nerves Flashcards
nerves of the upper limb: describe the origin, course and function of the axillary, radial, musculocutaneous, median and ulnar nerves in the upper limb; describe the organisation of the major muscles and muscle groups that these nerves supply and their sensory distribution; explain the consequences of injury to these nerves and explain how to test their functional integrity
what spinal segments do the upper limb and its limb girdle get sensory and motor nerve supplies from
C4-T1
what do spinal segments C3 to C7 give muscle movement supply to
shoulder girdle
what do spinal segments C5 and C6 give muscle movement supply to
shoulder joint and elbow flexors
what do spinal segments C7 and C8 give muscle movement supply to
elbow joint extensors
what do spinal segments C6 to C8 give muscle movement supply to
wrist musles and coarse hand muscles
what do spinal segments C8 and T1 give muscle movement supply to
fingers and thumb (small muscles of hand for fine movements)
what does the axillary nerve supply
winds round neck of humerus to supply C5 and C6 fibres to deltoid (main abductor of shoulder)
when can the axillary nerve be injured, and consequences
shoulder dislocations (travels under shoulder joint) and upper humeral fractures (e.g. surgical neck), resulting in loss of abduction and eventual wasting of deltoid and teres minor, as well as loss of sensory innervation to superolateral shoulder skin (innervated by superior lateral cutaneous nerve of arm, from axillary nerve)
where does radial nerve wind in arm
winds posterior to humerus in radial groove between attachements of medial and lateral bicep heads
what radial nerve fibres can be damaged by fractures of mid-humeral shaft (runs in radial groove), and what can this lead to
C7-T1 fibres, leading to loss of function of extensor muscles in forearm, causing muscle wastage (if happens high in limb), wrist drop and weakness of power grip (extension of wrist required, so flexor muscles work harder but can’t fully compensate)
where do radial nerve sensory losses by fractures of mid-humeral shaft affect
variable area on posterior surface of thumb and lateral dorsal hand (substantial overlap with other nerves)
what muscles do lateral and medial cords supply
only flexor muscles
what fibres are contained within lateral cord, and hence which muscle compartments is it principally concerned with
C5-C7, so muscles acting on shoulder and elbow
most important branch of lateral cord, and what does it supply
musculocutaneous branch, supplying elbow flexors (biceps brachii and brachialis), with biceps brachii also being the key muscle in supination
when may the musculocutaneous nerve be damaged
during breast cancer surgery for removal of lymph nodes (not trauma as well protected by muscles)
what fibres are contained within medial cord, and hence which muscle compartments is it principally concerned with
C8-T1, so muscles acting in forearm and hand
main branch of medial cord
ulnar nerve
what does the ulnar nerve supply
most intrinsic muscles in hand
what and where is the ulnar nerve most vulnerable to
compression, cuts and fractures where is passes posterior to medial epicondyle of humerus at elbow, self harm to wrist
consequences of ulnar nerve damage
weakness and wasting of many small muscles in hand (less serious than expected as really vital small muscles of hand, controlling fine movements of thumb and index finger, are served by median nerve), as well as loss of sensation to lateral half of ring finger, and little finger
why might clawing be seen in ulnar nerve damage, and why is distal damage more severe than proximal damage
loss of lumbrical contraction means loss of flexion of metacarpophalangeal joins and weakened extension of interphalangeal joints, causing unopposed activity of long muscles of fingers lying in forearm, also affecting PAD and DAB; more severe if injury at wrist (distal) than at elbow (proximal), as it innervates ulnar half of flexor digitorum profundus, so flexion of interphalangeal joints is weakened, so is less claw-like
where is sensory loss in median nerve injuries present
along medial part of hand, and medial (usually 1.5) fingers
what nerve do lateral and medial cords both contribute to formation of
median nerve
what fibres does the median nerve acquire from brachial plexus
C6-T1
what does median nerve supply (motor)
most of wrist and finger flexors in forearm, and most small muscles of thumb and index finger
what does median nerve supply (sensory)
lateral part of palmar hand
what sorts of activities does injury or entrapment of median nerve make impossible, and why
delicate hand activities e.g. writing, as wasting of lateral lumbricals and thenar eminence (except adductor pollicis, as supplied by ulnar nerve)
when does the median nerve often become entrapped
as it passes through carpal tunnel (carpal tunnel syndrome)
what spinal segment causes flexion of shoulder
C5
what spinal segments cause extension of shoulder
C6,7,8
what spinal segments cause flexion of elbow
C5,6
what spinal segments cause extension of elbow
C7,8
what spinal segments cause pronation of wrist
C7,8
what spinal segment causes supination of wrist
C6
what spinal segments cause flexion/extension of wrist
C6,7
what spinal segment causes abduction/adduction of digits in hand
C7
what spinal segments cause flexion/extension of fingers
C7,8
why isn’t sensory innervation (cutaneous nerve patterns( the same as dermatome innervation
nerve fibres supplying dermatomes might come from more than one peripheral nerve, due to recombination in plexus
what fibres form the long thoracic nerve
roots of C5,6,7
what muscle is affected by damage to long thoracic nerve
serratus anterior (long thoracic nerve is relatively superficial, so easily damaged)
main function of serratus anterior, and hence consequence if long thoracic nerve is damaged
holds down surface of scapula, so pressing against a wall will lead to winging of the scapula
what is the name of injuries to upper roots
Erb-Duchenne Palsy
when do injuries to upper roots occur, and what roots are commonly affected
stretch neck relative to shoulder, so especially affects C5 and C6 (trauma, childbirth)
what is the commmon presentation caused by injuries to upper roots
“Waiter’s Tip”, where many muscles in shoulder and arm are affected, with the forearm pronated by lack of biceps supination
what is the name of injuries to lower roots
Klumpke’s Palsy
common cause of injuries to lower roots, and what roots are commonly affected
over-abduction due to gripping overhead to break a fall, or at birth,, so overextends T1 (and sometimes C8)
what is the common presentation caused by injuries to lower roots
loss of activity to small muscles of hand (T1) via ulnar and median nerves results in clawed hand (wrist and finger flexors e.g. flexor carpi ulnaris, ulnar part of flexor digitorum profundus, are damaged, with extensors unopposed)
