Brachial Plexus Flashcards
What is the range of spinal nerves involved in the brachial plexus?
C1-4, C5-T1
What is the interscalene triangle?
The space formed between the anterior and medial scalene muscles.
How is the upper trunk of the brachial plexus formed?
By the joining of nerve roots C5-6.
What forms the lower trunk of the brachial plexus?
Nerve roots C8-T1.
What is the middle trunk of the brachial plexus?
It is formed by C7, which does not join with another nerve root.
How many sections do the trunks of the brachial plexus divide into as they pass beneath the clavicle?
6 sections: 3 anterior and 3 posterior.
What are the three cords formed around the axillary artery?
Medial, lateral, and posterior cords.
What forms the posterior cord of the brachial plexus?
All trunks of the brachial plexus.
What contributes to the middle trunk of the brachial plexus?
The middle trunk sends contributions with C5-6 from the lateral cord.
What forms the medial cord of the brachial plexus?
The two remaining nerves C8-T1.
What forms the radial nerve?
The posterior cord from C5-8 and T1.
Where does the radial nerve pass?
It passes axillary wall to deltoid and teres minor, follows the brachial artery in the arm, and innervates the triceps.
What branches does the radial nerve divide into after passing over the lateral epicondyle?
Deep and superficial branches.
What is the motor function of the radial nerve?
Initially supplies all three triceps heads.
What muscles receive motor innervation from the radial nerve?
Triceps, aconeus, brachioradialis, extensor carpi radialis longus.
What does the deep branch of the radial nerve supply?
Extensor carpi radialis longus and supinator.
What muscles are innervated by the posterior interosseous nerve?
Extensor digitorum, extensor digit minimi, extensor carpi ulnaris, extensor pollicis longus, extensor pollicis brevis, extensor indicis, and abductor pollicis longus.
How is sensory supply mainly provided by the radial nerve?
Mainly by the posterior cutaneous nerve.
What area does the sensory supply of the radial nerve cover?
A strip of skin down the center and back of the forearm and elbow joint.
What does the superficial branch of the radial nerve provide sensory innervation to?
The dorsal surface of the hand and lateral 3 ½ fingers, short of nail beds, and the web between the thumb and index finger.
What may trauma to the radial nerve result in?
Motor weakness in supination and/or extension of wrist (wrist drop) and extension of fingers.
What sensory losses may occur due to radial nerve trauma?
Loss to the posterior forearm, radial side of forearm, dorsal aspect of 3 ½ digits (excluding nail beds), and web space.
How is the radial nerve strength tested?
The patient resists against applied force using extensor pollicis longus.
What are the origins of the Median Nerve?
Lateral C5-6 and medial C8-T1, middle trunk C7
Where does the Median Nerve proceed after its origin?
Through axilla and lateral to brachial artery
Between which two muscles does the Median Nerve lie?
Brachialis and biceps
What happens to the Median Nerve as it continues towards the cubital fossa?
Passes over brachial artery, situated medially
What branches does the Median Nerve give off at the elbow joint?
Articular branch
Through which muscles does the Median Nerve continue after the cubital fossa?
Two heads of pronator teres and between two muscles of flexor superficialis
What are the two main branches of the Median Nerve in the forearm?
- Anterior interosseus nerve
- Palmar cutaneous nerve
What does the Anterior interosseus nerve supply?
Deep muscles in forearm
What does the Palmar cutaneous nerve innervate?
Skin of lateral palm
How does the Median Nerve enter the palm?
Through carpal tunnel
What are the terminal branches of the Median Nerve in the palm?
- Recurrent branch (supplies thenar)
- Palmar digital branch (innervates sensory supply to palmar surface, the thumb, index, and ½ ring finger)
What muscles does the Median Nerve innervate in the superficial layer?
- Pronator teres
- Flexor carpi radialis
- Palmaris longus
Which muscle does the Median Nerve innervate in the intermediate layer?
Flexor digitorum superficialis
What are the deep muscles innervated by the Median Nerve?
- Flexor digitorum profundus
- Flexor pollicis longus
- Pronator quadratus
What does LOAF stand for in relation to hand muscles?
- Lateral lumbricals (1st and 2nd)
- Opponens pollicis
- Abductor pollicis brevis
- Flexor pollicis brevis
What is the sensory distribution of the Median Nerve?
Palmar surface of thenar eminence, thumb, index, middle, and ½ ring finger, and associated nail beds
What is a common test for Median Nerve strength?
Pinch grip
What is a characteristic of carpal tunnel syndrome (CTS) related to the Median Nerve?
Caused by swelling of tendon sheath due to repetitive motion
What can happen to the thenar eminence muscles in extreme cases of CTS?
Atrophy due to nerve compression
How can the Median Nerve be damaged at the elbow?
Through supracondylar fracture
What appearance may result from damage to the Median Nerve at the elbow?
Permanent supination
True or False: The palmar cutaneous branch is lost in CTS.
False
Fill in the blank: The Median Nerve can become damaged at the elbow through _______.
supracondylar fracture
What spinal nerve roots form the ulnar nerve?
C8-T1
The ulnar nerve forms the medial cord of the brachial plexus.
Where does the ulnar nerve pass posteriorly?
Medial epicondyle of humerus
This area is a common location for injury.
What muscle does the ulnar nerve penetrate in the forearm?
Flexor carpi ulnaris
The nerve travels along the ulnar bone after penetrating this muscle.
What is Guyon’s canal?
Space between pisiform and hamate bones
The ulnar nerve terminates in superficial and deep branches here.
List the motor innervations provided by the ulnar nerve in the forearm.
- Flexor carpi ulnaris
- Flexor superficialis profundus
Which group of hand muscles does the ulnar nerve innervate that is associated with the little finger?
Hypothenar eminence
This group includes muscles that control the movement of the little finger.
Name the muscles innervated by the ulnar nerve that control the little finger.
- Opponens digiti minimi
- Abductor digiti minimi
- Flexor digiti minimi brevis
What other hand muscles does the ulnar nerve supply?
- Medial two lumbricals
- Adductor pollicis
- Palmaris brevis
- Interossei
What is the sensory supply area of the ulnar nerve?
Medial side of palm and corresponding medial dorsal surface, little finger and ½ ring
This includes sensory innervation to specific areas of the hand.
How is ulnar nerve strength tested?
Resist abduction of little finger
Where is damage to the ulnar nerve commonly located?
Medial epicondyle of elbow
Damage can occur due to compression or injury in this area.
What syndrome is caused by ulnar nerve compression within the cubital tunnel?
Cubital tunnel syndrome
What can cause stretching or compression of the ulnar nerve in the hand?
Hand extension and ulnar-deviated position
This is particularly common in cyclists.
What are extreme cases of ulnar nerve damage characterized by?
Inability to abduct and adduct fingers, reduced movement of little and ring fingers, loss of sensation
These symptoms are due to severe ulnar nerve damage.
What is the origin of the musculocutaneous nerve?
Formed from terminal branch of lateral cord of brachial plexus
The musculocutaneous nerve arises from the C5-C7 nerve roots.
Which spinal nerves contribute to the musculocutaneous nerve?
C5, C6, C7
These roots are part of the brachial plexus.
What muscles does the musculocutaneous nerve innervate?
Coracobrachialis, Biceps, Brachialis
These muscles are involved in arm flexion and stabilization.
What is the sensory function of the musculocutaneous nerve?
Innervates skin on lateral part of forearm through lateral cutaneous nerve
This provides sensory feedback from the skin in that area.
Where does the musculocutaneous nerve travel after innervating the biceps?
Passes lateral to tendon of biceps, then enters forearm
This pathway allows it to supply sensory innervation.
Is damage to the musculocutaneous nerve common?
No, very rare
The musculocutaneous nerve is well protected within the arm.
What spinal nerves are associated with the axillary nerve?
C5-6
Where does the axillary nerve travel in relation to the axillary artery?
Posterior to axillary artery and anterior to subscapularis
What are the two terminal branches of the axillary nerve?
- Posterior terminal branch (teres minor)
- Anterior terminal branch (deltoid)
What muscles receive motor supply from the axillary nerve?
- Deltoid
- Teres minor
What area does the sensory branch of the axillary nerve innervate?
Skin region inferior to the deltoid muscle
What is the small area innervated by the axillary nerve known as?
Regimental badge
What are common causes of axillary nerve damage?
- Dislocation of the glenohumeral joint
- Fracture of the surgical neck of the humerus
What are the effects of axillary nerve damage on muscle atrophy?
Atrophy of deltoid and teres minor, leading to palpation of acromion process and greater tubercle of humerus
What functional impairment occurs due to axillary nerve damage?
Weak and difficult shoulder abduction
What sensory loss occurs with axillary nerve damage?
Loss of sensation at the regimental badge
Fill in the blank: The axillary nerve is a branch of the _______.
Posterior cord
