The Brachial Plexus

How many divisions are present within the brachial plexus?

Six, three anterior and three posterior nerve fibres.

Roots

Dorsal scapular nerve Long thoracic nerve

Briefly describe the course of the brachial plexus, from start to finish.

It begins in the root of the neck, passes through the axilla, and enters the upper arm.

Lateral cord

Lateral pectoral nerve

Medial cord

Medial pectoral nerve Medial cutaneous nerve of arm Medial cutaneous nerve of forearm

Describe the route of the 'trunks' of the brachial plexus, after its formation

The trunks begin to move laterally, crossing the posterior triangle of the neck.

What is the brachial plexus?

This is a network of fibres that innervates the musculature and skin of the upper limb.

Musculocutaneous Nerve - Describe the anatomical course of this nerve NB: The musculocutaneous nerve is well recognised to have a varied anatomical course. It can interact with the median nerve, adhering to the nerve and exchanging fibres.

- This nerve arises from the lateral cord of the brachial plexus and leaves the axilla, piercing the coracobrachialis muscle near its point of insertion on the humerus. - The nerve the passes down the arm, anterior to the brachialis muscle but deep to biceps brachii, innervating them both - The nerve then emerges laterally to the biceps tendon and continues into the forearm as the lateral cutaneous nerve.

Musculocutaneous Nerve - Describe the sensory functions of this nerve

- This nerve gives rise to the lateral cutaneous nerve of the forearm. - This innervates the lateral half of the anterior forearm and a small lateral portion of the posterior forearm

Musculocutaneous Nerve - Describe the motor functions of this nerve (Hint: use BBC to remember the muscles innervated by this nerve)

- This nerve innervates the muscles in the anterior compartment of the arm - the biceps brachii, the brachialis, and the coracobrachialis muscles * These muscles all flex the upper arm at the shoulder and the elbow. In addition, the biceps brachii also performs supination of the forearm.

How many cords are present within the brachial plexus and what are they called?

- Three. - They are named the lateral cord, the posterior cord, and the medial cord.

Describe how the 'divisions' of the brachial plexus are formed

- Within the posterior triangle of the neck, each trunk divides into two branches. - One division travels anteriorly and the other posteriorly. - Thus, they are known as the anterior and posterior divisions We now have three anterior and three posterior nerve fibres. These divisions leave the posterior triangle and pass into the axilla region. They recombine in the next part of the brachial plexus.

Ulnar Nerve - Describe the anatomical course of this nerve.

1. After arising from the brachial plexus, this nerve descends down the medial side of the upper arm 2. At the elbow, it passes posterior to the medial epicondyle entering the forearm. - Here, this nerve is easily palpable and vulnerable to injury 3. Once in the forearm, this nerve pierces the two heads of flexor carpi ulnaris and travels alongside the ulna. - Three branches of this nerve arise in the forearm. 4. At the wrist, this nerve travels superficially to the flexor retinaculum. 5. This nerve enters the hand via the ulnar canal (or Guyon's canal) 6. This nerve terminates within the hand by giving off superficial and deep branches.

Median Nerve - What is the anatomical course of this nerve?

1. After this nerve originates from the brachial plexus in the axilla, the median nerve descends down the arm. - It does so initially lateral to the brachial artery. 2. Halfway down the arm the nerve crosses over the brachial artery and becomes situated medially. 3. This nerve enters the anterior compartment of the forearm via the cubital fossa. 4. In the forearm, this nerve travels between the flexor digitorum profundus and flexor digitorum superficialis muscles 5. The median nerve gives rise to two major branches in the forearm: a. Anterior interosseous nerve - Supplies the deep muscles in the anterior forearm. b.Palmar cutaneous nerve - Innervates the skin of the lateral palm. The median nerve enters the hand via the carpal tunnel, where it terminates by dividing into two branches:

Ulnar Nerve - Which muscles in the anterior forearm are innervated by this nerve

1. Flexor carpi ulnaris - Flexes and adducts the hand at the wrist. 2. Flexor digitorum profundus (medial half) - Flexes the fingers.

Ulnar Nerve - State the names of the three branches of this nerve that arise in the forearm and briefly state what they innervate

1. Muscular branch: innervates some muscles in the anterior compartment of the forearm. 2. Palmar cutaneous branch: innervates the skin of the medial half of the palm. 3. Dorsal cutaneous branch: innervates the skin of the medial 1 and 1/2 fingers, and the associated palm area.

Axillary Nerve - What are the two branches that form when this nerve divides within the posterior scapular region?

1. Posterior terminal branch - This branch provides motor innervation to the teres minor muscle and innervates the skin over the inferior part of the deltoid. 2. Anterior terminal branch - This branch provides motor innervation to the deltoid muscle

Median Nerve - State the name and innervations the two branches that are formed when this nerve terminates

1. Recurrent branch - Ths nerve innervates the thenar muscles. 2. Palmar digital branch - This nerve innervates the palmar surface and fingertips of the lateral three and half digits. Also innervates the lateral two lumbrical muscles.

Ulnar Nerve - Which muscles in the hand are innervated by this nerve

1. The hypothenar muscles (a group of muscles associated with the little finger) 2. Medial two lumbricals 3. Adductor pollicis 4. Interossei of the hand

Radial Nerve - Describe the anatomical course of this nerve

1. This nerve arises in the axilla region where it is situated posterior to the axillary artery. 2. This nerve exits the axilla inferiorly via the triangular interval, and it supplies the heads of the triceps brachii 3. This nerve then descends down the arm, travelling in the radial groove 4. As the nerve descends, it wraps around the humerus laterally, supplying the lateral head of the triceps brachii. - The nerve is accompanied with the deep branch of the brachial artery for the majority of its course 5. This nerve then moves anteriorly over the lateral epicondyle of the humerus, via the cubital fossa. 6. This nerve terminates by dividing into two branches

Median Nerve - What are the sensory functions of this nerve?

1. This nerve gives rise to the palmar cutaneous branch, which innervates the lateral part of the palm 2. This nerve also gives rise to the digital cutaneous branch, which innervates the lateral three and a half fingers on the palmar surface of the hand.

Axillary Nerve - What is the anatomical course of this nerve?

1. This nerve is formed in the axilla region and is a direct continuation of the posterior cord of the brachial plexus. 2. Immediately after its formation, this nerve lies posterior to the axillary artery and anterior to the subscapularis muscle 3. The nerve then descends to the inferior border of the subscapularis muscle and then exits the axilla posteriorly via the quadrangular space. - The nerve is also accompanied with circumflex humeral artery 4. This nerve terminates by dividing into two branches in the posterior scapular region: 5. This nerve also provides articular branches to the shoulder joint itself.

Which roots form the superior trunk?

A combination of C5 and C6 roots from this trunk.

Which roots form the inferior trunk?

A combination of C8 and T1 roots form this trunk

Which root forms the middle trunk?

A continuation of C7 forms this trunk

Describe how the 'trunks' of the brachial plexus are formed

At the base of the neck, the roots of the brachial plexus converge, forming three trunks. These structures are named by their anatomical position:

Posterior cord

Superior subscapular nerve Thoracodorsal nerve Inferior subscapular nerve

Axillary Nerve - Which nerve roots arise to form this nerve?

The nerve roots C5 and C6 innervate this major branch as it arises from the posterior cord

Musculocutaneous Nerve - Which nerve roots arise to form this nerve?

The nerve roots C5, C6 and C7 as it arises from the lateral cord.

Radial Nerve - Which nerve roots arise to form this nerve?

The nerve roots C5-C8 and T1 form this nerve as it is a continuation of the posterior cord

Median Nerve - Which nerve roots arise to form this nerve?

The nerve roots C6 - T1 form this nerve. - (Also contains fibres from C5 in some individuals). - This nerve is also derived from the medial and lateral cords.

Ulnar Nerve - Which nerve roots arise to form this nerve?

The nerve roots C8 and T1 form this nerve.

Describe the route of the 'roots' of the brachial plexus, after its formation

The ventral rami of these spinal nerves pass between the anterior and medial scalene muscles to enter the base of the neck

How many trunks are there in the brachial plexus and what are they called?

There are three trunks within the brachial plexus and they are named by their anatomical position: 1. The superior trunk 2. The middle trunk 3. The inferior trunk

Describe the route of the 'divisions' of the brachial plexus, after their formation

These divisions leave the posterior triangle and pass into the axilla region where they recombine

Which division of the trunk forms the medial cord?

This cord is formed by the anterior division of the inferior trunk

Which divisions of the trunk form the lateral cord?

This cord is formed by the following: 1. The anterior division of the superior trunk 2. The anterior division of the middle trunk

Which divisions of the trunk form the posterior cord?

This cord is formed by the following: 1. The posterior division of the superior trunk 2. The posterior division of the middle trunk 3. The posterior division of the inferior trunk

Axillary Nerve - What are the sensory functions of this nerve

This nerve gives off the superior lateral cutaneous nerve of the arm, which goes on to innervate the inferior region of the deltoid ( also known as the regimental badge area").

Ulnar Nerve - What are the motor functions of this nerve?

This nerve innervates muscles found in the anterior compartment of the forearm, and in the hand.

Radial Nerve - Motor Functions: Which muscles ae innervated by this nerve

This nerve innervates the triceps brachii, and the extensor muscles in the posterior compartment of the forearm. Motor Functions The radial nerve innervates the muscles located in the posterior upper arm and posterior forearm. In the upper arm, it innervates the three heads of the triceps brachii - which acts to extend the arm at the elbow. The radial nerve also gives rise to branches that supply the brachioradialis and extensor carpi radialis longus (muscles of the posterior forearm).

Axillary Nerve - What are the boundaries of the quadrangular space: a. superiorly b. inferiorly c. laterally d. medially

a) Subscapularis and teres minor. b) Teres major. c) Surgical neck of humerus. d) Long head of triceps brachii.

Describe how the 'roots' of the brachial plexus are formed

- At each vertebral level paired spinal nerves arise, (the ventral and dorsal root). - They leave the spinal cord as a mixed spinal nerve via the intervertebral foramina of the vertebral column. - They then divide into ventral and dorsal rami (divisions) - The roots of the brachial plexus are formed by the ventral rami of the spinal nerves C5 - T1, (the dorsal rami innervate the skin and musculature of the trunk)

How many major branches are found within the brachial plexus and what are they called?

- Five - They are named the following: 1. The Musculocutaneous Nerve 2. The Axillary Nerve 3. The Median nerve 4. The Radial Nerve 5. The Ulnar Nerve

Describe how the major branches of the brachial plexus are formed and briefly describe the course of the branches

- In the axilla and the proximal aspect of the upper limb, the three cords give rise to the major branches. - These nerves continue into the upper limb to provide innervation to the muscles and skin present

Describe how the 'cords' of the brachial plexus are formed

- Once the anterior and posterior divisions have entered the axilla, they combine together to form three nerves. - These nerves are named by their position relative to the axillary artery.

Axillary Nerve - What is the Quadrangular Space

- This is a gap in the muscles of the posterior scapular region. - It is a pathway for neurovascular structures to move from the axilla to the posterior shoulder and arm.

Axillary Nerve - Motor Functions: Which muscles does this nerve innervate?

- This major branch innervates the following: 1. Teres minor, which is innervated by the posterior terminal branch of this nerve 2. All of the deltoid muscles, which is innervated by the anterior terminal branch of this nerve.

Which spinal nerves form the roots of the brachial plexus?

C5, C6, C7, C8 and T1.

The brachial plexus is divided into five parts, state what these different parts are. (Hint = Read That Damn Cadaver Book)

1) Roots 2) Trunks 3) Divisions 4) Cords 5) Branches

Radial Nerve - What two branches form when this nerve terminates ?

1. Deep branch (motor) - innervates most of the muscles in that act to extend the wrist and finger joints and supinate the forearm 2. Superficial branch (sensory) - contributes to the cutaneous innervation of the hand and fingers.

Median Nerve - Motor functions; what muscles does this nerve innervate?

This nerve innervates the flexor muscles in the anterior compartment of the forearm (except the flexor carpi ulnaris and part of the flexor digitorum profundus, which is innervated by the ulnar nerve). Also supplies innervation to the thenar muscles and lateral two lumbricals in the hand.

Radial Nerve - What are the sensory functions of this nerve?

This nerve innervates the posterior aspect of the arm and forearm, and the posterior, lateral aspect of the hand.

Ulnar Nerve - What are the sensory functions of the nerv

here are three branches of the ulnar nerve that are responsible for its cutaneous innervation. Two of these branches arise in the forearm, and travel into the hand: Palmar cutaneous branch: Innervates the skin of the medial half of the palm. Dorsal cutaneous branch: Innervates the skin of the medial one and a half fingers, and the associated dorsal hand area. The last branch arises in the hand itself: Superficial branch - Innervates the palmar surface of the medial one and a half fingers.

Trunks

Suprascapular nerve Nerve to subclavius