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MSK > Lecture 3 Dermatomes & Mytomes > Flashcards

Lecture 3 Dermatomes & Mytomes Flashcards

1
Q

What is each neural segment called and what do they associate with/give rise to?

A

Neural level.

-contribute to the dermatomes and myotomes within upper and lower limbs

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2
Q

What contains the precursor cells of the nervous system?

A

Neural tube

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3
Q

How does the neural tube and somites form?

A
  • at 18 days
  • neural plate starts to invaginate forming the neural groove
  • eventually the neural folds approach each other where they meet in the midline and fuse forming the neural tube
  • by day 24
  • the cephalic (head) and caudal (tail) have closed
  • from day 20 onwards paired somites appear
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4
Q

What do somites form and how many are there?

A
  • day 30: there are 34-35 pairs of somites
  • as soon as they form they start to differentiate
  • differentiate into the sclerotome and the dermatomyotome
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5
Q

What does the sclerotome give rise to?

A

vertebrae and ribs (ventral)

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6
Q

What does the dermatomyotome give rise to?

A

Dermis and muscle (dorsal)

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7
Q

What are dermatomyotomes?

A

They develop in association with a specific neural level and take their nerve supply from the neural tube as a spinal nerve.

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8
Q

Why would skin and muscle have a common spinal nerve supply?

A

The skin and muscle are derived from a single dermatomyotome.

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9
Q

What is a dermatome?

A

Area of skin that is supplied by a single spinal nerve.

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10
Q

What map do you use to know the anatomical distributiom of dermatomes?

A

Foerster Dermatome Map

e.g. T4/T5:nipples, T10:umbilicus, L1:groin

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11
Q

Where does the axon of a nerve arise from?

A

The axon hillock.

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12
Q

What is the structure of a peripheral nerve?

A
  • each nerve fibre/axon is surrounded by the endoneurium
  • perineurium surrounds each fascile (bundle of nerve fibres)
  • epineurium surrounds the entire peripheral nerve
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13
Q

What does the endoneurium secrete?

A

Endoneurial fluid, which surrounds each fibre.

  • this increases during nerve irritation or injury.
  • this oedema in the nerve can be detected by an MRI
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14
Q

What is the function of the endoneurium and what is it made from?

A

Consists of an inner sleeve of material called the glycocalyx and a mesh of collgen.
-prevents certain molecules passing from blood into endoneurial fluid

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15
Q

What are vasa nervorum?

A

Nerves with high metabolic rates contain their own blood vessels in epineurium.

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16
Q

What is a spinal nerve?

A

A MIXED nerve that carries motor & sensory signals b/w the body and spinal chord.
-they are short and exist briefly as they pass through the intervertebral foramen (marks the difference b/w CNS and PNS)

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17
Q

What is a dorsal root?

A

Contain afferent, sensory nerve fibres ONLY.

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18
Q

What is a ventral root?

A

Contain efferent motor, autonomic nerve fibres ONLY.

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19
Q

How many pairs of spinal nerves are there?

A

31 (each pair leave out either side of the intervertebral foramina and branch into the rami)

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20
Q

What is each vertebra derived from?

A

2 adjacent somites (above and below)

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21
Q

What does the spinal chord run through?

A

Vertebral foramen (intervertebral foramina allow spinal nerves to leave)

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22
Q

Where does the spinal chord commence and end?

A

Inferior margin of medulla oblongata, at base os brain stem, and ends at the conus medullaris at L1/2

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23
Q

Why are the spinal chord segments not in line with the vertebrae?

A

Differential growth. The growth of the spinal chord is much slower than the rest of the body, so is shorter.

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24
Q

What is inferior/superior meaning?

A

Inferior is closer to bottom of body

Superior is closer to the top of the body

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25
Q

What is the cauda equina and where is it located?

A 
Below the conus medullaris.
Cauda equina (Horse's tail)
-long ROOTS from inferioir segments (lumbar/sacral/coccygeal) that descend to reach corresponding foramina
26
Q

What is the ratio of cervical spinal roots to cervical vertebrae?

A

8 pairs of roots
7 vertebrae
Therefore the roots emerge above the vertebral body

27
Q

What is the exception to this rule of cervical roots emerging above the ventral body?

A

C8 root

Between the C7 & T1 vertebrae

28
Q

How do spinal roots exit from T1 to L5?

A

They exit below (inferior to) the vertebrae.

29
Q

How do the sacral nerve roots exit?

A

Via the sacral foramina.

-the S5 and 1st coccygeal nerve exits by the sacral hiatus.

30
Q

What are rami, and the two types?

A

After emerging from intervertebral foramen, each spinal nerve divides into rami.
Posterior/dorsal rami: deep muscles/skin of dorsal trunk
Anterior/ventral rami: muscles and skin of upper & lower limbs and lateral/ventral trunk

31
Q

Which type of rami is shorter?

A

Dorsal/posterior

32
Q

What is a meningeal branch?

A

Branches off from spinal nerve and re-enters spinal canal via intervertebral foramen.
-supplies the vertebrae, ligaments, blood vessels and meninges.

33
Q

What is the meninges?

A

3 layers that enclose the spinal chord and brain. (pia mater, dura mater, arachnoid)
- meningitis: meninges cause the pain

34
Q

Which nerves give off a white ramus communicans and what are they?

A

Spinal nerves T1-L2.
Pre-ganglionic sympathetic nerve.

They give off a white ramus communicans which enters the sympathetic trunk via paravertebral ganglion (ganglion of sympathetic chain)

35
Q

Which nerves receive a grey ramus communicans and what are they?

A

All spinal nerves.
-postganglionic sympathetic nerve fibres, unmyelinated
They receive grey ramus communicans from their adjacent paravertebral ganglion.

36
Q

What do the posterior rami divide into?

A

Medial and lateral branches.

-these supply a strip of skin/muscle of the back in line with the intervertebral foramen.

37
Q

What is the anterior rami distribution?

A
  • distribution remains segmental for the skin/muscles of the trunk
  • C5-T1 and L1-S5 enter the limb buds
  • the anterior rami that supply the limbs immediately enet the brachial plexus (C5-T1) or the lumbosacral plexus (L1-S5)
38
Q

What is strange about the segments for the front of the trunk?

A

C4 & T2 are adjacent in the trunk because the segments inbetween these form the limbs.

39
Q

What parts of the limb do the anterior rami supply?

A

Supply both the ventral and dorsal skin of upper & lower limbs.

40
Q

What is a myotome?

A

Group of muscles supplied by a single spinal nerve.

41
Q

Why is area of anaesthesia likely to be smaller than expected if a single spinal nerve is damaged?

A

There is functional overlap between adjacent dermatomes.

-this overlap does not cross the axial line!

42
Q

What is the axial line?

A

The junction of 2 dermatomes supplied from discontinuous spinal levels.
(you get ventral and dorsal axial lines)

43
Q

What are the axial borders?

A

At the cephalic/caudal margins of the limb.

-mark the borders of the anterior and posterior compartments of the limb

44
Q

What does the rotation of the limbs do to the post/pre-axial borders of the limbs?

A

-preaxial border lies on the lateral side of the arm
-postaxial border lies on the medial side of the arm
(arms rotate internally)
-preaxial border lies on the anteromedial aspect of limb
-postaxial border lies on the posterolateral aspect of limb

45
Q

What does anteromedial mean?

A

Towards the front, in the middle.

46
Q

How can you easily recall the posterior/anterior boundaries?

A

They are marked by superficial veins.
Upper limb:
-Cephalic vein (preaxial)
-basilic vein (postaxial)

Lower limb:

  • long saphenous vein (preaxial)
  • short saphenous vein (postaxial)
47
Q

What does a plexus allow to happen?

A

It allows axons from a single spinal nerve to emerge in several different peripheral nerves.

48
Q

Is the dermatome map and the peripheral nerve territories the same?

A

NO! They are different.

49
Q

Give an example of what plexus’ allow:

A

They allow the peripheral nerve e.g. median nerve to contain axons from C6,7,8 territories- they overlap.

50
Q

What are peripheral nerve territories?

A

Areas of the skin supplied by peripheral nerves.

-they overlap sections of multiple dermatomes

51
Q

In a peripheral nerve can there fibres from more than one spinal nerve?

A

Yes. Within each peripheral nerve there can be fibres from more than one spinal nerve.

52
Q

Can fibres from one spinal nerve enter more than one peripheral nerves?

A

Yes they can enter many peripheral nerves.

53
Q

How does shingles present?

A

In a dermatomal distribution.

  • virus from chickenpox lies dormant in dorsal root ganglion.
  • when host is immunosuppressed, virus reactivates and travels through a peripheral nerve to the skin of a single dermatome.
54
Q

What is a motor unit & how does this differ from a myotome?

A

A single motor neuron and the skeletal fibre it innervates.

Whereas a myotome is supplied by the whole spinal nerve which consists of many motor units.

55
Q

Does a single myotome include several muscles?

A

Yes. Because many peripheral nerves originate from a single spinal nerve. Therefore a single myotome usually includes muscle fibres in several muscles.

56
Q

Why will not all the axons in a peripheral nerve supply the same myotome?

A

Because they arise from different spinal nerves.

57
Q

What are the myotomes of the upper limb?

A

C5: shoulder abduction/external rotation
C6: elbow flexion/wrist extension/supination
C7: elbow extension/wrist flexion/pronation
C8:finger flexion/finger extension
T1: finger adduction/abduction

58
Q

What are the myotomes of the lower limb?

A 
L2: hip flexion
L3: knee extension
L4: ankle dorsiflexion
L5: great toe extension
S1: ankle plantar-flexion
S2: great toe flexion
59
Q

How is Hilton’s Law applied?

A

Use the fact that nerves supplying the muscles moving the joint, also supply the joint capsule and the skin overlying it.

60
Q

What do the white and grey ramus communicans do?

A

They join the spinal nerve to the sympathetic chain which allows nerves to travel superior/inferior to their origin.

MSK (12 decks)

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