SCI 221 Exam 2 V3 | SCI 221 Human
Physiology with Intervention Skill-Based
(ISB) Experiential Learning | Q&A with
Rationale (SCI221 Exam 2) | Nightingale
College
1. Which ion is primarily responsible for the depolarization phase of an action potential in a
neuron?
A. Sodium (Na+)
B. Potassium (K+)
C. Calcium (Ca2+)
D. Chloride (Cl-)
Correct Answer: A
Rationale: During the depolarization phase, voltage-gated sodium channels open in
response to a threshold stimulus. This allows a rapid influx of sodium ions into the
intracellular fluid, making the membrane potential more positive. This shift is fundamental
for the propagation of the electrical signal along the axon.
2. In the sliding filament model of muscle contraction, which protein prevents the binding of
myosin to actin in a relaxed state?
A. Troponin
,B. Myosin
C. Tropomyosin
D. Titin
Correct Answer: C
Rationale: Tropomyosin is a regulatory protein that wraps around the actin filament and
blocks the active binding sites for myosin heads. In the absence of calcium, this protein
prevents the formation of cross-bridges, thereby maintaining the muscle in a relaxed state.
The movement of tropomyosin is eventually triggered by calcium binding to the adjacent
troponin complex.
3. What is the primary function of the sarcoplasmic reticulum in skeletal muscle fibers?
A. Synthesis of ATP
B. Conduction of action potentials to the interior of the cell
C. Storage and release of calcium ions
D. Production of contractile proteins
Correct Answer: C
Rationale: The sarcoplasmic reticulum is a specialized form of endoplasmic reticulum that
acts as a reservoir for calcium ions. When a muscle fiber is stimulated by an action
potential, the sarcoplasmic reticulum releases calcium into the sarcoplasm to initiate
contraction. Following contraction, calcium is actively pumped back into the reticulum to
allow for relaxation.
,4. Which part of the brain is primarily responsible for coordinating complex motor
movements and maintaining balance?
A. Cerebellum
B. Hypothalamus
C. Cerebrum
D. Medulla oblongata
Correct Answer: A
Rationale: The cerebellum is located posterior to the brainstem and is essential for fine-
tuning motor activities. It receives sensory input from the vestibular system and
proprioceptors to ensure smooth, coordinated movements. Damage to this area often
results in ataxia or a loss of equilibrium.
5. During the repolarization phase of an action potential, which event occurs to restore the
negative membrane potential?
A. Sodium channels open
B. Calcium ions enter the cell
C. The sodium-potassium pump stops working
D. Potassium channels open and K+ leaves the cell
Correct Answer: D
, Rationale: Repolarization occurs when voltage-gated potassium channels open, allowing
potassium ions to flow out of the neuron down their electrochemical gradient. This loss of
positive charge from the interior of the cell restores the negative resting membrane
potential. This phase is critical to prepare the neuron for the next subsequent stimulus.
6. What neurotransmitter is released at the neuromuscular junction to stimulate skeletal
muscle contraction?
A. Norepinephrine
B. Acetylcholine
C. Dopamine
D. Serotonin
Correct Answer: B
Rationale: Acetylcholine is the primary neurotransmitter used by motor neurons to
communicate with skeletal muscle fibers. It binds to nicotinic receptors on the motor end
plate, causing a localized depolarization known as an end-plate potential. This event is
what eventually triggers the action potential across the sarcolemma.
7. Which division of the nervous system is often referred to as the ‘rest and digest’ system?
A. Somatic nervous system
B. Sympathetic nervous system
C. Central nervous system
Physiology with Intervention Skill-Based
(ISB) Experiential Learning | Q&A with
Rationale (SCI221 Exam 2) | Nightingale
College
1. Which ion is primarily responsible for the depolarization phase of an action potential in a
neuron?
A. Sodium (Na+)
B. Potassium (K+)
C. Calcium (Ca2+)
D. Chloride (Cl-)
Correct Answer: A
Rationale: During the depolarization phase, voltage-gated sodium channels open in
response to a threshold stimulus. This allows a rapid influx of sodium ions into the
intracellular fluid, making the membrane potential more positive. This shift is fundamental
for the propagation of the electrical signal along the axon.
2. In the sliding filament model of muscle contraction, which protein prevents the binding of
myosin to actin in a relaxed state?
A. Troponin
,B. Myosin
C. Tropomyosin
D. Titin
Correct Answer: C
Rationale: Tropomyosin is a regulatory protein that wraps around the actin filament and
blocks the active binding sites for myosin heads. In the absence of calcium, this protein
prevents the formation of cross-bridges, thereby maintaining the muscle in a relaxed state.
The movement of tropomyosin is eventually triggered by calcium binding to the adjacent
troponin complex.
3. What is the primary function of the sarcoplasmic reticulum in skeletal muscle fibers?
A. Synthesis of ATP
B. Conduction of action potentials to the interior of the cell
C. Storage and release of calcium ions
D. Production of contractile proteins
Correct Answer: C
Rationale: The sarcoplasmic reticulum is a specialized form of endoplasmic reticulum that
acts as a reservoir for calcium ions. When a muscle fiber is stimulated by an action
potential, the sarcoplasmic reticulum releases calcium into the sarcoplasm to initiate
contraction. Following contraction, calcium is actively pumped back into the reticulum to
allow for relaxation.
,4. Which part of the brain is primarily responsible for coordinating complex motor
movements and maintaining balance?
A. Cerebellum
B. Hypothalamus
C. Cerebrum
D. Medulla oblongata
Correct Answer: A
Rationale: The cerebellum is located posterior to the brainstem and is essential for fine-
tuning motor activities. It receives sensory input from the vestibular system and
proprioceptors to ensure smooth, coordinated movements. Damage to this area often
results in ataxia or a loss of equilibrium.
5. During the repolarization phase of an action potential, which event occurs to restore the
negative membrane potential?
A. Sodium channels open
B. Calcium ions enter the cell
C. The sodium-potassium pump stops working
D. Potassium channels open and K+ leaves the cell
Correct Answer: D
, Rationale: Repolarization occurs when voltage-gated potassium channels open, allowing
potassium ions to flow out of the neuron down their electrochemical gradient. This loss of
positive charge from the interior of the cell restores the negative resting membrane
potential. This phase is critical to prepare the neuron for the next subsequent stimulus.
6. What neurotransmitter is released at the neuromuscular junction to stimulate skeletal
muscle contraction?
A. Norepinephrine
B. Acetylcholine
C. Dopamine
D. Serotonin
Correct Answer: B
Rationale: Acetylcholine is the primary neurotransmitter used by motor neurons to
communicate with skeletal muscle fibers. It binds to nicotinic receptors on the motor end
plate, causing a localized depolarization known as an end-plate potential. This event is
what eventually triggers the action potential across the sarcolemma.
7. Which division of the nervous system is often referred to as the ‘rest and digest’ system?
A. Somatic nervous system
B. Sympathetic nervous system
C. Central nervous system
