Dermatomes part 2 Flashcards
What is a myotome?
Group of muscles supplied by the same spinal nerve
What is a dermatome?
Area of skin supplied by the same spinal nerve
Is their overlap between dermatomes?
Yes, overlap between adjacent dermatomes
NO OVERLAP BETWEEN AXIAL LINES
(eg C5 will have overlap from C6 and C4 but none from T1)
What is an axial line?
Junction of two dermatomes supplied from discontinuous spinal levels
Where are axial lines?
Limbs have anterior and posterior axial lines
What do axial lines mark?
The centre of the ventral or dorsal compartments of the limb
(eg anterior or posterior compartments of forearm)
Rotation of limb buds
Upper limbs rotate externally 90 degrees
Lower limbs rotate internally 90 degrees
(elbow points backwards, knee points forwards)
Pre axial border
Portion of limb that lines cranial to axis of limb (eg tibia)
Post axial border
Portion of limb that lies caudal to axis of limb (eg fibular)
Preaxial border muscle in thigh
Sartorius
How are preaxial and post axial borders marked?
By superficial veins
Upper limb borders
Cephalic vein (pre axial) Basilic vein (post axial)
Lower limb borders
Long (great) saphenous vein (pre axial)
Short (small) saphenous vein (post axial)
Spinal nerves vs peripheral nerves
Peripheral nerves can contain fibres from multiple spinal nerves (fibres from one spinal nerve can enter many peripheral nerves)
Where does rearrangement of spinal nerves occur?
Plexuses
What rami combine in the plexuses and then split?
Ventral (anterior) rami
Where do axons from L2 go?
Obturator nerve
Femoral nerve
Lateral cutaneous nerve
Genitofemoral nerve
Consequence of L2 spinal nerve supplying multiple peripheral nerves
There is some overlap
eg. In L2 dermatome, multiple peripheral nerves will supply this area
What are peripheral nerve territories?
NOT DERMATOMES
Areas of skin supplied by peripheral nerve
(branches of brachial plexus/lumbosacral plexus)
Clinical spinal injury would mean…
Loss of sensory in dermatome areas
may be multiple peripheral nerve areas
Clinical peripheral nerve injury…
peripheral nerve supply lost
