A&P 1 101 - Portage Learning
Lab Exam 8: The Muscular System
Questions & Rationale
Section 1: Muscle Identification (Questions 1-10)
Q1: On the anterior shoulder model, the large, triangular muscle that caps the shoulder
joint and is responsible for arm abduction is indicated by the arrow. This muscle is the:
A. Pectoralis major
B. Trapezius
C. Deltoid [CORRECT]
D. Supraspinatus
Correct Answer: C
Rationale: The deltoid is named for its triangular shape (Greek letter delta, Δ). It
originates from the clavicle, acromion, and spine of the scapula and inserts on the
deltoid tuberosity of the humerus. Its primary action is arm abduction (all fibers), with
anterior fibers flexing and medially rotating, and posterior fibers extending and laterally
rotating. The pectoralis major (A) is anterior chest; trapezius (B) is posterior neck/upper
back; supraspinatus (D) is a rotator cuff muscle deep to deltoid that initiates abduction
but does not "cap" the shoulder.
Q2: On the anterior arm model, the prominent superficial muscle of the anterior
compartment that flexes the forearm at the elbow and is named for its two heads of
origin is indicated. This muscle is the:
, A. Brachialis
B. Triceps brachii
C. Biceps brachii [CORRECT]
D. Brachioradialis
Correct Answer: C
Rationale: The biceps brachii ("two-headed muscle of the arm") has long and short
heads originating from the supraglenoid tubercle and coracoid process of the scapula,
respectively. It inserts on the radial tuberosity and bicipital aponeurosis. It is the primary
elbow flexor when supinated and also supinates the forearm. The brachialis (A) is deep
to biceps and a stronger flexor; triceps brachii (B) is posterior and extends the elbow;
brachioradialis (D) is forearm muscle that flexes elbow in neutral position.
Q3: On the anterior torso model, the large, fan-shaped chest muscle that adducts and
medially rotates the arm is indicated by the arrow. This muscle is the:
A. Pectoralis major [CORRECT]
B. Pectoralis minor
C. Serratus anterior
D. Latissimus dorsi
Correct Answer: A
Rationale: The pectoralis major ("large chest muscle") is a convergent muscle with
clavicular and sternocostal heads. It originates from the medial clavicle, sternum, and
costal cartilages 1-6 and inserts on the intertubercular sulcus of the humerus. Its
primary actions are arm adduction, medial rotation, and flexion (clavicular head).
Pectoralis minor (B) is deep, protracts scapula; serratus anterior (C) is lateral thorax,
protracts and rotates scapula; latissimus dorsi (D) is posterior, also adducts and
extends arm.
Lab Exam 8: The Muscular System
Questions & Rationale
Section 1: Muscle Identification (Questions 1-10)
Q1: On the anterior shoulder model, the large, triangular muscle that caps the shoulder
joint and is responsible for arm abduction is indicated by the arrow. This muscle is the:
A. Pectoralis major
B. Trapezius
C. Deltoid [CORRECT]
D. Supraspinatus
Correct Answer: C
Rationale: The deltoid is named for its triangular shape (Greek letter delta, Δ). It
originates from the clavicle, acromion, and spine of the scapula and inserts on the
deltoid tuberosity of the humerus. Its primary action is arm abduction (all fibers), with
anterior fibers flexing and medially rotating, and posterior fibers extending and laterally
rotating. The pectoralis major (A) is anterior chest; trapezius (B) is posterior neck/upper
back; supraspinatus (D) is a rotator cuff muscle deep to deltoid that initiates abduction
but does not "cap" the shoulder.
Q2: On the anterior arm model, the prominent superficial muscle of the anterior
compartment that flexes the forearm at the elbow and is named for its two heads of
origin is indicated. This muscle is the:
, A. Brachialis
B. Triceps brachii
C. Biceps brachii [CORRECT]
D. Brachioradialis
Correct Answer: C
Rationale: The biceps brachii ("two-headed muscle of the arm") has long and short
heads originating from the supraglenoid tubercle and coracoid process of the scapula,
respectively. It inserts on the radial tuberosity and bicipital aponeurosis. It is the primary
elbow flexor when supinated and also supinates the forearm. The brachialis (A) is deep
to biceps and a stronger flexor; triceps brachii (B) is posterior and extends the elbow;
brachioradialis (D) is forearm muscle that flexes elbow in neutral position.
Q3: On the anterior torso model, the large, fan-shaped chest muscle that adducts and
medially rotates the arm is indicated by the arrow. This muscle is the:
A. Pectoralis major [CORRECT]
B. Pectoralis minor
C. Serratus anterior
D. Latissimus dorsi
Correct Answer: A
Rationale: The pectoralis major ("large chest muscle") is a convergent muscle with
clavicular and sternocostal heads. It originates from the medial clavicle, sternum, and
costal cartilages 1-6 and inserts on the intertubercular sulcus of the humerus. Its
primary actions are arm adduction, medial rotation, and flexion (clavicular head).
Pectoralis minor (B) is deep, protracts scapula; serratus anterior (C) is lateral thorax,
protracts and rotates scapula; latissimus dorsi (D) is posterior, also adducts and
extends arm.
