Muscle Embryology Flashcards
When does the notochord form, from which germ layer is it derived and what is its function?
It is formed during gastrulation from cells derived from the mesoderm and is a very important signalling system
The mesoderm becomes divided into four distinct regions. What is the order of these, from closest to the notochord, to furthest from the notochord?
Paraxial mesoderm
Intermediate mesoderm
Lateral plate mesoderm
Extra embryonic mesoderm
When does differentiation of the mesoderm occur?
Days 17-21
What part of the mesoderm forms the genitourinary system?
Intermediate mesoderm
What is the name of the cavity which separates the two parts of the lateral plate mesoderm?
Intraembryonic coelom
What is the names of the membranes which are later broken down to form the mouth and anus?
Oropharyngeal and cloacal membrane s
Which layer of the lateral plate mesoderm connects to the amniotic cavity?
Somatic layer
Which layer of the lateral plate mesoderm connects to the yolk sac?
Splanchnic layer
Which smooth muscles are formed by the ectoderm?
Pupillary muscles
Mammary glands
Sweat glands
From what part of the mesoderm is skeletal muscle formed?
Paraxial mesoderm
From what part of the mesoderm is smooth muscle formed?
Splanchnic layer of lateral plate mesoderm around the gut tube
From what part of the mesoderm is cardiac muscle formed?
Splanchnic layer of the lateral plate mesoderm around the heart tube?
What are somites?
Segmented blocks of paraxial mesoderm which are transformed into spheres and give rise to skeletal muscle
From what day in development do somites start to form?
Day 20
Somites develop in a craniocaudal sequence at a rate of…?
3 pairs per day
At the end of week five all of the somites are formed. How many somites are there?
42-44 pairs
Somitogenesis involves a mesenchymal-epithelial transition. T/F?
True
Describe the wave and clock mechanism which controls somite formation
Genes of the not h family, assisted by genes of the Wnt family tell the cells to switch between a permissive and non permissive state in a constantly timed fashion like a clock
A wave factor - FGf8 - then sweeps along the length of the embryo and interacts with the cells which are permissive at the tight time in the right area to cause somite formation
How many of each occipital, cervical, thoracic, sacral and coccygeal somites are there by the end of week 5?
Occipital - 4 pairs Cervical - 8 pairs Thoracic - 12 pairs Sacral - 5 pairs Coccygeal - 5-7 pairs
The cells in the ventral and medial area of the somite undergo an epithelial-mesenchymal transition to form the…?
Sclerotome
What does the sclerotome form?
Vertebrae and ribs
The cells in the dorsal half of the somite become the …?
Dermomyotome
How to myoblasts differentiate into muscle cells?
They undergo cell division under the influence of growth factors. When these growth factors are depleted they stop dividing, secrete fibroconectin onto the ECM and bind ti it via an integrin crucial step which aligns the cells into chains allowing fusion. Cell membranes then disappear and the myoblasts form multinucleated myotubes
What molecule mediates the differentiation of myoblasts?
Myogenin
Describe the signalling involved in dermomyotome differentiation into myoblasts
The neural tube secretes Wnt (activating) and BMP (inhibiting) proteins which combine to activate MYOD in the dermomyotome to create a group of muscle cell precursors which express MYF5
MYOD and MYF5 are transcription factors which activate muscle specific genes and enable differentiation into myoblasts
The secretion of which factors from the notochord induces sclerotome formation?
Noggin
Sonic hedgehog
Serum response factor is responsible for differentiation of what type of muscle?
Smooth muscle
Which transcription factors can enhance serum response factor activity?
Myocardin and myocardin related transcription factors
Tendons are derived from the sclerotome under the control of which transcription factor?
Scleraxis
The tinman gene is important in the development of what kind of muscle?
Cardiac muscle
In embryology, what does the dermatome form?
Dermis and connective tissue
What muscle is derived from the ventrolateral region of the myotome?
Abaxial muscle
What muscle is derived from the dorsomedial region of the myotome?
Primaxial muscle
What structures does the somatic layer of the lateral plate mesoderm form?
Body wall
CT and bones
