25 Dermatomes

Question 1

Dermatomes is about the sensory innervation of the skin by a single ____________ or a ______________.

Answer 1

spinal nerve/

spinal segment

Question 2

Each pair of the left and right roots can renamed as a ________________.

Answer 2

Spinal segment

Question 3

Dermatome maps are clinically useful in ________________ and ______________ etc as they are created by matching sensory loss on skin with the effected _______________.

Answer 3

Disc herniation/ surgical section;

spinal nerve/ spinal segment

Question 4

What are axial lines? Where they can be seen?

Answer 4

Boundary between the non-consecutive dermatomes;

upper anterior thoracic wall (shoulder), back of lower limb, scrotal region (L1 and L2 lies next to S2-4)

Question 5

What is special about the scrotal/ labial innervation?

Answer 5

L1 fibers in ilioguinal and genitofemoral nerves;
S2-4 fibers in pudendal nerve and posterior femoral cutaneous nerves;
Penis/ chlitoris is innervated partly by L1 and partly by S2-4

Question 6

Most dermatomes overlap, except some show little overlap, including?

Answer 6

1. those across axial lines in upper chest, limbs, perineal region;
2. trigeminal dermatomes (face) which in common usage include the oral cavity)

Question 7

Touch/pain fibers overlap more.

Answer 7

Touch

Question 8

Total damage of spinal nerve causes little loss of __________ but substantial loss of ___________ because?

Answer 8

touch;
pain;
pain fibers overlap less than touch fibers

Question 9

When do we use dermatome maps and when do we use peripheral nerve maps?

Answer 9

1. Dermatome maps:
   - lesions of spinal segments, roots, ganglia, spinal nerves, disc disorders
2. Peripheral nerve maps:
   - peripheral nerve injuries (compression, cut, crush)

Question 10

What is myotome?

Answer 10

Muscle mass innervated by a single spinal nerve or a ventral root, or a spinal segment (half)

Question 11

1. Brachioradialis? (elbow flexor)
2. Thumb adductors and opponens?
3. Big toe extensors?
4. Hamstrings? knee flexors

Answer 11

C6;
T1;
L5;
S1

Question 12

Which of the followings are stretch reflexes?
A. biceps jerk
B. brachioradialis jerk
C. triceps jerk
D. knee jerk
E. ankle jerk

Answer 12

All except B

caused by stimulus to bone rather than by muscle stretch

Question 13

L2,3,4:

Quadriceps femoris, satorius, pectineus: Femoral nerve (knee extension)

Adductors, obturator extensors, gracilis: Obturator nerve (hip adduction)

How to differentiate spinal lesion from a peripheral nerve lesion?

Answer 13

Lesion of spinal nerves > both functions are impaired

Lesion of peripheral nerve lesion > impairs one function only

Question 14

How to differentiate a spinal nerve lesion from a peripheral nerve lesion when the patient cannot perform biceps jerk?

Answer 14

No biceps jerk = lesion in musculocutaneous nerve// spinal lesion at C5,C6

if spinal = reduced brachioradialis jerk as well

if peripheral: no change in brachioradialis jerk as the radial nerve is not affected by the lesion

Question 15

T7-9 referred pain from?

Answer 15

Stomach, liver, gall bladder, pancreas