Development of Muscular System

Question 1

What does sclerotome become?

Answer 1

mesenchyme –> bone either through intramembranous ossification or endochondral ossification

Question 2

What does the sternum develop from?

Answer 2

somatic lateral plate mesoderm –> sternal bars –> sternum

Question 3

What part of the sclerotome do all the processes of a vertebra come from?

Answer 3

caudal dense part

Question 4

What are the hypaxial divisions?

Answer 4

cervical myotomes
thoracic myotomes
lumbar myotome
sacrococcygeal myotome

Question 5

What do thoracic myotomes form?

Answer 5

lateral and ventral flexor muscles of vertebral column

Question 6

What is prune-belly syndrome?

What is it due to?

Answer 6

partial or complete absence of abdominal musculature; primarly in males; associated w/ failure of testes to descend and malformation of urinary tract and bladder
due to absence/abnormality of hypomere migration

Question 7

As you go superior to inferior/cranial to caudal, what happens to hox genes?

Answer 7

go up in number

Question 8

What is the basic process of hyaline cartilage formation?

Answer 8

chondrification centers –> prechondrocytes –> chondroblasts –> chondrocytes

Question 9

What is pectus excavatum?

What causes it?

Answer 9

“funnel chest”; causes SOB, exercise intolerance, can shift heart
unknown cause

Question 10

What part of the mesoderm becomes the somites?

Answer 10

paraxial mesoderm

Question 11

What is a cervical rib and what is its clinical significance?

Answer 11

extra rib(s) that form on cervical vertebrae; can compress brachial plexus which can cause pain

Question 12

What does the hypomere become?

Answer 12

hypaxial muscles = all muscles besides true back muscles

innervated by ventral rami

Question 13

What do cervical myotomes form? (4)

Answer 13

scalene, prevertebral, geniohyoid, and infrahyoid muscles

Question 14

What part of the somite becomes sclerotome?

Where does it migrate?

Answer 14

ventromedial somite –> migrates around notochord and neural tube –> becomes vertebrae

Question 15

What does the dorsolateral part of a somite become?

Answer 15

myotome and dermatome

become muscle and dermis, respectively

Question 16

What happens in a gain of function mutation of a hox gene (expressed where it is not supposed to be)?

Answer 16

caudalization of area where it is newly expressed

Question 17

What does the annulus fibrosus form from?

Answer 17

sclerotome –> fibrocartilage –> annulus fibrosis

Question 18

What is endochondral ossification?

What bones do this?

Answer 18

mesenchyme –> hyaline cartilage –> bone

long bones, most bones except flat ones of skull and face

Question 19

What does the epimere become?

Answer 19

epaxial muscles = true back muscles

innervated by dorsal rami

Question 20

What happens in a loss of function mutation of a hox gene?

Answer 20

cranialization

area will look like whatever is superior to it

Question 21

What is intramembraneous ossification?

What bones do this?

Answer 21

mesencyme –> directly to bone

flat bones of skull, face, mandible, clavicle

Question 22

What do Hox genes do?

Answer 22

control the body plan along a cranio-caudal axis

Question 23

In what direction does the cephalic loose side of the sclerotome migrate?

Answer 23

superior/cephalic–> fuses with dense part of sclerotome above –> vertebra

Question 24

What are the two parts of the myotome?

Answer 24

epimere

hypomere

Question 25

What do ribs form from?

Answer 25

sclerotome cells that grow out of costal processes on early vertebrae
costal cartilage also comes from sclerotome

Question 26

What side of the sclerotome is the loose part?

Answer 26

cephalic/head side

Question 27

What is pectus carnatum?

what causes it?

Answer 27

“pigeon chest” usually causes no symptoms; pts remove for aesthetic purposes
unknown cause

Question 28

What does the nucleus pulposus form from?

Answer 28

notochord

Question 29

What side of the sclerotome is the dense part?

Answer 29

caudal/tail side

Question 30

What is poland syndrome?

What is it due to?

Answer 30

absence of pectoralis major and minor
sometimes absence of ribs
due to absence/abnormality of hypomere migration

Question 31

What does the sacrococcygeal myotome form?

Answer 31

pelvic diaphragm

Question 32

What does the lumbar myotome form?

Answer 32

quadratus lumborum

Question 33

In what direction does the caudal dense part of the sclerotome migrate?

Answer 33

caudal/inferior –> fuses with the loose part of the sclerotome above –> vertebra