Development of MSK System

Question 1

During what weeks is the embryo most susceptible for major abnormalities in the upper limb?

Answer 1

Weeks 4-6

Question 2

What germ layer makes up the notochord?

Answer 2

Mesoderm

Question 3

_________ Mesoderm is directly lateral to the Notochord, and gives rise to Somites.

Answer 3

Paraxial

Question 4

Paraxial Mesoderm gives rise to Somites. What do Somites further divide into?

Answer 4

Myotome (muscle)
Sclerotome (axial skeleton)
Dermatome (dermis)

Question 5

The Myotome gives rise to all muscles except…

Answer 5

Muscles of the eye

Question 6

When Somites are dividing, they split into what two parts? What do these parts give rise to?

Answer 6

Ventromedial part — makes Sclerotome

Dorsolateral part — makes Dermatome and Myotome

Question 7

The cells of the _________ migrate around the Notochord to form the Vertebral Column.

Answer 7

Sclerotome

Question 8

What are the key components of the Vertebral Column?

Answer 8

Notochord

Paraxial Mesoderm

Question 9

In the Vertebral Column development, each Sclerotome has what two parts?

Answer 9

Cephalic Loose

Caudal Dense

Question 10

What lies in between each Sclerotome segment?

Answer 10

Intersegmental Arteries

Question 11

In the process of Vertebral Column development, the (CEPHALIC/CAUDAL) half of the Sclerotome above will fuse with the (CEPHALIC/CAUDAL) half of the Sclerotome below.

Answer 11

Caudal

Cephalic

Question 12

As the Vertebral Column developments, these insert through the Sclerotome to attach to the Myotome (muscles).

Answer 12

Nerves

***Motor nerves are in muscle by week 5

Question 13

What germ layer are Somatic Motor Neurons from?

Answer 13

Neuroectoderm

Question 14

What germ layer are Preganglionic fibers (Sympathetic or Parasympathetic) from?

Answer 14

Neuroectoderm

Question 15

Does the Cephalic Loose or Caudal Dense part of the Sclerotome signify what number the vertebra will be?

Answer 15

Caudal Dense

***For example if the Caudal Dense part of C3 pairs with the Cephalic Loose part of C4, then the vertebra number being made is C3.

Question 16

T/F. Cervical nerves alway exit below their respective vertebra number, while Thoracic and Lumbar will exit above.

Answer 16

False. Cervical nerves exit ABOVE their respective vertebra, while Thoracic and Lumbar exit BELOW.

Question 17

What parts of the Vertebra does the Caudal Dense part of the Sclerotome give rise to?

Answer 17

Superior Articular Process
Transverse Process
Pedicle
Part of Vertebral Body
Part of Spinous Process

Question 18

What parts of the Vertebra does the Cephalic Loose part of the Sclerotome give rise to?

Answer 18

Inferior Articular Process
Part of Vertebral Body
Part of Spinous Process

Question 19

What is the Nucleus Pulpopus of the Intervertebral Disc derived from?

Answer 19

Leftover Notochord

***Mesoderm!

Question 20

The Notochord expands to form the Nucleus Pulposus, which is made of a ________ substance.

Answer 20

Mucoid

Question 21

This is composed of a fibrous tissue Sclerotome. It is fibrocartilage that surrounds the Nucleus Pulposus.

Answer 21

Annulus Fibrosus

Question 22

Ribs are also developed from __________ cells that grow out from costal processes of thoracic vertebrae.

Answer 22

Sclerotome

***Happens during 5th week

Question 23

T/F. Costal cartilage is made from lateral plate mesoderm.

Answer 23

False. It’s made from Sclerotome.

Question 24

What germ layer is the Sternum derived from?

Answer 24

Somatic layer of lateral plate mesoderm

Question 25

These are a group of related genes that control the body plan along a cranio-caudal axis. They help determine the shape of bones.

Answer 25

Hox Genes

Question 26

Which Hox genes give rise to Cervical Vertebrae?

Answer 26

Hox 4 | Hox 5

Question 27

Which Hox genes give rise to Ribs?

Answer 27

Hox 6

Question 28

Which Hox genes give rise to Floating Ribs?

Answer 28

Hox 9

Question 29

Which Hox genes give rise to Lumbar Vertebrae?

Answer 29

Hox 10

Question 30

Which Hox genes give rise to Sacral Vertebrae?

Answer 30

Hox 11

Question 31

Which Hox genes are involved in Gain of Function?

Answer 31

Hox 6 | Hox 10

Question 32

Explain what happens when there is a Gain of Function in Hox 6? What about Hox 10.

Answer 32

When Hox 6 is over expressed above (in cervical vertebrae area) then it causes CAUDALIZATION which will cause the cervical vertebrae to look like the vertebrae below, which would be thoracic vertebrae with ribs. When Hox 10 is over expressed above (in thoracic vertebrae area) then it causes CAUDALIZATION which will cause the thoracic vertebrae to look like the vertebrae below, which would be lumbar vertebrae.

Question 33

Which Hox genes are involved in Loss of Function?

Answer 33

Hox 4 Hox 5 Hox 10

Question 34

Explain what happens when there is a Loss of Function in Hox 4, Hox 5, or Hox 10.

Answer 34

If there is a loss of Hox 4 in cervical vertebrae 2-5, then CRANIALIZATION will occur which makes the cervical vertebrae look like the vertebrae above it. In this case, they will all look like C1. If there is a loss of Hox 5 in C3-T2, then CRANIALIZATION will occur and make them all look like C2. If there is a loss of Hox 10 in the lumbar vertebrae, then CRANIALIZATION will occur and make them all look like thoracic vertebrae.

Question 35

A Cervical Rib abnormality (due to GOF of Hox 6) can contribute to _______ _______ _______. This is when the Subclavian and/or the Brachial Plexus are compressed and can cause issues (i.e., decreased blood flow, nerve problems).

Answer 35

Thoracic Outlet Syndrome

Question 36

This is the term for the abnormality of Sternum protrusion. It occurs in males more often than females and usually isn't evident until 11 years of age. Cause is unknown.

Answer 36

Pectus Carinatum ("Pigeon Chest")

Question 37

This is the term for the abnormality of Sternum depression. The heart is displaced and can cause exercise intolerance. Occurs in males more often than females and is diagnosed in the 1st year of life.

Answer 37

Pectus Excavatum ("Funnel Chest")

Question 38

What does the Myotome divide into?

Answer 38

Epimere | Hypomere

Question 39

What does the Epimere and Hypomere each give rise to?

Answer 39

Epaxial muscles -- True muscles of back (Layers 4,5, and 6) Hypaxial muscles

Question 40

What are Epaxial muscles innervated by? What germ layer are they from?

Answer 40

Innervated by Dorsal Rami ***Dorsal Rami (somatic) consist of Motor and Sensory fibers. Motor is Neuroectoderm, while Sensory is Neural Crest.

Question 41

What are Hypaxial muscles innervated by? What germ layer are they from?

Answer 41

Innervated by Ventral Rami ***Ventral Rami (somatic) consist of Motor and Sensory fibers. Motor is Neuroectoderm, while Sensory is Neural Crest.

Question 42

Hypomere limb myoblasts that migrate dorsally form what?

Answer 42

Posterior compartments (i.e., Triceps, extensors, etc.) ***Innervated by terminal branches of posterior cord (Radial and/or Axillary N.)

Question 43

Hypomere limb myoblasts that migrate ventrally form what?

Answer 43

Anterior compartments (i.e., Flexors, Pronators) ***Innervated by terminal branches from lateral and medial cords (Median N, Ulnar N., and Musculocutaneous N.)

Question 44

This is the term for the absence of Pectoralis major and minor muscles. It is associated with Syndactyly and there is an absence of 2 to 4 ribs. Many times the Trapezius, Palmaris Longus, and Serratus Anterior Ms. will also be missing.

Answer 44

Poland Syndrome

Question 45

Why do Poland Syndrome and Prune-Belly Syndrome occur?

Answer 45

Due to an abnormal migration of hypaxial muscles ***Remember, Hypaxial muscles derived from Mesoderm. Mesoderm -- Paraxial -- Somite -- Myotome -- Hypomere -- Hypaxial

Question 46

This is the term for partial or complete absence of abdominal musculature. It primarily affects males and is associated with Cryptorchidism (failure of one or both testes to descend) and malformation of the urinary tract and bladder (urethral obstruction).

Answer 46

Prune-Belly Syndrome

Question 47

Prune-Belly Syndrome is caused by an abnormal migration of hypaxial muscles, but how are the associated symptoms of Cryptorchidism and malformation of the urinary tract and bladder caused?

Answer 47

Due to abnormalities of the Intermediate Mesoderm. ***Remember Mesoderm divides into Paraxial, Intermediate, and Lateral Plate. Intermediate gives rise to urogenital (kidneys and gonads).