Brachial plexus and anterior arm Flashcards
What does the brachial plexus innervate
Innervates muscles of the shoulder, arm, forearm and hand. Provides sensory innervation to the bones, skin, muscles and connective tissue of the shoulder and upper extremity.
When is a nerve plexus formed
formed when nerve fibres from 2 or more spinal segments intermingle then segregate to travel to a common anatomical region
What spinal segments does brachial plexus recieve motor and sensory fibres from
C5-T1
Where is the brachial plexus located
between the anterior and middle scalene
What are the different sections of the brachial plexus - in order
roots, trunks, divisions, cords, terminal branches
What are the roots
There is one root from each spinal segment and they are named from the spinal segment they represent (e.g., C5 root)
What are the different trunks
C5 and C6 roots join to form superior trunk. C8 and T1 roots join to form inferior trunk. C7 continues by itself to form middle trunk.
What do all trunks do
divide into an anterior and posterior division
Why is the segregation into anterior and posterior important
segregation because all fibres in anterior division will innervate anterior compartment muscles and all fibres in posterior division will innervate posterior compartment muscles
How does the mid-axillary line divide the arm
to form an anterior (pre-axillary/flexor) and a posterior (post-axillary/extensor) compartment.
How are the cords formed
The posterior divisions of the 3 trunks come together to form the posterior cord. The anterior division of the upper and middle trunk form the lateral cord. The anterior division of the lower trunk continues by itself to form the medial cord
How are the cords named
relative to their position to the axillary artery
What are the 5 terminal branches
axillary nerve, radial nerve, musculocutaneous nerve, ulnar nerve and median nerve
What does the posterior cord divide into
axillary and radial nerve
What does the lateral cord divide into
the musculocutaneous nerve and contributes to the median nerve by giving off the lateral root of the median nerve
What does the medial cord divide into
the ulnar nerve and contributes to the median nerve by giving off the medial route which joins the lateral route to form the median nerve proper.
What is the reference point to located components of the plexus
The terminal branches if the lateral and medial cords form the characteristic ‘M’ shape anterior to the axillary artery (most distinctive feature of plexus)
Which branch arises from the C5 root
the dorsal scapular nerve
What forms the long thoracic nerve
branches from C5, C6, C7 roots
What are the branches of the superior trunk
suprascapular nerve and the nerve to the subclavius
How many nerves do the cords give rise to in addition to the terminal branches
7
What branch does the lateral cord give off
lateral pectoral nerve
What branches does the posterior cord give off
upper and lower subscapular nerve and the thoracodorsal nerve
What branches does the medial cord give off
the medial pectoral nerve, the medial brachial cutaneous nerve and the medial antebrachial cutaneous nerve.
When does upper brachial plexus injury occur
during extreme lateral flexion of head (especially if shoulder is simultaneously depressed) – like when baby is being pulled out while its shoulders are trapped within the mother’s pelvis
What does upper brachial plexus injury damage
C5/C6 nerve roots or the superior trunk
What can upper brachial plexus damage result in
results in erb-duchenne paralysis (when arm hangs limply at the side and is internally rotated, forearm is also slightly pronated which slightly flexes the wrist)
What causes lower brachial plexus injury
during extreme abduction of the arm (e.g., falling from a ladder or a tree attempts to stop themselves by reaching for something overhead to hang on to)
What does lower brachial plexus injury damage
stress on C8-T1 root of inferior trunk itself
What does lower brachial plexus injury effect
causing muscles in the hand and forearm to be effected resulting in klumpke’s paralysis (claw hand – where fingers are flexed)
Which nerve innervates the serratus anterior muscle
the long thoracic nerve
Where is the long thoracic nerve located
travels along the lateral anterior wall, then is located on the superficial surface of the muscle
What does the serratus anterior do
protracts and upwardly rotates the scapula, it keeps the scapula tight against the thoracic cage during arm movements
What is a sign of long thoracic nerve injury
winging of scapula - it displays an obvious dorsal protusion
What does the axillary nerve innervate
the deltoid and teres major muscles. Provides sensory innervation to a portion of skin over the posterior lateral shoulder of the axillary.
Where does the axillary nerve travel
posteriorly through the quadrangular shape in order to innervate those muscles
When is the axillary nerve vulnerable to injury
when there is a fracture at the surgical neck of the humerus - could occur due to shoulder dislocation
What can axillary nerve injury result in
The loss of shoulder abduction above 15 degrees due to paralysis of the deltoid muscle. Paralysis of the teres minor muscle results in weakened external rotation at the shoulder and decreased stability of the shoulder joint because teres minor contributes to the rotator cuff. Loss of cutaneous sensation over the posterior lateral aspects of the shoulder.
What does the radial nerve supply
supplies all extensor compartment muscles of the arm and the brachioradialis and the supinator. It provides sensory innervation to the skin on the dorsal surface of the forearm and hand
Where does the radial nerve travel
It begins its distal journey by travelling posteriorly around the body of the humerus to lie within the radial groove, it comes to lie briefly within the flexor compartment of the arm as it travels across the elbow joint anterior to the lateral epicondyle of the humerus
At the elbow, what does the radial nerve divide into
superficial and deep branches
Where does the superficial branch of the radial nerve travel
The superficial branch is cutaneous and travels distally along the radius to reach the hand
What does the superficial branch of the radial nerve innervate
provides sensory innervation to the skin over the dorsum of the thumb and the radial half of the hand
Is the deep branch motor or sensory innervation
motor
Where does the deep branch of the radial nerve located
enters the posterior compartment of the forearm by piercing the supinator muscle within the posterior compartment of the forearm the radial nerve is now known as the posterior interosseous nerve (or PIN).
What does radial nerve injury cause
Wrist drop - by loss of innervation to the extensor muscles in the forearm
What do injuries proximal to the triceps innervation cause
Loss of elbow extension
What are characteristics of radial nerve injury
loss of sensation or paraesthesia over the dorsum of the thumb and lateral aspect of the hand
When is the radial nerve susceptible to injury
when there is a fracture of the shaft of the humerus or from compression due to the use of crutches etc…
What does the musculocutaneous branch innervate
provides motor innervation to the coracobrachialis, brachialis and biceps brachii before ending as the lateral antebrachial cutaneous nerve which provides cutaneous innervation to the skin of the lateral aspect of the forearm
What does damage to the musculocutaneous nerve cause
loss of its sensory component and loss of elbow flexion and weakened forearm supination
Where is the ulnar nerve located
travels distally to enter the forearm by crossing the elbow joint immediately posterior to the medial epicondyle of the humerus. Once in the forearm the ulnar nerve is parallel to the ulnar artery, they both travel distally along the medial aspect of the forearm towards the hand.
What does the ulnar nerve innervate
the flexor cardi ulnaris and half of the flexor digitorum profundus muscle. It provides cutaneous innervation to the medial 1/3 of the hand and motor innervation to the hypothenar muscles and all intrinsic hand muscles except thenar muscles and the first 2 lumbrical muscles
How is ulna normally damaged
entrapment as it passes behind the medial epicondyle or fracture of the medial epicondyle of the humerus.
What does ulnar entrapment cause
tardy ulnar palsy causing paraesthesia over the ring and little fingers and loss of fine motor control of the digits
What does more severe ulnar damage result in
wrist causes paralysis of the abductors and adductors of the digits, resulting in claw hand (little fingers and ring fingers are hyper-extended at the metacarpal phalangeal joint and flexed at the interphalangeal joint due to loss of lumbrical and interosseus muscle function in the extensor expansion of these digits).
Which artery does the median nerve accompany
the brachial artery as it crosses the elbow medial to the tendon of the biceps brachii
Which nerve does the median nerve give off after entering the forearm
the anterior interosseous nerve
What does the anterior interosseous nerve lie along
the interosseous membrane
What does the median nerve and the anterior interosseous nerve supply
proper provide motor innervation to all of the flexor compartment muscles of the forearm except for the flexor carpi ulnaris and the ulnar ½ of flexor digitorum profundus
How does the anterior interosseous nerve end
in the distal forearm - does not cross the wrist joint
What branch does the median nerve give off as it exits the carpal tunnel
The recurrent branch of the median nerve (motor)
What does the recurrent branch of the median nerve innervate
the 3 muscles of the thenar eminence
What does the median nerve do after it has passed through the carpal tunnel
continues distally, innervating the first 2 lumbrical muscles before becoming cutaneous to the skin of the index and middle fingers as well as to the lateral half of the palm
How does median nerve injury lead to carpal tunnel syndrome
Nerve is entrapped or inflamed as it enters the wrist under cover of the transverse carpal ligament
What does mild carpal tunnel syndrome cause
causes paraesthesia and pain along the thumb, index and middle fingers.
What does more severe carpal tunnel syndrome cause
cause atrophy of the thenar muscles and subsequent reduction of thumb movements
Where does the anterior compartment of the arm lie
in front of the humerus and in front of the medial and lateral intermuscular septa
What are the 3 muscles that make up the anterior compartment of the arm
the biceps brachii, the coracobrachialis and the brachialis.
What is the most anterior muscle of the arm
biceps brachii
Describe the shape of the biceps brachii
the 2 heads meet up to form a single belly, halfway down the arm. The belly narrows to form a 2 part tendon - the main part dives between the radius and the ulna and inserts on the radius tuberosity.
What happens to the lateral edge of the tendon
the tendon fans out into a thin sheet of fascia (bicipital aponeurosis) becoming continuous with the deep fascia surrounding the forearm
What does the bicepital aponeurosis give
an indirect attachment to the ulna
Where does the short head of the biceps arise
arises in common from the tip of the coracoid process of the scapula with the coracobrachialis muscle
Where is the long head of the biceps located
runs up the bicipital groove and passes inside the shoulder joint to reach its origin from the supraglenoid tubercle of the scapula
Which muscle lies behind the biceps
the brachialis
Describe the location of the musculocutaneous nerve
travels through the coracobrachialis muscle and then emerges deep to the biceps, where it runs down between biceps and brachialis to supply both of them. It then emerges to become the lateral cutaneous nerve of the forearm.
Where does the brachialis arise
from a broad area on the anterior humerus
What is the coracobrachialis
a slender muscle and a weak adductor
Where on the ulna does the brachialis attach
to the front of the proximal ulna on the ulna tuberosity
What happens when the brachialis contracts
it flexes the elbow joint
Which nerve supplies the lateral third of the brachialis
the radial nerve
Where do the biceps attach to the radius
at the proximal end on the radial tuberosity
What is the function of the biceps brachii
flexor of elbow joint and is a supinator of the forearm
When are the biceps more efficient at being a flexor
when the forearm is pronated - muscles are fully stretched
Which 2 nerves start out close together and when do they diverge
the median and ulnar, half way down the arm they diverge
Describe the location of the median nerve
stays close to the brachial artery, crossing in front of it. At the elbow it lies medial to the artery, then dives down between the brachialis tendon and pronator teres, and passes between the 2 heads of pronator teres to enter the forearm
Describe the location of the ulnar nerve
slants backwards, and runs down just medial to the triceps tendon and behind the medial epicondyle. It turns a sharp corner round the underside of the medial epicondyle, where there is a fibrous tunnel for it. It passes between the 2 heads of flexor capri ulnaris to enter the forearm.
What does the median nerve supply
pronator teres, flexor capri radialis, palmaris longus and pronator quadratus
Describe the location of the radial nerve
Just below the latissimus tendon, the radial nerve runs back between the long head and the medial head of triceps. As it passes round the humerus, it lies right on the bone, running between the medial and latera head of triceps. It runs beneath the lateral head to emerge right on the bone, above brachioradialis. Under cover of brachioradialis it reaches the lateral epicondyle
What does the radial nerve supply
the triceps, anconaeus, brachioradialis, all 3 wrist extensors and supinator.
Where does the brachioradialis arise
arises halfway up the humerus, just below the deltoid tuberosity. It is inserted on the distal radius
What is the function of brachioradialis
flexor of elbow
What does contraction of triceps cause
extension of elbow
What are the 3 heads of the triceps
long, lateral and a medial/deep head
Where does the long head of the triceps arise from
the infraglenoid tubercle of the scapula
Where does the lateral head of the triceps arise from
high up on the lateral side of the posterior humerus
Where does the medial head of the tricsps arise
from a broad area, lower down and more medially
When the 3 heads of the triceps converge where does its tendon insert
on the olecranon
Where does the anconaeus run
from the lateral epicondyle to the lateral aspect of the proximal ulna
What is the function of the anconaeus
a minor elbow extensor
