VASCULAR SUPPLY of the SPINAL CORD, DERMATOMES & MYOTOMES Flashcards
What are the key sources of blood supply to the spinal cord?
what are they branches of?
where do they enter/ lie?
where are they?
-
Segmental arteries
- Branches of the aorta
- Enter the vertebral canal via intervertebral foramina
- Numerous and provide additional blood flow along the spinal cord
- found in subarachnoid space
-
Longitudinal arteries
- Found in the subarachnoid space
- Includes the anterior and posterior spinal arteries
- 3 of them
- branch of the subclavian artery - Lie on the surface of the spinal cord
What are the longitudinal arteries?
How many are they?
Where do they branch from?
2x Posterior spinal arteries
Branches of vertebral and posterior inferior cerebellar arteries
1x Anterior spinal artery
Branch of vertebral artery
What are segmental arteries?
Where do they enter?
What are the types?
Where do they arise?
Reinforcement of supply via Segmental / Radicular branches
Arteries enter via the intervertebral foramina
Cervical (arise from vertebral arteries)
Thoracic (arise from intercostal arteries)
Lumbar (arise from lumbar arteries)
What are the types of venous drainage?
Where are the features of each?
Longitudinal veins on surface of cord
No valves, blood may flow in either direction
Internal vertebral venous plexus
Lies in extradural fat of epidural space
in vertebral canal
External vertebral venous plexus
Drains medullary cavity of the vertebral bodies and connects to segmental veins ( lumbar and azygos veins)
surrounds vertebrae
External and internal vertebral venous plexuses have connections
What happens on day 16-18 of gastrulation?
What does this structure fuse with on day 18?
~Day 16, mesodermal cells, which migrated through the primitive node begin to form a hollow structure called notochordal process
~Day 18, notochordal process fuses with endoderm becomes notochordal plate
Two edges of notochordal plate come together and fuse and become notochord
In what type of sequence do events from day 16-18 occur?
Where is the structure formed?
What does it activate?
Because these events occur in a cranial-to-caudal sequence, notochord is first formed near the cranial region
Notochord activates a signalling pathway involved in tissue differentiation and development such as neurulation (the embryonic process by which the neural plate folds to give rise to the neural tube)
What happens to paraxial mesoderm and what does this contribute to?
How does this change on day 20?
What can be determined?
What do somites differenciate into?
How many pairs?
In the head region of the embryo, paraxial mesoderm remains unsegmented
Contributes to the formation of bones and muscles in this area.
~ day 20 of gestation, in the occipital region, paraxial mesoderm becomes segmented and organizes into somites
Age of the embryo can be determined
New somites appear in craniocaudal sequence
Somites will differentiate into sclerotome, myotome and dermatome (i.e. dermatomyotome)
There are 4 pairs of occipital, 8 cervical, 12 thoracic, 5 lumbar, 5 sacral, and 8 to 10 coccygeal somites.
Some will regress, others form axial skeleton
What forms the sclerotome?
What is each vertebral body derived from?
Cells in the ventral and medial walls of the somite migrate to surround the neural tube and notochord
They form the sclerotome the vertebrae and ribs
Each vertebral body is derived from 2 adjacent somites
What structures do the cells of the somite give rise to, and how are they organized?**
A:
- Dorsomedial and ventrolateral edges of the upper somite region form precursors for muscle cells.
- Cells between these regions form the dermatome, which gives rise to the dermis of the skin.
- Together, the myotome (muscle precursors) and dermatome (skin precursors) form the dermatomyotome.
Outcome:
- Dermatomyotome of each somite gives rise to:
- Skeletal muscle (from the myotome)
- Dermis of skin (from the dermatome)
What do dorsomedial muscle cells/ ventrolateral muscle cells give rise to?
Dorsomedial muscles cells (epaxial dermatomyotome, i.e. epimere) will give rise to intrinsic back muscles
Ventrolateral muscle cells (hypaxial dermatomyotome, i.e. hypomere) will give rise all other trunk and limb muscles
What is myotome?
What does it give rise to?
Where are the cell bodies of motor neurons that will supply this myotome?
Where do Axons of motor neurons (to become spinal nerves later) from the spinal cord segment ?
Myotome is a group of muscles innervated by the same spinal nerve
The myotome gives rise to a skeletal muscle
The cell bodies of motor neurons that will supply this myotome are located anteriorly in the neural tube
Axons of motor neurons (to become spinal nerves later) from the spinal cord segment adjacent to their corresponding somite follow the dermatomyotome
What are most muscles of the body derived from/ innervated by?
What is used to test myotomes?
Most muscles of the body are derived from more than one myotome innervated by more than one spinal cord level
Selected joint movements are used to test myotomes
What is a dermatome?
What does the dermatome of eachsomite give rise to?
Where are the cell bodies od somatic sensory neurons located?
Dermatome is an area of skin innervated by a single spinal segment
The dermatome of each somite gives rise to the dermis of the skin
dorsal root ganglia, which develop from neural crest
What is this?
What causes it?
What happens after initial infection?
Where does the rash develop?
Shingles is caused by varicella/herpes zoster virus (VZV/HZV)
After initial infection (chickenpox) the virus lies dormant in a dorsal root ganglion. The virus can be reactivated in later life causing shingles.
The rash develops in the skin area supplied by the spinal nerve affected i.e. within a dermatome!
C4:
C6:
C7:
C8:
T10:
L5:
C4: Tip of the shoulder
C6: Thumb
C7: Middle finger
C8: Little finger
T10: Umbilicus
L5: Big toe
