Vascular Supply of the Spinal Cord, Dermatomes and Myotomes Lecture

Question 1

How many main sources of arterial supply are there to the spinal cord and where are they found?

Answer 1

2 sources of (longitudinal and segmental) arteries, found in the subarachnoid space

Question 2

How many longitudinal arteries are there?

Answer 2

2 - branches of the subclavian artery, and lie on the surface of the cord.

Question 3

How many segmental arteries are there?

Answer 3

Numerous - branches of the aorta, and they enter the vertebral canal via the intervertebral foramina.

Question 4

What are the different types of longitudinal artery?

Answer 4

There is 2 posterior spinal arteries - branches of the vertebral and posterior inferior cerebellar arteries.

There is 1 anterior spinal artery - a branch of the vertebral artery.

Question 5

What are segmental arteries and what do they do?

Answer 5

They are there for the reinforcement of supply via segmental/radicular branches.

Arteries enter via the intervertebral foramina.

Question 6

How is the blood in the spinal cord drained?

Answer 6

There are longitudinal veins on the surface of the cord, with no valves, so blood may flow in either direction. Made of the internal and external vertebral venous plexus.

Question 7

What is the internal vertebral venous plexus?

Answer 7

Lies within the vertebral canal, in the extradural fat of epidural space.

Question 8

What is the external vertebral venous plexus?

Answer 8

Anterior and Posterior versions - surround the vertebrae

Drains medullary cavity of the vertebral bodies and connects to segmental veins → lumbar and azygos veins.

Venous connections can result in metastasis of tumours.

Question 9

How is the notochord formed?

Answer 9

On day 16, mesodermal cells begin to form a hollow structure called the notochordal process. On Day 18, the notochordal process fuses with the endoderm → notochordal plate. Two edges of the notochordal plate then come together and fuse and become the notochord.

Question 10

What does the notochord do?

Answer 10

Activates a signalling pathway involved in tissue differentiation and development such as neurulation (neural plate folding to form neural tube, which becomes the nervous system)

Question 11

What does unsegmented paraxial mesoderm form?

Answer 11

In the head region of the embryo, and contributes to the formation of bones and muscles in the area.

Question 12

What happens on day 20 of gestation?

Answer 12

In the occipital region, paraxial mesoderm becomes segmented and organises into somites, in a craniocaudal sequence.

Question 13

What do the somites do?

Answer 13

They will differentiate into sclerotome, myotome, and dermatome.

Question 14

How many somites are there?

Answer 14

4 pairs of occipital, 8 cervical, 12 thoracic, 5 lumbar, 5 sacral, and 8-10 coccygeal somites. Some may regress and others will form the axial skeleton.

Question 15

How is the sclerotome formed?

Answer 15

Cells in the ventral and medial walls of the somite shift their position to surround the neural tube and notochord

Question 16

What is the sclerotome responsible for?

Answer 16

It goes on to form the vertebrae and the ribs. Each vertebral body is derived from 2 adjacent somites.

Question 17

How will the spinal nerves form?

Answer 17

Swelling of the neural tube will eventually develop into spinal nerves passing through the sclerotome cells towards the myotome - this pushes 2 somites together and allows the development of the vertebrae.

Question 18

How does the dermatomyotome form?

Answer 18

The myotome is first at either end of the dermotome, and then they later migrate and separate. - They act as precursors for muscle cells.

Question 19

What is the myotome?

Answer 19

Dorsomedial muscles cells (epimere), will give rise to intrinsic back muscles.

Ventrolateral muscle cells (hypomere) will give rise to all the other trunk and limb muscles (skeletal)

Question 20

How are myotome muscles innervated?

Answer 20

A myotome is a group of muscles innervated by the same spinal nerve. It gives rise to a skeletal muscle, and the cell bodies of motor neurons that will supply this myotome are located anteriorly in the neural tube.

Question 21

How to examine myotome muscles?

Answer 21

Most muscles of the body are innervated by more than one spinal cord level, so selected joint movements are used to test myotoms.

Question 22

How is dermatome innervated?

Answer 22

Dermatome is an area of skin innervated by a single spinal segment. The dermatome of each somite gives rise to the dermis.

Cell bodies of somatic sensory neurons are located in the dorsal root ganglia, which develop from the neural crest.

Question 23

What causes shingles?

Answer 23

Varicella Zoster Virus (VZV), can remain dormant in a dorsal root ganglion, and can be reactivated later in life following initial infection. The rash develops in the skin area supplied by the spinal nerve affected i.e. within a dermatome

Question 24

Where are the dermatomes?

Answer 24

C4: Tip of the shoulder
C6: Thumb
C7: Middle finger
C8: Little finger
T10: Umbilicus
L5: Big toe