Musculo-Neuro-Vascular Systems of Pectoral & Dorsal Regions

What is a muscle?

A contractile tissue consisting of cells called myocytes (muscle cells/fibres).

What is the origin of a muscle?

The proximal attachment of the muscle.

It usually remains relatively fixed during movement.

What is the insertion of a muscle?

The distal attachment of the muscle.

It is usually the attachment that moves during contraction.

What happens if the radial nerve is severed at the midshaft of the humerus?

The wrist extensors lose their nerve supply, causing the wrist to fall into flexion, producing wrist drop.

What are the two major divisions of the nervous system mentioned in this lecture?

• Central nervous system (CNS): brain and spinal cord

• Peripheral nervous system (PNS): nerves outside the brain and spinal cord.

What is the brachial plexus?

A network of nerves that emerges from the spinal cord region and provides the motor and sensory innervation of the upper limb.

Which spinal nerve roots form the brachial plexus?

C5–T1.

⭐ C5, C6, C7, C8, T1

How many roots does the brachial plexus have?

5 roots — C5, C6, C7, C8 and T1.

How many trunks does the brachial plexus have and what are they called?

3 trunks:

• Superior

• Middle

• Inferior

How many divisions does the brachial plexus have?

6 divisions — an anterior and posterior division from each trunk.

How many cords does the brachial plexus have?

3 cords:

• Lateral

• Posterior

• Medial

What are the five stages of the brachial plexus organisation?

Roots → Trunks → Divisions → Cords → Peripheral nerves

⭐️ Randy Travis Drinks Cold Pepsi

What determines the names/positions of the three cords of the brachial plexus?

Their relationship to the axillary artery.

Why is the brachial plexus clinically important?

It gives rise to the nerves that control the muscles of the upper limb and carry sensory information from the upper limb.

What is the recommended way of learning the brachial plexus according to the lecturer?

Repeatedly draw the brachial plexus, labelling as much as you can remember and comparing it with an anatomy atlas

What are the six muscles that connect the scapula to the axial skeleton?

Dorsal/posterior:

1. Trapezius

2. Levator scapulae

3. Rhomboid minor

4. Rhomboid major

Pectoral/anterior:
5. Pectoralis minor
6. Serratus anterior.

What is the origin of subclavius?

The junction of the first rib and its costal cartilage.

Where does subclavius insert?

The inferior surface of the middle third of the clavicle.

What is the innervation of subclavius?

Medial pectoral nerve (C8–T1).

What is the action of subclavius?

It stabilises the scapula by drawing it inferiorly and anteriorly against the thoracic wall.

What are the origins of trapezius?

• External occipital protuberance

• Nuchal ligament

• Spinous processes of C7–T12.

Where does trapezius insert?

Answer:

• Spine of scapula

• Acromion

• Lateral ⅓ of clavicle.

What nerve innervates trapezius?

Spinal accessory nerve (cranial nerve XI).

⭐ Important: Trapezius is the only upper-limb muscle in this lecture whose nerve does NOT come from the brachial plexus.

What are the major actions of trapezius?

• Retracts scapula — especially important for rowing

• Elevates scapula — upper fibres

• Depresses scapula — lower fibres

• Upwardly rotates scapula — upper fibres

What is the origin of levator scapulae?

The transverse processes of C1–C4.

Where does levator scapulae insert?

The superior part of the medial border of the scapula.

What is the innervation of levator scapulae according to this lecture?

Dorsal scapular nerve (C4–5).

What are the actions of levator scapulae?

• Elevates the medial border of the scapula

• Causes downward rotation of the scapula.

What is the origin of rhomboid minor?

Spinous processes of C7–T1.

Where does rhomboid minor insert?

The medial border of the scapula at the root of the spine.

What nerve innervates rhomboid minor?

Dorsal scapular nerve (C4–5).

What are the actions of rhomboid minor?

• Retracts the scapula

• Downwardly rotates the scapula.

What is the origin of rhomboid major?

Spinous processes of T2–T5.

Where does rhomboid major insert?

The medial border of the scapula, covering its inferior ⅔.

What nerve innervates rhomboid major?

Dorsal scapular nerve (C4–5).

What are the actions of rhomboid major?

• Retracts scapula

• Downwardly rotates scapula.

What spinal nerve roots form the dorsal scapular nerve?

C4–5

What is the course of the dorsal scapular nerve?

It passes inferiorly and medial to the medial border of the scapula.

Which muscles are innervated by the dorsal scapular nerve?

• Levator scapulae

• Rhomboid minor

• Rhomboid major.

What is the origin of pectoralis minor?

The anterior surfaces of ribs 3–5.

Where does pectoralis minor insert?

The coracoid process of the scapula.

What nerve innervates pectoralis minor?

Medial pectoral nerve (C8–T1).

What does pectoralis minor do?

It protracts and stabilises the scapula by pulling it anteroinferiorly onto the posterior thoracic wall.

From which cord does the medial pectoral nerve arise?

The medial cord of the brachial plexus.

What spinal roots contribute to the medial pectoral nerve?

C8–T1

What is the course of the medial pectoral nerve?

It passes inferiorly, deep to pectoralis minor, providing its innervation

Where does serratus anterior originate?

From the medial border of the scapula on its anterior surface.

Where does serratus anterior insert?

Its individual muscle slips insert onto the anterolateral surfaces of ribs 1–8.

What nerve innervates serratus anterior?

The long thoracic nerve (C5–7).

What are the main actions of serratus anterior?

• Protracts the scapula

• Stabilises the scapula against the thoracic wall

• Assists with upward rotation of the scapula.

Why is serratus anterior important for pushing and punching?

Because it protracts the scapula, moving it anteriorly around the thoracic wall

What spinal roots form the long thoracic nerve?

C5–C7.

Which muscle does the long thoracic nerve innervate?

Serratus anterior.

What is the course of the long thoracic nerve?

It passes inferiorly over the lateral surface of serratus anterior.

When is the long thoracic nerve particularly vulnerable according to the lecture?

When the limbs are elevated.

What happens if the long thoracic nerve is injured?

The serratus anterior becomes paralysed, causing loss of protraction and inability to hold the scapula firmly against the thoracic cage

What clinical sign can result from long thoracic nerve injury?

Winging of the scapula.

What is the memory aid for the long thoracic nerve roots?

“C5, 6, 7 — spread your wings and go to heaven.” 😭

C5–C7 → serratus anterior → winging if damaged.

How many heads does pectoralis major have?

Two:

• Clavicular head

• Sternocostal head.

What is the origin of the clavicular head of pectoralis major?

The medial half of the clavicle.

What is the origin of the sternocostal head of pectoralis major?

The sternum, upper six costal cartilages, and aponeurosis of external oblique.

Where does pectoralis major insert?

The lateral lip of the bicipital groove of the humerus.

What nerves innervate pectoralis major?

• Medial pectoral nerve — C8–T1

• Lateral pectoral nerve — C5–7.

What are the major actions of pectoralis major?

• Flexes the shoulder from an extended position

• Adducts the humerus

• Medially rotates the humerus.

Where does the medial pectoral nerve arise from?

The medial cord of the brachial plexus.

What roots contribute to the medial pectoral nerve?

C8–T1.

Where does the lateral pectoral nerve arise from?

The lateral cord of the brachial plexus.

What roots contribute to the lateral pectoral nerve?

C5–7

Where does the lateral pectoral nerve travel?

It descends deep to the pectoral muscles and innervates them from the posterior aspect.

What are the major origins of latissimus dorsi?

• Spinous processes of T6–L5 and S1–2 according to the lecture

• Thoracolumbar fascia

• Inferior ribs

• Posterior iliac crest

• Inferior angle of scapula.

Where does latissimus dorsi insert?

The floor of the bicipital groove of the humerus

What are the actions of latissimus dorsi?

It:

• Extends the humerus

• Adducts the humerus

• Medially rotates the humerus

• Produces downward rotation of the scapula.

What nerve innervates latissimus dorsi?

The thoracodorsal nerve (C6–8).

From which cord does the thoracodorsal nerve arise?

The posterior cord of the brachial plexus.

What spinal roots contribute to the thoracodorsal nerve?

C6–C8.

Which muscle does the thoracodorsal nerve innervate?

Latissimus dorsi.

What is the course of the thoracodorsal nerve?

It passes inferiorly between the scapula and thorax to reach latissimus dorsi, then runs obliquely/inferomedially along the muscle.

Which nerve → trapezius?

Spinal accessory nerve (CN XI).

Which nerve → levator scapulae + rhomboids?

Dorsal scapular nerve (C4–5).

Which nerve → serratus anterior?

Long thoracic nerve (C5–7).

Which nerve injury → winged scapula?

Long thoracic nerve injury → serratus anterior paralysis → winging of scapula

Which nerve → latissimus dorsi?

Thoracodorsal nerve (C6–8).

Which nerve → pectoralis major/minor?

Pectoral nerves.

• Medial pectoral → C8–T1

• Lateral pectoral → C5–7.