Axilla, Brachial Plexus Flashcards
What is the medial boundary of the axilla?
Serratus anterior.
What is the posterior boundary of the axilla?
Subscapular muscles.
What is the anterior boundary of the axilla?
Pectoral muscles.
What forms the apex of the axilla?
The junction between clavicle, scapula, and first rib.
What are the three main contents of the axilla?
Axillary vessels
Axillary lymphatics
Brachial plexus
Name the five groups of axillary lymph nodes.
Lateral
Subscapular
Pectoral
Central
Apical
What is the subclavian line?
It refers to the pathway and location where subclavian vessels and brachial plexus structures travel through the apex of the axilla (important for central line access or thoracic outlet syndrome).
What does the brachial plexus supply?
Motor and sensory innervation to the upper limb.
What does the radial nerve supply?
Dorsal compartments (extensors of upper limb).
What does the musculocutaneous nerve supply?
Flexors of the upper arm (ventral compartment).
What does the median nerve supply?
Flexors of forearm and hand – radial side (ventral compartment).
What does the ulnar nerve supply?
Flexors of forearm and hand – ulnar side (ventral compartment).
What nerves contribute to the cutaneous sensation of the hand?
- Median nerve: Lateral palm, thumb, index, middle, and half of ring finger
- Ulnar nerve: Medial palm, little finger, and half of ring finger
- Radial nerve: Dorsum of hand (thumb to half of ring finger – NOT fingertips)
What does a specific brachial plexus lesion result in?
Predictable patterns of motor and sensory loss depending on affected nerve(s).
What are dermatomes?
Skin areas supplied by sensory fibers of a single spinal nerve.
What dermatome corresponds to the thumb?
C6.
What dermatome corresponds to the middle finger?
C7.
What dermatome corresponds to the little finger and medial forearm?
C8 and T1.
What are myotomes?
Muscle groups innervated by motor fibers from a single spinal nerve.
What is the myotome for shoulder abduction?
C5.
What is the myotome for elbow flexion?
C5–C6.
What is the myotome for elbow extension?
C7.
What is the myotome for finger flexion and extension?
C8 (flexion), C7 (extension).
What is the myotome for finger abduction/adduction?
T1.
What causes Erb’s palsy?
Upper brachial plexus injury (C5–C6).
What are the symptoms of Erb’s palsy?
Arm hangs by the side (adducted)
Medially rotated shoulder
Extended elbow
“Waiter’s tip” position
Which myotomes and dermatomes are affected in Erb’s palsy?
C5–C6.
What causes Klumpke’s paresis?
Lower brachial plexus injury (C8–T1).
What are the symptoms of Klumpke’s paresis? 3
Weakness of intrinsic hand muscles
Claw hand
Possible Horner’s syndrome (if T1 sympathetic fibers involved)
How do you test T1?
- Sensation over medial side of the forearm
- Finger adduction/abduction (small hand muscles)
What is the key sensory deficit in radial nerve injury?
Loss of sensation over the dorsal web space between thumb and index finger.
What is the key motor deficit in radial nerve injury?
Weakness of wrist and finger extensors.
What classic clinical sign is seen in radial nerve injury?
Wrist drop – inability to extend the wrist and fingers.
What sensory areas are affected in ulnar nerve injury?
Medial aspect of palm, little finger, and medial half of the ring finger.
What motor deficit leads to the ‘ulnar claw’?
Inability to extend the 4th and 5th digits due to interossei and lumbrical weakness.
What is the ‘ulnar paradox’?
The closer the nerve lesion is to the hand, the worse the claw appears — because proximal lesions paralyze more muscles that counteract the claw.
What sensory loss occurs in median nerve injury?
Palmar surface from the thumb to the lateral half of the ring finger.
What is the motor deficit when attempting to make a fist in median nerve injury?
Inability to flex 2nd and 3rd digits – resulting in the ‘Hand of Benediction’.
