PCB 3703 Exam 2 V2 | PCB 3703 Human
Physiology | Actual Q&A with Rationale (PCB3703
Exam 2) | University of Central Florida
1. Which phase of the action potential is primarily characterized by the rapid opening of
voltage-gated sodium channels?
A. Repolarization phase
B. Depolarization phase
C. Hyperpolarization phase
D. Resting phase
Correct Answer: B
Explanation: The depolarization phase occurs when the membrane potential reaches
threshold, triggering the opening of activation gates on voltage-gated sodium channels.
This allows sodium ions to rush into the cell down their electrochemical gradient. The
rapid influx of positive charge causes the membrane potential to become more positive,
potentially reaching a peak of around +30 mV.
2. What is the specific role of the absolute refractory period in neuronal signaling?
A. To ensure one-way propagation of the action potential
B. To allow for temporal summation of signals
C. To increase the speed of saltatory conduction
,D. To prevent the cell from ever reaching threshold again
Correct Answer: A
Explanation: The absolute refractory period occurs when voltage-gated sodium channels
are either already open or in their inactivated state. During this time, it is impossible to
trigger another action potential regardless of the stimulus strength. This physiological
delay ensures that the action potential moves in a single direction along the axon toward
the terminal.
3. Which neurotransmitter is primarily released at the neuromuscular junction in skeletal
muscle?
A. Norepinephrine
B. Dopamine
C. Acetylcholine
D. Serotonin
Correct Answer: C
Explanation: Acetylcholine (ACh) is the specific neurotransmitter used by somatic motor
neurons to stimulate skeletal muscle fibers. When an action potential reaches the axon
terminal, ACh is released into the synaptic cleft and binds to nicotinic receptors. This
binding triggers an end-plate potential that leads to muscle contraction.
, 4. In the sliding filament theory, which protein mask the binding sites on actin during a
relaxed state?
A. Troponin I
B. Titin
C. Myosin heavy chain
D. Tropomyosin
Correct Answer: D
Explanation: Tropomyosin is a regulatory protein that wraps around the actin filament in
a resting muscle. It physically blocks the myosin-binding sites, preventing the formation of
cross-bridges. When calcium levels rise, it binds to troponin, which then shifts tropomyosin
out of the way to allow contraction.
5. Which hormone is synthesized by the hypothalamus but released by the posterior
pituitary?
A. Growth Hormone
B. Oxytocin
C. Thyroid Stimulating Hormone
D. Adrenocorticotropic Hormone
Correct Answer: B
Physiology | Actual Q&A with Rationale (PCB3703
Exam 2) | University of Central Florida
1. Which phase of the action potential is primarily characterized by the rapid opening of
voltage-gated sodium channels?
A. Repolarization phase
B. Depolarization phase
C. Hyperpolarization phase
D. Resting phase
Correct Answer: B
Explanation: The depolarization phase occurs when the membrane potential reaches
threshold, triggering the opening of activation gates on voltage-gated sodium channels.
This allows sodium ions to rush into the cell down their electrochemical gradient. The
rapid influx of positive charge causes the membrane potential to become more positive,
potentially reaching a peak of around +30 mV.
2. What is the specific role of the absolute refractory period in neuronal signaling?
A. To ensure one-way propagation of the action potential
B. To allow for temporal summation of signals
C. To increase the speed of saltatory conduction
,D. To prevent the cell from ever reaching threshold again
Correct Answer: A
Explanation: The absolute refractory period occurs when voltage-gated sodium channels
are either already open or in their inactivated state. During this time, it is impossible to
trigger another action potential regardless of the stimulus strength. This physiological
delay ensures that the action potential moves in a single direction along the axon toward
the terminal.
3. Which neurotransmitter is primarily released at the neuromuscular junction in skeletal
muscle?
A. Norepinephrine
B. Dopamine
C. Acetylcholine
D. Serotonin
Correct Answer: C
Explanation: Acetylcholine (ACh) is the specific neurotransmitter used by somatic motor
neurons to stimulate skeletal muscle fibers. When an action potential reaches the axon
terminal, ACh is released into the synaptic cleft and binds to nicotinic receptors. This
binding triggers an end-plate potential that leads to muscle contraction.
, 4. In the sliding filament theory, which protein mask the binding sites on actin during a
relaxed state?
A. Troponin I
B. Titin
C. Myosin heavy chain
D. Tropomyosin
Correct Answer: D
Explanation: Tropomyosin is a regulatory protein that wraps around the actin filament in
a resting muscle. It physically blocks the myosin-binding sites, preventing the formation of
cross-bridges. When calcium levels rise, it binds to troponin, which then shifts tropomyosin
out of the way to allow contraction.
5. Which hormone is synthesized by the hypothalamus but released by the posterior
pituitary?
A. Growth Hormone
B. Oxytocin
C. Thyroid Stimulating Hormone
D. Adrenocorticotropic Hormone
Correct Answer: B
