Lecture 15: Development Of MSK

Question 1

When do muscle and skeleton begin developing?

Answer 1

Late week 3 -> in 4th week we begin building somites

Question 2

Paraxial mesoderm gives rise to somites which divide into a ventromedial part and a dorsolateral part, what belongs to each part?

Answer 2

Ventromedial part = sclerotome

Dorsolateral part = dermatome and myotome

Question 3

During development of the vertebral column, sclerotomes divide into 2 segments, a caudal and cephalic part, which is loose and which is dense?

Answer 3

Caudal = dense 
Cephalic = loose

Question 4

All nerves exit the spinal cord above their vertebrae until you get to ______, all nerves below this point exit below their vertebrae

Answer 4

C8

C8 spinal cord exits below C7

Question 5

What does the caudal dense portion of the sclerotomes become?

Answer 5

Spinous process, transverse processes in the body of vertebra

Question 6

What does the cephalic loose portion of sclerotomes give you?

Answer 6

the body of the vertebrae

Question 7

What does the annulus fibrosus portion of the spinal column come from?

Answer 7

The rest of the cells of the sclerotome that did give rise to vertebrae

Question 8

Where is annulus fibrosus found?

Answer 8

It makes a ring around the nucleus pulposus (notochord)

Question 9

What substance is the annulus fibrosus made of?

Answer 9

Fibrocartilage

Question 10

What substance is the nucleus pulposus made of?

Answer 10

Mucoid substance

Question 11

What are ribs made out of?

Answer 11

Sclerotome cells that grow out from costal processes of thoracic vertebrae -> costal cartilage also come from sclerotome (paraxial mesoderm)

Question 12

What does the sternum develop from?

Answer 12

Somatic lateral plate mesoderm

Question 13

What does an abnormality in the cervical rib contribute to?

Answer 13

Thoracic outlet syndrome

Question 14

What mutation causes thoracic outlet syndrome?

Answer 14

A genetic mutation in Hox genes

Question 15

What is pectus carinatum?

Answer 15

Sternum protrusion -> “Pigeon’s chest”

Question 16

What is the most likely cause of pectus carinatum?

Answer 16

Abnormal cartilage growth

Question 17

What is pectus excavatum?

Answer 17

Sternum depression -> “Funnel chest” (opposite of pigeons chest)

Question 18

What is the most likely cause of pectus excavatum?

Answer 18

Either abnormal forces pulling on the sternum or abnormal formation of cartilage but it is unknown

• It is known that is has something to do wth abnormal development of the somatic layer of lateral cartilages

Question 19

What is caudalization of Hox genes?

Answer 19

You get Hox genes higher up than they should be resulting in vertebrae forming according to what the vertebrae look like where that Hox gene would normally be in

Question 20

What is cranialization of Hox genes?

Answer 20

Loss of a Hox gene resulting in the vertebrae taking the shape and characteristics of the vertebrae above them

Question 21

The myotome splits into 2 segments, what are they?

Answer 21

Epimere and hypomere

Question 22

What does the epimere portion of the myotome give rise to?

Answer 22

Epaxial muscles -> true muscles of the back

Question 23

What does the hypomere portion of the myotome give rise to?

Answer 23

Hypaxial muscles -> muscles in limbs, abdomen, chest and neck

Question 24

What is the epimere portion of the myotome innervated by?

Answer 24

Dorsal rami

Question 25

What is the hypomere portion of the myotome innervated by?

Answer 25

ventral rami

Question 26

What do epaxial muscular divisions form?

Answer 26

- Extensor muscles of neck and vertebral column (true back muscles)

Question 27

What does the hypaxial division of muscles give rise o?

Answer 27

- Limbs, abdomen, and chest (muscles) | - Cervical, thoracic, lumbar and sacrococcygeal myotomes

Question 28

What do sacrococcygeal myotomes give rise to?

Answer 28

Muscles of pelvic diaphragm

Question 29

What is Poland syndrome associated with?

Answer 29

Syndactyly

Question 30

What is absent in Poland syndrome?

Answer 30

Pectoralis major and minor

Question 31

What clinical symptoms are seen in Poland syndrome?

Answer 31

Ipsilateral breast hypoplasia | Absence of 2-4 ribs

Question 32

What is the problem underlying Poland syndrome?

Answer 32

The hypaxial part of the myotome didn't migrate properly

Question 33

What is prune belly syndrome?

Answer 33

Partial or complete absence of abdominal musculature

Question 34

Who does prune belly syndrome primarily affect?

Answer 34

Males

Question 35

What is prune belly syndrome associated with?

Answer 35

Cryptorchidism (failur of one or both testes to descend) Malformation of urinary tract and bladder (hypaxial part of myotomes failed to migrate properly)

Question 36

When are congenital abnormalities most likely to occur during development?

Answer 36

During weeks 3-8.

Question 37

Every muscle in your body arises from the mesoderm with the exception of the_______?

Answer 37

Iris (comes from neuroectoderm)

Question 38

Somites should be associated with _____ structures? | Somatic layer should be associated with ______structures?

Answer 38

Somites = superficial structures Somatic layer of lateral plate = deep structures

Question 39

Somites condense around which structure to build vertebrate?

Answer 39

The notochord (template for vertebral column)

Question 40

Why is the migration of cephalic loose and caudal dense sclerotome important?

Answer 40

Allows for the myotome to become attached to two different vertebrates so that you can cross a joint with a muscle.

Question 41

What forms the nucleus pulposus?

Answer 41

Notochord expansion

Question 42

A cervical rib abnormality arises from what kind of mesoderm?

Answer 42

Sclerotome of Paraxial mesoderm

Question 43

Pectus carinatum and excavatum is an abnormality in which layer of mesoderm?

Answer 43

Somatic layer of the lateral plate mesoderm.

Question 44

Sx seen in pectus excavatum?

Answer 44

- Compression of the heart and lung spaces | - Pt's often complain of dyspnea, excercise intolerance, and chest pain.

Question 45

In the paraxial mesoderm, which layer is the most dorsal?

Answer 45

Dermatome