Dermatomes
- Unilateral area of skin innervated by sensory fibres of a single spinal nerve.
- They show dermatomes as distinct zones yet there is extensive overlap between adjacent dermatomes.
- Two patterns of cutaneous innervation of upper limb
1) Segmental innervation (dermatomes)
2) Multisegmental peripheral innervation (peripheral nerves)
- Brachial plexus
- Most cutaneous nerves of upper limb derive from this plexus, formed by union of anterior rami of C5-T1 spinal nerves.
- Major nerve network- almost all branches arise in axilla
- Sympathetic fibres of each plexus root are received from gray rami of cervical ganglia
- As the network extends distally, there are:
- 5 roots:
C5-T1
- 3 trunks:
superior, medial, inferior
- 3 anterior and posterior regions
- 3 cords:
Lateral, posterior, medial
- 5 terminal branches (peripheral) :
Axillary, musculocutaneous, radial, median and ulnar nerve.
- Divided into suprascapular and infrascapular by clavicle
Supraclavicular branches of Brachial plexus
1. Dorsal scapular
Origin – posterior aspect of anterior ramus of C5, frequent contribution from C4
Structures innervated – rhomboids, occasionally levator scapulae
2. Long thoracic
Origin – posterior aspect of anterior rami of C5, C6, C7
Structures innervated – serratus minor
3. Suprascapular
Origin – superior trunk, fibers from C5, C6 and often C4
Structures innervated – supraspinatus & infraspinatus muscles; shoulder joint (glenohumeral joint)
4. Subclavian nerve
Origin – superior trunk, fibers from C5, C6 and often C4
Stuctures innervated - subclavius & strenoclavicular joint
Infraclavicular branches
- Lateral pectoral- mainly pectoralis major
- Musculocutaneous- anterior of arm, skin on lateral forearm
- Median- muscles of anterior forearm, thenar muscles of palm
- Medial pectoral- pectoralis minor
- Medial cutaneous nerve of arm- skin on medial arm
- Medial cutaneous nerve of forearm- skin on medial forearm
- Ulnar- most intrinsic muscles of hand, and skin
- Upper subscapular- superior of subscapularis nerve on scapula
- Lower subscapular- Inferior of subscapularis and teres major nerves
- Thoracordosal- latissimus dorsi
- Axillary- skin of superolateral arm, shoulder joint
- Radial- muscles in posterior arm and forearm, dorsum of hand
- Cervical plexus (C1-C5)
- From nerves to shoulder
- Example: Supraclavicular, suprascapular
Dermatomes of upper limb (location)
C3, C4
- Base of neck region- extends laterally over shoulder
C5
- Lateral aspect of arm
C6
- Lateral forearm and thumb
C7
- Middle and ring fingers/ middle 3 fingers and centre of posterior aspect of forearm.
C8
- Little finger, medial hand and forearm
TI
- Medial of forearm and inferior arm
T2
- Medial of superior arm and axilla skin
Bones
Humerus
· largest bone in the upper limb
· articulates with scapula (glenohumeral joint), with radius and ulna (elbow joint)
- proximal end: head, surgical and anatomical necks, greater and lesser tubercles
1. head - articulates with glenoid cavity of scapula
2. anatomical neck - indicates line of attachment of the glenohumeral joint capsule
3. surgical neck - narrow site distal to head tubercles, common site of fracture
· intertubercular (bicipital) groove: separates tubercle & protected passage for slender tendon of the long head of biceps muscle
- shaft: - deltoid tuberosity laterally: attachment of deltoid muscle
- oblique radial groove posteriorly: radial nerve and deep artery
- medial and lateral epicondyle: muscle attachment
- condyle: - made up of trochlea, capitulum & olecranon, coronoid and radial fossae
- lateral capitulum: articulate with head of radius
- trochlea: articulate with ulna
- anterior: - coronoid fossa: receives coronoid process of ulna (flexion)
- radial fossa: accommodates edge of head of radius (flexion)
- posterior: olecranon fossa: accommodates olecranon of ulna (extension)
Ulna
· stabilizing bone of forearm
· medial and longer
· articulate proximally with humerus and laterally with head radius
· articulation with humerus: 1) olecranon: projects proximally from the posterior aspect
(forms point of elbow), short lever for extension of elbow
2) coronoid process: projects anteriorly
· trochlear notch: - it's walls formed by olecranon and coronoid process
- articulates with trochlea of humerus
· tuberosity of ulna: - inferior to coronoid process
- attachment of tendon of brachialis muscle
· radial notch: - lateral side of coronoid process
- receives broad periphery of head of radius
· supinator crest: prominent ridge inferior to radial notch on the lateral surface of ulnar shaft
· supinator fossa: - between supinator crest and distal part of coronoid process
- deep part of supinator muscle attaches to both supinator crest and fossa
· shaft of ulna: thick & cylindrical proximally → tapers as it continues distally → small but abrupt enlargement at the narrow distal end (disc-like head of ulna & small, conical ulnar styloid process)
· does not reach & therefore does NOT participate in the radiocarpal (wrist) joint
Radius
· lateral and shorter
· proximal end: short head, neck, medially directed tuberosity
· head: - superior aspect is concave for articulation with capitulum of humerus
- peripherally articulates with radial notch on ulna
- covered with articular cartilage
· radial tuberosity: distal to medial part of neck, demarcates proximal end from shaft
· shaft: - gradually enlarges as it passes distally (in contrast to ulna)
- distal end – medial aspect: ulnar notch (accommodates head of ulna
- lateral aspect - ridge-like, terminating distally in radial styloid process
· dorsal tubercle of radius: lies between shallow grooves for passage of tendons of forearm muscles
· cross section:
- triangular (superficially directed base & deeply directed apex)
- apex: - formed by section of sharp interosseous border of radius & ulna
connects to interosseus membrane of forearm which run an oblique
- course (positioned to transmit forces received by radius (via hands)
to ulna (to transmit to humerus)
Muscles of Arm
1. Biceps brachii
- innervation: musculocutaneous nerve (C5, C6, C7)
- muscle action: supinates forearm & when supine, flexes forearm
2. Coracobrachialis
- musculocutaneous nerve (C5, C6, C7)
- helps flex and adduct arm; resists dislocation of shoulder
3. Brachialis
- Musculocutaneous nerve (C5, C6) & radial nerve (C5, C7)
- flexes forearm in all positions
4. Triceps brachii
- Radial nerve (C6, C7, C8)
- chief extensor of forearm; long head resists dislocation of humerus; especially important during
adduction
5. Anconeus
- radial nerve (C7, C8, T1)
- assists triceps in extending forearm; stabilizes elbow joint; may abduct ulna during pronation
Muscles of forearm
Flexor muscles (flexor-pronator compartment - anterior)
1. superficial layer
- 4 muscles
- pronator teres
- flexor carpi radialis
- palmaris longus
- flexor carpi ulnaris
- all attached proximally by a common flexor tendon to the medial epicondyle of humerus (the
common flexor attachment)
2. intermediate layer
- 1 muscle: flexor digitorum superficialis
3. deep layer
- 3 muscles
- flexor digitorum profundus
- flexor pollicis longus
- pronator quadratus
* all supplied by median or ulnar nerves
Extensor muscles (extensor-supinator compartment - posterior)
1. muscles that extend & abduct/adduct the hand at wrist joint
o extensor carpi radialis longus
o extensor carpi radialis brevis
o extensor carpi ulnaris
2. muscles that extend the medial 4 fingers
- extensor digitorum
- extensor indicis
- extensor digiti minimi
3. muscles that extend / abduct thumb
- abductor pollicis longus
- extensor pollicis brevis
- extensor pollicis longus
* all innervated by branches or radial nerve
Vessels
1) Main arteries
- Subclavian artery, Axillary artery, Brachial artery (supplies arm, superficial and palpable, forms humeral nutrient artery), Deep artery of arm.
- Ulnar and radial artery in forearm and wrist.
- In hand- ulnar artery enters via ulnar canal and terminates into superficial palmar arch. Radial artery terminates in deep palmar arch.
2) Main veins
- Superficial
Cephalic veins arise from lateral dorsal venous network in subcutaneous tissue, often visible through skin, communicates with median cubital vein and enters clavipectoral triangle. Joins axillary vein.
Basilic veins ascend from medial dorsal venous network, visible, merges with axillary vein.
Median antebrachial vein of forearm- highly variable
- Deep veins
Lie internal to deep fascia, paired, similar name as major limb arteries. (deep interosseous veins)
In forearm- are venae comitantes that anastomose from deep venous palmar arch.
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