Musculoskeletal Embryology

Question 1

What does paraxial mesoderm form during embryological development?

Answer 1

Somites

Question 2

What do somites divide into?

Answer 2

• Outer dermomyotome
• Inner sclerotome

Question 3

What does the dermomyotome divide into?

Answer 3

• Outer dermatome
• Inner myotome

Question 4

By what ossification do vault and face bones form?

Answer 4

Intramembranous ossification

Question 5

By what ossification do the base of the skull and elements of maxillae and mandible form?

Answer 5

Endochondral ossification

Question 6

How many pharyngeal arches are there?

Answer 6

5

Question 7

What does each pharyngeal arch contain?

Answer 7

• Mesoderm core with:
  > Artery
  > Cartilaginous element
  > Nerve

Question 8

What do pharyngeal arch arteries form?

Answer 8

Great arteries in the thorax + neck (eg. right 4th arch forms aortic arch)

Question 9

What do pharyngeal arch cartilages form?

Answer 9

Parts of the:
- Jaw
- Ear ossicles
- Hyoid bone
- Laryngeal arches

Question 10

What do pharyngeal arch nerves supply?

Answer 10

Muscles of the head + neck forming from pharyngeal arch mesoderm

Question 11

What do pharyngeal pouches form?

Answer 11

• Middle ear
• Various glands

Question 12

What is the only pharyngeal cleft not to disappear, and what does it form?

Answer 12

• 1st
• External auditory meatus

Question 13

What is the earliest axial support, and what is it made of?

Answer 13

• Notochord
• Rod of connective tissue around fluid-filled cells

Question 14

What does the notochord get replaced by?

Answer 14

Vertebrae

Question 15

Embryological development of the vertebrae

Answer 15

• Somites form from paraxial mesoderm
• Somites divide into outer dermomyotome + inner sclerotome
• Sclerotome surround the notochord
• IVD precursor forms in the middle of each sclerotome
• Caudal part of one sclerotome grows down to join cranial part of the adjacent
• Sclerotome mesenchyme forms into vertebrae, with the IVDs in between

Question 16

What happens to the notochord as vertebrae develop?

Answer 16

It persists and contributes to nucleus pulposus

Question 17

What does the myotome divide into?

Answer 17

• Dorsal epimere
• Ventral hypomere

Question 18

What does the epimere form?

Answer 18

Epaxial muscles (erector spinae + transversospinalis)

Question 19

What does the hypomere form?

Answer 19

Hypaxial muscles:
- Muscles of the trunk (eg. 3 layers of intercostals/anterolateral abdomen)
- Muscles of the neck
- Limb muscles

Question 20

What are muscles formed from the epimere innervated by?

Answer 20

Dorsal ramus of spinal nerves

Question 21

What are muscles formed from the hypomere innervated by?

Answer 21

Ventral ramus of spinal nerves

Question 22

What do smooth and cardiac muscles form from?

Answer 22

Lateral plate mesoderm

Question 23

Embryological development of human limbs

Answer 23

• Embryo develops limb buds
  > Mesoderm core surrounded by ectoderm
• Hypomere migrates into limbs to form muscles
• Mesenchyme in centre of limb condenses
• Cartilage model forms
• Ossification in week 8
• Digits separate via apoptosis by week 8

Question 24

What muscle masses are found in developing limbs?

Answer 24

• Dorsal
• Ventral

Question 25

What muscle group does the dorsal muscle mass form?

Answer 25

Extensors

Question 26

What muscle group does the ventral muscle mass form?

Answer 26

Flexors