Muscular Elements of the Thorax

Question 1

Prime mover

Answer 1

Main muscle that performs the greatest percentage of a move

Question 2

Fixator

Answer 2

Provides stability

Question 3

Synergist

Answer 3

Assists prime mover

Question 4

Antagonist

Answer 4

Opposes prime mover

Question 5

Origin

Answer 5

Where the muscle originates

Question 6

Insertion

Answer 6

Where muscle inserts

Movement of the muscle: Pulls the insertion towards the origin

Question 7

Nuchal Groove

Answer 7

Groove at the back of your neck, created by the nuchal ligament

Question 8

Locate:
Posterior median Furrow
Dimples indicating posterior superior iliac spines
Intergluteal dimples

Answer 8

Posterior Median Furrow: The line that does down the mid line of the back
Dimples indicating posterior superior illiac spines: Dimple like appearance on the medial lower back above the glutes

Intergluteal dimples: Dimples on the cheeks of the glutes

Question 9

Superficial (Extrinsic) Back muscles

Answer 9

Are associated with movements of the glenohumeral (shoulder) joint.
Thin compared to the deep muscles off the back

• Trapezius
• Lattissimus Dorsi
• Levator Scapulae
• Rhomoids

Question 10

Trapezius

Answer 10

Trapezius (Left & Right):
Innervated by the spinal accessory nerve (CN XI)

Superior (Descending) part:
O - Superior Nuchal line and the External Occipital protruberance
I - Lateral Third of the clavicle
A - Elevates the Scapula

Middle (transverse) Part:
O - Spinous process of T1-T4
I - Acromion (of the scapula)
A - Straight retractors (horizontal)

Inferior (Ascending) Part:
O - Spinous processes T5-T12
I - Spine (of the scapula)
A - Depresses the scapula

Question 11

Latissimus Dorsi

Answer 11

Innervated by the thoracodorsal nerve of the brachial plexus(C6-C8)

Vertebral part:
O - Spinous processes of T7-T12; Thoracolumbar fascia

Iliacal:
O - Iliac Crest

Costal:
O - Ribs 9-12

Scapular:
O- Inferior angle of the scapula

All parts:
I - Floor of the intertubercular groove (Bicipital groove) if the humerus

Attachment of insertion is on the anterior side

Actions:

• Adducts & Medially rotates the humerus at the glenohumeral joint
• Elevate the trunk (i.e. Pull up, Chin ups)
• Moves the trunk anteriorly (E.g. Cross country skiing, trunk goes forward, arms goes back)

Question 12

What determines the action of the muscle?

Answer 12

• Origin
• Insertion
• Moves insertion towards origin

Orientation of the fibers

Thickness and slopes

Question 13

Levator Scapulae

Answer 13

Innervated by the dorsal scapular nerve (C4-C5)

O - Transverse processes of C1 - C4
I - Medial 1/3 border of the scapula (superior to the spine (scapular spine))
A - Like the rhomboids, levator scapulae elevates the medial border of the scapulae; if the scapula is fixed, levator scapulae flexes the neck laterally

• *Origin and Insertion is how you can differentiate levator scapulae from rhomboids**
• *Insertion on the scapular is superior to rhomboids**

Levator means to lift
Levator Scapulae is a thick band

Question 14

Rhomboids

Answer 14

Innervated by the dorsal scapular nerve (C4 - C5)

The Rhomboid major is inferior to the rhomboid minor

Rhomboid minor:
O - Spinous processes of the C6-C7 vertebra
I - medial border of the scapula superior to the spine (spine of the scapula), below the 1/3)

Insertion is inferior to the insertion of the Levator scapulae

Rhomboid major:
O - Spinous processes of the T2-T5 vertebrae
I - Medial border of the scapula,inferior to the spine (scapular spine)

Both parts:
A - Retracts and elevates the medial border of the scapula

Question 15

Intermediate and deep (intrinsic) back muscles

Answer 15

Maintains posture and control movements of the vertebral column

Splenius capitus
Splenius cervicus
Erector Spinae

Question 16

Erector Spinae

Answer 16

A: Back extensors

Iliocostalis: most lateral muscle of the erector spinae
O - Iliac crest, the sacrum, and spinous processes of the lumbar vertebrae
I - angle of the ribs and the transverse processes of C4 and C^
A: Extends and laterally flexes the spine
Innervates - Spinal nerves (many)

**Inserts to ribs in slips (step/stair light pattern)

Longissimus: Large medial column of muscle of erector spinae
O- thoracolumbar fascia and transverse processes of lumbar vertebrae
I- transverse processes of thoracic vertebrae and lower ribs (3-12)
A: Extends and laterally flexes the spine
Innervates - Spinal Nerves (many)

Spinalis: Small medial column of muscle of erector spinae
O - Spinous processes of T11 - L2
I - Spinous processes of T1 - T8
Innervates - spinal nerves (many)

All the origin is caudal, insertions are all rostral

Question 17

Pectoralis Major

Answer 17

Latin Pectus means breast

Divided into two major parts with distinctive origins:

Clavicular part: Origin at the medial half of the clavical
- Clavicular head is superior
Sternocostal part: Origin at the sternum and the costal cartilages of the 2nd to 7th ribs, aponeurosis of the external oblique
- Sternal head is inferior

They act as antagonists because of the different origins

In males, pectoralis major shapes the surface anatomy
In females, pectoralis major lies deep to the breasts

All parts of the pectoralis major converges for insertion at the lateral border of the intertubercal (bicipital) groove of the humerus

Innervation is distinct:

• Clavicular part: lateral pectoral nerve of the brachial plexus
• Sternoclavicular part: medial pectoral nerve of the brachial plexus

Actions:
Clavicular part: Flexes the arm at the glenohumeral joint (synergist to anterior deltoid)

Sternocostal part: Extends the arm at the glenohumeral join from a flexed position)

Acting together: The two parts medially rotate the arm at the glenohumeral joint AND adduct the arm at the glenohumeral joint

Pectoralis Minor
O - Body of 3rd - 5th rib
I - Coracoid process of the scapula
Innervation - Lateral and medial pectoral nerve
A - Depresses and protracts the scapula

Question 18

Serratus Anterior

Answer 18

O - body of 1st to 9th ribs
I - medial border of scapula
Innervation - Long thoracic nerve of the brachial plexus
A - Laterally rotates the scapula (in arm abduction); stabilises scapula (Boxer muscles)