MSK - Dermatomes And Myotomes Flashcards

1
Q

What is a neural level?

A

A segment of the central nervous system

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2
Q

What does the ‘somite’ differentiate into in the fourth week of embryological development?

A
  • the sclerotome (ventral) which forms vertebrae and ribs

- the dermatomyotome (dorsal) which forms dermis and muscle

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3
Q

What do skin and muscle derived from a single dermatomyotome share?

A

A common spinal nerve supply

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4
Q

What do the ‘roots’ connect in the spine?

A

They connect each spinal nerve to a segment of spinal cord

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5
Q

What do dorsal (posterior) roots contain?

A

Afferent/sensory nerve fibres

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6
Q

What do ventral (anterior) roots contain?

A

Efferent/motor and autonomic nerve fibres

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7
Q

What are spinal nerves?

A

Parallel bundles of axons encased in connective tissue, which exist only briefly as they pass through the intervertebral foramen

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8
Q

How many spinal nerves are there?

A

31 pairs, which are numbered according to the level of vertebral column that they emerge from

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9
Q

What’s the difference between an epineurium, a perineurium and an endoneurium?

A

Epineurium covers the entire nerve, perineurium surrounds each fascicle and endoneurium is around each axon

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10
Q

What is a vertebral foramen?

A

A gap in the vertebra which the spinal cord runs through. Multiple vertebral foramina form the spinal canal.

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11
Q

What is a external segment?

A

The name given to a single vertebra, which differentiates from a sclerotome

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12
Q

Where does the spinal cord run?

A

Starts at inferior margin of medulla oblongata, ends as conus medullaris at L2

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13
Q

True or false - all spinal cord segments are perfectly aligned with their corresponding vertebrae?

A

False - long roots from inferior segments descend in cauda equina to exit at their respective foramina

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14
Q

Where does the first pair of spinal nerves emerge?

A

Between occipital bone and atlas

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15
Q

Where do C1-C7 emerge?

A

Above the corresponding vertebrae

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16
Q

Where does the spinal nerve (C8) exit?

A

Between vertebrae C7 and T1

17
Q

Where do S1-S4 exit?

A

Via four pairs of sacral foramina

18
Q

What are ‘rami’?

A

These are what the spinal nerve divides to form

19
Q

What does the posterior/dorsal ramus innervate?

A

Deep muscles and skin of the dorsal trunk

20
Q

What does the anterior/ventral ramus innervate?

A

Muscles and skin of the upper and lower limbs and lateral and ventral trunk

21
Q

What is a myotome?

A

A group of muscles supplied by a single spinal nerve (or spinal nerve root)

22
Q

What is a dermatome?

A

An area of skin supplied by a single spinal nerve or spinal nerve root

23
Q

What is a motor unit?

A

A motor neuron and the skeletal muscle fibres it innervates

24
Q

What’s the difference between a myotome and a motor unit?

A

1 spinal nerve contains the neurons of many motor units, but supplies one myotome

25
Q

What is an axial line?

A

A junction of two dermatomes supplied from discontinuous spinal levels

26
Q

What do axial lines on the limbs mark?

A

The centre of either the ventral or dorsal compartments of the limb

27
Q

What are peripheral nerve territories?

A

Areas of skin supplied by the peripheral nerves eg. branches of the lumbar plexus

28
Q

If a rash is seen in a patient which only affects the skin of a single dermatome, what is likely to have caused it?

A

Viral infection by Herpes Zoster (shingles)