Musculoskeletal and Limb Embryology - Acht

Question 1

Function of the notochord?

Answer 1

• defines the axis
• has a mechanical role in forming the neural groove and tube, somites, and musculoskeletal system

Contributes to:
vertebral bodies
intervertebral discs

Question 2

What is mesenchyme?

Answer 2

Embryonic connective tissue

• it is derived from mesoderm and the neural crest
• mutlipotent, differentiate into myoblasts, chondroblasts, osteoblasts, fibroblasts, etc.

Question 3

Significance of 4th week in development?

Answer 3

• Embryo transitioning into being a closed structure
• begins the formation of all organs
• time most susceptible to teratigens

Question 4

What specific things are forming in the 4th week?

Answer 4

Neural tube begins to close
Cephalo-caudal and lateral folding
Appearance of somites/somitomeres
Genesis of organ systems
Appearance of pharyngeal arches (face and neck)
Otic and optic development begins
Limb buds appear

Question 5

Scleretomes of each somite will eventually form?

Where in the somite are the scleretomes located?

Answer 5

Bones

located medially

Question 6

Dermomyotomes of each somite will eventually form?

Where in the somite are the dermomyotomes located?

Answer 6

Skin and muscle

laterally

Question 7

As bones develop, what tissue is the bone replacing?

Answer 7

Bone is replacing hyaline cartilage

Question 8

Where are bone ossification centers before and after birth?

Answer 8

Before birth they are only at the center of the bone. After birth they also form at the ends and grow toward the middle

This forms the epiphyseal plates

Question 9

What is an abnormality in connective tissue causing:
excessive long bone growth
Fibrillin-1 gene
Long, thin limbs
Can affect heart, vessels, bones, lungs, eyes

Answer 9

Marfan syndrome

Question 10

Osteogenesis imperfecta

Answer 10

Defect in type I collagen gene in most cases
Autosomal dominant or recessive
Extreme bone fragility
Frequent fractures
Hypermobile joints

Question 11

What is the difference between acromegaly and gigantism?

Answer 11

Acromegaly
Excess growth hormone after growth plates closed
Large, heavy bones especially face, hands and feet

Gigantism
Excess growth hormone during childhood before growth plates close
Overall large size: height and organs; normal proportions

Question 12

How do you treat congentital hip?

Answer 12

Harness or cast to keep legs in outward and somehwat immobile position

Because of the incomplete formation of acetabulum

Question 13

Vertebrae are made from?

Answer 13

2 adjacent segments of two adjacent scleretomes

C1 vertebra made from O4 and C1 scleretomes
C2 vertebra made from C1 and C2

Question 14

What forms the nerves coming off of the spinal cord?

Answer 14

Von Ebner’s fissures between the dense and loose connective tissue in the scleretomes - go on to form the nerves

Question 15

What is spina bifida occulta?

How do you recognize it?

Answer 15

The bottom of the lumbar neural arch is not formed

Tuft fg hair in this region

Question 16

What is pectus excavatum?

Answer 16

Creates as indented-looking chest

• Can fix using surgery
• Often no symptoms, but possible that is compresses heart/lungs (fatigue, rapid pulse, resp infections, murmur, angina)

Question 17

What period is the embryo’s critical period for limb development?

Answer 17

weeks 4-8

Question 18

WHich directions do the upper and lower limbs rotate in development?

Answer 18

upper limb rotates 90deg laterally

lower limb rotates 90deg medially

Question 19

What are the terms for no limb development, partial absence, and flipper-like extremeties?

Answer 19

Amelia = no limbs (bilateral or unilateral)
Meromelia = partial absence of limbs
Phocomelia = hand or foot-like appendage attached almost directly to torso; form of meromelia; phoco- means “seal”;  flipper-like extremity

Question 20

What is a teratogen that causes abnormal limb development?

Answer 20

Thalidomide

Question 21

What is syndactyly?

Answer 21

Webbing between digits is not removed by noraml apoptosis

Question 22

The epimere will develop into what muscles?

Answer 22

epimere = the deep extensors of the back

hypomere = limb muscles, and trunk muscles

Question 23

What is Poland syndrome?

Answer 23

Congenital malformation or absence
of pectoralis major muscle (unilateral)
and often including ipsilateral webbing of
the fingers.

Question 24

What is Prune Belly Syndrome?

Answer 24

Poor development of abdominal muscles causing skin to wrinkle; undescended testicles and urinary tract problems

Question 25

What kinds of bones does achondroplasia affect?

Answer 25

It affects only the long bones. This is why it is the most common form of dwarfism

Question 26

What is the nucleus pulposis derived from?

Answer 26

notochord!

weird right?

Question 27

What occurs in the meningocele form of spina bifida?

Answer 27

The neural arch is not formed. The spinal cord is normal and stays in the right spot and the meninges are forced into the gaps between the vertebrae. Forming a cyst filled with CSF

Question 28

What occurs in the Myelomeningocele form of spina bifida?

Answer 28

The lack of neural arch allows the meninges into the gaps between the vertebrae, matters become more complicated because the spinal crd actually follows into this cystal space as well.

Question 29

What is the name of the disorder characterized by a fusing of any of the cervical vertebrae?

Answer 29

Klippel Feil Syndrome

Question 30

What is a congenital abnormality that can easily lad to scoliosis?

Answer 30

Hemivertebra

Somewhere in the spine there is a vertebrae that is only partially formed as wedge, making the structure all topple-y

Question 31

Why can cervical ribs cuase problems like thoracic outlet syndrome?

Answer 31

There are a lot of vessels and nerves going through the area to supply the upper extremity

(brachial plexus, axillary nerve)

Question 32

How does the AER (Apical Ectodermal ridge) help in limb development?

Answer 32

secretes fibroblast growth factors that induce underlying mesenchyme to proliferate, so that the limb lengthens but the distal aspect of limb is inhibited from terminal differentiation.

the limb develops from proximal to distal.

Question 33

What is pattern of development of a somite to striated skeletal muscle?

Answer 33

Somites -> myotomes -> mesenchyme -> myoblasts -> myotubes -> multinucleated muscle fibers -> striated (skeletal) muscle

(just be familiar)

Question 34

The posterior division of the ventral ramus of the ventral root supplies what muscles?

Answer 34

extensors of the limb

Question 35

The anterior division of the ventral ramus of the ventral root supplies what muscles?

Answer 35

flexors of the limb

flexors of shoulder

Question 36

Whats the difference between endochondral and intramembrous bone formation?

Answer 36

Endochondral: all bones of axial and appendicular skeleton, except part of the clavicle
3 cell types involved: chondrocytes, osteoblasts, osteoclasts

chondrocytes derived from paraxial & lateral plate mesoderm, neural crest for cartilage of face & neck; osteoclasts arise in hematopoetic system

Intramembranous: face and skull
mesenchyme cells derived from neural crest cells & paraxial mesoderm of the head give rise directly to osteoblasts

Question 37

Where does the smooth muscle of the body come from?

Answer 37

Smooth muscle is derived from splanchnic mesoderm that lines the developing gut.

Neural crest cells contribute smooth muscle to eye muscles.

Cardiac muscle is derived from splanchnic mesoderm of the developing heart.

Small muscles of glands (myoepithelial cells) from ectoderm