3 - Dermatomes and Myotomes Flashcards Preview

M - MSK (Unknown) > 3 - Dermatomes and Myotomes > Flashcards

Flashcards in 3 - Dermatomes and Myotomes Deck (29)
Loading 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!!!