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BIOL251 / BIOL 251 Module & Lab 2
2026/2027 Human Anatomy & Physiology I
with Lab - Portage Learning
Q1: Which type of muscle tissue is found in the walls of internal organs, is striated, and is
involuntary?
A. Skeletal muscle
B. Smooth muscle
C. Cardiac muscle [CORRECT]
D. Multi-unit smooth muscle
Correct Answer: C
Rationale: Cardiac muscle is found exclusively in the heart, contains striations, and is under
involuntary control. While smooth muscle is also involuntary, it lacks striations. Skeletal muscle
is striated and voluntary.
Q2: During muscle contraction, which specific band of the sarcomere decreases in length?
A. A-band
B. I-band [CORRECT]
C. Z-disc
D. M-line
Correct Answer: B
Rationale: The I-band contains only thin (actin) filaments. During the sliding filament theory, the
thin filaments slide toward the center of the sarcomere, causing the I-band to shorten. The A-
band remains constant because the thick (myosin) filaments do not shorten, and the Z-disc
represents the boundary and stays in place.
Q3: What is the primary role of ATP in the sliding filament mechanism of muscle contraction?
A. To bind to actin
B. To break the cross-bridge between actin and myosin
,2
C. To provide the energy required for the myosin head to detach from actin [CORRECT]
D. To release calcium from the sarcoplasmic reticulum
Correct Answer: C
Rationale: ATP is required for the myosin head to detach from the actin binding site after the
power stroke. Without ATP, the cross-bridge cannot be broken, resulting in a state of rigor mortis.
Q4: Which structure is responsible for transmitting the action potential from the sarcolemma to
the sarcoplasmic reticulum?
A. Troponin
B. T-tubules [CORRECT]
C. Terminal cisternae
D. Sarcoplasm
Correct Answer: B
Rationale: T-tubules are inward extensions of the sarcolemma that allow the action potential to
penetrate deep into the muscle fiber, ensuring synchronous calcium release from the
sarcoplasmic reticulum throughout the fiber.
Q5: Acetylcholinesterase is present at the neuromuscular junction to:
A. Bind to the acetylcholine receptor
B. Stimulate the release of calcium
C. Degrade acetylcholine rapidly to terminate the signal [CORRECT]
D. Block the reuptake of acetylcholine
Correct Answer: C
Rationale: Acetylcholinesterase breaks down acetylcholine into acetic acid and choline in the
synaptic cleft. This rapid degradation ensures that the muscle contraction stops when the nerve
signal ceases, allowing for precise muscular control.
Q6: Which specific protein complex binds calcium, causing tropomyosin to shift and expose the
myosin binding sites on actin?
, 3
A. Actin
B. Myosin
C. Troponin [CORRECT]
D. Tropomyosin
Correct Answer: C
Rationale: When calcium binds to troponin C, it causes a conformational change in the troponin-
tropomyosin complex, physically moving tropomyosin away from the myosin-binding sites on
the actin filament, thereby allowing cross-bridge cycling to occur.
Q7: Which phase of a single muscle twitch represents the time between stimulus application and
the beginning of tension development?
A. Contraction phase
B. Latent phase [Correct] [CORRECT]
C. Relaxation phase
D. Tetanus phase
Correct Answer: B
Rationale: The latent phase is the brief delay between the arrival of the action potential and the
beginning of cross-bridge cycling and tension development; this time is consumed by excitation-
contraction coupling.
Q8: A weightlifter is holding a heavy barbell stationary in mid-air. What type of contraction is
this?
A. Isotonic concentric contraction
B. Isotonic eccentric contraction
C. Isometric contraction [CORRECT]
D. Twitch contraction
Correct Answer: C
Rationale: In an isometric contraction, the muscle generates force, but the load is not moved.
Since the muscle length does not change, it is classified as isometric.
BIOL251 / BIOL 251 Module & Lab 2
2026/2027 Human Anatomy & Physiology I
with Lab - Portage Learning
Q1: Which type of muscle tissue is found in the walls of internal organs, is striated, and is
involuntary?
A. Skeletal muscle
B. Smooth muscle
C. Cardiac muscle [CORRECT]
D. Multi-unit smooth muscle
Correct Answer: C
Rationale: Cardiac muscle is found exclusively in the heart, contains striations, and is under
involuntary control. While smooth muscle is also involuntary, it lacks striations. Skeletal muscle
is striated and voluntary.
Q2: During muscle contraction, which specific band of the sarcomere decreases in length?
A. A-band
B. I-band [CORRECT]
C. Z-disc
D. M-line
Correct Answer: B
Rationale: The I-band contains only thin (actin) filaments. During the sliding filament theory, the
thin filaments slide toward the center of the sarcomere, causing the I-band to shorten. The A-
band remains constant because the thick (myosin) filaments do not shorten, and the Z-disc
represents the boundary and stays in place.
Q3: What is the primary role of ATP in the sliding filament mechanism of muscle contraction?
A. To bind to actin
B. To break the cross-bridge between actin and myosin
,2
C. To provide the energy required for the myosin head to detach from actin [CORRECT]
D. To release calcium from the sarcoplasmic reticulum
Correct Answer: C
Rationale: ATP is required for the myosin head to detach from the actin binding site after the
power stroke. Without ATP, the cross-bridge cannot be broken, resulting in a state of rigor mortis.
Q4: Which structure is responsible for transmitting the action potential from the sarcolemma to
the sarcoplasmic reticulum?
A. Troponin
B. T-tubules [CORRECT]
C. Terminal cisternae
D. Sarcoplasm
Correct Answer: B
Rationale: T-tubules are inward extensions of the sarcolemma that allow the action potential to
penetrate deep into the muscle fiber, ensuring synchronous calcium release from the
sarcoplasmic reticulum throughout the fiber.
Q5: Acetylcholinesterase is present at the neuromuscular junction to:
A. Bind to the acetylcholine receptor
B. Stimulate the release of calcium
C. Degrade acetylcholine rapidly to terminate the signal [CORRECT]
D. Block the reuptake of acetylcholine
Correct Answer: C
Rationale: Acetylcholinesterase breaks down acetylcholine into acetic acid and choline in the
synaptic cleft. This rapid degradation ensures that the muscle contraction stops when the nerve
signal ceases, allowing for precise muscular control.
Q6: Which specific protein complex binds calcium, causing tropomyosin to shift and expose the
myosin binding sites on actin?
, 3
A. Actin
B. Myosin
C. Troponin [CORRECT]
D. Tropomyosin
Correct Answer: C
Rationale: When calcium binds to troponin C, it causes a conformational change in the troponin-
tropomyosin complex, physically moving tropomyosin away from the myosin-binding sites on
the actin filament, thereby allowing cross-bridge cycling to occur.
Q7: Which phase of a single muscle twitch represents the time between stimulus application and
the beginning of tension development?
A. Contraction phase
B. Latent phase [Correct] [CORRECT]
C. Relaxation phase
D. Tetanus phase
Correct Answer: B
Rationale: The latent phase is the brief delay between the arrival of the action potential and the
beginning of cross-bridge cycling and tension development; this time is consumed by excitation-
contraction coupling.
Q8: A weightlifter is holding a heavy barbell stationary in mid-air. What type of contraction is
this?
A. Isotonic concentric contraction
B. Isotonic eccentric contraction
C. Isometric contraction [CORRECT]
D. Twitch contraction
Correct Answer: C
Rationale: In an isometric contraction, the muscle generates force, but the load is not moved.
Since the muscle length does not change, it is classified as isometric.
