MSK 4 - Dermatomes, Myotomes + Segmental Innervation of Limbs Flashcards

1
Q

Segmentation is a fundamental design of biological systems, the CNS is segmented throughout - what is each neural segment called?

A
  • A neural level (e.g.: C6)
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

From which somites do the vertebrae/ribs and dermis/muscle differentiate from?
What do dermamyotomes develop in association with?

A

Vertebrae + Ribs = Sclerotome
Dermis + Muscle = Dermamyotome

Sclerotome + DMT are formed from differentiation of somites on either side of the neural tube.

DMT’s develop in association with specific neural level of spinal cord + take nerve supply with them from neural tube as a spinal nerve. Skin + Muscle derived from 1 DMT have a common spinal nerve supply as a consequence

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

Outline the structure of a nerve (from in to out)

A
  • Single axon wrapped in myelin sheath , surrounded by endoneurium.
  • Axons bunched into fascicles, perineurium surrounding fascicles.
  • Connective tissue + blood vessels in between separate fascicles
  • Epineurium surrounds entire nerve, with spinal nerves running underneath it.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

What type of nerve fibres do the dorsal (posterior) and ventral (anterior) roots contain in a spinal cord section?
What are the “spinal nerves” + how many are there?

A
Dorsal = afferent/sensory nerve fibres
Ventral = efferent/motor + autonomic nerve fibres
  • Spinal nerves are bundles of mixed (motor + sensory) axons which exist briefly and pass through the intervertebral foramen, marking the division between the PNS + CNS
  • 31 pairs numbered according to the level of the vertebral column they appear from.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

What is each vertebra derived from?
Where does the spinal cord run through?
Where does the spinal cord start + finish?
Where do long roots from segments inferior to the finish descend in?

A
  • Parts of 2 adjacent somites, e.g.: vertebra C2 is derived from sclerotome C2 + C3
  • The vertebral foramina (the spinal canal)
  • Spinal cord starts at inferior margin of medulla oblongata + ends at conus medullaris (at L2 level)
  • Inferior segments descend in as a part of the cauda equina and exit at their respective foramina.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

Which spinal nerves exit above corresponding vertebrae?

Which spinal nerves exit below corresponding vertebrae?

A
  • C1-C7 spinal nerve exit above corresponding vertebrae
  • C8 exists between C7 + T1
  • T1-L5 exit below corresponding vertebrae
  • S5 + Co1 exit via sacral hiatus (posteriorly)
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

What 3 things do mixed spinal nerves divide into?

What do these divisions supply?

A

1) The posterior/dorsal ramus - supplies deep muscles and skin of dorsal trunk
2) Anterior/ventral ramus - supplies muscles and skin of upper and lower limbs, and ventral trunk
3) Meningeal branch - re-enters spinal canal through intervertebral foramen, supplying vertebrae, ligaments, blood vessels + meninges.

NB: be able to label spinal nerve divisions - see slide 15

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

What do the dorsal + ventral rami divide again into?

What do these divisions supply?

A
  • Dorsal rami further divides into medial + lateral branches. They supply the skin of the back in a ‘tidy’ segmental manner (i.e.: dermatomes)
  • Ventral rami enter plexuses to supply the limbs (brachial plexus for upper limbs, lumbro-sacral plexus for lower limbs).
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

Define “dermatome” and “myotome”

A

Myotome = group of muscles supplied by single spinal nerve

Dermatome = area of skin supplied by single spinal nerve

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

What are anterior and posterior axial lines of limbs and what is their function?
What are pre-axial and post-axial borders?

A
  • Limbs have A + P axial lines which are junctions of two dermatomes. There is functional overlap between adjacent dermatomes, but not across these axial lines - which mark the centre of ventral or dorsal limb compartments.
  • Boundaries of dorsal and ventral compartments on limbs marked by superficial veins.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

Fibres from one spinal nerve can enter multiple peripheral nerves - give an example of this.
Where does the rearrangement of these nerves occur?

A
  • Fibres from C6 spinal nerve enters the musculocutaenous, radial and median nerve (this concept is key) - via the brachial plexus
  • Rearrangement occurs in the plexuses
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

Can fibres from multiple spinal nerve combine to form a peripheral nerve? If yes, give an example.

What is the outcome of this?

A

Yes - e.g.: spinal nerves from C5,6 + 7 combine to form musculocutaenous nerve

  • Outcome of this are peripheral nerve territories (these are NOT dermatomes), but areas of skin supplied by peripheral nerve. Branches of brachial plexus for upper limb + lumbro-sacral for lower. They often overlap sections of multiple dermatomes.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

Summarise the 2 key concepts of peripheral and spinal nerves

A

1) Within each peripheral nerve there may be fibres from multiple spinal nerves
2) Fibres from spinal nerves may enter multiple peripheral nerves

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

What is the clinical relevance of dermatomes?

A
  • Viral infections - affect the skin of a single dermatome. E.g.: VZV can reactivate and travel through peripheral nerve to the skin of a single dermatome (typically T2)
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

What is a motor unit?
How many neurones of motor units does a spinal nerve contain?
How many spinal nerves supply 1 myotome?

A
  • A motor unit = a motor neuron and the skeletal muscle fibres it innervates.
  • 1 spinal nerve contains neurones of many motor units
  • 1 spinal nerve supplies 1 myotome
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

What movements of the upper limb are supplied by these myotomes …

  • C5, C6, C7, C8 + T1
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 abduction/finger adduction
17
Q

What movements are the lower limb are supplied by these myotome …

  • L2, L3, L4, L5, S1 + S2
A
L2 = hip flexion
L3 = knee extension
L4 = anke dorsiflexion
L5 = great toe extension 
S1 = ankle plantar-flexion
S2 = great toe flexion
18
Q

What is Hilton’s Law?

A

The nerves crossing a joint supply …

1) The muscles acting on it
2) The skin over the insertion of those muscles
3) The joint itself