Arm, Forearm

Question 1

What is the arm?

What is the leg?

Answer 1

• Arm then forearm
  
  • The arm refers only to the portion of the upper limb between the shoulder and the elbow, not the entire upper limb.
• Thigh then leg
  
  • The leg refers only to the portion of the lower limb between the knee and the ankle, not the entire lower limb.

Question 2

What are the three muscles in the anterior arm?

What are nerve are they all innervated by?

What do the muscles do?

Answer 2

• The musculocutaneous nerve (C5 and C6) innervates the 3 muscles in the anterior arm: the biceps brachii, the brachialis, and the coracobrachialis.
  
  • coracobrachialis flexes the arm at the shoulder
  • brachialis flexes the forearm at the elbow
  • biceps brachii flexes at both of these joints, as well as supinating the forearm.

Question 3

What are the muscles in the anterior forearm?

What nerves innervate them?

What do the muscles do?

Answer 3

• The median nerve innervates all muscles of the anterior forearm except one and a half (the flexor carpi ulnaris and the medial half of the flexor digitorum profundum).
  
  • Median nerve also innervates five muscles in the hand.
• The ulnar nerve innervates a few aneterior forearm muscles, in addition to flexors in the hand.
  
  • Innervates the flexor carpi ulnaris and the medial half of the flexor digitorum profundus in the anterior forearm, and all of the intrinsic hand muscles not innervated by the median nerve. Its dermatome is the medial one and a half digits, including both the anterior (palmar) and posterior (dorsal) sides. Hitting the “funny bone” refers to transient trauma of this nerve as it passes under the medial epicondyle of the humerus; next time this happens to you, notice that it’s only the medial half of the ring finger that gets the “pins and needles” sensation, not the lateral half.

Question 4

posterior arm

What is the one muscle, and what nerve innervates it?

Blood supply?

What nerve innervates the dermatome?

Answer 4

• The radial nerve (posterior division fibers from C5 through C8) innervates all of the muscles of the posterior arm (and forearm)
• Innervates triceps brachii (the only posterior arm muscle)
• Radial nerve courses with deep (profunda) brachial artery, through the triangular interval

Question 5

posterior forearm:

What are the muscles, and what nerve innervates all of them?

What nerves innervate the dermatome?

Answer 5

• After innervating the posterior arm muscle (triceps brachii), the radial nerve continues into the posterior forearm to innervate all muscles there, as well
  
  • The posterior forearm contains twelve muscles which are responsible for extension of the wrist and digits, and supination of the forearm.
• Radial nerve also continues down as a cutaneous branch into the dorsum of the hand; the full dermatome of the radial nerve consists of the posterior arm, posterior forearm, and the dorsum of the lateral 3½ digits; excluding the nail beds.

Question 6

What is in the anterior and posterior compartments of the arm?

Answer 6

In the arm, there are two compartments:

• anterior compartment
  
  • 3 muscles: biceps brachii, brachialis, coracobrachialis
  • All innervated by musculocutaneous nerve (C5-C7)
  • Blood supply = brachial artery
• posterior compartment
  
  • 1 muscle: triceps brachii
  • Innervated by the radial nerve
  • Blood supply = deep profunda brachial artery

Question 7

What is in the anterior and posterior compartments of the forearm?

Answer 7

• Anterior forearm:
  
  • Innervated mostly by the median nerve (except one and a half muscles innervated by the ulnar nerve)
  • Blood supply from ulnar artery
• Posterior forearm:
  
  • Innervated by the radial nerve
  • Blood supply from radial artery
• The radial artery and the ulnar artery anastomose in the hand, by forming two arches, the superficial palmar arch, and the deep palmar arch

Question 8

What are the muscles of the rotator cuff?

What are they innervated by?

Answer 8

• Commonality = they are all innervated by nerve fibers from the C5 and C6 spinal cord segments
• Rotator cuff is a common name for the group of 4 distinct muscles and their tendons that provide strength and stability during motion of the shoulder. They are also referred to as the SITS muscle with reference to the first letter of their names: Supraspinatus, Infraspinatus, Teres minor, Subscapularis
  
  • supraspinatus = an abductor of the arm at the shoulder
  • infraspinatus = a external/lateral rotator of the arm at the shoulder
  • teres minor = a external/lateral rotator
  • subscapularis = internal/medial rotator
• Suprascapular nerve innervates 2 of the 4 muscles: the supraspinatus and infraspinatus
• Axillary nerve innervates teres minor (main nerve, the only one that isn’t collateral!)
• upper and lower subscapular nerves innervate subscapularis (collateral off posteiror cord)

Question 9

Which nerves contribute to innervation of the forearm?

Answer 9

A: The axillary nerve innervates two muscles in the shoulder: the deltoid and the teres minor. Its dermatome is the lateral shoulder. It does not contribute to innervation of the forearm.

(A)(correct answer)

(B)The median nerve innervates almost all of the muscles of the anterior forearm.

(C)The musculocutaneous nerve innervates skin of the lateral forearm through its lateral antebrachial cutaneous branch.

(D)The radial nerve innervates all muscles of the posterior forearm.

(E)The ulnar nerve innervates 1½ muscles of the anterior forearm.

Question 10

median nerve

Answer 10

• The median nerve innervates almost all muscles in the forearm and a few muscles in the lateral hand. It also innervates some skin of the lateral hand.
• The median nerve contains anterior division fibers from C6 through T1, and thereby innervates mostly flexors within the forearm and hand.
• Innervates all of the muscles of the anterior forearm except for:
  
  • the flexor carpi ulnaris and the medial half of the flexor digitorum profundum

Question 11

musculocutaneous nerve

Answer 11

• The musculocutaneous nerve innervates skin of the lateral forearm through its lateral antebrachial cutaneous branch.

More:

The musculocutaneous nerve contains anterior division fibers of C5 and C6. We would predict that it should innervate flexors that act mostly at the shoulder and/or elbow, and that would be an accurate prediction. The three muscles this nerve innervates are the three muscles found in the anterior arm: the biceps brachii, the brachialis, and the coracobrachialis. The nerve can be found piercing the substance of the coracobrachialis, which can help with its identification in the cadaver. The coracobrachialis flexes the arm at the shoulder; the brachialis flexes the forearm at the elbow; and the biceps brachii flexes at both of these joints, as well as supinating the forearm. After giving off small muscular branches to the other two anterior arm muscles, the remainder of the nerve continues as a cutaneous nerve, the lateral antebrachial cutaneous nerve, which innervates the skin of the lateral forearm.

Question 12

radial nerve

Answer 12

• The radial nerve innervates all muscles of the posterior forearm and arm
• Its dermatome includes these same areas, as well as much of the dorsum of the hand
• It’s a posterior collateral nerve

More:

The radial nerve is composed of posterior division fibers from C5 through C8. It innervates all of the muscles of the posterior arm and forearm, which are predominantly extensors. To get into the posterior compartment of the arm, the radial nerve passes through the triangular interval, bounded by the long head of the triceps brachii laterally, the lateral head of the triceps brachii laterally, and the teres major superiorly. The deep (profunda) brachial artery travels alongside the radial nerve.

After innervating the triceps brachii and the other posterior arm muscles, the radial nerve continues into the posterior forearm to innervate all muscles there, as well. It also continues down as a cutaneous branch into the dorsum of the hand; the full dermatome of the radial nerve consists of the posterior arm, posterior forearm, and the dorsum of the lateral 3½ digits; excluding the nail beds.

Question 13

ulnar nerve

Answer 13

• The ulnar nerve innervates 1½ muscles of the anterior forearm, and many of the flexors of the hand
  
  • Specifically, it innervates the flexor carpi ulnaris and the medial half of the flexor digitorum profundus in the anterior forearm, and all of the intrinsic hand muscles not innervated by the median nerve

Question 14

Which nerve has a dermatome that does NOT overlie its myotome?

Answer 14

• The muculocutaneous nerve
  
  • ​The myotome of the musculocutaneous nerve is the anterior arm (coracobrachialis, biceps brachii, brachialis). Its dermatome is the lateral forearm (through the lateral antebrachial cutaneous nerve).
  • In this case, the dermatome (forearm) does not overlie the myotome (arm).

Question 15

axillary nerve

What myotome and dermatome does it innervate?

Answer 15

The axillary nerve innervates the deltoid and teres minor, and the skin covering these muscles (lateral shoulder).

Question 16

Answer 16

D:

• The radial and axillary nerves contain posterior division fibers (extensors), whereas the median, musculocutaneous, and ulnar nerves contain anterior division fibers (flexors).
• The axillary nerve only innervates the deltoid and teres minor muscles. Thus, any other extensor must be innervated by the radial nerve.
  
  • (Ex: extensor digitorum, extensor indicis, extensor digiti minimi, extensor pollicis longus, extensor pollicis brevis, extensor carpi radialis longus, extensor carpi radialis brevis, and extensor carpi ulnaris).

Question 17

Which two terminal nerves innervate extensor muscles?

Which one does more?

Answer 17

• The radial and axillary nerves contain posterior division fibers (extensors)
  
  • (Think RA-P.)
• Whereas the median, musculocutaneous, and ulnar nerves contain anterior division fibers (flexors).
• The axillary nerve only innervates the deltoid and teres minor muscles. Thus, any other extensor in the upper limb must be innervated by the radial nerve.
  
  • Ex: extensor digitorum, extensor indicis, extensor digiti minimi, extensor pollicis longus, extensor pollicis brevis, extensor carpi radialis longus, extensor carpi radialis brevis, and extensor carpi ulnaris

Question 18

Answer 18

B: The supraspinatus and infraspinatus are innervated by the suprascapular nerve. The subscapularis is innervated by the upper and lower subscapular nerves. The only rotator cuff muscle not innervated by a collateral nerve is the teres minor, which is innervated by the axillary nerve (a terminal nerve).

(A)The medial brachial cutaneous nerve arises from the medial cord; there is no medial trunk (the trunks are upper, middle, and lower; also can be called superior, middle, and inferior).

(B)(correct answer)

(C)The lateral antebrachial cutaneous nerve arises from the musculocutaneous nerve (a terminal nerve).

(D)The dorsal scapular nerve comes off of the brachial plexus before the divisions, and therefore does not contain designated “anterior” or “posterior” division fibers.

(E)The upper and lower subscapular nerves share a muscle in common: the subscapularis (the lower also innervates the teres major). The middle subscapular nerve (also called the thoracodorsal nerve) innervates the latissimus dorsi, and does not contribute to innervation of the subscapularis.

Question 19

movements of arm at glenohumeral joint

Answer 19

Question 20

movements at elbow joint

Answer 20

• “pure hinge joint”
  
  • Limited to just flexion and extension, actions that occur in sagittal plane.
• ankle joint is also “pure hinge joint”
• knee is “modified hinge joint” - can rotate

Question 21

biceps brachii

Answer 21

• Crosses elbow joint and shoulder joint
• Has 3 actions:
  
  • Biceps brachii acts to flex the forearm at the elbow
  • Biceps brachii acts to flex the arm (weakly) at the shoulder
  • Biceps brachii acts to supinate the forearm at the elbow

Question 22

review superficial, intermediate, and deep

muscles of the anterior forearm

Answer 22

Question 23

review superficial and deep muscles

of posterior forearm

Answer 23

• Radial - ABduction, extension,
• Median - ABduction, flexion, opposition
• Ulnar - ADduction

Question 24

what do you see?

Answer 24

Question 25

what do you see?

Answer 25

Question 26

bones of elbow joint * which bone has greater articulation with humerus? * where does the ulna articulate, where does radius articulate?

Answer 26

* the ulna * the ulna has a hook-like projection called the **olecranon** that articulates into a depression on the posterior aspect of the humerus called the **olecranon fossa**. * On the anterior surface, the ulna can swing around the **trochlea** (Greek: “pulley”) of the humerus. This creates the hinge joint configuration of the elbow. * The radius tapers to a small head at its proximal end, and thereby has a much smaller articulation with the humerus. The **head articulates with the capitulum of the humerus** and helps stabilize the elbow as a hinge joint.

Question 27

what passes through the carpal tunnel? sx carpal tunnel?

Answer 27

* Tendons: **four each from the flexor digitorum profundus and flexor digitorum superficialis** (one each for digits 2 through 5), and the **flexor pollicis longus**. * **Median nerve** * Carpal tunnel syndrome may result from compression of the median nerve in this area * Sx include **numbness, tingling, or shooting pain in the distribution of the lateral 3½ digits**. In _severe cases, atrophy of the intrinsic hand muscles innervated by the median nerve can result_ (thenar eminence muscles and lumbricals for digits 2 and 3).

Question 28

**Guyon's canal**

Answer 28

* The **ulnar artery and ulnar nerve** pass into the hand through their own canal, Guyon’s canal. * Less common than carpal tunnel syndrome, Guyon’s canal can be a site of compression of the ulnar nerve.

Question 29

actions at wrist joint * what are the 2 wrist joints called? * does ab or adduction have a greater range of movement?

Answer 29

* wrist joint = the **radiocarpal and ulnocarpal joints** * flexion and extension, and abduction and adduction. * **ADduction** \> abduction. The range of abduction is generally much less than adduction, which reflects the fact that the **radiocarpal joint has a much larger surface of contact than the radioulnar joint**.

Question 30

anterior forearm muscles - superficial layer * name the four muscles, their action, and innervation

Answer 30

* The **flexor carpi radialis (FCR), palmaris longus, and flexor carpi ulnaris (FCU)** all contribute to flexion of the hand at the wrist joint. * common attachment to the medial epicondyle of the humerus * The FCR can also cause deviation of the hand toward the radial side, which is _abduction_. The FCU can also cause deviation of the hand toward the ulnar side, which is _adduction_ * The _pronator teres_ is also anatomically in this group; however, because it does not cross the wrist joint, it must not act at that joint. Instead, it is an important _pronator of the forearm_

Question 31

anterior forearm muscle - intermediate layer * name the one muscle, action, and innervation

Answer 31

* just the **flexor digitorum superficialis** (FDS) * Innervated by the **median nerve**, this muscle sends individual tendons to the PIP joints of digits 2 through 5. * **role as a flexor of the PIP joints**. * also attaches proximally to the medial epicondyle of the humerus.

Question 32

anterior forearm muscle - deep layer * name the muscles, action, and innervation

Answer 32

* most distal-acting flexors * Most of these muscles are innervated by the **anterior interosseus nerve (**AIN), which is a deep branch of the **median** **nerve** that rides on the anterior aspect of the interosseus membrane. * The **flexor digitorum profundus (FDP) flexes the distal interphalangeal joints**. * The _FDP is also notable for its split innervation_: its **lateral half (to digits 2 and 3) is innervated by the median nerve, whereas the medial half (to digits 4 and 5) is innervated by the ulnar nerve**. * The **flexor pollicis longus flexes the thumb at the interphalangeal joint**; it is also innervated by the AIN of the **median nerve**. * The **pronator quadratus**, a parallelogram- to rectangular-shaped muscle. Also innervated by the AIN of the median nerve.

Question 33

## Footnote extension at the MCP joints is accomplished by \_\_\_\_\_, but at the PIP and DIP joints, extension is accomplished by \_\_\_\_\_\_.

Answer 33

e**xtension at the MCP joints is accomplished by the _muscles of the posterior forearm_**, but **at the PIP and DIP joints, extension is accomplished by _intrinsic hand muscles_**.

Question 34

muscles of posterior forearm - first layer * attachment? * innervation? * unique one?

Answer 34

* they all attach to the **lateral epicondyle** of the humerus * they are all innervated by the **radial nerve** * there are **two extensor carpi radialis muscles (longus and brevis**) that **extend the hand at the wrist** and can cause radial deviation (**abduction**). * There’s an **extensor carpi ulnaris** that **extends the hand at the wrist** and can cause ulnar deviation (**adduction**) * **extensor digitorum that extends the digits** 2 through 5 at the **metacarpophalangeal joints**, and an **extensor digiti minimi that assists with extension at the MCP joint of the pinkie** * _extension at the MCP joints is accomplished by the muscles of the posterior forearm, but at the PIP and DIP joints, extension is accomplished by intrinsic hand muscles._ * **brachioradialis** - also nnervated by the radial nerve and its function is a bit unusual: * despite being innervated by the radial nerve (which is composed of posterior division fibers), it is a **flexor of the forearm at the elbow**, not an extensor. Specifically, the brachioradialis flexes the forearm at the elbow when the forearm is in a mid-prone, mid-supine position (like drinking from a glass).

Question 35

posterior foream - deep layer * name 5 muscles * what's their innervation

Answer 35

* All except the supinator are innervated by the PIN (**posterior interosseous nerve**); this maxes sense because the **PIN arises from the radial nerve** immediately after the radial nerve crosses the supinator. * The **supinator** does just as it says: supinates the forearm. * The **abductor pollicis longus** abducts the thumb at the MCP joint. * The **extensor pollicis brevis** and **longus** extend the thumb at the MCP joint. * the **extensor indicis extends the index finger** at the MCP joint.

Question 36

anatomic snuffbox * which tendons form it? * what results from fracture of scaphoid

Answer 36

* Abductor Pollicis Longus, Extensor Pollicis Brevis, Extensor Pollicis Longus * The floor is the **scaphoid bone** and the **radial artery** passes through the middle of the snuffbox. * A fracture of the scaphoid, which may result from FOOSH may result in **loss of blood flow from the radial artery** (retrograde flow) and result in **avascular necrosis** of the portion of the scaphoid that is in contact with the distal radius.

Question 37

review movements at elbow and radioulnar joints * nerves for flexion and extension at elbow? * nerves for pronation and supination at wrist? * nerves for flexion, extension, abduction, adduction at wrist?

Answer 37

Question 38

Answer 38

## Footnote The answer is (B). The flexor digitorum profundus is innervated by both the median nerve (for its attachments in digits 2 and 3) and the ulnar nerve (for its attachments in digits 4 and 5); both are terminal branches of the brachial plexus. (A)The flexor digitorum superficialis is entirely innervated by the median nerve. (B)(correct answer) (C)The extensor digitorum is entirely innervated by the radial nerve. (D)The biceps femoris is a muscle of the posterior thigh, innervated by both the tibial and common fibular nerves; however, these are terminal branches of the lumbosacral plexus, not the brachial plexus. (E)The flexor digitorum longus is entirely innervated by the tibial nerve; it is located in the posterior leg.

Question 39

flexor digitorum profundus vs flexor digitorum superficialis

Answer 39

* profundus goes all the way, to the DIP joints * innervated by both median and ulnar nerves * superficialis goes to PIP joints * innervated by median nerve

Question 40

Answer 40

The answer is (D). The two muscles involved in pronation are the pronator teres and pronator quadratus, both of which are innervated by the median nerve. (A)The extensor carpi radialis longus and brevis, and extensor carpi ulnaris (among other extensors of the wrist) are innervated by the radial nerve. (B)The supinator is innervated by the radial nerve. (C)The brachioradialis is innervated by the radial nerve. (D)(correct answer) (E)The extensor carpi ulnaris is innervated by the radial nerve.

Question 41

Answer 41

The answer is (E). Nine tendons pass through the carpal tunnel: **four from the flexor digitorum superficialis, four from the flexor digitorum profundus, and one from the flexor pollicis longus. Seven of these nine tendons correspond to muscle bellies that are innervated by the median nerve** (with exception of two from the flexor digitorum profundus that are innervated by the ulnar nerve). The nerve passing through the carpal tunnel is also a branch of the median nerve. (A)The roof of the carpal tunnel, which prevents bowstringing, is the flexor retinaculum. (B)The abductor pollicis longus is located in the posterior forearm and does not enter the carpal tunnel. It is the flexor pollicis longus tendon that passes through the carpal tunnel. (C)The posterior interosseus nerve is a branch of the radial nerve and does not pass through the carpal tunnel. (D)Median nerve impingement is the primary cause of carpal tunnel syndrome, not ulnar nerve impingement.

Question 42

Answer 42

The answer is (C). The muscles attached to the **medial epicondyle (including flexor carpi radialis, palmaris, and flexor carpi ulnaris) primarily function in flexing the hand at the wrist**. The pronator teres also attaches to this point, and primarily functions in pronation. The flexor carpi radialis and ulnaris also play roles in abduction and adduction of the hand at the wrist, respectively, although these are less significant functions. (A)**The gastrocnemius flexes the leg at the knee and plantar flexes the foot at the ankle.** (B)**The extensor indicis, like the extensor digitorum and extensor digiti minimi, only is strong enough to act as far distally as the metacarpophalangeal joints. The proximal and distal interphalangeal joints are extended by lumbricals**. (D)The main muscles attaching to the calcaneus are the gastrocnemius, plantaris, and soleus, with smaller attachments by the extensor digitorum brevis and a few intrinsic foot muscles. None of these muscles is involved in eversion (the job of fibularis muscles); **the gastrocnemius, plantaris, and soleus are most involved in plantar flexion at the talocrural joint (the gastrocnemius also assists in flexion of the leg at the knee).** (E)The flexor carpi radialis, extensor carpi radialis longus, and extensor carpi radialis brevis muscles are flexors and extensors, respectively; acting together, they can also cause **abduction of the hand at the wrist, not adduction**.

Question 43

Answer 43

The answer is (A). **The deep fibular nerve innervates the muscles of the anterior leg, which include the extensor hallucis longus (and tibialis anterior and extensor digitorum longus,** choices (B) and (E), as well). (A)(correct answer) (B)The tibialis anterior is innervated by the deep fibular nerve. (C)The fibularis brevis is in the lateral compartment and is innervated by the superficial fibular nerve. (D)The soleus is in the posterior compartment and is innervated by the tibial nerve. (E)The extensor digitorum longus is innervated by the deep fibular nerve.

Question 44

Answer 44

## Footnote The answer is (C). Both the extensor pollicis longus and extensor pollicis brevis are innervated by the radial nerve (in fact, a**ny muscle in the upper limb with extensor in its name is innervated by the radial nerve**). (A)The abductor pollicis longus is innervated by the radial nerve; the flexor pollicis longus is innervated by the median nerve. (B)The flexor carpi ulnaris is innervated by the ulnar nerve; the flexor carpi radialis is innervated by the median nerve. (C)(correct answer) (D)The pronator teres is a muscle of the forearm innervated by the median nerve; the peroneus (fibularis) tertius is a completely unrelated muscle in the leg, innervated by the deep fibular nerve. Peroneus and fibularis can be used interchangeably. (E)The tibialis anterior is innervated by the deep fibular nerve; the tibialis posterior is innervated by the tibial nerve.

Question 45

Answer 45

The answer is (D). * The **only muscle that causes flexion of the thumb at the interphalangeal joint is the flexor pollicis longus, which is innervated by the anterior interosseus nerve** (AIN), a branch of the median nerve. * AIN (Kiloh-Nevin) syndrome may be tested by the inability to make an “**OK**” sign with the hand (_inability to flex at the thumb interphalangeal joint, and weakness with flexing the fingers at the distal interphalangeal joints leads to a “triangle” sign, without rounding of the thumb and index finger_) (A) Flexion of the hand at the wrist is accomplished by the flexor carpi radialis, palmaris longus, and flexor carpi ulnaris, which are innervated by the median nerve (not AIN branch) and ulnar nerves, respectively. (B) The flexor digitorum profundus is responsible for flexion at the distal interphalangeal joints; the portion flexing the fourth and fifth digits is innervated by the ulnar nerve. (C) Abduction of the thumb is accomplished by the abductor pollicis longus (innervated by the radial nerve) and the abductor pollicis brevis (innervated by the recurrent branch of the median nerve). (E )Extension of the digits at the metacarpophalangeal joints is accomplished by the extensor digitorum, extensor indicis, and extensor digiti minimi (for the fifth digit); these are all innervated by the radial nerve.

Question 46

extrinsic muscles: * finger and wrist flexors innervation * extensors innervation

Answer 46

* Flexors: Most of these are innervated by the **median nerve**, _with the exception being the Flexor Carpi Ulnaris and the Flexor Digitorum Profundus to the small and ring fingers,_ which are innervated by the **ulnar nerve** * Extensors: These extrinsic muscles are all innervated by the radial nerve