Dermatomes, myotomes and segmental innervation

Question 1

what is a neural level anatomically?

Answer 1

Each neural segment is a neural level

Question 2

when are pairs of somites formed?

Answer 2

4th week gestation

Question 3

What does the neural tube contain?

Answer 3

Precursor cells of nervous system

Question 4

What does the sclerotome form?

Answer 4

Vertebrae and ribs

Question 5

What does the dermatomyotome form?

Answer 5

Dermis and muscle

Question 6

Two parts of somite

Answer 6

sclerotome (ventral underneath myotome)

Dermatomyotome (dorsal)

Question 7

How do dermatomyotomes develop?

Answer 7

From somites (dorsal part)
In association with a specific neural level
Take their nerve supply with them from neural tube

Question 8

What is the nerve associated with dermatomyotome known as?

Answer 8

Spinal nerve

Question 9

What occurs if skin and muscle are derived from a single dermatomyotome?

Answer 9

They have a common spinal nerve supply

Question 10

Nerve structure

Answer 10

Endoneurium (around axons)
Perineurium (around fasicle of axons)
Epineurium (around entire nerve)

(have blood vessels within to supply them)

Question 11

What do roots do?

Answer 11

Connect each spinal nerve to a segment of spinal cord

Question 12

What do dorsal roots contain?

Answer 12

Afferent (towards CNS)

sensory nerve fibres ONLY

Question 13

Where are dorsal roots located?

Answer 13

Posterior of spinal cord

Question 14

What do ventral roots contain?

Answer 14

efferent (away from CNS)

motor and autonomic nerve fibres ONLY

Question 15

Where are ventral roots located?

Answer 15

Anterior of spinal cord

Question 16

What does dorsal root ganglion contain?

Answer 16

Cluster of cell bodies of sensory neurons from periphery

Question 17

What do spinal nerves contain?

Answer 17

Mixed motor and sensory nerves

Question 18

Where are spinal nerves found?

Answer 18

Only briefly as they pass through intervertabral foramen

when dorsal root and ventral root come together

Question 19

What does the interbvertabral foramen mark?

Answer 19

The division between CNS and PNS

Question 20

How many spinal nerves are there and how are they named?

Answer 20

31

named according to the level of vertabrae that they emerge from

Question 21

What are vertebral segments derived from?

Answer 21

Differentiate from sclerotomes

Each one derived from pair of adjacent somites (overlap)

Question 22

Where does the spinal cord run?

Answer 22

Through vertebrae foramen

known as spinal canal when they are stacked

Question 23

How do the spinal nerves leave the spinal canal?

Answer 23

Via intervertebral foramina

Question 24

where does spinal cord begin and end?

Answer 24

inferior margin Medulla oblongata 
Conus medullaris (L2)

Question 25

are spinal cord segments in line with their vertebrae?

Answer 25

NO (vertabra is longer than cord)

Question 26

What is cauda equina?

Answer 26

Lower part of spinal canal | contains spinal nerves but not cord

Question 27

How do the roots from inferior spine exit vertebrae if they are not in line with their segment?

Answer 27

Long roots from inferior spinal cord often have to descend down into cauda equina and exit at their intervertabral foramina

Question 28

Where does the first spinal nerve emerge?

Answer 28

Cervical nerves | C1 (between occipital bone and atlas)

Question 29

where do C1 - C7 spinal nerves emerge?

Answer 29

Above their corresponding vertebrae

Question 30

Where does C8 spinal nerve emerge?

Answer 30

Between C7 and T1

Question 31

Where do T1 and L5 spinal nerves exit?

Answer 31

Below their corresponding verterbrae

Question 32

where do s1-s4 nerves exit?

Answer 32

Sacral bones are fused together | Exit via 4 pairs of sacral foramina

Question 33

Where do S5 and Co1 exit?

Answer 33

Sacral hiatus

Question 34

What are rami?

Answer 34

Mixed spinal nerves divide into them

Question 35

Branches of spinal nerve

Answer 35

Dorsal rami Ventral rami Rami communicantes Meningeal branch

Question 36

Dorsal ramus

Answer 36

Posterior and small | Supplies deep muscles of skin and dorsal trunk

Question 37

Ventral ramus

Answer 37

Anterior and larger | Supplies muscles and the skin of upper and lower limbs and lateral and ventral trunk

Question 38

Meningeal branch

Answer 38

Re-enters spinal canal through intervertebral foramina Supplies vertebrae, ligaments, blood vessels and meninges

Question 39

Rami communicantes

Answer 39

Part of the autonomic nervous system

Question 40

Grey rami communicantes

Answer 40

Contains unmyelinated post ganglionic nerve fibres Travels from a sympathetic ganglion to adjacent spinal nerve Supply the periphery ALL SPINAL NERVES RECIEVE

Question 41

White rami communicantes

Answer 41

Myelinated Come off between T1 and L2 Preganglionic nerve fibres of sympathetic system Connects spinal cord to sympathetic chain

Question 42

What do the dorsal/posterior rami do?

Answer 42

Divide into medial and lateral branches | Supply the skin of the back

Question 43

What is a dermatome?

Answer 43

Area of skin supplied by a single spinal nerve

Question 44

What do the ventral/anterior rami do?

Answer 44

Complicated | Enter plexuses to supply limbs

Question 45

Junction on anterior chest dermatome

Answer 45

C4 and T2 (T1 supplies upper limbs instead)

Question 46

Learn dermatome map ella

Answer 46

LEARN ITTT (Foerester map)

Question 47

Key sections dermatome map:

Answer 47

T4/T5 - nipples T10 - umbilicus L1 - Groin