Development of Muscular System

Question 1

Mesoderm

What is derived from Paraxial?

What is derived from Intermediate?

What is derived from Lateral Plate?

Answer 1

• Somites
  
  • Myotome (All Skeletal Muscle - Except Constrictor & Dilator Pupillae)
  • Sclerotome (Axial Skeleton)
  • Dermatome (Dermis)
• Urogential
  
  • Kidneys & Gonads
• Connective Tissue
  
  • Blood, Lymph, Mesenteries, Cardiovascular

Question 2

Skeletal System

Somites are divided into two parts, what is the name of each and what is in each part?

What does the sclerotome do?

Answer 2

Ventromedial Part: Sclerotome

Dorsolateral Part: Dermatome & Myotome

Migrates down around Notochord and up around Neural Tube (Shh) to start development of vertebrae

Question 3

Bone Development

What is the embryonic CT in the Sclerotome called?

What is Intramembranous Ossification? What Bones use this process?

What is Endochondral Ossification? What Bones use this process?

Answer 3

• Mesenchyme
• Mesenchyme –> Bone
  
  • Flat Bones, Facial Bones, Clavicle
• Mesenchyme –> Hyaline Cartilage –> Bone
  
  • Long Bones, Pelvis, Pectoral Girdle

Question 4

Vertebral Column

What are the key components?

What parts make up the Sclerotome?

What is the process?

How do you determine which vertebrae number it will be?

Answer 4

Notochord and Paraxial Mesoderm

Caudal Dense Part & Cephalic Loose Part

Caudal 1/2 of Sclerotome “A” fuses with Cephalic 1/2 of Sclerotome “B”

Number of Caudal 1/2 of Sclerotome determines the Level

Question 5

Vertebral Column

What part of vertebrae develops from Caudal Dense and Cephalic Loose aspects of Sclerotome?

Answer 5

Superior Aspect of Vertebral Body and Vertebral Arch

Inferior Aspect of Vertebral Body

Question 6

Intervertebral Discs

What are the two parts and what are they made from?

Answer 6

• Nucleus Pulposus
  
  • Notochord expands to form Nucleus Pulposus
• Annulus Fibrosis
  
  • Fibrous Tissue (Fibrocartilage) from Sclerotome

Question 7

Ribs and Sternum

How do ribs and sternum develop?

Answer 7

• Ribs
  
  • Sclerotome Cells grow out from Costal Processes of Thoracic Vertebrae
    
    • Costal cartilage also from sclerotome
• Sternum
  
  • Somatic Lateral Plate Mesoderm

Question 8

Cervical Rib

What does this contribute to?

What can be compressed?

Answer 8

Thoracic Outlet Syndrome

Subclavian A. and Brachial Plexus

Question 9

Pectus Carinatum

What is it and what is another name for it?

Who is affected more?

Answer 9

Sternum Protrusion

Pigeon Chest

Boys more affected than girls

Question 10

Pectus Excavatum

What is it and what is it also called?

What anatomical consequences occur and what are associated symptoms?

Answer 10

Sternum Decompression

Funnel Chest

Compresses Heart and shifts to one side (Left > Right)

SOB, Pain/Fatigue w/ Exercise, Exercise Intolerance

Question 11

Hox Genes

What are they?

What happens with Gain of Function?

What happens with Loss of Function?

What is Hox 9 responsible for?

Answer 11

Group of related genes that control body plan along cranio-caudal axis

Caudalization (takes on identity of more caudal segment)

Cranialization (takes on identity of more cranial segment)

Floating Ribs

Question 12

Myotome

What is the Epimere? What is it innervated by?

What is the Hypomere? What is it innervated by?

Answer 12

• Epaxial muscles (true muscles of the back)
  
  • Dorsal Rami
• Hypaxial muscles
  
  • Ventral Rami

Question 13

Muscles

What are in the Epaxial Division?

What are in the Hypaxial Divisions? (Cervical, Thoracic, Lumbar, Sacrococcygeal)

Answer 13

Extensor muscles of neck and vertebral column

Cervical Myotomes: scalene, prevertebral, geniohyoid and infrahyoid muscles

Thoracic Myotome: lateral and ventral flexor muscles of vertebral column

Lumbar Myotome: Quadratus Lumborum

Sacrococcygeal Myotome: Muscles of Pelvic Diaphragm

Question 14

Poland Syndrome

What is it and how does it occur?

What is it associated with?

What are the physical features?

Answer 14

• Absence of Pectoralis Major and Minor
  
  • Absence of Hypaxial Migration
• Syndactyly (Fusion of Digits)
• Ipsilateral breat hypoplasia (not well developed) and absence of 2-4 ribs

Question 15

Prune Belly Syndrome

What is it characterized by?

How does it occur?

Who does it primarily affect?

Associated with what?

Answer 15

• Partial/Complete absence of abdominal musculature
• Absence/Abnormal Migration of Hypomere cells into anterior abdominal wall
• Males
• Associated:
  
  • Cryptorchidism (failure of one or both testes to descend)
  • Malformation of Urinary Tract and Bladder (Urethral Obstruction)