3 - Dermatomes and Myotomes Flashcards
Label this diagram of the lumbar spine vertebrae
Label this sagittal view of the lumbar spinal vertebrae
What is each neural segment referred to?
Neural level
How does the dermatome form embryologically?
- Day 30 the somites have formed about 34-35 pairs and these differentiate
- Skin and muscle from a single dermatomyotome are innervated by the same spinal nerve
What is a
- dermatome
- myotome
-
Dermatome: Area of skin supplies by a single spinal nerve
Myotome: Group of muscles suplied by a single spinal nerve
What does the endoneurium consist of?
Mesh of collagen and glycocalyx
What happens to a nerve during irritation/injury?
The endoneurial fluid in the endoneurium increases. This oedema can be viewed on MRI
What are the blood vessels of nerves?
Vaso nervorum found in the epineurium
What is a spinal nerve?
- Mixed nerve that carries motor, sensory and autonomic.
- Caused by joining of dorsal and ventral roots.
- There are 31 and they are very short as they pass through intervertebral foramen and quickly become a peripheral nerve
What type of nerves run through the ventral root?
Autonomic and motor
What is a spinal canal?
Multiple vertebral foramina
What fills the spinal canal?
- Spinal Cord: Inferior margin of medulla oblongata to conus medullaris at L2
- Cauda Equina: Below L2, spinal roots of L,S,Coccygeal region
Where do each of the spinal nerves originate from?
Coccygeal only has one pair of spinal nerves
What are rami?
When the spinal nerve leaves the intervertebral foramen it splits into:
- posterior/dorsal rami: deep muscles and skin of dorsal trunk
- anterior/ventral ramus: muscles and skin of upper and lower limbs and ventral/lateral trunk
- small meningeal branch: Reenters spinal canal and supplies vertebrae, ligaments, blood vessels and meninges
What does the posterior rami split into?
Medial and lateral branches that supply the narrow strip of skin and muscle in line with the intervertebral foramen
What is an axial line?
Junction of two dermatomes supplied from discontinous spinal levels.
Mark the centre of the ventral or dorsal limb in embryo
No functional overlap like with continuous spinal levels
What does the ventral rami split into?
- Segmental on the trunk but then splits for the upper and lower limbs
- Brachial (C5-T1) and lumbo-sacral (L1-S5) plexus
Why is the area of anesthesia smaller than you expect with a spinal injury using the dermatome map?
There is a functional overlap of adjacent spinal nerves, e.g C5 will encroach on C4 and C6
What are axial borders?
- At the cephalic and caudal margin of the limb bud and mark the posterior and anterior compartments of the limb bud
What happens to the spinal nerves in the limbs?
Anterior rami split into plexuses to supply limbs. They rearrange and one spinal nerve can be in multiple peripheral nerves
What spinal nerves supply the musculocutaneous nerve?
C5, 6, 7 for the lateral forearm
What is Herpes Zoster?
- Shingles where chicken pox virus travels through cutaneous nerve and remains dormant in dorsal root ganglion
- When host is immunosuppressed varicella zoster virus travels via peripheral nerve to affect a single dermatome of skin
What is a motor unit?
A motor neuron and the skeletal muscle fibre it innervates
What are the myotomes of the upper limb?
What are the myotomes of the lower limb?
What spinal nerves does the peripheral femoral nerve contain?
L2,3 and 4 but the nerves still only supply their own dermatome when they pass through it
If you are stabbed in femoral nerve what will happen?
- Any myotomes supplied by L2, 3 and 4 will be paralysed
- Therefore cannot hip flex, hip adduct, ankle dorsiflex
What is a neural level?
The lowest level of fully intact sensation and motor function!!!
