Session 1b - The Arm And Brachial Plexus

Question 1

What comprises the proximal humerus?

Answer 1

Head, anatomical neck, surgical neck, greater, lesser tubercle, deltoid tuberosity and radial/spiral groove

Question 2

What does the shaft of the humerus form distally?

Answer 2

Expands distally to form medial and lateral epicondyles (bony prominences…)

Further bony prominences at distal humerus:
- trochlea - articulates with trochlear notch of ulna at the elbow joint
- capitellum - articulates with head of radius at the elbow joint

Question 3

What do intermuscular septa do?

Answer 3

Extend from deep brachial fascia which surrounds arm separates arm into anterior and posterior compartments

Question 4

What muscles are in the anterior compartment of the arm?

Answer 4

• Biceps brachii
• brachialis
• coracobrachilis
• flexors and innervated by the musculocutaneous nerve

Question 5

Where is the biceps brachii?

Answer 5

• Lies most superficially in the ant arm
• two heads - long and short
• proximal both att to the scapula ;
• long head - supraglenoid tubercle
• short - coracoid process
• tendon of long head pierces capsule of shoulder joint - helps stabilise joint
• two muscle bellies converge to their insertion via a common tendon onto radial tuberosity of radius

Question 6

What is the movement of the biceps brachii?

Answer 6

Flexor of elbow joint
Also contributes to flexion of shoulder joint
Supinator of the forearm when elbow is flexed

Question 7

Where does the brachialis lie?

Answer 7

• Lies Deep to biceps
• Proximally attached to anterior aspect of the distal half of the shaft of the humerus
• Crosses elbow joint to insert distally upon the ulna tuberosity

Question 8

What is the movement of the brachialis?

Answer 8

Flexor of elbow joint

Question 9

Where does the coracobrachialis lie?

Answer 9

• deep and much smaller muscle
• att proximally to the coracoid process of the scapula
• att distally to the medial aspect of middle of humerus

Question 10

What is the movement of the coracobrachialis?

Answer 10

Crosses shoulder joint and acts as a weak flexor

Question 11

What muscle is located in the posterior compartment of the arm?

Answer 11

Triceps brachii
- three muscle bellies/heads that converge via a common tendon onto a single insertion point - olecranon of the ulna

Question 12

What is the movement of the triceps brachii?

Answer 12

• muscle crosses posterior aspect of elbow joint - contracts - extends elbow

Question 13

What are the long heads of the triceps?

Answer 13

• long head
• lateral head
• medial head

Question 14

Where does the long head of the tricep originate from?

Answer 14

Long - infraglenoid tubercle of the scapula
- most medial part of triceps

Question 15

Where does the lateral head originate from?

Answer 15

Posterior humerus - proximal to the radial groove

Question 16

Where does the medial head originate from?

Answer 16

Posterior humerus - distal to the radial groove

Question 17

Where does the medial head originate from?

Answer 17

Posterior humerus - distal to the radial groove

Question 18

What can the long head of the triceps brachii do?

Answer 18

Due to attachment to scapula can contribute to extension of shoulder joint and extension of elbow joint

Question 19

What is the triceps brachii innervated by?

Answer 19

Radial nerve

Question 20

What course does the radial nerve take?

Answer 20

Major terminal branch of brachial plexus
- winds around posterior aspect of the humerus in the radial (spiral) groove between the medial and lateral heads of the triceps

Question 21

What may cause injury to the radial nerve?

Answer 21

Runs along surface of bone so a fracture of the shaft of the humerus can cause injury

Question 22

What may cause injury to the radial nerve?

Answer 22

Runs along surface of bone so a fracture of the shaft of the humerus can cause injury

Question 23

What is plexus used to describe in anatomy?

Answer 23

Complex networks of nerves and blood vessels

Question 24

What is plexus used to describe in anatomy?

Answer 24

Complex networks of nerves and blood vessels

Question 25

What is plexus used to describe in anatomy?

Answer 25

Complex networks of nerves and blood vessels

Question 26

What is plexus used to describe in anatomy?

Answer 26

Complex networks of nerves and blood vessels

Question 27

What is the brachial plexus?

Answer 27

Network of nerves that provides motor and sensory innervation to the upper limb.

Question 28

What is the brachial plexus formed by?

Answer 28

Formed by spinal nerves that leave the lower cervical spinal cord segments and the first thoracic spinal cord segment : spinal nerves C5,C6,C7,C8 and T1 - mixed nerves which carry motor and sensory fibres.

Question 29

What segments is the brachial plexus discussed in?

Answer 29

Roots
Trunks
Divisions
Cords
Branches

Question 30

What are the roots of the b.p?

Answer 30

Five spinal nerves C5-T1 exit spinal cord and collectively become the brachial plexus - found in the neck

Question 31

What are the roots of the b.p?

Answer 31

Five spinal nerves C5-T1 exit spinal cord and collectively become the brachial plexus - found in the neck

Question 32

What are the trunks of the brachial plexus?

Answer 32

Located in neck formed from roots
- C5 and C6 combine to form the superior trunk
- C7 continues as the middle trunk
- C8 and T1 combine to form the inferior trunk

Question 33

What are the divisions of the brachial plexus?

Answer 33

Each trunk divides into an anterior and a posterior division under the clavicle

Question 34

What are the cords of the brachial plexus?

Answer 34

Formed by various combinations of the anterior and posterior divisions
Named relative to their positions around the second part of the axillary artery

Lateral cord - from anterior divisions of the superior and middle trunks
Posterior cord - posterior divisions of all the trunks
Medial cord - anterior division of the inferior trunk

Question 35

What are the branches of the brachial plexus?

Answer 35

Located in the axilla, former from cords
- travel distantly to reach the structures that they innervate e.g. shoulder, arm, forearm or hand
- axillary - branch from posterior cord
- radial - continuation of posterior cord
- Musculocutaneous - branch from lateral cord
- ulnar - branch from medial cord
- median - branches from lateral and medial cords

Question 36

Describe the axillary nerve

Answer 36

Innervated deltoid and teres minor and a small region of skin over upper lateral arm
- branch of posterior cord and contains fibres from spinal nerves C5 and C6
- runs close to surgical neck of humerus and is vulnerable to injury in fractures of the surgical neck of the humerus or dislocation of the humeral head

Question 37

Describe the radial nerve

Answer 37

Innervated triceps in the posterior arm and all muscles in the posterior compartment of the forearm which are extensors of the wrist and digits. Innervated region of skin over arm,forearm and hand

It is the continuation of the posterior cord and contains fibres from C5 - T1.
• It runs along the radial (spiral) groove on the posterior surface of the humerus and is vulnerable in mid-shaft fractures of the humerus.

Question 38

Describe the musculocutaneous nerve

Answer 38

The musculocutaneous nerve innervates the three muscles in the anterior compartment of the arm: biceps brachii, brachialis and coracobrachialis.
• It arises from the lateral cord and contains fibres from spinal nerves C5 - C7.
• After supplying motor fibres to three muscles named above, it continues as a sensory nerve that innervates a region of skin over the lateral forearm.
• Because of its location, the musculocutaneous nerve is rarely injured in isolation.

Question 39

What do median and ulnar nerves innervate?

Answer 39

The median and ulnar nerves do not innervate any muscles in the arm. These nerves innervate muscles in the anterior forearm and the hand.

Question 40

Describe the median nerve

Answer 40

The median nerve is formed from contributions from both the lateral and medial cords.
• Normally, it contains fibres from C6-T1, but in some individuals, it may contain fibres from C5-T1.
• It innervates most of the muscles of the anterior forearm, which are flexors of the wrist and digits.
• It also innervates the small muscles of the thumb.
• It provides sensory innervation to skin over the lateral aspect of the palm of the hand and over the lateral digits*.
• It is most vulnerable in the arm as it crosses the anterior aspect of the elbow, in a region called the cubital fossa.

Question 41

Describe the ulnar nerve

Answer 41

The ulnar nerve is formed by the continuation of the medial cord, after it has given a contribution to the median nerve.
• It contains fibres from spinal nerves C8 - T1.
• It innervates most of the small muscles in the hand and therefore is vital for fine movements of the digits.
• It also innervates skin over the medial aspect of the hand and medial digits*.
• It is vulnerable to injury behind the medial epicondyle as it lies in a superficial position here (it is easily palpable in this location).

Question 42

What occurs in an Axillary nerve injury?

Answer 42

Because of its close proximity to the surgical neck of the humerus, the axillary nerve can be injured by fractures in this region (which are common in the elderly) or dislocation of the shoulder joint. The motor fibres of the axillary nerve innervate deltoid and teres minor. Its sensory fibres innervate a patch of skin over the upper lateral arm. Injury to the axillary nerve can therefore result in weakness or paralysis of deltoid – this presents functionally as difficulty abducting the shoulder - and altered sensation or numbness over the upper lateral arm.

Question 43

What is the CR of the radial nerve injury?

Answer 43

As it travels along the radial groove of the posterior humerus, the radial nerve lies very close to the bone, thus fractures of the humeral shaft can injure the nerve. This can lead to weakness or paralysis of the muscles that are innervated by the radial nerve ‘downstream’ of the point at which the nerve is injured. As most of the radial nerve fibres that supply the triceps have already branched and entered the triceps at the point of the mid-humerus, the triceps itself is not likely to be significantly affected by damage to the radial nerve at this level. However, it will likely affect movements at the wrist because the radial nerve innervates all the muscles of the posterior forearm, which extend the wrist and digits.

Question 44

What is the CR of the radial nerve injury?

Answer 44

As it travels along the radial groove of the posterior humerus, the radial nerve lies very close to the bone, thus fractures of the humeral shaft can injure the nerve. This can lead to weakness or paralysis of the muscles that are innervated by the radial nerve ‘downstream’ of the point at which the nerve is injured. As most of the radial nerve fibres that supply the triceps have already branched and entered the triceps at the point of the mid-humerus, the triceps itself is not likely to be significantly affected by damage to the radial nerve at this level. However, it will likely affect movements at the wrist because the radial nerve innervates all the muscles of the posterior forearm, which extend the wrist and digits.

Question 45

What is the CR of the ulnar nerve injury?

Answer 45

The ulnar nerve is vulnerable in the lower arm as it travels behind the medial epicondyle – it is superficial here. Fractures of the medial epicondyle may injure the nerve. Injury to the nerve at this level leads to motor impairments of the hand (as it innervates most of the small muscles of the hand) and causes sensory impairment in the hand (the medial side and the medial 1½ fingers). It is extremely common to knock the elbow in this region - referred to as the ‘funny bone’. A blow to the nerve here causes pain and tingling in the same regions of the hand.

Question 46

What is Erbs’s Palsy? (Upper brachial plexus injury)

Answer 46

In this type of injury - which is uncommon - the upper parts of the brachial plexus are affected. It may involve C5 - C6, or C5 - 7. The typical picture is one of paralysis of the lateral rotators of the shoulder and the extensors of the wrist. The affected limb typically appears medially rotated with the wrist flexed.

It is typically caused by trauma – specifically mechanisms that stretch the head away from the shoulder. This may be seen when someone is thrown from a motorbike or a horse. It may also be seen in new-borns if the baby’s shoulder becomes stuck during delivery and its neck is excessively stretched to one side.

Question 47

What is Klumpke’s palsy? (Lower brachial plexus injury)

Answer 47

This type of injury is also uncommon. The lower parts of the brachial plexus are affected, classically C8 and T1. The typical picture is one of paralysis of the small muscles of the hand. Again, it is most often caused by trauma – specifically mechanisms that forcefully and suddenly pull the arm upwards – this stretches the lower nerves of plexus. It may be sustained in babies during delivery if their arm is forcefully pulled superiorly to aid delivery.

Question 48

What is horners syndrome?

Answer 48

Horner’s syndrome is the triad of drooping of the eyelid (ptosis), a constricted pupil (miosis) and lack of sweating (anhidrosis) on one side of the face. It results when the sympathetic nerve supply to the face is interrupted. The T1 spinal nerve carries sympathetic fibres which are destined to supply the face. Therefore, a brachial plexus injury affecting the T1 nerve root may result in Horner’s syndrome as well.

Question 49

What is a brachial plexus block?

Answer 49

This is a form of regional anaesthesia and can be used as an alternative to general anaesthesia for surgery on the upper limb. Under ultrasound guidance, local anaesthetic is infiltrated around the nerves of the plexus, which anaesthetises the upper limb.