Development of MSK System Flashcards
During what weeks is the embryo most susceptible for major abnormalities in the upper limb?
Weeks 4-6
What germ layer makes up the notochord?
Mesoderm
_________ Mesoderm is directly lateral to the Notochord, and gives rise to Somites.
Paraxial
Paraxial Mesoderm gives rise to Somites. What do Somites further divide into?
Myotome (muscle)
Sclerotome (axial skeleton)
Dermatome (dermis)
The Myotome gives rise to all muscles except…
Muscles of the eye
When Somites are dividing, they split into what two parts? What do these parts give rise to?
Ventromedial part — makes Sclerotome
Dorsolateral part — makes Dermatome and Myotome
The cells of the _________ migrate around the Notochord to form the Vertebral Column.
Sclerotome
What are the key components of the Vertebral Column?
Notochord
Paraxial Mesoderm
In the Vertebral Column development, each Sclerotome has what two parts?
Cephalic Loose
Caudal Dense
What lies in between each Sclerotome segment?
Intersegmental Arteries
In the process of Vertebral Column development, the (CEPHALIC/CAUDAL) half of the Sclerotome above will fuse with the (CEPHALIC/CAUDAL) half of the Sclerotome below.
Caudal
Cephalic
As the Vertebral Column developments, these insert through the Sclerotome to attach to the Myotome (muscles).
Nerves
***Motor nerves are in muscle by week 5
What germ layer are Somatic Motor Neurons from?
Neuroectoderm
What germ layer are Preganglionic fibers (Sympathetic or Parasympathetic) from?
Neuroectoderm
Does the Cephalic Loose or Caudal Dense part of the Sclerotome signify what number the vertebra will be?
Caudal Dense
***For example if the Caudal Dense part of C3 pairs with the Cephalic Loose part of C4, then the vertebra number being made is C3.
T/F. Cervical nerves alway exit below their respective vertebra number, while Thoracic and Lumbar will exit above.
False. Cervical nerves exit ABOVE their respective vertebra, while Thoracic and Lumbar exit BELOW.
What parts of the Vertebra does the Caudal Dense part of the Sclerotome give rise to?
Superior Articular Process Transverse Process Pedicle Part of Vertebral Body Part of Spinous Process
What parts of the Vertebra does the Cephalic Loose part of the Sclerotome give rise to?
Inferior Articular Process
Part of Vertebral Body
Part of Spinous Process
What is the Nucleus Pulpopus of the Intervertebral Disc derived from?
Leftover Notochord
***Mesoderm!
The Notochord expands to form the Nucleus Pulposus, which is made of a ________ substance.
Mucoid
This is composed of a fibrous tissue Sclerotome. It is fibrocartilage that surrounds the Nucleus Pulposus.
Annulus Fibrosus
Ribs are also developed from __________ cells that grow out from costal processes of thoracic vertebrae.
Sclerotome
***Happens during 5th week
T/F. Costal cartilage is made from lateral plate mesoderm.
False. It’s made from Sclerotome.
What germ layer is the Sternum derived from?
Somatic layer of lateral plate mesoderm
These are a group of related genes that control the body plan along a cranio-caudal axis. They help determine the shape of bones.
Hox Genes
Which Hox genes give rise to Cervical Vertebrae?
Hox 4
Hox 5
Which Hox genes give rise to Ribs?
Hox 6
Which Hox genes give rise to Floating Ribs?
Hox 9
Which Hox genes give rise to Lumbar Vertebrae?
Hox 10
Which Hox genes give rise to Sacral Vertebrae?
Hox 11
Which Hox genes are involved in Gain of Function?
Hox 6
Hox 10
Explain what happens when there is a Gain of Function in Hox 6? What about Hox 10.
When Hox 6 is over expressed above (in cervical vertebrae area) then it causes CAUDALIZATION which will cause the cervical vertebrae to look like the vertebrae below, which would be thoracic vertebrae with ribs.
When Hox 10 is over expressed above (in thoracic vertebrae area) then it causes CAUDALIZATION which will cause the thoracic vertebrae to look like the vertebrae below, which would be lumbar vertebrae.
Which Hox genes are involved in Loss of Function?
Hox 4
Hox 5
Hox 10
Explain what happens when there is a Loss of Function in Hox 4, Hox 5, or Hox 10.
If there is a loss of Hox 4 in cervical vertebrae 2-5, then CRANIALIZATION will occur which makes the cervical vertebrae look like the vertebrae above it. In this case, they will all look like C1.
If there is a loss of Hox 5 in C3-T2, then CRANIALIZATION will occur and make them all look like C2.
If there is a loss of Hox 10 in the lumbar vertebrae, then CRANIALIZATION will occur and make them all look like thoracic vertebrae.
A Cervical Rib abnormality (due to GOF of Hox 6) can contribute to _______ _______ _______. This is when the Subclavian and/or the Brachial Plexus are compressed and can cause issues (i.e., decreased blood flow, nerve problems).
Thoracic Outlet Syndrome
This is the term for the abnormality of Sternum protrusion. It occurs in males more often than females and usually isn’t evident until 11 years of age. Cause is unknown.
Pectus Carinatum (“Pigeon Chest”)
This is the term for the abnormality of Sternum depression. The heart is displaced and can cause exercise intolerance. Occurs in males more often than females and is diagnosed in the 1st year of life.
Pectus Excavatum (“Funnel Chest”)
What does the Myotome divide into?
Epimere
Hypomere
What does the Epimere and Hypomere each give rise to?
Epaxial muscles – True muscles of back (Layers 4,5, and 6)
Hypaxial muscles
What are Epaxial muscles innervated by? What germ layer are they from?
Innervated by Dorsal Rami
***Dorsal Rami (somatic) consist of Motor and Sensory fibers. Motor is Neuroectoderm, while Sensory is Neural Crest.
What are Hypaxial muscles innervated by? What germ layer are they from?
Innervated by Ventral Rami
***Ventral Rami (somatic) consist of Motor and Sensory fibers. Motor is Neuroectoderm, while Sensory is Neural Crest.
Hypomere limb myoblasts that migrate dorsally form what?
Posterior compartments (i.e., Triceps, extensors, etc.)
***Innervated by terminal branches of posterior cord (Radial and/or Axillary N.)
Hypomere limb myoblasts that migrate ventrally form what?
Anterior compartments (i.e., Flexors, Pronators)
***Innervated by terminal branches from lateral and medial cords (Median N, Ulnar N., and Musculocutaneous N.)
This is the term for the absence of Pectoralis major and minor muscles. It is associated with Syndactyly and there is an absence of 2 to 4 ribs. Many times the Trapezius, Palmaris Longus, and Serratus Anterior Ms. will also be missing.
Poland Syndrome
Why do Poland Syndrome and Prune-Belly Syndrome occur?
Due to an abnormal migration of hypaxial muscles
***Remember, Hypaxial muscles derived from Mesoderm.
Mesoderm – Paraxial – Somite – Myotome – Hypomere – Hypaxial
This is the term for partial or complete absence of abdominal musculature. It primarily affects males and is associated with Cryptorchidism (failure of one or both testes to descend) and malformation of the urinary tract and bladder (urethral obstruction).
Prune-Belly Syndrome
Prune-Belly Syndrome is caused by an abnormal migration of hypaxial muscles, but how are the associated symptoms of Cryptorchidism and malformation of the urinary tract and bladder caused?
Due to abnormalities of the Intermediate Mesoderm.
***Remember Mesoderm divides into Paraxial, Intermediate, and Lateral Plate. Intermediate gives rise to urogenital (kidneys and gonads).
