3 - Dermatomes and Myotomes Flashcards

1
Q

Label this diagram of the lumbar spine vertebrae

A
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2
Q

Label this sagittal view of the lumbar spinal vertebrae

A
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3
Q

What is each neural segment referred to?

A

Neural level

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4
Q

How does the dermatome form embryologically?

A
  • 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
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5
Q

What is a

  • dermatome
  • myotome

-

A

Dermatome: Area of skin supplies by a single spinal nerve

Myotome: Group of muscles suplied by a single spinal nerve

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6
Q

What does the endoneurium consist of?

A

Mesh of collagen and glycocalyx

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7
Q

What happens to a nerve during irritation/injury?

A

The endoneurial fluid in the endoneurium increases. This oedema can be viewed on MRI

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8
Q

What are the blood vessels of nerves?

A

Vaso nervorum found in the epineurium

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9
Q

What is a spinal nerve?

A
  • 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
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10
Q

What type of nerves run through the ventral root?

A

Autonomic and motor

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11
Q
A
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12
Q

What is a spinal canal?

A

Multiple vertebral foramina

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13
Q

What fills the spinal canal?

A

- Spinal Cord: Inferior margin of medulla oblongata to conus medullaris at L2

- Cauda Equina: Below L2, spinal roots of L,S,Coccygeal region

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14
Q

Where do each of the spinal nerves originate from?

A

Coccygeal only has one pair of spinal nerves

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15
Q

What are rami?

A

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

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16
Q

What does the posterior rami split into?

A

Medial and lateral branches that supply the narrow strip of skin and muscle in line with the intervertebral foramen

17
Q

What is an axial line?

A

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

18
Q

What does the ventral rami split into?

A
  • Segmental on the trunk but then splits for the upper and lower limbs

- Brachial (C5-T1) and lumbo-sacral (L1-S5) plexus

19
Q

Why is the area of anesthesia smaller than you expect with a spinal injury using the dermatome map?

A

There is a functional overlap of adjacent spinal nerves, e.g C5 will encroach on C4 and C6

20
Q

What are axial borders?

A
  • At the cephalic and caudal margin of the limb bud and mark the posterior and anterior compartments of the limb bud
21
Q

What happens to the spinal nerves in the limbs?

A

Anterior rami split into plexuses to supply limbs. They rearrange and one spinal nerve can be in multiple peripheral nerves

22
Q

What spinal nerves supply the musculocutaneous nerve?

A

C5, 6, 7 for the lateral forearm

23
Q

What is Herpes Zoster?

A
  • 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
24
Q

What is a motor unit?

A

A motor neuron and the skeletal muscle fibre it innervates

25
Q

What are the myotomes of the upper limb?

A
26
Q

What are the myotomes of the lower limb?

A
27
Q

What spinal nerves does the peripheral femoral nerve contain?

A

L2,3 and 4 but the nerves still only supply their own dermatome when they pass through it

28
Q

If you are stabbed in femoral nerve what will happen?

A
  • Any myotomes supplied by L2, 3 and 4 will be paralysed
  • Therefore cannot hip flex, hip adduct, ankle dorsiflex
29
Q

What is a neural level?

A

The lowest level of fully intact sensation and motor function!!!