Dermatomes + Myotomes

Question 1

How many pairs of somites do we have?

Answer 1

34-35

Question 2

What do somites differentiate into?

Answer 2

Sclerotome
Dematomyotome > dermatome + myotome

Question 3

What forms the vertebrae + ribs?

Answer 3

Sclerotome

Question 4

What arises from the Sclerotome?

Answer 4

Vertebrae + ribs

Question 5

What arises form the dermatome?

Answer 5

Dermis

Question 6

What arises form myotome?

Answer 6

Muscle tissue

Question 7

What forms muscle tissue?

Answer 7

Myotomes

Question 8

What forms the dermis?

Answer 8

Dermatomes

Question 9

What do skin + muscles from the same dermatomyotome have?

Answer 9

A common spinal nerve supply

Question 10

Why do skin + muscles from the same dermatomyotome have a common spinal nerve supply?

Answer 10

Dermatomyotome develop with a specific neural level of spinal cord + take their nerve supply from neural tube as a spinal nerve

Question 11

Describe the structure of a nerve

Answer 11

• Each axon is surrounded by endoneurium
• Many of these together forms a fascicle
• Each fascicle is surrounded by perineurium
• Fascicles are grouped + get surrounded by epineurium

Question 12

• Each exon is surrounded by ***
• Many of these together forms a ***
• Each fascicle is surrounded by ***
• Fascicles are grouped + get surrounded by ***

Answer 12

• Each exon is surrounded by endoneurium
• Many of these together forms a fascicle
• Each fascicle is surrounded by perineurium
• Fascicles are grouped + get surrounded by epineurium

Question 13

Name of the blood vessels in the epineurium

Answer 13

Vasa nervorum

Question 14

What is the dermatome at the umbilicus?

Answer 14

T10

Question 15

What dermatome is the groin?

Answer 15

L1

Question 16

What dermatome are the nipples?

Answer 16

T4/5

Question 17

What is the dermatome of the middle finger?

Answer 17

C7

Question 18

Where do spinal cords run through?

Answer 18

Vertebral foramen

Question 19

What makes up the spinal canal?

Answer 19

Multiple vertebral foramina

Question 20

Spinal nerves leave the spinal canal through…

Answer 20

Intervertebral foramina

Question 21

Where is the start and end of the spinal cord?

Answer 21

Start - Inferior margin of medulla oblongata
End - Conus medullaris at L1

Question 22

Where is the cauda equina?

Answer 22

Below the conus medullaris

Question 23

List the spinal nerves and where they exit the vertebral column

Answer 23

C1-C7 - exit above corresponding vertebrae
C8 - exits between C7 + T1
T1-L5 - exit below corresponding vertebrae
S1-S4 - exit via 4 pairs of sacral foramina
S5-Co1 - exit via sacral hiatus

Question 24

How many spinal bones are there for each region?

Answer 24

Cervical - 7
Thoracic - 12
Lumbar - 5
Sacral - 5 fused
Coccygeal - 4 fused

Question 25

What does the dorsal ramus supply?

Answer 25

Deep muscles + skin of dorsal trunk

Question 26

What does the ventral ramus supply?

Answer 26

Muscles + skin of upper + lower limbs Lateral + ventral trunk

Question 27

Each spinal nerve divides off a meningeal branch, what happens to them?

Answer 27

- renters spinal canal via intervertebral foramen - supplies vertebrae, ligaments + meninges

Question 28

Define dermatome

Answer 28

Area of skin supplied by a single spinal nerve

Question 29

Define myotome

Answer 29

Group of muscles supplied by a single spinal nerve

Question 30

Define axial line

Answer 30

Junction of two dermatomes supplied from discontinuous spinal level

Question 31

What are the meninges of the spinal cord? From centre out

Answer 31

Pia mater Arachnoid Dura mater

Question 32

How do upper limbs rotate during development? Where do the pre and post axial borders lie?

Answer 32

Upper limbs rotate **externally** **Pre-axial**: lateral side of arm **Post axial**: medial side of arm

Question 33

How do lower limbs rotate during development? Where do the pre and post axial borders lie?

Answer 33

Lower limbs rotate **internally** **Pre-axial**: anteromedial aspect of leg **Post-axial**: posterior aspect of leg

Question 34

Define a motor unit

Answer 34

A single motor neurone + the skeletal muscle fibres it innervates

Question 35

Myotomes of the lower limbs

Answer 35

**L2** - hip flexion **L3** - knee extension **L4** - ankle dorsiflexion **L5** - great toe extension **S1** - ankle plantarflexion **S2** - great toe flexion

Question 36

What is a clinical neural level?

Answer 36

Lowest level of fully intact sensation and motor function

Question 37

Outline the embryological development of dermatomes

Answer 37

1- CNS develops from paired somites 2- somites differentiate to form dermatomyotome 3- these develop in association with a specific neural level of the spinal cord >> associated with specific spinal nerve 4- dermatome portion of dermatomyotome forms the dermis >> area of skin supplied by corresponding spinal nerve

Question 38

Myotomes of the upper limb

Answer 38

**C5** - shoulder ABduction - external rotation **C6** - elbow flexion - wrist extension - supination **C7** - elbow extension - wrist flexion - pronation **C8** - finger flexion + extension **T1** - finger ABduction + ADuction

Question 39

Myotome of C5

Answer 39

Shoulder ABduction External rotation

Question 40

Myotome of C6

Answer 40

Elbow flexion Wrist extension Supination

Question 41

Myotome of C7

Answer 41

Elbow extension Wrist flexion Pronation

Question 42

Myotome of C8

Answer 42

Finger flexion + extension

Question 43

Myotome of T1

Answer 43

Finger ABduction + ADduction

Question 44

Myotome of L2

Answer 44

Hip flexion

Question 45

Myotome of L3

Answer 45

Knee extension

Question 46

Myotome of L4

Answer 46

Ankle dorsiflexion

Question 47

Myotome of L5

Answer 47

Great toe extension

Question 48

Myotome of S1

Answer 48

Ankle plantarflexion

Question 49

Myotome of S2

Answer 49

Great toe flexion