Arm Anatomy
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1
What anatomical extent defines the arm?
From the shoulder to the elbow.
2
What two types of movements occur between the arm and forearm at the elbow joint?
Flexion-extension and pronation-supination.
3
What structures divide the arm into anterior and posterior muscular compartments?
The humerus and medial and lateral intermuscular septa.
4
Where is the chief action of both anterior and posterior arm muscle groups located?
At the elbow joint.
5
Which muscles make up the anterior compartment of the arm?
Biceps brachii, brachialis, and coracobrachialis.
6
Which nerve supplies the anterior compartment muscles of the arm?
Musculocutaneous nerve (\$C_5\text{--}C_7\$).
7
Which muscles make up the posterior compartment of the arm?
Triceps brachii and anconeus.
8
Which nerve supplies the posterior compartment muscles of the arm?
Radial nerve (\$C_5\text{--}T_1\$).
9
Why are humans biomechanically better pullers than pushers with the upper extremity?
Flexor muscles are longer in all positions and humans tend to supinate.
10
Which muscle is particularly critical for elevating the body out of a chair or wheelchair?
Triceps brachii.
11
What are the proximal attachments (origins) of the two heads of the biceps brachii?
Short head: tip of coracoid process of scapula; Long head: supraglenoid tubercle of scapula.
12
What are the distal attachments (insertions) of the biceps brachii?
Tuberosity of the radius and fascia of the forearm via the bicipital aponeurosis.
13
What are the primary actions of the biceps brachii?
Supinates the forearm, flexes the forearm when supine, and the short head resists shoulder dislocation.
14
What is the arterial blood supply to the biceps brachii?
Brachial artery.
15
Does the biceps brachii have an attachment to the humerus?
No, both heads attach to the scapula.
16
Approximately what percentage of the population possesses a third head of the biceps brachii?
Approximately 10%.
17
Why is the biceps brachii classified as a three-joint muscle?
It crosses and produces movement at the glenohumeral, elbow, and radio-ulnar joints.
18
What ligament holds the long head of the biceps brachii tendon in the intertubercular groove?
Transverse humeral ligament.
19
Why is the long head tendon of the biceps brachii described as intracapsular but extrasynovial?
It travels within the fibrous capsule of the GH joint but remains outside the synovial cavity encased in its own sheath.
20
What triangular membranous band extends from the biceps tendon across the cubital fossa?
Bicipital aponeurosis.
21
Which vessels and nerves does the bicipital aponeurosis pass obliquely over and protect?
Brachial artery and median nerve.
22
What is the proximal attachment of the brachialis?
Distal half of the anterior surface of the humerus.
23
What is the distal attachment of the brachialis?
Coronoid process and tuberosity of the ulna.
24
Which muscle serves as the main flexor of the forearm and the only pure flexor?
Brachialis.
25
Which nerves provide dual innervation to the brachialis?
Musculocutaneous nerve (\$C_5, C_6\$) and radial nerve (\$C_5, C_7\$).
26
Why is the brachialis unaffected by forearm pronation or supination?
It inserts onto the ulna, which does not rotate during pronation/supination.
27
What are the proximal and distal attachments of the coracobrachialis?
Proximal: tip of coracoid process of scapula; Distal: middle third of medial surface of humerus.
28
Which nerve pierces and innervates the coracobrachialis?
Musculocutaneous nerve (\$C_5\text{--}C_7\$).
29
What actions are performed by the coracobrachialis?
Helps flex and adduct the arm, and stabilizes the glenohumeral joint.
30
Why is the coracobrachialis considered a shunt muscle?
It resists downward dislocation of the humeral head during heavy carrying.
31
Which major nerve runs deep to the coracobrachialis and may be compressed by it?
Median nerve.
32
What are the proximal attachments (origins) of the three heads of the triceps brachii?
Long head: infraglenoid tubercle of scapula; Lateral head: posterior humerus superior to radial groove; Medial head: posterior humerus inferior to radial groove.
33
What is the distal attachment of the triceps brachii?
Proximal end of the olecranon of the ulna and fascia of the forearm.
34
Which head of the triceps brachii crosses the glenohumeral joint to aid in extension and adduction?
Long head.
35
Which head of the triceps brachii is the "workhorse" of forearm extension, active at all speeds and resistance levels?
Medial head.
36
Which head of the triceps brachii is the strongest and recruited primarily against resistance?
Lateral head.
37
What bursa lies deep to the distal triceps tendon between it and the olecranon?
Subtendinous olecranon bursa.
38
What is the arterial blood supply to the triceps brachii?
Deep brachial artery (profunda brachii artery).
39
What are the proximal and distal attachments of the anconeus?
Proximal: lateral epicondyle of humerus; Distal: lateral surface of olecranon and superior posterior surface of ulna.
40
Which nerve innervates the anconeus?
Radial nerve (\$C_7, C_8, T_1\$).
41
What are the actions of the anconeus?
Assists triceps in extending the forearm, stabilizes the elbow joint, and abducts the ulna during pronation.
42
Where does the brachial artery begin and end?
Begins at the inferior border of the teres major and ends in the cubital fossa opposite the neck of the radius.
43
Into which two terminal branches does the brachial artery divide in the cubital fossa?
Radial artery and ulnar artery.
44
Where does the median nerve cross relative to the brachial artery in the arm?
Crosses from the lateral side to the medial side anterior to the artery.
45
What is the largest branch of the brachial artery with the most superior origin?
Deep brachial artery (profunda brachii artery).
46
Which nerve accompanies the deep brachial artery through the radial groove?
Radial nerve.
47
Into which two collateral arteries does the deep brachial artery divide?
Middle collateral and radial collateral arteries.
48
Which artery accompanies the ulnar nerve posterior to the medial epicondyle of the humerus?
Superior ulnar collateral artery.
49
Where does the inferior ulnar collateral artery arise relative to the elbow crease?
Approximately 5 cm proximal to the elbow crease.
50
Do the median and ulnar nerves give off motor branches in the arm?
No, they pass through without supplying branches to the arm.
51
Where does the musculocutaneous nerve begin?
Opposite the inferior border of the pectoralis minor.
52
What is the terminal cutaneous continuation of the musculocutaneous nerve?
Lateral cutaneous nerve of the forearm (lateral antebrachial cutaneous nerve).
53
Which superficial vein does the lateral cutaneous nerve of the forearm course with?
Cephalic vein.
54
What does the radial nerve pierce to enter the anterior compartment of the arm between brachialis and brachioradialis?
Lateral intermuscular septum.
55
Where does the radial nerve divide into its deep and superficial branches?
Anterior to the lateral epicondyle of the humerus.
56
What muscular arch does the deep branch of the radial nerve pass through to become the posterior interosseous nerve?
Tendinous arch of the supinator muscle.
57
What is the sensory distribution of the superficial branch of the radial nerve?
Cutaneous innervation to the dorsum of the hand and fingers.
58
Which nerve branch arises from the median nerve in the proximal forearm to innervate the deep flexor compartment?
Anterior interosseous nerve.
59
Which muscle does the anterior interosseous nerve dive deep to?
Pronator teres.
60
What septum does the ulnar nerve pierce at the middle of the arm to enter the posterior compartment?
Medial intermuscular septum.
61
Through which bony canal behind the medial epicondyle does the ulnar nerve pass to enter the forearm?
Cubital tunnel (posterior to medial epicondyle and medial to olecranon).
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