E - Dermatomes Flashcards
What is the definition of a dermatome
A strip of skin innervated by a single spinal nerve
Why are dermatomes of clinical diagnostic importance?
They allow clinicians to determine damage to the spinal chord and if present, the extent of that damage
Where do dermatomes originate?
The third week of embryogenesis - tri laminar disc
Which structure do dermatomes originate?
The paraxial mesoderm
Where is the paraxial mesoderm?
The portion of the mesoderm directly adjacent to the neural tube
From day 20, what does the paraxial mesoderm develop into?
44 different segments called somites. 13 of these break down, leaving 31.
Each of the 31 somites develops into…
1 spinal nerve
Each of the somites have…
Ventral (front facing) and dorsal (back facing) segments
Ventral portion of somites
Sclerotome - precursor to ribs and vertebral column
Dorsal portion of somites
Dermomyotome - myotome proliferates and the dermatome disperses to form the dermis of the skin
As precursor of the limbs grow (skin)…
The dermis associated stretches with their development, and forms the Keegan and Garrett dermatome map of 1948
The two clinically accepted dermatome maps
Keegan and Garret map of 1948, Foerster Map of 1933
What does the 1948 dermatome map depict?
Dermatomes in a way which correlates with segmental progression of limb development
What does the 1933 dermatome map depict?
The upper limb being innervated by T1-T3 (spinal nerves) and follows their distribution of pain from angina or a myocardic infarction
Most commonly used dermatome map
1933 Forester Map - used in the ASIA scale to assess spinal injury
What do both dermatome maps depict?
Limb progression around an axial line, with there being only a small overlap between adjacent dermatomes
Dermatomes can be used to diagnose the presence of…
A spinal chord lesion after a traumatic injury
First step of spinal chord injury assessment
Cotton wool with light touch along limbs and torso to test for light touch sensation along different dermatomes
Second step of spinal chord injury assessment
Responsiveness to pain - patient is asked to close eyes and asked to say when they feel a pin make contact with their skin
Why are light touch and pain assessed differently in spinal chord injury assessment?
Their nerve fibres travel in different parts of the spinal chord.
Why is spinal chord assessment taken out?
To note any regions of paresthesia, to ascertain whether there is nerve involvement, and to determine whether it is at a spinal root or peripheral level.
