Arm Anatomy Flashcards
How many compartments are there in the upper arm?
2
What type of muscles are contained within the anterior compartment?
Flexor muscles
Which muscles are found within the anterior (flexor) compartment of the arm?
- Biceps brachii
- Coracobrachialis
- Brachialis
How are the anterior compartment of the arm muscles innervated?
Musculocutaneous nerve (C5-C7)
What type of muscles are contained within the posterior compartment?
Extensor
Which muscles are found within the posterior (extensor) compartment of the arm?
Triceps brachii
How are the posterior compartment of the arm muscles innervated?
Radial nerve (C5-T1)
How many heads does the biceps brachii have?
2 - a long and a short head
What are the origins of the heads of the biceps brachii?
Long head - originates at supraglenoid tubercle of scapula and runs along inter-tubercular groove of humerus
Short head - originates at the coracoid process of scapula
Which muscles runs along the inter-tubercular groove of humerus?
Long head of the biceps brachii
What is the insertion point of the heads of biceps brachii?
Radial tuberosity
What is the function of biceps brachii?
Flexor of forearm at elbow joint
What is the origin of the brachialis?
Distal anterior humerus
What is the insertion of the brachialis?
Medial aspect of the ulnar tuberosity
Is brachialis deep or superficial to biceps brachii?
Deep
What is the function of brachialis?
Flexor of forearm at elbow joint
How many heads are there to the triceps brachii?
3 - long, medial and lateral
(Medial head runs superficial to the lateral head)
Where does the triceps brachii insert?
All 3 heads merge, form a tendon, and insert at the olecranon process of the ulnar bone
What are the origins of the triceps brachii?
Long head - infraglenoid tubercle of the scapula
Medial head - humerus (inferior to the radial groove)
Lateral head - humerus (superior to the radial groove)
What is the root of the radial nerve?
C5-T1 (arising from the posterior cord of the brachial plexus)
What is the path of the radial nerve?
Travels posteriorly along the humerus in the radial groove
Winds it’s way around the humerus laterally at the mid-shaft so vulnerable to damage if fracture in this area
What does the superficial branch of the radial nerve innervate?
- Cutaneous sensation of posterior forearm
- Lateral aspect of dorsal of hand
- Dorsal surface of lateral three and a half digits
What does the deep branch of the radial nerve innervate?
- Extensor muscles in posterior forearm
At what point does the radial nerve split into a superficial and deep branch?
Passes anterior to lateral epicondyle through the cubital fossa to enter the forearm THEN divides
Prior to its division, what does the radial nerve innervate?
Triceps brachii
What other nerve is involved in innervating triceps brachii?
Lateral head of triceps brachii is also innervated by axillary nerve
What is the root of the axillary nerve?
C5-C6, and arises from the posterior cord of the brachial plexus
How does a radial nerve injury present?
- Wrist drop
- Loss of sensation to the lateral aspect of the dorsum of hand
What is the function of the musculoctaenous nerve?
Innervation of the muscles of the flexor compartment of the upper arm
What is the root of the musculocutaenous nerve?
C5-C7 (arising from the lateral cord of the brachial plexus)
What does the musculocutaneous nerve become?
The lateral cutaneous nerve of the forearm, providing sensory innervation
What is the path of musculocutaenous nerve?
Enters coracobrachialis muscle and runs through flexor compartment superficial to brachialis muscle and deep to biceps brachii muscle –>
Pierces deep fascia lateral to biceps brachii to emerge lateral to biceps tendon and brachioradialis
How does an injury to the musculocutaenous nerve present?
- Weak flexion at elbow and shoulder, weak supination of forearm
- Loss of sensation over lateral aspect of forearm
What root does the median nerve arise?
C6-T1
What is the motor function of the median nerve?
Flexor and pronator muscles of anterior compartment of forearm, thenar muscles and lateral two lumbricals in the hand
What is the sensory function of the median nerve?
Palmar cutaneous branch: lateral aspect of palm
Digital cutaneous branch: lateral three and a half fingers of anterior surface of hand
What is the path of the median nerve?
Descends the upper arm LATERALLY to brachial artery
Crosses brachial artery to enter the anterior compartment of the forearm through cubital fossa and run medially
Runs through carpal tunnel to enter hand
How does a median nerve injury present?
@ wrist = loss of thumb opposition and atrophy (ape hand)
Distal injury - lateral lumbrical weakness (median claw)
Proximal injury = weakness of forearm muscles and hand of benediction (can only close medial 2 fingers on asking to make a fist)
How does ulnar nerve injury present?
- Weak thumb adduction
- Claw-like hand deformity
- Loss of sensation over little finger and medial aspect of ring finger
What is the root of the ulnar nerve?
C8-T1 (from the medial cord of the brachial plexus)
What is the motor function of the ulnar nerve?
2 muscles of anterior forearm (flexor carpi ulnaris and medial half of flexor digitorum profundus) and intrinsic muscles of the hand (apart from thenar muscles and 2 lateral lumbricals
What is the sensory function of the ulnar nerve?
Medial one and a half fingers and associated palmar area
What is the route of the ulnar nerve?
Travels distally between the axillary artery and axillary vein and is medial to the brachial artery
At the midpoint of the arm it pierces the medial fascial septum to enter the posterior compartment of the arm
Passes between the medial epicondyle and the olecranon in the groove for the ulnar nerve to enter the anterior compartment of the forearm
What is the arterial supply of the arm?
Subclavian artery–> axillary artery –> brachial artery
When does the subclavian artery become the axillary artery?
Where crosses the 1st rib
When does the axillary artery become the brachial artery?
At the level of inferior border of teres major muscle
At what level does the brachial artery divide into the radial and ulnar artery?
Level of neck of radius
What branches does the brachial artery give off prior to becoming the radial and ulnar artery?
- Profunda brachii (deep artery of arm) - runs between triceps and radial nerve
- Humeral nutrient artery
- Superior and inferior ulnar collateral arteries (superior ulnar artery travels with the ulnar nerve)
Where is the briachial artery relative to the humerus?
Medial
What are the superficial veins to the arm?
- Cephalic
- Basilic - in subcut tissue until pierces brachila fascia to run deep next to brachial artery
What are the deep veins are the arm?
- Ulnar vein
- Radial vein
^^join to become the brachial vein, emptying int ot eh axillary vein
When does the formation of the limb buds begin?
Week 4
From what is the limb bud derived?
Mesenchymal cells in the somatic layer of lateral plate mesoderm
At mid-humeral level, where does the cephalic vein lie?
Above the brachial fascia
