When do the Muscle Systems start to develop?
Where does all of skeletal muscle in the body come from?
(Bonus: What is the one exception?)
The Myotome of the Paraxial Mesoderm
(Constrictor / Dialator Pupilae of the Eye)
For organization of the Somite, what two parts is the Somite broken into, and what occupies those parts?
Dermatome and Myotome
It makes sense that the Sclerotome would be more medial, since it forms the vertebrae that are the very center line of the body.
The Sclerotome (Mesoderm) becomes Mesenchyme before it makes cartilage and bone. What is Mesenchyme?
Embryonic connective tissue. It has mesoderm in it, but may have other cell types as well.
What are the parts of the Sclerotome?
Cephalic Loose part, on top of a Caudal Dense part
What do the Sclerotomes do to create the vertebral column?
They separate between the Cephalic Loose part and the Caudal Dense part, and then merge with the other half of the scleratome above / below them.
When are muscles being innervated?
Late Week 3 / Early Week 4
What structures of a typical vertebra are composed of the Cephalic Loose part of the Sclerotome?
What about the Caudal Dense part?
The Cephalic Loose part of the Sclerotome gives rise to the inferior half of the vertebral body.
Everything else comes from the Caudal Dense portion, including all of the processes and facets.
What forms the Nucleus Pulposus as it degenerates?
What forms the Annulus Fibrosus?
Fibrous tissue from the Sclerotome.
Where do Ribs come from?
They grow out of the Costal Processes of Thoracic Vertebrae
(Therefore they are also made of Sclerotome)
Where does the Sternum come from?
Somatic Layer of the Lateral Plate Mesoderm
(Starts as two separate sternal bars)
What clinical problem can be caused by a Cervical Rib?
Thoracic Outlet Syndrome
What is Pectus Carinatum?
Pidgeon Chest (Sternal Protrusion)
What is Pectus Excavatum?
What are the complications / Symptoms?
(A sternal depression of the chest)
The heart can become compressed, leading to shortness of breath, exercise intolerance, etc.
What does a gain of function of a Hox gene cause in the nearby Vertebrae?
Superior vertebrae begin to look more inferior
Eg: Cervical vertebrae begin to look more like Thoracic vertebrae - gain of function of Hox 6
Hox pulls down.
What does a loss of function of a Hox gene cause?
Vertebrae begin to look more superior.
Hox pulls down,
so less Hox goes up.
Where do Hox 4, 5, and 6 act?
Hox 4: Upper Cervical
Hox 5: Mid to Lower Cervical
Hox 6: Lower Cervical to Upper Thoracic
Where do Hox 9, 10, and 11 act?
Hox 9: Lower Thoracic / Upper Lumbar
Hox 10: Upper Lumbar / Lower Sacral
Hox 11: Upper Sacral / End Coccygeal
What specific structure requires Hox 9 to exist?
What organizational part of the Somite gives rise to Muscles?
The Dorsolateral Part
(This part becomes both the Myotome and the Dermotome)
What two parts does a Myotome split into?
Epimere (Epaxial / true muscles of the back / dorsal rami)
Hypomere (Hypaxial muscles / all of the other muscles / ventral rami)
Think about the embryo on its belly like a lizard. Up would be dorsal (epi) and down would be ventral (hypo)
What are the four divisions of the Hypaxial part of Myotomes?
Cervical, Thoracic, Lumbar, Sacrococcygeal
What does the Cervical division of the Hypaxial Myotome give rise to?
Scalene, Prevertebral, Geniohyoid, and Infrahyoid Muscles.
Muscles of the front / sides of the neck
What does the Thoracic division of the Hypaxial Myotome give rise to?
Lateral and Ventral Flexor Muscles
(Rectus Abdominus and Obliques)
What does the Lumbar division of the Hypaxial Myotome give rise to?
Just one muscle:
What does the Sacrococcygeal division of the Hypaxial Myotome give rise to?
Muscles of the pelvic diaphragm
What is Poland Syndrome?
What is it associated with?
Absence or underdevelopment of Pectoralis Major or Minor Muscle.
(Hypomere doesn't migrate into the chest)
Associated with abnormal breast development on the side of the deficiency and syndactyly.
Other muscles will compensate, and function is not reduced
What is Prune Belly Syndrome?
Who is primarily affected?
What is associated?
Absence of Abdominal Musculature
"Cryptorchidism" Failure of the testicles to decend.
Malformation of the Urinary Bladder