Development of the Muscular System Flashcards
Mesoderm forms into paraxial, intermediate and lateral plate mesoderm… what does paraxial form?
Paraxial forms somites which forms the myotome ( all muscle but pupil), sclerotome (skull/vertebral column), and dermtome (dermis)
What does the intermediate mesoderm (next to paraxial) form?
the urogenital system (including kidneys and gonads)
What does the lateral plate form (somatopleure and splanchnopleure)?
Connective tissue including blood, lymph, mesenteries and cardiovasuclar
The somite can be divided into two parts, dorsal lateral and ventral medial, what do they become?
Ventral medial becomes the sclerotome and dorsal lateral top part becomes the dermatome and bottom half becomes the myotome
Where does the sclerotome go once it is cut into the ventral medial part?
Migrates down to notochord and around the neural tube to help form vertebral body
What does the sclerotome form and what does that become?
mesenchyme (mesoderm), which is embryonic connective tissue
What are the two different ways to make bone from mesenchyme?
intramembranous ossification and endochondral ossification
How is bone made by intramembranous ossification, examples?
The mesenchyme is in the shape of the bone it wants to become and then becomes it (flat bones parietal, frontal, face bones)
How is bone made by endochondral ossification, examples?
Mesenchyme forms hyaline cartilage in the shape of the bone and then forms the bone (Long bones (femur, humerus, pelivis, etc))
What cartilage precursor is used to form most of the bones in your body?
Hyaline cartilage: is a chondrification center which goes to prechondrocytes, to chondroblasts, to chondrocytes (later)
What are the two components of the sclerotome when forming the vertebral column, as well as other players?
Caudal dense part (lower hlaf) Cephalic losse part (upper half) each set of losse/dense parts have a myotome to form the muscles, as well as dermotome, and surface ectoderm
What occurs to form the beginning of the vertebral column?
The cephalic loose sclerotome will migrate up to meet with caudal dense, and caudal dense will migrate down to meet with loose.
After fusing dense and loose sclerotome, what happens to the myotome?
It migrates and connects the upper vertebrae and lower vertebrae, instead of muscle on one bone
How do nerves get made during the formation of the vertebral column?
The spinal cord connects to the muscle to form the nerves/ motor neurons (week 3/4!)
Where are the intersegmental arteries located after the formation of the vertebral cloumn?
They are on the sides of the vertebrae
What components of the vertebra come from cephalic loose and caudal dense parts?
What are the 2 parts of the intervertebral discs, and how are they made?
Nucleus Pulposus: from degenrating notochord
Annulus Fibrosis: from fibrocartilage from sclerotome
How are the ribs and costal cartilage formed?
From the sclerotome that grow out of the costal processes of thoracic vertebrae
How is the sternum formed?
Comes from the somatic layer of the lateral plate mesoderm, starts as sternal bars and fuse to form sternum
What occurs when there is a cervical rib that is formed during development?
Causes thoracic outlet syndrome, which can compress the subclavian artery/nerve
What is pectus carinatum?
Pigeon chest! (zach Greene) sternum protrudes, more pronounced as getting older (more boys)
What is pectus excavatum?
funnel chest! sternum depression, compresses heart and shift to left side: can’t breathe, exercise intolerance
What are hox genes?
group of genes that control the body plan along a cranio-caudal axis
What happens to hox genes when there is caudalization TAIL (gain of function)?
If there is an overexpression of Hox 6 in C vert, it will overexpress and change C vertebra to look more like vertebra below (T)
What is cranialization HEAD (loss of function) of hox genes and what occurs?
lose Hox 4 in C2, vertebrae will look like C1, if lose Hox 5 (C3-T2) will look like C2,
What does Hox 9 express?
Floating ribs
What are the hox genes that signal for formation of different vertebra?
Hox 4,5,6,9,10,11 (from C → Sacral)
What two parts does the myotome divide into?
Epimere and Hypomere
What does the epimere form?
Epaxial muscles (back muscles) innervated by dorsal rami (ramous)
What does the hypomere form?
Hypaxial muscles (all other muscles) innervated by ventral rami
What allows for the flexion and extension of limbs and shoulders?
Hypaxial muscles
Mucles derived from mytomal epaxial divisions?
extensor muscles of neck ,vertebral column and back
Cervical myotomes (hypaxial division) give rise to?
scalene, prevertebral, geniohyoid, and infrahyoid muscles
Thoracic myotomes (hypaxial division) give rise to?
lateral and ventral flexor muscles of vertebral column
Lumbar myotomes (hypaxial division) give rise to?
Quadratus lumborum
Sacrococcygeal myotome (hypaxial division) give rise to?
pelvic diaphragm
What is poland syndrome and how does it occur?
absense of migration of cells of hypomere into chest: not pectoralis major/minor, sometimes missing ribs
What is Prune-belly syndrome and how does it occur?
Partial/complete absence of abdominal musculature due to absense of migration of hypomere into abdomen… **males**, can include cryptorchidism (testes don’t descend) and malformation of urinary tract
