dermatomes and myotomes

Question 1

what is a dermatome

Answer 1

an area of skin supplied by a single spinal nerve

Question 2

how do dermatomes develop

Answer 2

the neural tube develops from the notochord and ask this happens pairs of somites begin to appear. they then differentiate into sclerotome (which then develops into the ribs and vertebrae) and the dermomyotome which later forms the dermatome (skin) and myotome (muscle). They develop in association with spinal chord level and take the nerve supply with them from the neural tube. therefore skin and muscle from same dermamyotome have same spinal nerve supply.

Question 3

which area does the posterior rami supply

Answer 3

divide and supply skin of back in a segmental way.

Question 4

which area does the anterior rami supply

Answer 4

also supplies some of the trunk but then is also much more complex as it enters limbs via plexus. not segmental

Question 5

draw picture of foerster dermatome map

Answer 5

DRAW

Question 6

what is a spinal nerve, where is it and how many are there?

Answer 6

a mixed nerve that carries motor and sensory autonomic signals between spinal chord and body. its very short and exists passing through the ventral foreman. there are 31 pairs of these and they are numbered according to the level of the vertebral column they are from.

Question 7

draw picture of spinal nerve

Answer 7

point at which dorsal nerve root (carries impulses back to spinal cord) and ventral nerve root (carries impulses away from spinal chord) meet. DRAW

Question 8

what is the vertebral foramen

Answer 8

the space between the vertebral body and the lamina through which the spinal chord runs. lined up together this forms the spinal canal

Question 9

what are the intervertebral foramina

Answer 9

gaps between the attachments of the adjacent process’ this is the space through which nerves leave.

Question 10

what does 1 vertebra develop from

Answer 10

1 somite

Question 11

explain the arrangement of the spinal chord

Answer 11

c1-c7 = cervical nerves 
t1-t12= thoracic nerves 
l1-l5= lumbar 
s1-s5= sacral nerves 
last nerve = coccygeal nerve 
spinal chord starts from medulla oblongata and finishes at conus medullaris(L2) this where the  caudal equina begins.

Question 12

where are spinal nerves found in association with their corresponding vertebra

Answer 12

from C7 onwards they are all found below their corresponding vertebra. before this they are above

Question 13

what are the 2 rami

Answer 13

after exiting via the intervertebral foramen the spinal nerve splits into posterior (dorsal) rams and anterior (ventral) ramus.

Question 14

what does the posterior rams supply

Answer 14

supplies deep muscles and skin of dorsal trunk

Question 15

what does the anterior ramus supply

Answer 15

supplies muscles and skin of upper and lower limbs and lateral and ventral trunk.

Question 16

what does the meningeal branch supply

Answer 16

supplies vertebrae, ligaments, blood vessels and meninges of the vertebral column. its a very small nerve which reenters the intervertebral foramen.

Question 17

what is the role of the grey ramus communicans

Answer 17

its a never from the adjacent paravertebral ganglion of the sympathetic nervous system …?

Question 18

what is the axial line

Answer 18

line down centre of limbs. prevents functional overlap of dermatomes over this line even if there may be overlap between adjacent dermatomes.

Question 19

describe the rotation of the limbs during foetal development

Answer 19

legs rotate inwards and arms rotate outwards. this means the knee is facing forwards and the thumb faces upwards

Question 20

what are the pre axial and post axial boarders

Answer 20

they are the boarders found on the anterior and posterior parts of the limb during rotation these also change position. label where these are found

Question 21

what are the markers of where the pre axial and post axial boarders are on the arms and legs

Answer 21

arms - post axial = basilic vein
arms - pre axial = cephalic vein
legs- pre axial = long saphenous vein
legs - post axial= short saphenous vein