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1

Brachial plexus

-Made up of ventral rami of C5-T1, allows these rami to be distributed to more than one terminal branches
-Minimizes functional loss following C-spine injury
-However damage to one terminal nerve would completely paralyze muscles innervated by that nerve

2

Terminal branches of the brachial plexus

-Musculocutaneous, from the lateral cord (C5, C6, C7)
-Axillary, from the posterior cord (C5, C6)
-Radial, from posterior cord (C5-T1)
-Median, from lateral and medial cords (middle branch forming the M w/ musculocutaneous and ulnar, C5-T1)
-Ulnar, from the lateral cord (C8, T1)

3

Branching pattern of the brachial plexus 1

-The ventral rami of C5+C6 form the upper trunk
-Ventral ramus of C7 forms middle trunk
-Ventral rami of C8+T1 forms lower trunk
-Each trunk divides in two, giving off one posterior division and one anterior division
-All 3 posterior divisions converge to form the posterior cord (looks continuous w/ middle trunk)
-The anterior division of the middle trunk and the anterior division of the upper trunk converge to form the lateral cord (looks continuous w/ the upper trunk)

4

Branching pattern of the brachial plexus 2

-The anterior division of the lower trunk becomes the medial cord (nothing joins it, thus only has C8+T1)
-The posterior cord produces axillary (C5+C6) and radial (C5-T1) nerves
-The lateral cord produces the musculocutaneous nerve (C5-C7) and contributes to the median nerve (C5-T1)
-The medial cord produces the ulnar nerve (C8+T1) and contributes to the median nerve (C5-T1)

5

Relationships of the brachial plexus

-Nerves w/in the anterior compartment (musculocutaneous, median, ulnar) usually innervate flexors of the arm/hand
-Nerves of the posterior compartment (axillary, radial) usually innervate extensors of the arm/hand
-The cords are named based on their relationship w/ the axillary artery

6

Other divisions of the brachial plexus

-Suprascapular nerve (C5,6) comes off of the upper trunk and innervates the supraspinatus and infraspinatus muscles
-Lateral pectoral nerve (C5,6,7) comes off the lateral cord and innervates the pec major muscle only (not the pec minor)
-Thoracodorsal nerve (C6,7,8) comes off the posterior cord and innervates the latissimus dorsi
-Medial pectoral nerve (C8 + T1) comes off the medial cord and innervates the pectoralis major and minor

7

Upper brachial plexus lesion

-Erb-duchenne palsy due to excessive traction/tearing/stretching of the C5, C6 rami or upper trunk
-Can be due to pulling on babies head in birth canal while the babies' shoulder is caught on the mother's pubic bone
-Affected limb is held tight against the chest and medially rotated w/ flexed wrist (due to unopposed antagonist muscles)
-Paralyzes the suprascapular (supraspinatus and infraspinatus) and axillary muscles (deltoid and teres minor)
-Leads to adducted and medially rotated arm
-Musculocutaneous, and radial nerves weakened (musculocutaneous more effected), thus there is extension at elbow and flexion of wrist

8

Lower brachial plexus lesion

-Klumpke's palsy due to tearing of C8, T1 rami or lower trunk
-Usually happens w/ upper limb is positioned over head and stretched excessively
-Muscles innervated by the ulnar nerve are paralyzed, pt is unable to use small intrinsic extensor muscles of the hand
-Thus the unopposed antagonist (flexors) cause a claw hand look (flexing of the 4th and 5th DIP/PIPs w/ extension of the MCP)
-All interossei muscles are paralyzed and the medial two lumbricals are paralyzed, thus the claw hand shows the opposite of the actions of the interossei/lumbricals when asking pt to extend their fingers

9

Cutaneous nerve innervation of the upper limb 1

-Cutaneous branches arise from all 5 terminal branches of the brachial plexus, the nerves that supply the areas of skin are different from dermatomes (which look at SC levels, not peripheral nerves)
-The skin by the lateral shoulder is innervated by the axillary nerve

10

Cutaneous nerve innervation of the upper limb 2

-Just below the shoulder, on the lateral aspect of the bicep, the skin is innervated by the radial nerve
-Inferior to this, on the forearm, the musculocutaneous innervates the skin
-Fingers: the first 3 digits innervated by the median nerve and the last digit (pinky) innervated by the ulnar nerve (the 4th digit, ring finger, is innervated by both)
-Skin of dorsum of hand: medial is ulnar, lateral is superficial radial
-Skin of palm of hand: medial is ulnar, lateral is median

11

Dermatomes of the upper limbs

-Look at the SC segments, not peripheral nerves, that innervate the skin
-Only need to know where to test C6, C7, and C8 innervation
-C6: thumb (first digit)
-C7: middle (or index) finger
-C8: pinky (fifth digit)

12

Lumbosacral plexus

-Formed by ventral rami of L1-S3
-Embryologic origin of the plexus is similar to brachial plexus in that at first the nerves that innervate flexors are in the anterior compartment and nerves innervating extensors are in posterior compartment
-But due to the medial rotation of lower limbs during development (as opposed to the lateral rotation of the upper limbs), the compartments become reversed (anterior compartment goes posterior, vice versa)
-Thus the extensors for the knee (nerves and muscles) and foot (dorsiflex) are anterior and the flexors of the knee and foot (plantarflex) are posterior

13

Compartments of the upper leg

-Unlike the arm (which has only anterior and posterior compartments) the leg also has a medial compartment for adduction (medial compartment innervated by obturator nerve, L2/3/4)
-The anterior compartment extends at the knee (innervated by femoral nerve, L2/3/4)
-Posterior compartment flexes at the knee (innervated by the tibial nerve L4/5/S1/2/3, exception: biceps femurs short head innervated by common fibular L4/5/S1/2)
-Together the common fibular (peroneal) and tibial nerves make up the sciatic nerve

14

Muscles in each compartment of upper leg

-Anterior compartment (knee extensors, by femoral): Vastus medius, rectus femoris, vastus lateralis, vastus intermedius, sartorius
-Posterior compartment (knee flexors, by tibial except biceps femoris short head is common fibular): Semimembranosus, semitendinosus, bicep femoris long head (also extends hip) and short head
Medial compartment (leg adductors, by obturator except hamstring part of magnus is tibial): Adductor longus, adductor brevis, adductor magnus, and gracilis

15

Dermatomes of the lower limb

-Locations for testing lower limb dermatomes
-L4 at the kneecap, medial side of the foot, and inner surface of big toe
-L5 on toes 2-4 and sole of foot
-S1 on little toe, lateral side of foot, and straight down the back of the leg

16

Cutaneous nerves of the lower limb 1

-Femoral nerve: passes under inguinal ligament to enter the anterior compartment, innervates skin on the anterior thigh
-Obturator nerve passes through the obturator canal to enter the medial compartment, innervates the skin on the medial thigh
-Common fibular (peroneal) nerve: is exposed on the lateral side of the leg just below the knee (is frequently damaged)

17

Cutaneous nerves of the lower limb 2

-At the lateral side of the leg below the knee the common fibular nerve divides into the deep and superficial fibular nerves
-The superficial fibular nerve (going to the lateral compartment of the lower leg) innervates the skin on the lateral and anterior side of the lower leg
-The deep fibular nerve (going to the anterior compartment of the lower leg) innervates the skin of the web btwn the big and second toe