Anatomy I: Muscle Development

Quiescent satellite cell

What is shown at #1

Activated satellite cell

What is shown at #2

Myogenic progenitor (myoblast)

What is shown at #3

Myocyte

What is shown at #4

Myotube

What is shown at #5

Myofiber

What is shown at #6

Dermomyotome

The ____________ occupies the dorsolateral region of the somite, and it maintains much of its epithelial structure

1. The dermatome

2. The myotome

3. Proliferating myoblasts

What are the three functionally distinct regions of the dermomyotome?

Muscle precursor cells (myoblasts) from the dorsomedial and ventrolateral lips will migrate beneath the dermomyotome to produce the myotome

What produces the myotome?

The darkest red (myotome)

What color in this picture becomes muscle?

Intercostal musculature and the deep muscles of the back

Myoblasts to the neural tube form the _____________ and the ____________________

Body wall, limbs, and tounge

Those myoblasts farthest from the neural tube produce the muscles of the __________, ____________, and _______________

1. Myogenesis (with myoblast proliferation, differentiation, and fusion)

2. Fibrogenesis

3. Adipogenesis

What are the three processes that fetal skeletal muscle development involves?

regulated by a convoluted network of intrinsic and extrinsic factors monitored by myogenic regulatory factor genes in two or three phases, and genes that code for kinases

What is myogenesis regulated by?

achieved by the proliferation and differentiation of myogenic cells

What is prenatal muscle development achieved by?

cascade actions of muscle satellite cells

What achieves postnatal muscle growth?

does not

In general, the number of muscle fibers does/does not change after birth.

Fetal Myogenesis

_________________ is critical for efficient muscle growth

1. Small proportions of progenitor cells in the myotome proliferate and differentiate into myoblasts

2. Myoblasts withdraw from the cell cycle and begin to differentiate and fuse to each other to construct myotubes and primary myofibers

3. Myoblasts near primary muscle fiber proliferate and fuse to form secondary muscle fibers (actin and myosin)

What are the steps in muscle formation?

1. In the late fetal stage, some myogenic cells become quiescent, forming satellite cells

2. Satellite cells first proliferate and then differentiate and fuse with existing muscle fibers, leading to postnatal growth in size of hypertrophy

3. Satellite cells in adult muscle remain quiescent unless activated by extrinsic stimuli (injury or exercise)

4. Activated satellite cells repair or regenerate fibers in the affected muscle

What steps happen in adults when we need to go through secondary myogenesis (muscle regeneration)?

Head muscles

All the skeletal musculature in the vertebrate body except the _______ comes from the dermomyotome of the somite

Pax3

What factor induces muscle proliferation?

Migration by embyronic progenitors -> Proliferation into myoblasts (Pax3) -> Determination into myotubes (Myf5) -> Differentiation into myofibers (Myogenein) -> Formation of specific muscle

What are the steps of myofiber formation, with the transcription factors associated with them?

Pax7

What factor is responsible for the initiation of an activated satellite cell to proliferate?

MyoD (ventral)

Myf5 (dorsal)

What factor is responsible differentiation of a myogenic progenitor (myoblast) into a myocyte?

Myogenin

What factor is responsible for myocytes to fuse to form a myotube?

1. Myf5 is used on the dorsal side of the body that acts after the embryonic progenitor cells are induced to proliferate from Pax3. The signal comes from WNTS from the neural tube, then Myf5 starts the determination stage, followed by Myogenin doing the differentiation stage.

2. MyoD is used on the ventral side of the body which acts after the embryonic progenitor cells are induced to proliferate from Pax3 and BMP4 blocks the signal, so MyoD is expressed instead of Myf5. The signal comes from WNTS from the ectoderm so MyoD starts the determination stage, followed by Myogenin, doing the differentiation stage.

What is the difference between Myf5 and MyoD?

This family of transcription factors includes MyoD, Myf5, myogenin, and MRF4/5

What does the myogenic regulatory factors family include?

activating genes critical for muscle formation

*no MyoD = NO MUSCLE

What is MyoD critical for?

Basement membrane

Satellite cells are outside of the muscle fiber, but share what?

Muscle fiber

What is this image showing?

Satellite cell

What is the green portion of this image

High Notch/Sprouty and low Wnt

Satellite cells express high levels of ___________ to remain in a quiescent state

Wnt

Upon activation of satellite cells, such as during injury or exercise, _____________ singaling increases.

Wnt7a

What drives the symmetric expansion of satellite stem cells and the migration of satellite cells in general?

Satellite cells switch to Notch signaling, while Wnt7a drives the growth of already existing myotubes and myofibers, thereby inducing hypertrophy

When the satellite cell returns to quiescence, what steps can occur to induce hypertrophy?

Cell that means "silent", or not doing anything

What is a Quiescent satellite cell?

The first pharyngeal arch's mesoderm

Also includes the neural crest cells, coming from the first pharyngeal arch

What is the origin of the masseter muscle?

- development of the masseter muscle is influenced by functional requirements, such as the transition from suckling to biting to chewing

What are the unique characteristics of the masseter muscle

Habitual teeth clenching or grinding (bruxism); excessive gum chewing, and even genetics

What can masseter muscle hypertrophy be caused by?

Satellite cells

**This will lead to muscle hypertrophy**

What cell is going to be more active in a patient that has bruixm than a patient that does not have burixim?

Smooth muscle

What type of muscle is derived from a mix of mesoderm and neural crest cells?

Blood vessels and smooth muscle

What do Neural crest cells play a vital role in developing?

Therapeutic revascularization and Periodontal ligament regeneration

What is the development of vascular smooth muscle cells crucial for in dentistry?

Cardiac

There is no fusion from mesoderm to ____ muscle

Skeletal

There is fusion from mesoderm to ________ muscle

Delamination

What is 1

Migration

What is 2

Proliferation

What is 3

Determination

What is 4

Differentiation

What is 5

Formation of specific muscles

What is 6

Embryonic progenitors

What is the green sticker

myoblasts

What is the yellow sticker

Myotubes

What is the pink sticker

Myofibers

What is the blue sticker