Muscles of the Thorax Flashcards
List the layers of the back muscles and the muscles that belong to each layer
Superficial (most superficial to deep): trapezius, latissimus dorsi, serratus posterior
- act largely on upper limb and ribs (serratus posterior only)
Intermediate (lateral to medial): iliocostalis, longissimus, spinalis
Deep: transversospinalis which encompasses the 3 deep muscles. Superficial to deep: semispinalis, multifidus, rotatores
What comprises the shoulder complex?
3 bony articulations and one physiological coupling
Bony articulations (synovial joints):
- Sternoclavicular joint
- Acromioclavicular joint
- Glenohumeral joint: ball and socket
Physiological coupling: scapulo-thoracic joint (depends on the SC and AC joints as well as muscles and bursae that separate them)
- Allows scapula to slide over thoracic cage
What muscles border the scapulothoracic joint?
Bordered by subscapularis posteriorly and serratus anterior anterior-medially
Scapulothoracic joint movements involve the subscapularis sliding over serratus anterior
Describe the 6 movements of the scapula
- elevation
- depression
- retraction
- protraction
- medial rotation/downward rotation: inferior angle turns toward midline
- lateral rotation/upward rotation: inferior angle turns away from midline
What muscles cause scapular elevation
Superior/descending portion of trapezius
Levator scapulae
Rhomboid major
Rhomboid minor
What muscles cause scapular depression
Inferior/ascending portion of trapezius
Pectoralis minor
What muscles cause scapular retraction
All parts of the trapezius
Rhomboid major
Rhomboid minor
What muscles cause scapular protraction
Pectoralis minor
Serratus anterior
What muscles cause medial rotation/ downward rotation of the scapulae
Levator scapulae
Rhomboid minor
Rhomboid major
Pectoralis minor
What muscles cause lateral rotation/ upward rotation of the scapulae
Superior/descending and inferior/ascending portion of trapezius
Serratus anterior
Trapezius
- origin
- insertion
- action
- innervation
- origin:
Superior/descending part: Superior nuchal line and external occipital
protuberance
Middle part: Spinous
processes of T1-T4
Inferior/ascending part: Spinous processes of T5-T12
- insertion:
Superior part: Lateral third of clavicle
Middle part: Spine and acromion of scapula
Inferior part: Spine of scapula
- action:
all parts: retraction
superior/inferior part: upward rotation of scapula
superior part: scapular elevation
inferior part: scapular depression - innervation: accessory nerve (CNXI)
Levator scapulae
- origin
- insertion
- action
- innervation
- origin: Transverse processes of C1-C4
- insertion: Medial border of the scapula
(superior to the spine) - action:
downward rotation of
scapula, elevates scapula
if scapulae are fixed, levator scapulae will cause neck to flex laterally
- innervation:
dorsal scapular nerve
Rhomboid minor
- origin
- insertion
- action
- innervation
- origin: Dorsal spinous processes of the C6-C7 (or C7-T1) vertebra
- insertion: Medial border of the
scapula (~at the level
of the spine; superior to r. major) - action: Retraction, elevation and downward rotation of scapula
- innervation: Dorsal scapular nerve
Rhomboid major
- origin
- insertion
- action
- innervation
- origin: Dorsal spinous processes of the T2-T5
vertebrae - insertion: Medial border of the
scapula (below the
spine; inferior to r.
minor) - action: Retraction, elevation
and downward
rotation of scapula - innervation: Dorsal scapular nerve
Latissimus Dorsi
- origin
- insertion
- action
- innervation
- origin: Spinous process of T7-T12,
thoracolumbar fascia, iliac crest, ribs 9-12, inferior angle
of scapula - insertion: Floor of intertubercular
groove of humerus - action: Adduction, extension, medial rotation of humerus;
If humerus fixed: elevates the trunk (ex. pull-up);
moves trunk anteriorly (ex. cross-
country skiing)
- innervation: Thoracodorsal nerve
Iliocostalis
- origin
- insertion
- action
- innervation
- origin: Iliac crest, the sacrum, and the erector spinae
aponeurosis - insertion: Angle of the ribs and the
transverse processes of C4-C6 - action: Extends and laterally flexes the spine
- innervation: spinal nerves (many)
Longissimus
- origin
- insertion
- action
- innervation
- origin: Thoracolumbar fascia,
sacrum, transverse processes of lumbar and thoracic vertebrae - insertion: Transverse processes of thoracic and cervical vertebrae, lower ribs (3-12)
- action: Extends and laterally flexes the spine
- innervation: Spinal nerves (many)
Spinalis
- origin
- insertion
- action
- innervation
- origin: Dorsal spinous processes of T11-L2
- insertion: Dorsal spinous processes of
T1-T8 (cervicis inserts higher on cervical vertebrae as well) - action: Extends and the spine; laterally flexes thoracic/cervical spine
- innervation: Spinal nerves (many)
connect dorsal spinous processes with caudal origins and rostral insertions
Serratus posterior superior
- origin
- insertion
- action
- innervation
- origin: Dorsal spinous processes of C7-T3
- insertion: Upper borders of ribs 2-5
- action: Elevates ribs (contributes to inhalation); proprioception in posterior thoracic cage (contains high density of proprioceptors)
- innervation: Intercostal nerves (many)
Serratus posterior inferior
- origin
- insertion
- action
- innervation
- origin: Dorsal spinous processes of T11-L2
- insertion: Inferior borders of ribs 9-12
- action: Depresses ribs (contributes to exhalation); proprioception in posterior thoracic cage (contains high density of proprioceptors)
- innervation: Intercostal nerves (many)
Multifidus
- origin
- insertion
- action
- innervation
- origin: Sacrum and transverse processes of thoracic vertebra (+ articular processes of C4-C7)
- insertion: Dorsal spinous processes of
vertebrae superior to origin - action: Extends and laterally flexes the spine; also active in
rotation and proprioceptive
feedback; stabilizer of the vertebral column - innervation: Spinal nerves (many)
Multifidus: fibres are obliquely oriented;
Splenius capitus and cervicis
- origin
- insertion
- action
- innervation
- origin: Dorsal spinous processes C7-
T3 (up to T6) - insertion: Mastoid
process of the temporal bone (capitus); transverse
processes of the superior cervical vertebrae (cervicis). - action: Extends,
rotates, and
laterally flexes
the neck - innervation: Spinal nerves (cervical)
Pectoralis major
- origin
- insertion
- action
- innervation
- origin: Clavicular part: medial half of the clavicle;
Sternal part: sternum and the costal cartilages of the 2nd to 7th ribs, aponeurosis of the external oblique - insertion: Lateral border of the
intertubercular (bicipital) groove of the humerus - action:
All fibres: horizontal
flexion, adduction, medial rotation of humerus
Clavicular part: flexion of humerus
Sternal part: extension of
humerus (from flexed
position)
- innervation: Lateral pectoral nerve (clavicular); Medial pectoral nerve
(sternal)
Pectoralis minor
- origin
- insertion
- action
- innervation
- origin: body of ribs 3-5
- insertion: coracoid process of scapula
- action: Protracts, depresses and
downwardly rotates
scapula - innervation: Lateral and medial pectoral
nerves (mostly the medial
one)
Serratus anterior
- origin
- insertion
- action
- innervation
- origin: Body of ribs 1-9
- insertion: Medial border of scapula, anterior side
- action: Protracts, and upwardly rotates
scapula - innervation: Long thoracic
nerve
Diaphragm
- origin
- insertion
- action
- innervation
- origin: Lumbar vertebrae, ribs 7-12, and xiphoid process
- insertion: All fibres converge to insert on a central tendon
- action: Flattens in
inhalation to
increase volume of
the thoracic cavity
(when relaxes,
decreases volume
to promote
exhalation) - innervation: Phrenic nerve
External intercostals
- origin
- insertion
- action
- innervation
- origin: Inferior border of the upper rib
- insertion: Superior border of inferior rib
- action: Elevates lower rib to promote
inhalation during
quiet breathing - innervation: Intercostal nerves
Internal intercostals
- origin
- insertion
- action
- innervation
- origin: superior border of the inferior rib
- insertion: inferior border of superior rib
- action: Depresses ribs during forced
exhalation (not
involved in quiet
breathing) - innervation: Intercostal nerves
Give the overall action of the erector spinae group
Bilateral contraction produces spinal extension
Unilateral contraction produces lateral flexion
Identify the pectoralis major and its divisions
Identify the pectoralis minor
Identify the serratus anterior
Identify intercostal muscles (all 3 layers)
