25-01-22 - Arm and Forearm Flashcards
Learning outcomes
- Describe the muscles of the Arm; their innervation, origins and insertions
- Describe the movements at the elbow and the muscles that carry them out
- Describe the boundaries, contents and relations of the cubital fossa
- Describe the afferent and efferent limbs of the biceps triceps and brachioradialis reflexes
- Describe the muscles of the forearm; their innervation, origins and insertions
How many muscles does the arm consist of?
How many fascial compartments does the arm consist of?
How nay muscles are in each compartment?
What 3 things are contained in the large medial neurovascular bundle?
What 2 things are located round the back of the arm?
- The arm consists of 4 muscles
- The arm consists of 2 fascial compartments, anterior and posterior
- In the anterior compartment, there are 3 muscles, one of which has 2 heads
- In the posterior compartment, there is 1 muscle with 3 heads
• In the large medial neurovascular bundle, there is:
1) The brachial artery
2) The median nerve
3) The ulnar nerve for the short time
• Around the back of the arm, there is:
1) The radial nerve
2) Profunda brachii artery
What are all the muscles in the anterior compartment of the arm innervated by?
How does the musculocutaneous nerve enter into the anterior compartment of the arm?
What does it do after it supplies these muscles?
What are the 3 muscles in the anterior compartment of the arm?
What fibres innervate each muscle?
What movements does each muscle perform?
- All the muscles in the anterior compartment of the arm are innervate by the musculocutaneous nerve
- It disappears through the coracobrachialis to enter the anterior compartment of the arm, where is supplies all of these muscle
- After it supplies all of these muscles, it passes out between the biceps brachii and brachialis and heads down superficially into the lateral forearm
- Here it becomes the lateral cutaneous nerve of the forearm, supplying sensation to the skin of the lateral forearm
• 3 muscles of the anterior compartment of the arm:
1) Biceps Brachii
• Innervated by C5, C6, and C7 fibres from musculocutaneous nerve
• Crosses shoulder, elbow, and proximal radio-ulnar joints
• Action at shoulder is weak and almost irrelevant, and acts more as stability for the Glenohumeral joint
• Biceps brachii is the synergist in flexion of the elbow
• In a flexed elbow, biceps brachii is the most powerful supinator of the forearm, and will pull the radial head into the supination position e.g screwdriver motion with flexed or extended elbow
• If the forearm is fully extended and pronated, the biceps wont help flex the elbow
• This is why chin ups are easier than pullups, chin ups recruit the biceps brachii, as the hand is supinated
2) Brachialis
• Innervated by C5 and C6f fibres
• Prime mover (agonist) in elbow flexion
3) Coracobrachialis
• Innervated by C5, C6, and C7 fibres
• Responsible for flexion and adduction at the GH joint
• Main function is stability
Where do the long and short head of the biceps brachii originate from?
What 2 inserts does the biceps brachii have distally?
Where do they attach?
Where is the origin of the brachialis?
Where does it insert?
Where does the coracobrachialis originate and insert?
- The long head of the biceps brachii goes up, through the glenohumeral joint, originating at the supraglenoid tubercle of the scapula
- The short head goes up and originates at coracoid process on the superior border of the head of the scapula
- Distally, it has 1 tendinous attachment and one aponeurotic attachment, in the form of the bicipital aponeurosis, which is a broad tendinous fascial sheet
- The tendinous attachment distally is to the radial tuberosity, which is a bump on the side of the radius where the biceps brachii inserts
- More superficially, it has the bicipital aponeurosis, which passes over the medial forearm and inserts into softs tissues, and by extension, the ulna, where it forms a dense fibrous sheet underneath superficial fascia
- The brachialis’ origin is the anterior surface of the distal half of the humerus
- It inserts onto the coronoid process of the ulna
- The coracobrachialis originates from the coracoid process of the scapula and inserts in the brachium of the arm (part of arm from shoulder to elbow)
- The coracobrachialis originates at the same place as the short head of the biceps (coracoid process), and comes roughly from the same direction as the short head of the biceps
What type of reflex is the biceps reflex?
How is this process carried out?
Why does this happen?
What spinal segments are tested?
- The biceps reflex is a deep tendon reflex
- This is done by placing a thumb on the biceps tendon and hitting it with a tendon hammer, which will elicit a jerk reflex
- This is due to afferents from muscle spindles synapsing directly on efference alpha motor neurons
- This tests C5 and C6 spinal segments
What muscle is present in the posterior compartment of the arm?
What muscle is sometimes considered the 4th head of the triceps?
What nerve innervates the triceps brachii in the posterior compartment of the arm?
Where do muscular branches of the triceps form?
What nerve roots/fibres innervate the triceps brachii and the aconeus?
What movement are they responsible for?
What else are the muscles responsible for?
What will spiral groove fractures affect?
Why wont they affect the triceps?
- The triceps brachii is the muscle present in the posterior compartment of the arm
- The aconeus is sometimes considered the 4th head of the triceps brachii
- The triceps brachii is innervated by the radial nerve
- Muscular branches of the triceps brachii form above the spiral groove (broad but shallow oblique depression for the radial nerve and deep brachial artery on the lateral border of humeral bone)
1) Triceps Brachii
• Innervated by roots/fibres C6, C7, C8
• Early branching of muscular branches to the long and lateral heads
• The triceps brachii are responsible for extension of the elbow joint
• The long head of the triceps is for stability
2) Aconeus
• Innervates by nerve roots/fibres C7, C8, T1
• Aids triceps brachii in extension of the elbow
• Abducts the ulna during pronation
• Gives the elbow stability
• The aconeus tenses the joint capsule of the elbow to prevent it getting pinches in extension
- Spiral groove fractures will affect the posterior forearm
- Spiral groove fractures will not affect the triceps brachii in the posterior compartment of the arm as the muscular branches have come off above the spiral
What muscle is present in the posterior compartment of the arm?
What are the origins of the 3 heads of the triceps brachii?
Where do these 3 head converge?
What movement will the triceps allow for?
What does the long head also cross?
What muscle is sometimes considered the 4th head of the triceps?
What does it assist in?
What does it prevent?
- The triceps brachii is the only muscle in the posterior compartment of the arm
- The origin of the long head is the infraglenoid tubercle of the scapula
- The origin of the medial head is the posterior surface of the humerus, inferior to the radial grove
- The origin of the lateral head is the posterior surface of the humerus, superior to the spiral groove
- These 3 heads come down and converge onto the olecranon of the ulna, where they insert
- The triceps brachii will all for the extension of the elbow
- The long head crosses the GH joint, so it can also help in extension, but les action here, and more action in extension of the elbow
- The aconeus is sometimes considered the 4th head of the triceps
- It assists the triceps in the extension of the elbow
- The aconeus tenses the joint capsule of the elbow to prevent it getting pinches in extension
What type of reflex is the triceps reflex?
How is this process carried out?
Why does this happen?
What spinal segments are tested?
- The triceps reflex is a deep tendon reflex
- This process is done by hitting the tendon of the triceps brachii with a tendon hammer, which elicits an extension jerk
- This is due to afferents from muscle spindles synapsing directly on efference alpha motor neurons
- This tests the C6 and C7 spinal segments
What 4 nerves and 2 arteries do we have running from the arm into the forearm?
• Nerves running from the arm into the forearm:
1) Ulnar nerve
• Initially runs medially, then passes round the back of the medial epicondyle (a protuberance above or on the condyle of a long bone) of the humerus, where it is vulnerable to fracture
2) Median nerve and brachial artery
• Runs anterior to the elbow
3) Musculocutaneous nerve
• Becomes lateral cutaneous nerve of the forearm
4) Radial nerve and profunda brachial artery
• Radial nerve runs posteriorly, but raps around the spiral grove and ends up passing anteriorly to the elbow
• When we think about the radial nerve, we want to think about posterior things, apart from when we get to the elbow, a region known as the cubital fossa
What is the cubital fossa?
What are the 3 borders that form the cubital fossa?
What are they made from?
What forms the roof of the cubital fossa?
What does this structure help prevent?
What 2 muscles does the floor of the cubital fossa consist of?
What vein lies superficially and anterior to all of these structures?
What is it used for?
- The cubital fossa is a triangular depression anterior to the elbow formed from 3 borders
- The 3 borders that form the cubital fossa:
1) Imaginary border – transverse/horizontal line between lateral and medial epicondyles
2) Medial border – formed from the lateral border of the pronator teres muscle
3) Lateral border – formed from the medial border of brachioradialis muscle
- The roof of the cubital fossa is formed by bicipital aponeurosis
- This structure helps to prevent damage to structures during venepuncture, as it lies deep to superficial veins, but on top of arteries and nerves we don’t want to damage
• The floor of the cubital fossa consists of:
1) Supinator muscle – raps around muscles underneath the cubital fossa
2) Brachialis muscle – comes down from the arm to inset into the coronoid process of the ulna
- The median cubital vein is superficial and is anterior to all of these structures
- It is the target for venepuncture
What are the 4 structures in the cubital fossa from medial to lateral?
• In the cubital fossa from medial to lateral there is the:
1) Median nerve
2) Brachial artery
3) Biceps tendon
• Goes down to radial tuberosity (prominence where muscles and connective tissues attach)
4) Radial nerve
• The radial nerve splits into deep and superficial branches at this point
• He superficial branch comes down the lateral side of the forearm, and supplies skin on the back of the hand
• The deep branch pierces through the supinator muscle to enter the posterior forearm and supply muscles in the posterior forearm
What are muscles in the anterior forearm named?
What type of muscles are all of those found in the anterior forearm?
What is the origin of all the muscles in this compartment?
What is the innervation of muscles in this compartment?
What are the 3 layers of the anterior compartment of the forearm?
- Muscles in the anterior forearm are named functionally
- All the muscles in the anterior forearm are flexors and pronators
- All muscles come from a common flexor origin on the medial epicondyle of the humerus (with some exceptions)
- All muscles in the anterior compartment of the forearm are innervated by the median nerve, except 1.5 muscles, which are innervate by the ulnar nerve
• The 3 layers of the anterior compartment of the forearm:
1) Superficial
2) Intermediate
3) Deep
What are the 4 muscles in the superficial layer of the anterior compartment of the forearm?
What are they each innervated by?
Where can they be found?
What movements are they responsible for?
• Muscles in the superficial layer of the anterior compartment of the forearm:
1) Pronator teres
• Innervated by roots C6 and C7 of the median nerve
• Crosses forearm at oblique angle
• Origin – humeral head
• Insertion – lateral surface of distal radius
• Responsible for pronation of the forearm
2) Flexor carpi radialis
• Innervated by roots C6 and C7 of the median nerve
• On the radial side
• Responsible for flexion of the wrist
3) Palmaris longus
• Innervated by roots C7 and C8
• Absent in approximately 15% of people
• Vestigial muscle (remaining in a form not fully developed or able to function)
• Useful for climbing animals that extend claws, but not much use in humans
• Helps tense skin of palm
• Very long muscle that inserts into fascia in the palm of the hand called palmar aponeurosis
• Can take vestigial long tendon and use it as a replacement in the knees
4) Flexor carpi ulnaris
• Innervated by roots C7 and C8 of the ulnar nerve
• 1 of the 1.5 muscles supplies by the ulnar nerve and not the median nerve
• Flexes wrist at the ulnar side
• Has a humeral and ulnar head
• Between these 2 heads, the ulnar nerve will enter the anterior compartment, which runs deep to its tendon all the way down to the hand
What is the muscle in the intermediate layer of the anterior compartment of the forearm?
What is it innervated by?
Where does this nerve sit in relation to this muscle?
What attachments does it have?
How many tendons does it have?
Where do they travel and insert?
- In the intermediate layer of the anterior compartment of the forearm is the flexor digitorum superficialis
- It is innervated by roots C7, C8, and T1 of the median nerve
- The median nerve is immediately underneath the flexor digitorum superficialis, and appears on its medial aspect, which can make it quite prone to injuries
- The flexor digitorum superficialis has humeral, ulnar, and radial attachments
- This muscle has 4 tendons that come down the wrist (1 for each digit), which go through the carpel tunnel and insert onto the middle phalanges of each digit
What are the 3 muscles found in the deep layer of the anterior compartment of the forearm?
What are they each innervated by?
Where do they insert?
• The 3 muscles found in the deep layer of the anterior compartment of the forearm:
1) Flexor digitorum profundus
• Medial aspect is innervated by roots C8 and T1 of the Ulnar nerve
• Lateral aspect is innervated by roots C8 and T1 of Anterior interosseous nerve, which is a branch of the median nerve that supplies muscles of the deep compartment
• Distal phalanges insertion
2) Flexor pollicis longus
• Innervated by roots C8 and T1 off the anterior interosseus ligament
• Runs up to the distal phalanx of the thumb
3) Pronator quadratus
• Innervated by roots C8 and T1 of the interosseus ligament
• Square muscle deep to the wrist
• Inserts at the distal anterior surface of the radius
Label this diagram of origins and insertions in the anterior compartment of the forearm
What does the brachial artery lie deep to in the cubital fossa?
How does the brachial artery leave the cubital fossa?
Where does the ulnar artery run?
Where does the radial nerve run?
- The brachial artery goes into the cubital fossa, where it lies deep to the pronator teres
- It then heads out as the radial artery on the radial side and the ulnar artery on the ulnar side
- The ulnar artery runs deeply till we get to the wrist where it runs more superficially
- The ulnar artery runs with the ulnar nerve underneath the tendon of flexor carpi ulnaris (superficial layer of anterior compartment of forearm) all the way down to the wrist
- The radial nerve will run underneath the muscle called brachioradialis (in anterior compartment of arm) until we get to the wrist, where it is more superficial
What is the carpal tunnel?
What is the carpal tunnel closed over by?
What are the 4 things contained within the carpal tunnel?
- The carpal tunnel is a connection between the flexor forearm and the hand
- The carpal tunnel is closed over by the flexor retinaculum
• The carpal tunnel contains:
1) The 4 tendons of the flexor digitorum superficialis
2) Tendons of the flexor digitorum profundus
3) Flexor pollicis longus
4) Median nerve – on the lateral side of flexor digitorum superficialis
What type of muscles are present in the posterior compartment of the forearm?
Where is the common extensor origin?
What is the innervation of muscles in this compartment?
What are the 3 layers of muscle in this compartment?
- In the posterior compartment of the forearm, there are extensors and supinators
- The common extensor origin is the lateral epicondyle of the humerus (with some exceptions)
- The innervation of muscles in this compartment is the radial nerve, which changes it name at some point to the posterior interosseus nerve
• 3 layers of muscle in this compartment:
1) Superficial
2) Outcropping
3) Deep
Where is the brachioradialis found?
What group is it considered part of?
What 2 reasons is this unique?
How is it innervated?
Where is the origin of the brachioradialis?
Where is the insert of the brachioradialis?
When will it supinate and pronate half way?
What muscle is it considered to be?
• The brachioradialis is found anteriorly and functions anteriorly
• It is part of the superficial group of the posterior compartment of the forearm
• It is part of this group despite:
1) Being involved as a synergist in elbow flexion, not extension
2) Being ½ pronator and ½ supinator
- The brachioradialis is innervated by roots C5, C6 and C6 of the radial nerve, but has a flexion action
- The origin of the brachioradialis is the humerus, above the lateral epicondyle, from the supracondylar ridge
- The insert of the brachioradialis is the distal radius
- From the fully pronated position, it will supinate about half way
- From the full supinated position, it will pronate about half way
- The brachioradialis is considered to be the drinking muscle – it holds the hand vertically and flexes the elbow
What type of reflex is the supinator reflex?
How is this process carried out?
Why does this happen?
What spinal segments are tested?
- The supinator reflex is a deep tendon reflex
- This process is actually carried out by hitting the brachioradialis muscle at its insertion in the distal forearm with a tendon hammer (not supinator), which elicits a flexion jerk
- This is due to afferents from muscle spindles synapsing directly on efference alpha motor neurons
- This tests the C5 and C6 spinal segments
What is the common extensor origin in the superficial layer of the posterior compartment of the forearm?
What are the 5 muscles in this compartment?
What are they each innervated by?
- The common extensor origin in the superficial layer of the posterior compartment of the forearm is the lateral epicondyle of the humerus
- The 5 muscles in this compartment:
1) Extensor carpi radialis longus
• Radial nerve – roots C6 and C7
2) Extensor carpi radialis brevis
• Deep radial nerve – roots C7 and C8
• After the radial nerve branches in the cubital fossa, it is known as the deep branch of the radial nerve
3) Extensor digitorum • Deep radial nerve – roots C7 and C8 • Inserts into the extensor expansion • extensor expansions (also known as the extensor hood or dorsal digital expansion) are triangular aponeuroses by which the extensor tendons insert onto the phalanges. • Passes into dorsum (back) of 4 digits
4) Extensor digiti minimi
• Separate muscle for extension of small finger
• Deep radial nerve – roots of C7 and C8
5) Extensor carpi ulnaris
• Deep radial nerve – roots C7 and C8
Why are outcropping muscles called this?
What are the 3 outcropping muscles of the posterior compartment of the forearm?
What are they each innervated by?
What occurs when these muscles come together?
What does this form?
What is the anatomical snuff box used for?
What 2 things is it crossed by?
What does it contain?
What is its floor made from?
What can pain in the anatomical snuff box indicate?
- Outcropping muscles are called this because they appear from deep to superficial muscles, and all 3 muscles head up towards the thumb
- The 3 outcropping muscles:
1) Abductor policis longus
• Posterior interosseus nerve – roots C7 and C8
• The posterior interosseus nerve is what we call the deep radial nerve after it has passed through the supinator into the posterior compartment
2) Extensor policis brevis (short)
• Posterior interosseus nerve – roots C7 and C9
3) Extensor policis longus (long)
• Posterior interosseus nerve – roots C7 and C8
• The abductor policis longus and extensor policis brevis are close together, with extensor policis longus being slightly more medial and separate
• This separation causes a triangular grove on the back of the hand called the anatomical snuff box between the tendons of the muscles
• The anatomical snuff box is a useful landmark
• It is crossed by:
1) The cephalic vein
2) The dorsal cutaneous branch of the radial nerve
- The anatomical snuff box contains the radial artery
- Its floor is made from the scaphoid and trapezium
- Pain in the anatomical snuff box can indicate a scaphoid fracture
What are the two muscles present in the deep layer of the posterior compartment of the forearm?
What are they each innervated by?
What fingers have individual extensors?
What happens when we hold down certain digits?
• Muscles of the deep layer of the posterior compartment of the forearm:
1) Supinator
• Deep radial nerve – roots C7 and C8
• Raps all the way from the ulna, all the way round the radius
• Is pierced by the deep branch of the radial nerve, with forms the posterior interosseus nerve
2) Extensor indicis
• Posterior interosseus nerve – roots C7 and C8
• Lies deep to superficial muscles then pops up and goes to the index finger
- The first and small finger (extensor digite minime) have their own individual extensor
- This is why when we hold down your digits, and try to extend the middle or ring fingers independently from the others, we can’t
Origins and insertions of muscles of the forearm
What occurs to the radial nerve as it runs down the forearm?
Where do posterior interosseus arteries run?
Where is the radial artery found?
- As the radial nerve runs down the forearm, it becomes a deep branch in the cubital fossa, and supplies the extensor muscles of the superficial layer of the posterior compartment of the forearm
- After it pierces the supinator to get into the posterior compartment, it becomes the posterior interosseous nerve, supplying the outcropping muscles
- Small branches of posterior interosseus arteries down the back of the interosseus membrane,
- Radial artery at the anatomical snuff box in the wrist
What 3 cutaneous nerves do we have in the forearm?
Where do they reach originate from?
What should we think when thinking posterior?
• The forearm we have:
1) The posterior cutaneous nerve of the forearm
• Branch of the superficial radial nerve
2) Lateral cutaneous nerve of the forearm
• Continuation of the musculocutaneous nerve
3) Medial cutaneous nerve of the forearm
• Comes from the medial cord of the brachial plexus
• When thinking posterior, think radial
Muscles of posterior compartment of the forearm
