Extensor Forearm and Hand

Question 1

`describe dermatomes

describe cutaneous nerves

what is the difference?

Answer 1

`dermatome: area of skin supplied by a single segment of the spinal cord

a cutaneous nerve: these are the branches of ventral and dorsal rami that innervate the skin.

• carry somatic sensory nerve fibers from the receptors for conscious sensation
• carry visceromotor nerve fibers to errector pili muscles, sweat glands, and smooth muscle in walls of blood vessels supplying skin

Question 2

where are the C5, 6, 7,8, and T1 dermatomes?

Answer 2

C5- brachial
C6- shoot gun
C7- flick them off middle finger
C8- ulnar side
T1- under arm

Question 3

what are the cutaneous nerves of the upper limb?

hint: follow cords of brachial plexus. start with axillary n

Answer 3

think about the cords first:

for the anti brachial:

1. posterior anti brachial comes off the radial nerve (from the posterior cord)
2. medial anti brachial comes off the medial cord (straight from cord)
3. lateral anti brachial comes off the musculocutaneous (lateral cord)

now for the locations which do make sense:
-musculocutaneous is lateral part of the antebrachial
-medial antebrachial is medial part of the brachial
and
-posterior antebrachial: back of forearm

now for the brachial:

• first think medial cord—> medial brachial which is in that location
• next think posterior brachial–> radial nerve bc comes off posterior cord
• next think lateral cord, but this is tricky bc we have a superior and inferior lateral brachial —> from axillary n (superior) and radial nerve (inferior) respectively. just memorize axillary

-also have intercostal branch from T2 that does inner inner arm

• then lastly in the hand:
• ulnar n: does palmar branch and dorsal branch medially (including digital of that hand)
• radial n: dorsal rest of whatever the ulnar doesn’t do *but median does the digital tips
• median nerve: anterior palmar and palmar digital and posterior- just the digital of 1, 2, 3, and half of 4

*think radial likes the back bc it comes off the posterior cord

Question 4

describe the borders of the anatomical snuff box what is the content

Answer 4

content is the radial artery passing from anterior ante brachium to dorsum of hand

floor: styloid process of the radius, scaphoid, and trapezium
roof: antebrachial fascia
posterior border: tendon of extensor pollicus longus
anterior border: abductor pollicis longus and extensor pollicis brevis
*remember: longus, brevis, longus

Question 5

describe the extensor retinaculum. where does it attach? how many tunnels?

do muscles pass deep or superficial?

Answer 5

attaches to dorsal radius to form SIX osseofibrous tunnels

-muscles pass deep

Question 6

what is the extensor expansion

Answer 6

serves as insertion for lumbricals and interossei

-helpful for the extensor digitorum to form expansions at the MCP joints

Question 7

what is the function of collateral ligaments n the MCP, PIP, DIP joints

Answer 7

they tighten during flexion to provide greater stability when gripping

Question 8

describe the course of the radial nerve

what is the blood supply?

is it always a motor nerve?

injury to the radial nerve causes?

Answer 8

injury to the radial nerve causes wrist drop

radial nerve arises from the brachial plexus on the posterior cord

• in the axilla it gives 3 branches:
• long head triceps
• medial head triceps
• posterior cutaneous brachial nerve
• runs through the radial groove of the humerus
• also splits in to the inferior lateral cutaneous brachial

then hits superior to the medial epicondyle and innervates the brachioradialis and the extensor carpi radialis and the aconeous muscles

• through the supinator it branches to the extensor compartment and is known as the deep radial nerve or the posterior interossesous nerve
• the part that doesn’t branch continues on as the superficial radial nerve which is now sensory. it runs deep the the brachioradialis, lateral to the radial artery, and then emerges with the artery at the snuffbox

Question 9

describe lymphatic drainage of the upper limb

Answer 9

you have a superficial and a deep drainage

1. superficial:
   from medial structures (cubital nodes to lateral axillary nodes) and lateral structures (pass through apical nodes)
2. deep:
   passes through lateral axillary nodes

Question 10

describe the superficial muscles of the extensor compartment

Answer 10

attaching at the supracondylar:
1. brachioradialis : flexes elbow when forearm is slightly supinated/ extended (beer raising). attaches at the bottom of the radial styloid process

2. extensor carpi radialis longus: extends wrist and abducts hand (radials always does abduction and this is a flexor so it does wrist extension)
   - if you use finger to say 2, then see it attaches at the base of the 2nd metacarpal bone

-both innervated by the radial nerve and artery

now from the lateral epicondyle and all innervate by the deep radial nerve/posterior interosseous and deep radial artery

3. extensor carpi radialis brevis: does same thing as the longus so wrist extension and abduction
   use finger to say 3rd, attaches at base of 3rd metacarpal
   -can tell bc crossed by outcroppers
4. extensor digitorum: use fingers to say 4 with thumb down and attaches at extensor expansion for digits 2 through 5.
   does extension of MIP, PIP, DIP of digits 2 through 5 and extends wrist
   aka communins
5. extensor digit minimi - works on pinky: does MIP, DIP, PIP of 5th finger and extends wrist. insets at extensor expansion of digit 5 *actually gets interosseous recurrent artery but…whatever
6. extensor carpi ulnaris: inserts at base of metacarpal 5 and does adduction and extension of wrist

few patterns:
digitorum and digiti minimi both have ‘digit’ so both attach through extensor expansions
-all extensor superficial muscles extend the wrist

Question 11

describe the deep muscles of the extensor compartment

innevation and blood supply?

Answer 11

all innervated by the deep radial nerve and posterior interosseous ARTERY

1. supinator: supinates forearm *RADIAL N CROSSES HERE TO BECOME DEEP RADIAL NERVE/POSTERIOR INTEROSSESOUS NERVE
   - origin is the lateral epicondyle of humerus and inserts on radius lateral side
2. extensor pollicis longus: extends thumb at IP jt *forms medial border of snuffbox or posterior border
   - inserts in base of distal phalanx of thumb
3. extensor pollicis brevis: extends thumb at metacarpophalangeal jt (because it is brevis) and with the abductor pollicus longus, forms the anterior/ lateral border of the snuffbox
   - inserts in base of proximal phalanx of thumb
4. extensor indicis : deep to extensor digitorum. extends index finger MIP, PIP, DIP joints MORE MEDIAL, towards pinky
   - inserts in extensor digitorum of 2nd finger
5. abductor pollicis longus: abducts thumb. with the extensor pollicis brevis, forms anterior /lateral border of snuffbox
   origin: interosseous membrane of ulnar and radius. inserts on RADIAL side of base 1
6. aconeous fans btwn lateral epicondyl and olecranon. innervated by radial n and artery

Question 12

describe the path of the radial artery

Answer 12

the radial artery arises in the cubital fossa from the brachial artery. It continues superficial through the brachioradilis and the extensor carpi radials

• in fact this is how you take the radial pulse
• then it gets to the anatomical snuffbox and emerges as it wraps to the DORSAL part of the hand (think again, radial likes the back)
• then it goes through the interossesous membrane of the 1st finger and enters the deep palmar arch.

DEEP PALMAR ARCH

• supplies 2 branches to the princeps policus
• and 1 br to the lateral (side closer to the thumb) part of the radiailis indicis (name makes sense)