Development of Muscular System

Question 1

What is skeletal muscle derived from?

Answer 1

Paraxial mesoderm

Question 2

What is cardiac and visceral smooth muscle derived from?

Answer 2

Splanchnic Mesoderm

Question 3

What is vascular smooth muscle derived from?

Answer 3

Local Mesenchyme

Question 4

What developmental anatomy do the skeletal muscles of truck and limbs originate from?

Answer 4

Somites

Question 5

What part of the somite does the dermomyotome derive from?

Answer 5

The dorsolateral or dorsal part of the somite under the influence of Wnts

Question 6

What part of the dermatomyotome undergoes an epithelial to mesechymal transformation? And what happens when this occurs?

Answer 6

The dorsomedial and dorsolateral edges

They become myogenic – called Myotome

Question 7

What is the myotome a precursor for?

Answer 7

For skeletal muscle of the trunk and limbs

Question 8

What regulatory factors form the intrinsic muscles of the back? What domain is this?

Answer 8

Myf5 and MyoD

Primaxial domain

Question 9

What myogenic regulatory factor induces the muscles of the abdominal walla nd the limbs of the infrahyoid muscles? What domain is this?

Answer 9

MyoD

Abaxial domain

Question 10

What happens after myogenic cells become comitted byoblasts?

Answer 10

They being to synthesize actin and myosin

They reach their definitive location in the embroy and secrete adhesive glycoprotein, fibronectin.

They align in chains of myoblasts – which fuse to become multinucleated myotubes (requires M-cadherin)

Question 11

What mediates myofiber and sarcomere formation?

Answer 11

Troponin and tropomyosin

Create a differentiated muscle cell/muscle fiber

Question 12

When is skeletal muscle fiber formatino completed?

Answer 12

At birth!

Question 13

What accomplishes myogenic postnatal growth of skeletal muscle? What mediates their expression?

Answer 13

Myogenic stem cells – satellite cells

Pax 3 and Pax 7

Question 14

What are some proposed strategies for the formatin of individual skeletal muscles?

Answer 14

• Change in fiber direction
• Fusion of adjacent myotomes
• Longitudinal splitting
• Tangential splitting into layers
• Atrophy of a part
• Migration

Question 15

How do skeletal muscles become innervated?

Answer 15

Myotome is divided into Epaxial (dorsal) and Hypaxial (ventral) portions

Epaxial portion of myotome (intrinsic muscles of back) receives motor innervation from dorsal primary rami.

Hypaxial portion of dermatome (ventrolateral body wall and limb muscles) receives motor innervation from ventral primary rami.

Question 16

What are the master regulators of smooth muscle gene expression?

Answer 16

Serum Response Factor (SRF)

Myocardin

Question 17

What does smooth muscle orignate from?

Answer 17

Splanchnic mesoderm

Question 18

What are smooth muscles able to do postnatally?

Answer 18

Divide in response to extracellular signals

Question 19

What is cardiac muscle derived from?

Answer 19

Splanchnic mesoderm of the primary and secondary heart fields

Question 20

What transcription factors regulat cardiac myocyte formation?

Answer 20

GATA 4 & 6, Foxp1, Nkx2.5 and twist

Also BMP and FGF

Question 21

What is muscular dystrophy?

Answer 21

Family of genetic diseases exhibiting progressive weakness and deterioration of skeletal muscle cells without CNS or peripheral nervous pathology

Duchenne Type: most common, x-linked recessive, affects boys in early childhood, myocytes lack dystrophin

Becker’s Type: later onset and milder condition

Question 22

What is congenital torticollis?

Answer 22

Fixed rotation and tilting of the head to one side

More common on rights side

May have congential hip dysplasia too

Question 23

What is Prune Belly Syndrome?

Answer 23

Three defects:

1) absence of abdominal muscles
2) undescended testicles
3) bladder and urinary tract abnormalities

Prenatal accumulation of fluid in the lower abdomen due to urinary system snomalies may interfere with devo or cause degen of ab muscles

Question 24

What is Poland Sequence?

Answer 24

Characterized by absence of pectoralis major and the pectoralis minor muscles

Nipple on that side is displaced laterally or missing

Rib cage hypoplastic, Upper limb anomalies – shortened limb segments and hand defects (syndactyly and brachydactyly)

Twice as common on right side, and more prevalent in males