Human Anatomy Week 9 - Shoulder and Pectoral Region (Notes)

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Questions and Answers

What is the primary function of the pectoralis minor muscle?

Medially rotates the arm

Elevates the ribs

Stabilizes the scapula (correct)

Adducts the humerus

Which of the following muscles primarily causes the upward rotation of the scapula?

Teres major

Serratus anterior (correct)

Deltoid

Pectoralis major

What is the role of the subacromial and subdeltoid bursae?

Facilitate arm flexion

Stabilize the clavicle

Connect muscles to bones

Reduce friction during shoulder movements (correct)

Which nerve innervates the teres major muscle?

Lower subscapular nerve Signup and view all the answers

What action does the supraspinatus muscle initiate?

Abduction of the arm Signup and view all the answers

What occurs when the inferior angle of the scapula tips away from the spine?

Anterior tipping of scapula Signup and view all the answers

Which function is primarily associated with the movements of the sternoclavicular joint?

Elevation and depression of the clavicle's distal end Signup and view all the answers

What anatomical structure is NOT a true attachment between the shoulder girdle and the axial skeleton?

Scapulothoracic joint Signup and view all the answers

Which muscles are responsible for creating gliding motion at the acromioclavicular joint?

Pectoralis minor and upper trapezius Signup and view all the answers

What is the anatomical significance of the conoid tubercle on the clavicle?

It anchors the clavicle to the scapula Signup and view all the answers

What describes the joint type of the acromioclavicular joint?

Synovial planar Signup and view all the answers

Which ligament is NOT a major stabilizer of the acromioclavicular joint?

Costoclavicular ligament Signup and view all the answers

What role does the articular disc play in the sternoclavicular joint?

Divides the joint into two separate cavities Signup and view all the answers

Which anatomical space is bounded by the teres major, long head of triceps, and lateral head of triceps?

Quadrangular space Signup and view all the answers

What characterizes the glenohumeral joint compared to other joints?

It has a significant degree of laxity Signup and view all the answers

What is the primary function of the coracoacromial ligament in the shoulder?

Helps form a roof over the glenohumeral joint Signup and view all the answers

How many degrees of abduction are contributed by the scapula when fully raising the arm overhead?

60 degrees Signup and view all the answers

What anatomical feature is primarily responsible for deepening the glenoid fossa?

The labrum Signup and view all the answers

Which of the following best describes the scapulothoracic joint?

A functional relationship without a joint classification Signup and view all the answers

Which muscle is primarily responsible for the retraction and downward rotation of the scapula?

Rhomboids major and minor Signup and view all the answers

What is a common consequence associated with weakness in the serratus anterior muscle?

Scapular winging Signup and view all the answers

What role does the axillary recess play in shoulder abduction?

Creates space for the humeral head to migrate inferiorly Signup and view all the answers

Which nerve innervates the latissimus dorsi muscle?

Thoracodorsal nerve Signup and view all the answers

What is the origin of the levator scapulae muscle?

Transverse processes of C1-C4 Signup and view all the answers

Which movement do the inferior fibers of the trapezius muscle primarily facilitate?

Scapular depression Signup and view all the answers

Study Notes

Overview of the Shoulder

Clavicle:
- Only bone with true articulation with the axial skeleton.
- S-shaped bone with convexities on both ends.
- Allows for greater shoulder elevation.
Scapula:
- Plays a crucial role in shoulder mobility and stability.
- Has three distinct areas: superior, inferior, and spine.
- No direct joint attachment to the posterior thorax.
Humerus:
- Forms the glenohumeral joint.
- Head of humerus articulates with the glenoid fossa.
- Surgical neck is a common fracture location.
Surface Projections:
- Spine of scapula, medial border, inferior angle, clavicle, acromion process, coracoid process, and greater tuberosity of humerus are palpable landmarks.

Anatomical Spaces at the Shoulder

Triangular Space:
- Located between teres minor, teres major, and long head of triceps.
- Passes circumflex scapular artery.
Triangular Interval:
- Bounded by the long head of triceps, teres major, and lateral head of triceps.
- Located between radial nerve and profunda brachial artery.
Quadrangular Space:
- Has four sides: teres minor, long head of triceps, teres major, and shaft of humerus.
- Passes axillary nerve and posterior circumflex artery.
Triangle of Auscultation:
- Located between trapezius, latissimus dorsi, and rhomboid major.
- Allows for clear auscultation of lung sounds.
Clavipectoral Triangle:
- Located between clavicle and deltoid.
- Useful for palpating the coracoid process.

Sternoclavicular and Acromioclavicular Joints

Sternoclavicular (SC) joint:
- Saddle joint, but functions like a ball and socket.
- Has an articular disc dividing the joint.
- Supported by multiple ligaments: anterior SC ligament, interclavicular ligament, Costoclavicular ligament.
Acromioclavicular (AC) Joint:
- Synovial planar joint.
- Contains the Acromioclavicular, Coracoclavicular, Trapezoid and Conoid Ligaments.
- Susceptible to separation.
Scapulothoracic Joint:
- Not a true joint, but a functional relationship between the scapula and thoracic cage.

Glenohumeral Joint

Structure:
- Ball and socket joint with a shallow glenoid fossa.
- Relies heavily on ligaments and muscles for stability.
- Capsule is loose, allowing for greater range of motion.
Movements:
- Flexion/extension, abduction/adduction, external/internal rotation, horizontal abduction/adduction.
Scapulothoracic Rhythm:
- Combined movement of glenohumeral and scapulothoracic joints are needed for full shoulder movement overhead.
Capsule and Ligaments:
- Superior, middle, and inferior glenohumeral ligament, coracohumeral ligament, coracoacromial ligament, supraspinatus muscle.
- Posterior side: labrum, fibrous joint capsule, biceps tendon.
Cavity:
- Large synovial cavity encases the joint and the biceps tendon.
Bursae:
- Subacromial (subdeltoid) bursa and subscapularis bursa.
- Both are prone to inflammation.

Muscles Connecting to the Spine

Posterior Muscles:
- Trapezius, levator scapula, rhomboids, latissimus dorsi.
Trapezius:
- Originates from the skull, ligamentum nuchae, and C7-T12 processes.
- Inserts on clavicle, acromion, and scapular spine.
- Actions: elevation, depression, upward rotation.
Latissimus Dorsi:
- Originates from T7-12 processes, thoracolumbar fascia, ribs 8-12, and indirectly from the ilium.
- Inserts at the humerus.
- Actions: extension, adduction, medial rotation.
Levator Scapula:
- Originates from C1-C4 transverse processes.
- Inserts on the medial border of the scapula.
- Actions: elevation, downward rotation, inferior glenoid tilt.
Rhomboid Major & Minor:
- Originate from C7-T5 spinous processes.
- Insert on medial border of scapula to the inferior angle.
- Actions: retraction, downward rotation.

Muscles Connecting to Thoracic Wall

Anterior Muscles:
- Pectoralis major, pectoralis minor, serratus anterior, subclavius, sternocleidomastoid.
Pectoralis Major:
- Originates from clavicle and sternum.
- Inserts at the humerus.
- Actions: adduction, flexion, extension, medial rotation.
Pectoralis Minor:
- Originates from ribs 3-5.
- Inserts on coracoid process of scapula.
- Actions: protraction, downward rotation, depression.
Serratus Anterior:
- Originates from ribs 1-8.
- Inserts on the medial border of scapula.
- Actions: protraction, upward rotation, stabilization.
Subclavius:
- Depresses and stabilizes clavicle.
Sternocleidomastoid:
- Not directly related to the shoulder; it acts on the neck.

Scapular Stability

Serratus anterior stabilizes the scapula
Serratus anterior originates on ribs 1-8 and inserts on the medial border of the scapula
It pulls the medial border down and forward, causing upward rotation
It also pulls the medial border toward the spine and rib cage, stabilizing the scapula on the back
Gravity and muscles downwardly rotate the scapula

Pectoral Fascia

Covers the pectoralis major muscle
Continuous with the fascia of the abdominal wall and the axillary region

Clavipectoral Fascia

Deep to the pectoral fascia
Contains the costocoracoid membrane
Costocoracoid membrane connects the subclavius, clavicle, and pec minor to the axillary fascia
Nerves and blood vessels pass through this fascia
Contains the lateral pectoral nerve, cephalic vein, and thoracoacromial artery
Contains the suspensory ligament of the axilla which connects the pec minor and axillary fascia

Intrinsic Shoulder Muscles

Teres major
- Originates on the inferior angle of the scapula
- Inserts on the humerus' medial lip of the intertubercular groove
- Action: adducts and medially rotates the arm
- Nerve: lower subscapular nerve C5, C6
Deltoid
- Originates on the lateral ⅓ of the clavicle, acromion, and scapular spine
- Inserts on the deltoid tuberosity of the humerus
- Action:
  - Clavicular fibers: flex and medially rotate the arm
  - Acromial fibers: abduct the arm
  - Spinal fibers: extend and laterally rotate the arm
- Nerve: axillary nerve C5, C6

Subacromial And Subdeltoid Bursae

Found deep to the deltoid muscle
Inflammation can cause pain over the supralateral point of the shoulder

Rotator Cuff

Supraspinatus
- Originates on the scapular supraspinous fossa
- Inserts on the superior facet of the greater tubercle of the humerus
- Action: initiates arm abduction and helps hold the humeral head in the glenoid fossa
- Nerve: suprascapular nerve C4, C5, C6
Infraspinatus
- Originates on the scapular infraspinous fossa
- Inserts on the middle facet of the greater tubercle of the humerus
- Action: laterally rotates the arm, holds the humeral head in the glenoid fossa
- Nerve: suprascapular nerve C5, C6
Teres minor
- Originates on the middle lateral border of the scapula
- Inserts on the inferior facet of the greater tubercle of the humerus
- Action: laterally rotates the arm, holds the humeral head in the glenoid fossa
- Nerve: axillary nerve C5, C6
Subscapularis
- Originates on the subscapular fossa
- Inserts on the lesser tubercle of the humerus
- Action: adducts and medially rotates the arm, holds the humeral head in the glenoid fossa
- Nerve: upper and lower subscapular nerves C5, C6, C7

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Description

This quiz covers the key anatomical structures and spaces of the shoulder, including the clavicle, scapula, and humerus. You'll learn about their functions, relationships, and relevant surface projections. Test your knowledge of this crucial area for mobility and stability.