Dermatomes

Question 1

How do dermamyotomes develop?

Answer 1

Develop in association with a specific neural level of the embryonic neural tube level.

Question 2

What is the neural tube? What does it do with its neural supply?

Answer 2

The neural tube is the precursor of what will eventually become the adult spinal cord.
Takes its neural supply with it irrespective of where it ends up in the body.

Question 3

What supply’s the dermis and muscle of a dermamyotome?

Answer 3

Spinal segmental nerve

Question 4

What is a segmental nerve?

Hint: location and structure.

Answer 4

at each vertebral level the spinal cord gives out a pair of nerves= 1 left and 1 right
nerves exit the vertebral column through inter-vertebral foramina
- each of these nerves is known as a spinal segmental nerve
a vertebral level and a neuronal level are 2 different entities
dorsal roots (sensory/afferent) + ventral roots (efferent) motor(skeletal muscle) putonomic(smooth muscle + glands)

Question 5

What happens when the spinal nerve emerges through the intervertebral foramen?

Answer 5

it divides into 2 branches
1⃣️posterior or dorsal ramus(small)- divides further into medial and lateral branches
2⃣️anterior or ventral ramus(large)

Question 6

What nerves supply the lower limb?

Answer 6

supplied by the lumbar and sacral spinal segments (L1-S4)
Lumbar plexus (L1-L4) and sacral plexus (L4-S4)

Question 7

Describe the lumbar.

Hint: location.

Answer 7

forms behind Psoas major
nerves emerging lateral to psoas➡️femoral (L2-L4), iliohypogastric, ilioinguinal and lateral cutaneous nerve of the thigh
nerves emerging medial to Psoas➡️Obturator nerve and lumbosacrao trunk

Question 8

What is an axial line? How many does each limb have? Why are they useful and how are they marked.

Answer 8

The line of junction of 2 dermatomes supplied from discontinuous spinal levels.
The limbs have anterior and posterior axial lines
The axial lines can mark boundaries between flexor and extensor compartments.
These borders are marked out by veins- cephalic and basilic (UL)
- great saphenous and small saphenous veins (LL)

Question 9

What is the spinal cord?

Hint: structure, starts, ends, runs, length.

Answer 9

a cylindrical column of: Millions of nerve cell bodies (grey matter) + Millions of neuronal axons (white matter)
starts where the medulla of the brain ends
ends as the conus medullaris (where it’s membranes tapers into a ligament-filum terminae
it runs under the column of the vertebral column and through successive vertebral foramina of most but not all vertebrae of the vertebral column (ends roughly L2/3)
it is shorter than vertebral column

Question 10

What is a dermamyotome?

Answer 10

Embryonic precursors of the dermis and muscle units