MSS16 Brachial Plexus And Nerve Distributions Flashcards
Skin and Limb muscles
Supplied by nerve plexuses from Ventral rami of spinal nerves
Flexor compartment (richer nerve supply): supplied by Anterior division of ventral rami
Extensor compartment: supplied by Posterior division of ventral rami
***Innervation of upper limb skin and muscles
Brachial plexus:
5 parts:
- Root (within prevertebral musculature): Ventral rami of C5-C8, T1
- Trunks (posterior triangle of neck): upper/middle/lower
- Divisions (behind clavicle): anterior/posterior
- Cords (upper 1/2 of axilla): lateral/medial/posterior
- Branches (arise from all parts of the plexus except divisions): nerve fibres from different spinal levels
記: RooT of DC
Posterior triangle of neck
Borders:
- Clavicle
- Trapezius
- Sternal head of sternocleidomastoid muscle
Axilla
5 planes:
1. Apex
- Lateral wall
- long + short head of biceps
- coracobrachialis - Medial wall
- serratus anterior - Anterior wall
- pectoralis major + minor - Posterior wall
- latissimus dorsi
- subscapularis
- teres major
Inlet of axilla:
- behind clavicle
- in front of superior margin of scapula
- lateral to 1st rib
Branches of the brachial plexus
Root:
1. **Dorsal scapular nerve (C5)
(levator scapulae, rhomboid minor / major)
2. **Long thoracic nerve (C5-7)
(serratus anterior: lesion of nerve —> winging of scapula)
Upper trunk:
1. ***Suprascapular nerve (C5-6)
(supraspinatus, infraspinatus)
2. Nerve to Subclavius (C5-6)
Division:
- NO branches
Lateral cord:
- Lateral pectoral nerve (C5-7)
* **2. Musculocutaneous nerve (C5-7)
* **2.5. Median nerve (lateral root) (C6-7) (0.5 branch, other 0.5 from medial cord)
Medial cord:
- Medial pectoral nerve (C8)
- Medial cutaneous nerve of arm (T1)
- Medial cutaneous nerve of forearm (C8-T1)
* **4. Ulnar nerve (C8-T1)
* **4.5. Median nerve (medial root) (C8-T1) (0.5 branch)
Posterior cord:
- Upper subscapular nerve (C5-6)
- Thoracodorsal nerve (C6-8)
- Lower subscapular nerve (C5-6)
* **4. Axillary nerve (C5-6)
* **5. Radial nerve (C5-T1)
Relation between brachial plexus and axillary artery
Cords are named according to their relationship to the ***2nd part of Axillary artery (lateral, medial, posterior cords)
***Main nerves of upper limb
- Musculocutaneous nerve
- Median nerve
- Ulnar nerve
- Radial nerve
- Axillary nerve
Musculocutaneous nerve
Anterior C5-7
Muscles:
- ***Anterior arm muscles
Skin (落一層):
- Lateral forearm (lateral cutaneous nerve)
Injury:
- affects flexion and supination of forearm but not completely lost (compensated by accessory muscles e.g. brachioradialis (accessory flexor), supinator)
Median nerve
Anterior C6-T1
- travel in anterior compartment of arm
- between intermediate and deep layers of anterior forearm muscles
- partly overlapped by palmaris longus tendon (vulnerable at front of wrist)
- relationship of **Median nerve to Brachial artery in arm / cubital fossa: halfway down the arm, Median nerve crosses the Brachial artery from **lateral to medial side
Muscles:
- All muscles in anterior forearm except 1.5 muscle (Flexor carpi ulnaris, ***medial 0.5 of Flexor digitorum profundus)
- 1st + 2nd Lumbricals (carpal tunnel)
- **Thenar muscles (except **Adductor pollicis: ulnar nerve)
Skin:
- Lateral 2/3 palm (Palmar cutaneous nerve: do not enter carpal tunnel)
- Palmar surface and nail-beds of lateral 3.5 digits (Nerve within carpal tunnel)
Injury:
- depend on site of injury:
-
**Compression syndrome in carpal tunnel (vulnerable at front of wrist)
- sensory loss
- loss of muscular and joint proprioception
- impaired **thumb movements
- -> no opposition, flexion, abduction
- -> **wasting of thenar eminence
- -> becomes **adducted, laterally rotated (Ape hand) (opposition: abduction + medial rotation) - Injury above the elbow
- -> additional effects: weaker wrist flexion and loss of pronation
Ulnar nerve
Anterior C8-T1
- travel down Medial side of anterior compartment of arm
- -> pierces medial intermuscular septum
- -> reach posterior compartment where it is palpable (and vulnerable!)
- -> ***behind medial epicondyle of humerus (vulnerable)
- -> moves back to anterior compartment of forearm
- -> quite superficial in front of wrist
- -> medial to Ulnar artery, lateral to Flexor carpi ulnaris tendon and Pisiform bone (次序: 最出—>最入: Ulnar artery, Ulnar nerve, Flexor carpi ulnaris tendon, Pisiform bone)
- NO branches in arm
Muscles:
- 1.5 muscles in anterior forearm (**Flexor carpi ulnaris, **medial 0.5 of Flexor digitorum profundus)
- **- most Intrinsic muscles of the hand
Skin:
- Medial part of the palm
- Palmar aspect of medial 1.5 or 2.5 fingers (superficial branch)
- Dorsal aspect of the same fingers are supplied by dorsal branch given off in the distal third of the forearm
Injury:
- depend on site of injury
- Wasting of **Hypothenar + **Interosseous muscle
- -> motor loss involving ***fine movements of the fingers
- MCP joints hyperextended + IP joints flex
- -> ***Claw-hand (extensor expansion normally Flex MCP + Extend IP)
Radial nerve
Posterior C5-T1
- Passes from axilla to posterior side through the ***Triangular interval
- -> winds around back of humerus (radial groove)
- -> enters anterior compartment of arm by piercing lateral intermuscular septum just above lateral epicondyle
- -> divides into Deep + Superficial branches at or below lateral epicondyle
- Deep branch (dorsal interosseous nerve): pierces Supinator muscle and wraps around neck of radius (vulnerable here) to reach the posterior compartment of the forearm
- Superficial branch (cutaneous) (deep to brachioradialis): emerges in the snuff-box and gives off digital branches
Muscles:
- ALL posterior muscles in Arm + **Forearm (*Extensors)
Skin:
- Posterior and lateral surfaces of arm
- Posterior forearm
- Dorsum of hand (small area)
Injury:
- paralysis of Extensors of wrist and digits (least disabling compared with median and ulnar nerve lesions)
- **–> Wrist drop
Axillary nerve
Posterior C5-6
- Leaves axilla by passing backward through the ***Quadrangular space
- -> winds around the posterolateral aspect of surgical neck of humerus (may be affected by shoulder dislocation)
Muscles:
- ***Deltoid
- ***Teres minor
Skin:
- small area on Lateral side of arm near insertion of deltoid
Injury:
- cannot abduct the arm beyond 45o (initial abduction by Supraspinatus)
Dermatome
- Area of skin supplied by single spinal (segmental) nerve (NOT cutaneous nerve)
- due to formation of nerve plexuses –> dermatome different from cutaneous innervation fields
Axial line
Line of junction of 2 dermatomes supplied from discontinuous spinal levels
***Dermatome maps
C5: upper lateral side of arm C6: pad of thumb C7: pad of index finger C8: pad of little finger T1: medial aspect of elbow
–> can be tested for sensation with minimal overlap (一定唔會關其他level事)
