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Sem 2 - MSK > Dermatomes And Myotomes > Flashcards

Dermatomes And Myotomes Flashcards

1
Q

What is each neural segment known as?

A

Each neural segment is known as a neural level.

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2
Q

When do somites get produced?

A

4th week of gestation

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3
Q

What does the sclerotome differentiate into?

A

Vertebrae and ribs

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4
Q

What does the dermatomyotome differentiate into?

A

Dermis (dermatome) Muscle (myotome)

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5
Q

What do the skin and muscle derived form a single dermatomyotome have in common?

A

They have a common spinal nerve supply because they have been developed in association with a specific neural level of the spinal cord.

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6
Q

What are roots? What are the two types?

A

Roots connnect each spinal nerve to a “segment” of the cord. Dorsal (posterior) roots contain afferent / sensory nerve fibres ONLY. Ventral (anterior) roots contain efferent / motor and autonomic nerve fibres ONLY.

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7
Q

What are spinal nerves?

A

Parallel bundles of axons encased in connective tissue. They are mixed motor and sensors and exist briefly as they pass through the intervertebral foramen which marks the devision between the CNS & PNS

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8
Q

How many pairs of spinal nerves do we have?

A

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

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9
Q

What is the nerve structure?

A
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10
Q

Whhat does the spinal cord run through?

What are multiple of these called?

How do spinal nerves leave this structure?

A

The spinal cord runs through the vertebral foramen.

Multiple vertibral foramina make up the spinal canal.

Spinal nerves leave the spinal canal via intervertrbral foramina.

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11
Q

When does the spinal cord start and finish?

A

The spinal cord starts at inferior margin of medulla oblongata.

It ends at conus medullaris at L2.

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12
Q

Where do the first pair of cervical nerve emerge?

A

They emerge between occipital bone and atlas (C1)

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13
Q

Where do thse nerves exit?

C1-C7?

C8?

T1-L5?

S1-S4?

S5 and Co1?

A

C1-C7 exit above

C8 between C7 and T1

T1-L5 exit below corresponding vertebrae

S1-S4 exit via 4 pairs of sacral foramina

S5 and Co1 exit via sacral hiatus (posterior)

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14
Q

What is a ramous?

A

Ramous is latin for branch. So they are branches of mixed spinal nerves.

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15
Q

What do spinal nerves divide into?

A

MIxd spinal nerves divide into rami:

Posterior / dorsal ramus: deep muscles and skin of the dorsal trunk (small)

Anterior / ventral ramus : muscles and skin of the upper and lower limbs and lateral and ventral trunk (large)

Meningeal branch: reenters the sponal canal through intervertebral foramen and supplied the vetrbrae, ligaments, blood vessles and meninges.

Rami communicantes: components of the autonomic system

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16
Q

What are the dorsal / posterior rami?

A

These rami (spinal nerves) divide again into medial and lateral branches.

They supply the skin of back in ‘tidy’ segmental manner

Narrow strip of muscle / skin in line with intervertebral foramen.

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17
Q

What are the ventral / anterior rami?

A

Complicated!

Segmental for the trunk

They enter plexuses to supply the limbs. eg brachial plexus for the upper limb and lumbo-sacral plexus for the lower limbs.

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18
Q

What dermatome map should be used?

A

Should use the foerster map (1933) as this is the one used in clinical practise.

19
Q

Define myotome

A

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

20
Q

Define dermatome

A

Area of skin supplied by a single spinal nerve (or spinal root nerve)

21
Q

In what way do dermatomes overlap?

A

There is functional overlap between adjacent dermatomes. BUT, not across the axial line.

22
Q

What is an axial line?

A

The junction of two dermatomes supplied from discontinuous spinal levels.

Limbs have an anterior and posterior axial lies.

They mark the centre of either the ventral or dorsal compartments of the limb.

23
Q

What are axial borders?

A

Boundaries of dorsal (posterior) and ventral (anterior) compartments.

They are marked by superficial veins.

24
Q

What are the axial borders of the upper limb?

A

Cephalic vein (pre-axial)

Basilic vein (post-axial)

25
Q

What are the axial borders of the lower limb?

A

Long (great) saphenous vein (pre-axial)

Short (small) saphenous vein (post-axial)

26
Q

What is the relationship between spinal nerves and peripheral nerves?

A

Peripheral nerves often contain neurones from several spinal nerves.

Fibres from one spinal nerve can enter multiple peripheral nerves.

The rearrangement occurs in plexuses.

27
Q

What are peripheral nerve territories?

A

Peripheral nerve territories are NOT dermatome.

These are areas of the skin supplied by the peripheral nerves.

They are branches of the brachial plexus in the upper limb and branches of the lumbosacral plexus in the lower limb.

They often overlap sections of dermatomes (conistant with their spinal nerve content)

28
Q

What is Herpes Zoster and why is it clinically relevent?

A

Shingles!

It is a viral infection that almost always affects the skin of a single dermatome.

It is caused by the reactivation of Varicellar zoster virus (chickenpox).

This virus travels through a cutaneous nerve and remians dormant in a dorsal root ganglion after chicken pox.

When host is ‘immunosuppressed’ VZV’ reactivates and travels through peripheral nerve to skin of a single dermatome.

29
Q

What is the difference between a myotome and a motor unit?

A

A motor unit is a motor neurone and the skeletal muscle fires or innervates it.

One spinal nerve contains the neurones of many motor units.

One spinal nerve supplies one myotome

30
Q

What is the role of the C5 myotome?

A
  • Shoulder abduction
  • External rotation
  • weak contribution to elbow flexion
31
Q

What is the role of the C6 myotome?

A
  • Elbow flextion
  • Wrist extention
  • Supination
  • Internal rotation of the shoulder
32
Q

What is the role of the C7 myotome?

A
  • Elbow extention
  • Wrist flextion
  • Pronation
  • Weak contribution to finger flexion and extension.
33
Q

What is the role of the C8 myotome?

A
  • Finger flexion
  • Finger extention
  • Thumb extention
  • Wrist ulnar deviation
34
Q

What is the role of the T1 myotome?

A
  • Finger abduction
  • Finger adduction.
35
Q

What is the role of the L2 myotome?

A

Hip flexion

36
Q

What is the role of the L3 myotome?

A
  • Knee extention
  • Hip adduction
37
Q

What is the role of the L4 myotome?

A

Ankle dorsiflexion

38
Q

What is the role of the L5 myotome?

A
  • Great toe extension
  • Ankle eversion
  • Hip extension
39
Q

What is the role of the S1 myotome?

A
  • Ankle plantar-flexion
  • Ankle eversion
  • Hip extension (or S5)
40
Q

What is the role of the S2 myotome?

A
  • Great toe flexion
  • Knee flexion (some sources sau S1 for this)
41
Q

What s Hilton’s law?

A

The nerve supplying the muscles extending directly across and acting at a given joint also innervate the joint.

42
Q

What are some applications of Hilton’s law?

A

The femoral nerve (L 2,3,4)..

Supplies the quadriceps femoris group of muscles.

It extends the knee joint.

It also supplies the skin overlying the knee joint.

Myotome for knee extension is L3.

Dermatome for overlying anterior knee is L3.

43
Q

What is the clinical relevance of Hilton’s law?

A

Femoral nerve injury: -Anaesthesia in cutaneous distribution of femoral nerve and its branches.

Paralysis in muscles supplied by femoral nerve (distal to site of injury).

44
Q

What is a neural level?

A

Lowest level of absolute function.

This might be different to vertebral levels as there are lots of discrepancies.

Sem 2 - MSK (22 decks)

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