Week 4 - Upper limb + nerves Flashcards
What is special about brachioradialis?
It’s in the posterior compartment of the arm (lateral epicondyle) but is a flexor of the elbow
What are the three main muscles attaching to the humerus from the medial side? What do they do?
Latissimus Dorsi
Pectoralis Major
Teres Major
- These are adductors and medial rotators
- Because PM is anteriorly, it is also a flexor of the shoulder joint
- Because LD and TM are posterior, they are also extensors of the shoulder joint
What are the lateral rotators of the shoulder?
ONLY infraspinatus - it is the only posterior muscle that attaches on to the lateral side of the humerus
What is the action of the deltoid?
It’s an abductor - it passes lateral to the shoulder joint
Which two muscles are involved in abduction of the shoulder past ~110 degrees?
Trapezius and serratus anterior - these rotate the scapula upwards so the glenoid faces upwards
Which two muscles restore a rotated upwards scapula to it’s original position?
Rhomboids + Pec minor`
Which part of the scapula does pec minor act on, and in what direction?
Pulls the corocoid down
What is the role of serratus anterior? What happens when it is paralysed?
Pulls the opposite end of the scapula downwards than that of pec minor - i.e. pec minor pulls one side, SA pulls the other.
When SA is paralysed, the medial end of the scapula is left drifting, which makes it ‘wing’ as pec minor continues to pull the lateral edge.
Which muscles does the axillary nerve supply?
Deltoid and teres minor
Which nerve feeds trapezius?
11th cranial nerve
What is the antagonist muscle of the rhomboids?
Trapezius
Where do the roots of the brachial plexus come from?
VENTRAL RAMI of spinal nerves
Where are the roots and trunks of the BP?
In the neck
Where are the cords and branches of the BP?
In the axilla
How would you tell if the upper trunk of the brachial plexus was damaged?
UT feeds into suprascapular branch, so if it’s not working, infraspinatus is paralysed.
This causes the medial rotation of the arm and the tone of the medial rotators is much stronger - the lateral rotator has been lost.
What is the root value of a nerve?
The root value of a nerve is the ventral rami from which it originates
Which muscles of the shoulder are developmentally posterior?
All of them, except the pectoral
Describe how the brachial plexus gets to the armpit
Extends from spinal cord, through cervicoaxillary canal in the neck, over the first rib and into the armpit
Which structures form the M structure of the BP?
Musculocutaneous nerve Lateral cord Median nerve Median cord Ulnar nerve
What makes up the upper trunk of BP?
C5 & C6
WHat makes up the lower trunk of BP?
C8 & T1
Which nerve innervates lats?
Thoracodorsal branch
Which nerve innervates subscapularis and T major?
Subscapular x2
From which cords does the long thoracic nerve come from, and what does it innervate?
Comes from C5, C6 and C7
Innervates serratus anterior
What forms the posterior cord?
The three posterior divisions of C5, C6
What are the posterior cord branches?
Thoracodorsal
Axillary
Radial
Subscapular
Which compartment of the arm is fed by the posterior cord?
The posterior/extensor
Which compartment of the arm does the radial nerve feed?
The posterior compartment, because it’s from the posterior cord
Which cords feed the anterior compartment of the arm?
Medial and lateral cords –> flexor muscles are fed by these
Describe the action of musculocutaneous nerve in the arm?
Supplies the bicep and brachialis, passing between them, then becomes lateral cutaneous nerve for the forearm
What are the roles of the median and ulnar nerves in the arm?
Innervate all anterior muscles of the forearm and hand, including intrinsic hand muscles, as these are developmentally anterior
Where is the surgical neck of the humerus and why is it called that?
Axillary nerve (posterior cord, fibres from C5 and C6) winds around the posterior side of the upper end of the humerus and enters the deltoid. A fracture in this area could cause the nerve to get trapped in the callus, weakening the deltoid/paralysing it --> surgical neck
Which roots have fibres in the posterior cord?
ALL OF THEM
From which roots does the median nerve have fibres?
All of them
Made up of branches from the anterior medial and lateral
What does the median nerve innervate?
Supplies all anterior muscles of the forearm apart from FCU and 1/2 FDP
Supplies thenar muscles after passing through carpal tunnel
Then becomes cutaneous, supplying the anterior side of thumb and first two fingers + 1/2 ring finger
Where does the ulnar nerve come from?
The lateral cord, fibres from C8 and T1
Describe the path of ulnar nerve through the arm
- Moves on medial side of arm, posterior to medial epicondyle, through cubital tunnel
- Straight down to wrist
- At wrist, passes through tunnel at hook of hamate
- Splits into deep and superficial branches
What is the path of the median nerve down the arm?
With brachial artery
Goes through pronator teres - is deep to FDS
Emerges at wrist, goes through carpal tunnel
What does the ulnar nerve innervate?
FCU and 1/2 FDP in forearm
All remaining anterior muscles in the hand not fed by median nerve aka all interossei, adductor pollicis and hypothenar
Also the skin of the hand on the medial side (anterior and posterior)
Describe the course of the radial nerve through the arm
Crosses posterior to humerus in spiral track
Moves through triceps
Divides near the elbow, superficial nerve is cutaneous
Deep radial passes beneath extensor muscles, running between ulna and radius
Loses all fibres within the forearm
What does the radial nerve innervate?
The triceps
Entire posterior compartment of the forearm
Deep radial also supplies posterior interosseous
What does irritation of a nerve cause?
Sensory effects - altered sensation (paresthesia)/pain
Motor effects - muscle twitches
What does total loss of nerve conduction cause?
Loss of sensation
Weakness/paralysis of muscle
Loss of movement can lead to atrophy and alteration of contour
What’s a common cause of compression or stretch of a nerve?
Altered bony features i.e. bony spurs, or a tumour
What does entrapment do to a nerve?
Early irritation is followed by total loss of conduction
What are phantom sensations caused by?
Irritation of cut nerve fibres
How is the axillary nerve often injured?
At the surgical neck of the humerus
How is the radial nerve injured?
At the spiral sulcus of the humerus
How is the radial nerve injured when it’s in the posterior interosseous area?
By fractures with dislocation - superior R-U joint
Where are the two areas the ulnar nerve is often entrapped?
- At the medial epicondyle, in the bone and fibrous arch
2. Near the hamate bone (Guyon’s canal)
What are four effects of muscle paralysis?
- Loss of movement
- Wasting
- Antagonist tone and limb position i.e. infraspinatus paralysis
- Compensatory mechanisms i.e. angle for supraspinatus and abduction
What is the axillary artery a continuation of?
The subclavian artery across the first rib
What is the course of the brachial artery?
Down the medial side of the arm, to the cubital fossa. It then splits into radial and ulnar artery
Where do you find the ulnar artery?
With the ulnar nerve in the lower 2/3 of the forearm
Where do you find the radial artery?
Along the radius
Then going through the anaomical snuff box
