BIO 201 Exam 3 V1 | BIO 201 A&P |
StraighterLine | Q&A with Rationale (BIO
201 Exam 3)
1. Which of the following serves as the functional unit of a skeletal muscle fiber?
A. The sarcomere
B. The myofibril
C. The sarcoplasmic reticulum
D. The sarcolemma
Answer: A
Rationale: The sarcomere is defined as the region between two successive Z discs. It is
considered the smallest contractile unit of a muscle fiber because it contains the organized
arrangement of actin and myosin. During contraction, these filaments slide past one
another to shorten the sarcomere’s length.
2. During muscle contraction, which ion is primarily responsible for binding to troponin to
expose the active sites on actin?
A. Calcium
B. Potassium
C. Sodium
D. Magnesium
,Answer: A
Rationale: Calcium ions are released from the sarcoplasmic reticulum upon excitation of
the muscle cell. These ions bind to troponin, which induces a conformational change in the
tropomyosin complex. This change shifts tropomyosin away from the myosin-binding sites
on the actin filament, allowing cross-bridge formation.
3. Which neurotransmitter is released at the neuromuscular junction to initiate a muscle
action potential?
A. Dopamine
B. Norepinephrine
C. Serotonin
D. Acetylcholine
Answer: D
Rationale: Acetylcholine (ACh) is the specific neurotransmitter utilized by somatic motor
neurons at the neuromuscular junction. When ACh binds to receptors on the motor end
plate, it opens chemically gated ion channels. This influx of sodium leads to the
depolarization of the sarcolemma and the generation of an action potential.
4. The ‘all-or-none’ principle in muscle physiology refers to the fact that:
A. An entire muscle organ contracts completely or not at all
B. The force of contraction is independent of the stimulus frequency
, C. All motor units in a muscle fire simultaneously
D. A single muscle fiber contracts completely or not at all when threshold is reached
Answer: D
Rationale: The all-or-none law states that once a threshold stimulus is applied to a single
muscle fiber, it will contract to its fullest extent under those specific conditions. It does not
apply to the whole muscle organ, which can show graded responses via recruitment of
more motor units. Individual fibers do not produce partial contractions in response to
varying stimulus intensities above the threshold.
5. Which structure in the muscle fiber acts as a storage site for calcium ions?
A. T-tubules
B. Sarcoplasmic reticulum
C. M-line
D. Mitochondria
Answer: B
Rationale: The sarcoplasmic reticulum (SR) is a specialized smooth endoplasmic reticulum
that surrounds each myofibril. Its primary physiological role is to sequester calcium ions
during relaxation and release them into the sarcoplasm during stimulation. This release is
crucial for initiating the sliding filament mechanism.
StraighterLine | Q&A with Rationale (BIO
201 Exam 3)
1. Which of the following serves as the functional unit of a skeletal muscle fiber?
A. The sarcomere
B. The myofibril
C. The sarcoplasmic reticulum
D. The sarcolemma
Answer: A
Rationale: The sarcomere is defined as the region between two successive Z discs. It is
considered the smallest contractile unit of a muscle fiber because it contains the organized
arrangement of actin and myosin. During contraction, these filaments slide past one
another to shorten the sarcomere’s length.
2. During muscle contraction, which ion is primarily responsible for binding to troponin to
expose the active sites on actin?
A. Calcium
B. Potassium
C. Sodium
D. Magnesium
,Answer: A
Rationale: Calcium ions are released from the sarcoplasmic reticulum upon excitation of
the muscle cell. These ions bind to troponin, which induces a conformational change in the
tropomyosin complex. This change shifts tropomyosin away from the myosin-binding sites
on the actin filament, allowing cross-bridge formation.
3. Which neurotransmitter is released at the neuromuscular junction to initiate a muscle
action potential?
A. Dopamine
B. Norepinephrine
C. Serotonin
D. Acetylcholine
Answer: D
Rationale: Acetylcholine (ACh) is the specific neurotransmitter utilized by somatic motor
neurons at the neuromuscular junction. When ACh binds to receptors on the motor end
plate, it opens chemically gated ion channels. This influx of sodium leads to the
depolarization of the sarcolemma and the generation of an action potential.
4. The ‘all-or-none’ principle in muscle physiology refers to the fact that:
A. An entire muscle organ contracts completely or not at all
B. The force of contraction is independent of the stimulus frequency
, C. All motor units in a muscle fire simultaneously
D. A single muscle fiber contracts completely or not at all when threshold is reached
Answer: D
Rationale: The all-or-none law states that once a threshold stimulus is applied to a single
muscle fiber, it will contract to its fullest extent under those specific conditions. It does not
apply to the whole muscle organ, which can show graded responses via recruitment of
more motor units. Individual fibers do not produce partial contractions in response to
varying stimulus intensities above the threshold.
5. Which structure in the muscle fiber acts as a storage site for calcium ions?
A. T-tubules
B. Sarcoplasmic reticulum
C. M-line
D. Mitochondria
Answer: B
Rationale: The sarcoplasmic reticulum (SR) is a specialized smooth endoplasmic reticulum
that surrounds each myofibril. Its primary physiological role is to sequester calcium ions
during relaxation and release them into the sarcoplasm during stimulation. This release is
crucial for initiating the sliding filament mechanism.
