Embryology Muscle Development

Question 1

What are the three different germ tissues that give rise to the skeleton?

Answer 1

• Neural crest cells
• Mesoderm - somite - sclerotome
• Mesoderm - somatic lateral plate mesoderm

Question 2

Neural crest cells become which structures?

Answer 2

• Bone
• cartilage associated with face and hyoid
• anterior cranial base and Vault
• clavicle

Question 3

mesoderm - somite - sclerotome become which structures?

Answer 3

• Vertebrae
• Ribs
• Posterior cranial base and vault

Question 4

mesoderm - somatic lateral plate mesoderm (LPM) become which structures?

Answer 4

• Sternum
• Scapula
• Pelvis
• Limb bones

Question 5

Describe endochondral ossification.

Answer 5

Mesenchyme differentiates into hyaline cartilage which is then replaced by bone

Question 6

Describe intramembranous ossification.

Answer 6

Mesenchyme differentiates directly into bone.

(mainly in the skull)

Question 7

Where are the primary and secondary ossification centers located?

Answer 7

Diaphysis of the bone.

Question 8

What is contained within the metaphysis of the bone?

Answer 8

Epiphyseal growth plate.

Question 9

Which bones are formed by intramembranous ossification?

Answer 9

• Cranial Vault
• Facial bones
• Clavicles

Question 10

Cranio-caudal patterning of the axial skeleton starts with what?

Answer 10

Expression of homeobox (hox) genes by the somites

Question 11

What do Hox genes determine?

Answer 11

• Regional identities of the somites along the cranial - caudal access.
• Specify segment identity along the limbs

Question 12

Describe vertebral development.

Answer 12

1. The notochord signals sclerotome cells to migrate around the neural tube forming the vertebra.
2. Notochord degrades except for the segmented portion that forms the nucleus pulposus of the intervertebral disc.
3. Resegmentation occurs, forming the intervertebral foramina

Question 13

Describe scull development.

Answer 13

• Develops from sclerotome and neural crest cells
• Through a mixture of endochondral and intramembranous ossification.

Question 14

The ________ is the dividing line for germ layer contribution to the skull

Answer 14

hypophyseal or pituitary fossa of the sphenoid bone

Question 15

The blue bones indicate development from which germ tissue? And the red?

Answer 15

Neural crest cells

sclerotome

Question 16

Which structures of the skull are cartilaginous viscerocranium (chondrocranium/endocondral)?

Answer 16

• Mandibular condyle
• Ossicles
• Styloid process

Question 17

In general neurocranium and viscerocranium, respectively, refer to what?

Answer 17

• Neurocranium refers to the bone that house the brain
• Viscerocranium refers to bones of the face

Question 18

Which structures of the skull are considered membranous neurocranium?

Answer 18

Cranial vault (frontal, parietal, nasal, lacrimal bones)

Question 19

Which structures of the skull are considered membranous viscerocranium?

Answer 19

• Maxilla
• Mandible
• Zygomatic Arch

Question 20

When do limb buds appear? And when are they completed?

Answer 20

• 26 days
• 8 weeks

Question 21

What determines where limbs will appear along the body’s access?

Answer 21

Hox genes

(Upper Limb buds are somites 8 - 12 lower limb buds are somites 24 - 29)

Question 22

Somatic mesoderm cells migrate to form the ______ of the upper and lower limb buds approximately opposite segments _____.

Answer 22

• mesenchymal core
• C5 - T1 and L2 - S3

Question 23

____ models undergo endochondral ossification to give rise to the bones of the limbs.

Answer 23

Hyaline cartilage

Question 24

Define apical ectodermal ridge.

Answer 24

Thickened ectoderm at the distal border of the limb bud that induces adjacent mesoderm to remain undifferentiated and proliferate rapidly (progress zone). the more proximal mesoderm condenses and differentiates into hyaline cartilage models of limb bones

Question 25

What is another name for Progress Zone.

Answer 25

Undifferentiated zone

Question 26

Primary ossification centers are present by the \_\_\_\_week

Answer 26

12th

Question 27

Describe hand and foot development.

Answer 27

Distal portion of the **limb bud flattens** Wrist & ankle form thru **circular constriction** Fingers and toes form through selective **apoptosis**

Question 28

How are digits developed?

Answer 28

BMPs causes mesenchymal cells to either: 1. **Undergo apoptosis** in interdigital tissue 2. **Become chondrocytes** to form bone precursors of the hand

Question 29

During week 6 the limbs lie in a _____ plane and in week 8 they are in a \_\_\_\_\_plane.

Answer 29

* coronal * parasagittal

Question 30

What produces the adult pattern of dermatome innervation in embryonic development?

Answer 30

Limb rotation from the sagittal to the parasagittal plane. Upper Limb rotate 90 degrees posteriorly Lower limb rotates 180 degrees anteriorly (arm flexor m. go from being medial to anterior and leg flexor m. go from being anterior to posterior)

Question 31

Somite (paraxial mesoderm) become which structure or tissue?

Answer 31

* myotomes, which diferentiate into skeletal muscle * epimere = intrinsic back muscles, hypomere = limb & body wall msk (splanchnic lateral plate mesoderm become smooth & cardiac msk)

Question 32

What is myotome cell migration?

Answer 32

Each somite is associated with a single spinal nerve. Cells from the myotome of a single spinal nerve migrate outwards in a segmented manner. (muscles also migrated during body development and this is why dermatomes and myotomes don't line up with each other and most muscles have more than one myotome associated with them)

Question 33

Answer 33

Question 34

How are adult skin dermatomes formed in regard to muscle precursor cell migration?

Answer 34

Muscle precursor cells migrate into the mesenchyme of the hypaxial region and sensory fibers in the spinal nerve accompany them.

Question 35

Describe myogenesis.

Answer 35

Embryonic muscle cells elongate & fuse to form multinucleated myotubes. Myofilaments (actin & myosin) form within the myotubes.

Question 36

What are the different skeletal muscle fiber types?

Answer 36

Slow oxidative fibers (postural muscles) Fast oxidative glycolytic fibers Fast glycolytic fibers (quick powerful movements) (molecular signaling determines which fiber type muscle cells become)

Question 37

Anterior divisions of the anterior rami innervate the ___ compartment of the extremities and posterior divisions of the anterior rami innervate the ____ compartment of the extremities

Answer 37

* flexor * extensor (i.e. Musculocutaneous nerve, tibial nerve and radial nerve, common fibular nerve)

Question 38

Sclerotome of the paraxial mesoderm become which structures?

Answer 38

vertebrae annulus fibrosus Ribs Posterior skull

Question 39

Syndetome of the paraxial mesoderm (somite) become which structures?

Answer 39

epaxial tendons

Question 40

Describe somitogenesis.

Answer 40

At the end of the third week the paraxial mesoderm differentiates into somitomeres (paired on either side of the neural tube. These mature into mature somites in a cranial-caudal progression.