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MSK > Session 2: Dermatomes > Flashcards

Session 2: Dermatomes Flashcards

1
Q

Define dermatome.

A

An area of the skin that is supplied by a single spinal nerve.

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2
Q

The skin and muscle that derive from the same single dermatomyotome have a special feature. Which?

A

They have a common spinal nerve supply.

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3
Q

What are vasa nervorum?

A

Blood vessels found within the epineurium that supply the high metabolic requirements of the nerves.

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4
Q

What type of fibres does the dorsal root transmit?

A

Sensory fibres. It’s an afferent root.

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5
Q

What type of fibres does the ventral root transmit?

A

Motor or autonomic fibres. It’s an efferent root.

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6
Q

How many pairs of spinal nerves are there?

A

31.

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7
Q

What does the sclerotome differentiate into?

A

The vertebrae but also the ribs in the thoracic region.

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8
Q

What does the spinal cord run through?

A

The vertebral foramen.

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9
Q

What does multiple vertebral formina form?

A

The spinal canal.

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10
Q

Where do nerves leave the spinal canal?

A

Through gaps in between vertebrae called the intervertebral foramina.

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11
Q

Where does the spinal cord begin?

A

The inferior margin of the medulla oblongata at the base of the brain stem.

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12
Q

Where does the spinal cord end?

A

Around L2 at the conus medullaris. Usually at the L1/L2 level.

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13
Q

What is below the spinal cord?

A

The cauda equina.

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14
Q

What is the cauda equina?

A

A bundle of spinal nerves that start where the spinal cord ends, around L1/L2 - L2.

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15
Q

How many cervical spinal roots are there?

A

8

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16
Q

How many cervical vertebrae are there?

A

7

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17
Q

Where is cervical spinal root 1 located?

A

Just above cervical vertebrae 1 (C1).

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18
Q

Where is cervical spinal root 4 located?

A

Just above cervical vertebrae 4 (C4) and below C3 so C3/C4.

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19
Q

Where is cervical spinal root 8 located?

A

Below cervical vertebrae 7 (C7) and above thoracic vertebrae 1 (T1) so C7/T1.

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20
Q

Is this the pattern of all the spinal roots?

A

In the cervical region the spinal root of the given vertebrae is above the vertebrae. However in the thoracic region for example the spinal root for the given thoracic vertebrae is located below its corresponding vertebrae.

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21
Q

Where is thoracic spinal root 4 located?

A

Below thoracic vertebrae 4 (T4) and above thoracic vertebrae 5 (T5) so T4/T5.

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22
Q

After the spinal nerve emerges from the intervertebral foramen, what happens?

A

Each spinal nerve divides into rami.

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23
Q

What rami is the spinal nerve divide into?

A

Into the dorsal (posterior) ramus and the ventral (anterior) ramus and a small meningeal branch.

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24
Q

What does the dorsal ramus supply?

A

The deep muscles and skin of the dorsal trunk.

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25
Q

What does the ventral ramus supply?

A

The muscles and skin of the upper and lower limbs and also the lateral and ventral trunk. Both ventral and dorsal skin of th upper and lower limbs!

26
Q

What’s largest; the dorsal ramus or ventral ramus?

A

The ventral ramus is much larger.

27
Q

What is the meningeal branch?

A

A small branch that pinch off from where the spinal nerve divides into the ventral and dorsal rami.

28
Q

What does the meningeal branch supply?

A

It goes back into the spinal canal through the intervertebral foramen. It supplies the vertebrae, ligaments of the vertebral column, blood vessels and meninges.

29
Q

What is the grey ramus communicans?

A

Each spinal nerve receives a branch that is the grey ramus communicans. It contains post-ganglionic nerve fibres of the autonomic nervous system. It is composed largely of unmyelinated neurons.

30
Q

Label the diagram.

A
31
Q

Where does the ventral rami that supply upper limbs enter?

A

A complex network of nerves called the brachial plexus that is located at C5-T1.

32
Q

Where does the ventral rami that supply the lower limb enter?

A

Into a complex network of nerves calle the lumbosacral plexus that goes from L1-S5.

33
Q

Why are the dermatomes C4 and T2 adjacent to each other on the anterior trunk?

A

Because the anterior rami from C5-T1 enter the brachial plexus to supply the upper limb. This means that they do not have a cutaneous distribution to each other on the trunk.

34
Q

Why do we not lose all sensation in a dermatome if the corresponding spinal nerve is damaged?

A

Because there is overlap between adjacent dermatomes. This means that if you get a single spinal nerve damage the area of loss of sensation will probably be smaller than one would imagine.

35
Q

Define axial line.

A

The junction of two dermatomes supplied from discontinous spinal levels.

36
Q

Explain axial line.

A

The junction of two dermatomes supplied from discontinuous spinal levels. This can be seen for example in the upper limbs where (C5 and T2), (C6 and T1) for example lay adjacent to each other. Even though C5 and T2 lay adjacent to each other in the upper limb the spinal nerves on a spinal level do not (by the vertebrae).

37
Q

Why is the axial line important?

A

Because there is no functional overlap across an axial line. This means that C5 has no overlap of nerves to T2.

38
Q

How does the upper limb rotate?

A

Laterally 90 degrees

39
Q

How do the lower limbs rotate?

A

Medially through around 90 degrees.

40
Q

What are the axial borders?

A

They are the cephalic and caudal margin of the limb bud and mark the borders of the anterior and the posterior compartments of the limbs.

41
Q

Where is the pre-axial border of the upper limb?

A

Lateral side of the arm.

42
Q

Where is the post-axial border of the upper limbs?

A

On the medial side of the arm in line with the thumb.

43
Q

Where is the pre-axial border on the lower limbs?

A

Anteromedial aspect of the limb.

44
Q

Where is the post-axial border of the lower limbs?

A

On the posterior or sometimes called posterolateral aspect of the limb.

45
Q

The dorsal and ventral compartements of the borders are marked by something. What?

A

By superficial veins.

46
Q

What marks the pre-axial border in the upper limbs?

A

The cephalic vein.

47
Q

What marks the post-axial border in the upper limbs?

A

The basilic vein.

48
Q

What marks the pre-axial border in the lower limbs?

A

The long/great saphenous vein.

49
Q

What marks the post-axial border of the lower limbs?

A

The short/small saphenous vein.

50
Q

What do the brachial plexus and the lumbosacral plexus do?

A

The allow an axon from a signle spinal nerve to follow multiple different roues through the plexus and therefore emerge in several different peripheral nerves.

51
Q

What does a root value of C6-T1 indicate?

A

This is the root value of the median nerve. This means that it receives axons from C6, C7, C8 and T1 spinal nerves. This also means that if you damage T1 you will not lose the entire sensation of the median nerve.

52
Q

What do the axons that orignate in the C6 spinal nerve and travel to the median nerve supply?

A

Skin that is both in the C6 dermatome and the median nerve territory.

53
Q

What do the axons that originate in the C7 spinal nerve and travel in the median nerve supply?

A

The skin in both the C7 dermatome and the median nerve territory.

Since both the C7 spinal nerve and the C6 spinal nerve supply the median nerve territory it shows how there is overlap in the peripheral nerve territories.

54
Q

From which vertebra/spinal root do fibres form the musculocutaneous nerve?

A

From C5, C6 and C7.

55
Q

What does the musculocutaneous nerve supply? Which dermatome does it correspond to?

A

The skin of the lateral forearm. This is via the terminal cutaneous branch and the lateral cutaneous branch of the fore arm.

Part of the C6 dermatome.

56
Q

What is the root value of the musculocutaneous nerve?

A

C5-C7

57
Q

What is the root value of the femoral nerve?

A

L2-L4.

58
Q

What do the fibres of the L2 enter?

A

The lumbosacral plexus.

59
Q

The L2 fibres enter the lumbosacral plexus and will divide here. What will it divide into?

A

Multiple peripheral nerves like:

The femoral nerve

The obturator nerve

The lateralfemoral cutaneous nerve

The genitofemoral nerve

The illioinguinal nerve

All of these nerves can be found in the L2 dermatome.

60
Q

What does the L4 dermatome exclusively map?

A

The saphenous branch of the femoral nerve.

61
Q

What does the L3 dermatome exclusively map?

A

The anterior femoral cutaneous nerve.

62
Q

The area of skin supplied by a peripheral nerve does not correspond to the dermatome map. What does this mean?

A

That the peripheral nerves contains fibres from multiple dermatomes.

Also one dermatome may be supplied by multiple peripheral nerves because the fibres within a single spinal nerve may enter multiple different peripheral nerves.

MSK (28 decks)

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