Transversum
P - Pleuroperitoneal folds
B - Body wall
D - Dorsal Mesentery of the esophagus

Question 9

Discuss the week 3 development of the diaphragm

Answer 9

Septum Transversum develops from the ventral body wall growing dorsally to separate the heart from the liver. It forms the central tendon of the diaphragm, innervated by the phrenic nerves.

It eventually fuses with the pleuroperitoneal membranes and esophagus mesentery to complete the primordial diaphragm (p.p. membrane actually makes up the majority of the dorsal portion.

The esophageal mesentery forms the median portion and crura of the diaphragm

Question 10

What makes smooth muscle in the GI tract?

Answer 10

Splanchnic mesenchyme around the primordial gut endoderm develops into the smooth muscle in the GI tract. Somatic mesoderm gives rise to the smooth muscle in the walls of the blood and lymphatic vessels

Question 11

Poland Syndrome

Answer 11

Uncommon. Absence of pectoralis muscle, and sometimes nearby structures like ribs or mammary glands. Does not usually cause disability since other shoulder muscles and pick up the slack.