Week 3: Development of the Musculoskeletal System

Question 1

What is the paraxial mesoderm?

Answer 1

The paraxial mesoderm is broken down into somites that can be divided into different components.

• Ventromedial Side
• Dorsolateral Side

Question 2

What is on the ventromedial side of the somite of the pariaxial mesoderm?

Answer 2

Scleratomes–> give rise to the axial skeleton

Question 3

What is on the dorsolateral side of the somite of the pariaxial mesoderm?

Answer 3

Dermatomes–> give rise to dermis

Myotomes–> give rise to all the muscles of the body except for the constrictor pupillae & dilator pupillae muscles

Question 4

What type of cells does the scleratome of the dorsolateral compartment of the somite of the pariaxial mesoderm give rise to?

Answer 4

The scleratome gives rise to multipotent mesenchyme stem cells that will build the vertebral column and the skull

Question 5

What are the 2 types of ossification that occurs from these multipotent mesenchyme cells that originate from the ventromedial aspect of these somites of scleratomes?

Answer 5

The produced direct ossification through:
1.) Intramembraneous Ossification (mesenchyme cells–>
bone)
ex: flat bones, skull bones, and bones of face,
clavicle

2.) Endochondrial Ossification (mesenchyme–>
cartilagenous bone)
ex: long bones, bones of the pelvis, pectoral girdle

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Question 6

How does the cephalic loose and the caudal dense interact on the different scleratomes to create the vertebral column?

Answer 6

The caudal dense which is the scleratome more rostral will expand downwards as the cephalic loose will move more upwards. The both of them will intertwine and create the begining of a vertebral column.

Question 7

What are the different components of the vertebral discs and where do they originate from?

Answer 7

The nucleus pulposus is made from the notochord.

The annulus fibrosis is made form the scleratome.

Question 8

How are the ribs made and where do they come from?

Answer 8

The ribs are made from the scleratome and they will grow from the costal facets of the built vertebral column.

Question 9

What is thoracic outlet syndrome and what are the problems with this disease?

Answer 9

Thoracic Outlet Syndrome is a problem with the scleratome where there is an extra rib that develops of the neck of the individual.

Complications: brachial plexus compression, disturbance with vasculature of the aortic arch

Question 10

What is pectus carinatum and what are its complications?

Answer 10

It is caused by a ventromedial abnormality to the scleratome which causes the sternum to fold inwards.

*Complications can be problems to the heart and lungs; trouble breathing

Question 11

Pectus excavatum?

Answer 11

It is caused by the scleratome problem of the ventromedial side of a somite that causes the sternum to cave inwards. This causes major problems with the heart and lungs as it causes the heart to shift to the left.

Sx: complete SOB, pain with excercise, lungs cant get enough air

Question 12

What are the HOX genes and how do they influence scleratome differentiation in the mesodermal layer of the embryo? What is a gain of function mutation for the HOX gene?

Answer 12

The HOX genes are a bunch of genes that can either be methylated or acetylated for activation by the DNA programming within them.

**The problem arises when a supposedly methylated gene is actually activated causing the structure to start to be activated.

RESULT: The result is a different looking vertebrae in the wrong region. An example of this would be the activation of a thoracic vertebrae in the lumbar region. This is a gain of function mutation for this type of gene!

Question 13

What happens when you have loss of function mutation of a HOX gene?

Answer 13

A loss of function mutation will cause the HOX gene from the particular scleratome to look similar to the scleratome right above it.

Question 14

Where do all the muscles of the embryo develop from except the contrictor pupillae and the dilator pupillae?

Answer 14

These will develop from the myotomes from the dorsolateral side of a somite.

Question 15

How does the myotome differentiate to become the epimeres and the hypomeres to produce different muscles?

Answer 15

The myotome will become differentiated into both epimeres and hypomeres.

Epimeres will become the true epaxial muscles= true back muscles

Hypomere–> will give rise to the hypaxial muscles; all other muscles

Question 16

What muscles are produced from the epimere of the myotome?

Answer 16

Epaxial Muscles/ True Back Muscles–>

errector spinae muscles, transversal spinalis, splenis capitus, extensor muscles of the back and neck

Question 17

What muscles are produced from the hypomere of the myotome?

Answer 17

Hypaxial Muscles of the Hypomere (all the rest of the muscles of the human body)

Question 18

What are the different types of hypaxial muscles that are produced from each of the different layers of the myotomes?

Answer 18

Cervical hypaxial myotomes–> scalene, prevertebral muscles, geniohyoid muscle, infrahyoid muscles

Thoracic hypaxial myotomes–> lateral and ventral flexor muscles of the vertebral column

Lumbar hypaxial Myotomes–> produce the quadratus lumborum

sacrococcygeal hypaxial myotomes–> produce the muscles of the pelvic diaphragm

Question 19

What is Polands Disease and what is it caused by?

Answer 19

Polands disease is a disease resulting from the loss of migration of the hypaxial mesodermal layer to the chest area.

Results in: Loss of Pectoralis Major M. and Pectoralis Minor M.

Question 20

What is Prune Belly Syndrome?

Answer 20

Prune Belly Syndrome results from the loss of abdominal muscle migration from the hypomere to the abdominal cavity. This causes a loss of the muscles in this area.