Week 1: innervation patterns of the limbs

Question 1

Describe the structure of the brachial plexus.

Answer 1

1. Ventral rami of C5,6,7,8, T1
2. Trunks
   - Upper: C5 and C6
   - Middle: C7
   - Lower: C8, T1
3. Divisions: each trunk splits into Anterior and posterior (total 6 divisions)
4. Cords dividing into terminal branches:
   - Lateral (anterior divisions of Upper and middle): musculocutaneous and median
   - Posterior (combined from 3 posterior divisions): Axillary and Radial
   - Medial: Median and Ulnar

Other nerves that come from plexus -suprascapular from upper trunk

• thoracodorsal from posterior cord
• medial pectoral n.from A of lower trunk

Question 2

What does damage to one spinal cord segment in the brachial plexus lead to?

Answer 2

-weaken several muscles but no paralysis because it flows to multiple nerves

Question 3

What does damage to one terminal nerve of the brachial plexus lead to?

Answer 3

-paralyze all muscles innervated by that nerve e.g. paralysis of median nerve leads to loss of SS to skin via cut. branches of median and paralysis of muscles innervated by median

Question 4

Which nerves of the brachial plexus are derived from the anterior divisions of the plexus? Which from posterior division?

Answer 4

Anterior: Musculocutaneous, median, and ulnar Posterior: Axillary and radial

Question 5

Describe Erb-Duchenne palsy (waiter’s tip deformity)?

Answer 5

Upper brachial plexus lesion

• results from excessive stretching of C5,C6 roots or upper trunk of brachial plexus
• can be from too much tension on head during childbirth so that shoulder is impacted against mother’s pubic bone

Nerves affected and presentation

• suprascapular: loss of infraspinatus innervation (lateral rotator)–>medially rotated limb
• axillary: loss of abduction
• musculocutaneous (C5-7): weakness of elbow flexors–>elbow extension
• radial (C5-8, T1): weakness of wrist extensor–>slight wrist flexion

Question 6

Describe Klumpe’s Palsy (lesion of lower brachial plexus).

Answer 6

Caused by tearing of C8, T1 ventral rami

-can be due to childbirth, limb delivered first and is pulled on -from excessive stretching of armpit region

Presentation

• muscles innervate by ulnar nerve are paralyzed
• Claw hand when asked to extend fingers-fingers 4 and 5 in claw

Question 7

What is the distribution of SS innervation for the musculocutaneous (MC), median (M), ulnar (U), radial (R), and axillary (A) nerves.

Answer 7

Question 8

Describe the lumbosacral plexus and its terminal branches (and their spinal root components)

Answer 8

• Femoral n. (L2, L3, L4)
• Obturator n. (L2, L3, L4)

Sciatic is composed of:

• Tibial (L4, L5, S1, S2, S3)
• Common peroneal (fibular) nerve: (L4, L5, S1, S2)

Question 9

What are the ideal locations for testing indivdiual lower limb dermatomes while avoiding areas of overlap?

Answer 9

L4: kneecap and inner surface of big toe

L5: toes 2-4 and sole of foot

S1: little toe adn straight down back of limb

Question 10

Where on the lower limb can you test for the femoral nerve?

Answer 10

Anterior thigh

If woman kept in lithotomy position too long–>compresses nerve against inguinal ligament, leads to anesthesia or paresthesia of skin on anterior thigh

Question 11

Where on the lower limb can you test the obturator nerve?

Answer 11

Medial part of thigh. Damage can occur to this nerve from pelvic fractures.

Question 12

What locations would you test the SS innervation of superficial fibular nerve and deep fibular nerve?

Answer 12

• Superficial fibular: anterior shin and dorsum of middle toes.
• Deep fibular: on dorsal webbing between big and second toes. Courses through anterior compartment of leg and vulnerable to damage due to muscle hypertrophy or edema “shin splints”
• common fibular nerve vulnerable to damage due to course on lateral side of head of fibula. Most commonly injured nerve of lower limb.