Lecture 3 - Dermatomes and myotomes

Question 1

How many pairs of somites

Answer 1

34-35 pairs of somites (Day 30)

Question 2

Sclerotome

Answer 2

Differentiated somite
Ventral
Gives rise to vertebrae and ribs

Question 3

Dermatomyotome

Answer 3

Differentiated somite
Dorsal
Forms the dermis - dermatome
Forms the muscle - myotome

Question 4

Why does the skin and muscle have the same common spinal nerve supply

Answer 4

Derived from the same dermatomyotome

Question 5

Dermatome

Answer 5

Area of skin that is supplied by a single spinal nerve

Question 6

T4/T5

Answer 6

Nipples

Question 7

T10

Answer 7

Umbilicus

Question 8

L1

Answer 8

Groin

Question 9

Posterior (dorsal) rami

Answer 9

After emerging from the intervertebral foramina each nerve root divides into rami

Into medial and lateral branches that supply the skin and deep muscles of the back in a segmental manner

Each dorsal ramus supplies a narrow strip of muscle and skin in line with the intervertebral foramen

Question 10

Anterior (ventral) rami

Answer 10

Complicated distribution

Segmental for the skin and muscle of the trunk

Supply both the anterior (ventral) and posterior (dorsal) skin of the upper and lower limb

C5-T1 - upper limbs (brachial plexus)

L1- S5 - lower limbs (lumbosacral plexus)

Question 11

C5 - T1

Answer 11

Brachial plexus
Upper limbs
No cutaneous distribution on the trunk

Question 12

L1-S5

Answer 12

Lumbosacral plexus

Lower limbs

Question 13

Adjacent dermatomes in anterior trunk

Answer 13

C4 and T2

Question 14

Functional overlap

Answer 14

Overlap between adjacent dermatomes

When a spinal nerve is damaged, the area that loses sensation (anaesthesia) is smaller than expected due to the overlap

Overlap does not extend across an axial line

Question 15

Hilton’s Law

Answer 15

Nerve supplying the joint capsule also supplies th muscles moving the joint and the overlying skin

Question 16

Neural level (clinical)

Answer 16

Lowest level of fully intact sensation and motor function

Question 17

What does the neural tube consist of

Answer 17

Precursor cells for the nervous system

Question 18

Neurone

Answer 18

Electrically excitable cell that receives, processes and transmits information via chemical and electrical signals

Question 19

Nerve

Answer 19

Enclosed bundle of axons and associated cell bodies e.g Schwann cells in the peripheral nervous system

Question 20

Endoneurium

Answer 20

Encloses each axon
Made of glycocalyx and a collagen mesh
Contains endoneurial fluid
Prevents certain molecules from the blood crossing

Question 21

Nerve irritation or injury

Answer 21

Endoneurial fluid increases

Oedema detected by MRI

Question 22

Fascicles

Answer 22

Bundles of axons enclosed by perineurium

Question 23

Perineurium

Answer 23

Covers fascicles

Question 24

Epineurium

Answer 24

Covers group of fascicles

Contains nerve blood supply- vasa nervorum

Question 25

Spinal nerve

Answer 25

Mixed nerve - motor - sensory - autonomic signals Exit vertebrae via intervertebral foramina

Question 26

Dorsal nerve root

Answer 26

Afferent Sensory fibres from the sensory receptors towards the spinal cord

Question 27

Ventral nerve root

Answer 27

EFFERENT Carries motor or autonomic fibres that are leaving the spinal cord

Question 28

Spinal cord

Answer 28

Origin- inferior margin of the medulla oblongata (base of brain stem) Up to L1/L2 level - Conus Medullaris

Question 29

Cauda Equina

Answer 29

Continuation of spinal cord after L2

Question 30

Where do the cervical spinal roots emerge from in relation to the cervical vertebrae

Answer 30

7 vertebrae and 8 nerves First 7 cervical spinal roots run above the vertebrae The 8th cervical spinal root runs below C7 (C7/T1)

Question 31

Where does the 5th sacral and 1st coccygeus nerve root exit from

Answer 31

Sacral hiatus

Question 32

After the spinal nerve exits the intervertebral foramen, what does it do?

Answer 32

Splits into: - Dorsal rami - Ventral rami - Meningeal branch - receives grey ramus communicans

Question 33

Meningeal branch

Answer 33

Supplies the: - vertebrae - vertebral ligaments - blood vessels - meninges

Question 34

Grey ramus communicans

Answer 34

- Joins spinal nerve once exits intervertebral foramen - From adjacent paravertebral ganglion of the sympathetic trunk - Contains postganglionic nerve fibres of ANS (unmyelinated)

Question 35

Axial line

Answer 35

Junction of 2 dermatomes supplied from discontinuous spinal levels

Question 36

Axial borders

Answer 36

At the cephalic and caudal margins of the limb bud Mark the border of the anterior and posterior compartments of the limb

Question 37

Preaxial

Answer 37

Upper limb - Rotates and lies laterally (thumb is lateral) | Lower limb - Rotates and lies medially (Big toe is medial)

Question 38

Peripheral nerves

Answer 38

Contain different contributions of axons from different spinal nerves Map pain

Question 39

Myotomes

Answer 39

Group of muscles supplied by a single spinal nerve

Question 40

Motor unit

Answer 40

Motor neurone and skeletal muscle fibre it innervates