Session 4 - Dermatomes

Question 1

What does the scleretome develop into?

Answer 1

-Vertebrae and ribs

Question 2

What does dermamyotome develop into?

Answer 2

-Dermis and muscles

Question 3

What does the neural tube of an embryo develop into?

Answer 3

-The spinal cord

Question 4

What is filum terminale?

Answer 4

-The slender tapering terminal of the spinal cord

Question 5

What is the conus medullaris?

Answer 5

-The conical end of the spinal cord, at the level of the first lumbar vertebrae

Question 6

Where does the spinal cord start and end?

Answer 6

-Begins at medulla of brain and finishes at the conus medullaris at L2/L3 where it tapers into a ligament

Question 7

How does the spinal cord run through the vertebrae?

Answer 7

-Through the spinal canal formed by successive vertebral formina

Question 8

What is the function of the vertebral column?

Answer 8

-To cover the spinal cord for protection

Question 9

What is an intervertebral foreman?

Answer 9

-An opening formed in the midline between two successive vertebrae

Question 10

What is are paired segmental nerves?

Answer 10

-The pair of spinal nerve (L+R) which specifically arise from every level of the spinal cord

Question 11

How do segmental nerves leave the spinal canal?

Answer 11

-Through intervertebral foreman

Question 12

Do segmental nerves/spinal nerves leave the spinal canal superior or inferior to their corresponding vertebral levels?

Answer 12

-In the cervical cord, spinal nerves exit superior to their corresponding vertebrae and in the thoracic, lumbar and sacral cords the segmental nerves leave inferior to the corresponding levels

Question 13

Why is it clinically relevant that nerves leave the spinal canal through intervertebral foramen?

Answer 13

-The intervertebral foramen are heavily offset from the spinal cord where the nerve root lies and the nerve can become strangulated (foramen hernia strangulation)

Question 14

Are the segments of the spinal cord all peripherally attached to each other?

Answer 14

-No, each spinal segment has independance of connection to the periphery (although the segments themselves are neurally connected to each other)

Question 15

What do sensory nerve supply?

Answer 15

-Discrete segments of skin known as terratories

Question 16

What do motor nerves supply?

Answer 16

-Myotomes

Question 17

What is a neural level and how does it differ to a vertebral level?

Answer 17

-A neural level is a segment of the spinal cord
-A vetebral level is the vertebrae of the spine
They are in different anatomical locations

Question 18

Why, and where, does the spinal cord vary in its thickness?

Answer 18

-Thicker in its cervical and lumbar segments as it has excessive neural tissue for the upper and lower limb, respectively

Question 19

Why are segmental nerves described as mixed spinal nerves?

Answer 19

-As the spinal nerve leaves the intervertebral foramen it branches into small dorsal and large ventral rami which contain both sensory and motor functions

Question 20

What happens to dorsal rami as it emerges from the intervertebral foramen?

Answer 20

-It divides into medial and lateral branches; one of which is sensory and the other is motor and sensory

Question 21

From where does the upper limb receive its nerve supply?

Answer 21

• Brachial plexus

- T2 roots

Question 22

From where does the lower limb receive its nerve supply?

Answer 22

-The lumbar plexus (L1-L4)
-The sacral plexus (L4-S4)
NB. lumbar and sacral plexus overlap half and half of L4

Question 23

From which landmark muscle do the nerves of the lumbar plexus emerge?

Answer 23

-Psoas major

Question 24

Which nerve emerge laterally to psoas major?

Answer 24

• The femoral
• Iliohypogastric
• Ilioinguinal
• Lateral cutaneous nerve of the thigh

Question 25

Which nerves of the lumbar plexus emerge medial to psoas major?

Answer 25

- The obturator nerve | - The lumbosacral trunk

Question 26

Where does the sacral plexus form?

Answer 26

-In the pelvic cavity

Question 27

What does the sacral plexus supply?

Answer 27

- Pelvic region - Gluteal region - Perineal region - The lower limb via sciatic nerve

Question 28

What is meant by functional overlap of dermatomes?

Answer 28

-An area of skin may be supplied by 2 successive spinal nerves

Question 29

Why is overlap functionally beneficial?

Answer 29

-Reduces the probability of skin patches without sensory nerve supply when there is damage to a single spinal nerve.

Question 30

What happens to the ordered segmentation of dermatomes which originally forms in an embryo?

Answer 30

-It is altered during development as they become pulled into the limb buds during griwth and differentiation

Question 31

What are axial lines?

Answer 31

-Junctions between non-successive dermatomes eg C6 and T1

Question 32

What are pre and post-axial borders?

Answer 32

-The anterior and posterior axial lines

Question 33

How do dermatomes differ from nerve terratories?

Answer 33

- Dermatomes are the spinal level which serves the specific area of skin - Nerve territories refers to the specific nerve which supplies the area of skin

Question 34

Describe the dermatomes of the anterior upper limb

Answer 34

- C4 - over the tip of the shoulder - C5- Radial third of upper arm to mid forearm - C6- The thumb and the middle forearm and arm - C7-2nd, 3rd and 4th digit and accompanying palm to a V - C8- 5th digit, accompanying palm to just over wrist - T1- Ulnar forearm to mid upperarm - T2- Axilla

Question 35

Describe the dermatomes of the posterior upper limb

Answer 35

- C4 - Shoulder - C5 - midline of arm to lateral edge - C6-Lateral third forearm and thumb - C7- Middl three fingers and middle third of forearm to elbow - C8 - 5th digit and medial forearm to midpoint - T1 - Medial third forearm from midpoint to axilla - T2-Axilla

Question 36

Which of the lumbar/sacral plexuses mainly supplies the anterior/posterior lower limb?

Answer 36

- Lumbar supplies anterior | - Sacral supplies posterior

Question 37

Describe the dermatomes of the anterior lower limb

Answer 37

- L1 - groin - L2- superior half of thigh - L3- Inferior half of thigh - L4 - Medial half leg - L5-Lateral half of leg and first three digits of foot with associated dorsum - S1- lateral two digits ans associated dorsum - S2/3 - Penis

Question 38

Describe the dermatomes of the posterior lower limb

Answer 38

- S5/S4/S3 - Gluteal region in rings - S2-Middle stripe of thigh and leg - S1 - sole of foot - L5- lateral border of leg - L4- medial border of leg - L3- medial border of thigh - L2- lateral border of thigh

Question 39

Describe the nerve territories of the anterior upper limb

Answer 39

- Shoulder -> supraclavicular - Regimental badge-> axillary - Lateral third of arm-> Posterior antebrachial cutaneous - Middle third of arm ->Meidial antebrachial cutaneous - Medial third of arm -> intercostal brachial and medial brachial cut. - Lateral half of forearm -> Lateral antebrachial cutaneous - Medial half of forearm-> Medial antebrachial cutaneous

Question 40

Describe the cutaneous innervation (nerve territories) of the lower limb

Answer 40

- Lateral third thigh- Lateral femoral cutaneous nerve - Middle third of thigh and knee-> Anterior femoral cutaneous - Medial third-> split into 3 from sup to inf-? genitofemoral, ilioinguinal and obturator - Lateral leg-> Lateral sural cutaneous nerve - Medial leg -> Saphenous nerve

Question 41

What does a somite differentiate into?

Answer 41

- Ventral somite differentiates into scleretome | - Dorsal somite differentiates into dermomyotome