PCB 3703 Final Exam V3 | PCB 3703 Human
Physiology | Actual Q&A with Rationale (PCB3703
Final Exam ) | University of Central Florida
1. During the depolarization phase of an action potential in a typical neuron, which ionic
movement is primarily responsible for the change in membrane potential?
A. Efflux of Potassium ions
B. Efflux of Sodium ions
C. Influx of Sodium ions
D. Influx of Chloride ions
Correct Answer: C
Explanation: The depolarization phase is characterized by the rapid opening of voltage-
gated sodium channels. This allows sodium ions to flow into the cell down their
electrochemical gradient, making the interior more positive. This process continues until
the membrane potential reaches a peak value near the equilibrium potential for sodium.
2. In the sliding filament theory of muscle contraction, what role does Calcium (Ca2+) play in
initiating the cross-bridge cycle?
A. It actively pumps sodium out of the sarcoplasmic reticulum.
B. It binds to myosin to activate the ATPase enzyme.
,C. It provides the energy required for the power stroke.
D. It binds to troponin, causing a conformational change that moves tropomyosin.
Correct Answer: D
Explanation: Calcium release from the sarcoplasmic reticulum is the critical trigger for
skeletal muscle contraction. When calcium binds to the troponin complex, it induces a
structural shift in tropomyosin that uncovers the myosin-binding sites on the actin
filament. This allows the myosin head to attach and begin the contraction process.
3. Which of the following characterizes the function of the Sinoatrial (SA) node in the human
heart?
A. It serves as the secondary pacemaker in case of AV node failure.
B. It acts as the primary pacemaker by reaching threshold most rapidly.
C. It delays the electrical impulse to allow for ventricular filling.
D. It conducts impulses directly to the Purkinje fibers.
Correct Answer: B
Explanation: The SA node is located in the right atrium and possesses the fastest intrinsic
rate of spontaneous depolarization. By reaching threshold before other latent pacemakers,
it sets the rhythm for the entire heart under normal physiological conditions. This
dominance ensures a coordinated contraction sequence starting from the atria.
, 4. Which hormone is secreted by the posterior pituitary gland and is primarily responsible for
water reabsorption in the kidneys?
A. Aldosterone
B. Atrial Natriuretic Peptide (ANP)
C. Oxytocin
D. Antidiuretic Hormone (ADH/Vasopressin)
Correct Answer: D
Explanation: ADH is synthesized in the hypothalamus and stored in the posterior pituitary
until physiological triggers like high plasma osmolarity occur. It acts on the collecting ducts
of the nephron to insert aquaporins, thereby increasing water permeability. This
mechanism allows the body to conserve water and produce concentrated urine.
5. In the nephron, where does the majority of glucose reabsorption occur under normal
physiological conditions?
A. Loop of Henle
B. Proximal Convoluted Tubule
C. Distal Convoluted Tubule
D. Collecting Duct
Correct Answer: B
Physiology | Actual Q&A with Rationale (PCB3703
Final Exam ) | University of Central Florida
1. During the depolarization phase of an action potential in a typical neuron, which ionic
movement is primarily responsible for the change in membrane potential?
A. Efflux of Potassium ions
B. Efflux of Sodium ions
C. Influx of Sodium ions
D. Influx of Chloride ions
Correct Answer: C
Explanation: The depolarization phase is characterized by the rapid opening of voltage-
gated sodium channels. This allows sodium ions to flow into the cell down their
electrochemical gradient, making the interior more positive. This process continues until
the membrane potential reaches a peak value near the equilibrium potential for sodium.
2. In the sliding filament theory of muscle contraction, what role does Calcium (Ca2+) play in
initiating the cross-bridge cycle?
A. It actively pumps sodium out of the sarcoplasmic reticulum.
B. It binds to myosin to activate the ATPase enzyme.
,C. It provides the energy required for the power stroke.
D. It binds to troponin, causing a conformational change that moves tropomyosin.
Correct Answer: D
Explanation: Calcium release from the sarcoplasmic reticulum is the critical trigger for
skeletal muscle contraction. When calcium binds to the troponin complex, it induces a
structural shift in tropomyosin that uncovers the myosin-binding sites on the actin
filament. This allows the myosin head to attach and begin the contraction process.
3. Which of the following characterizes the function of the Sinoatrial (SA) node in the human
heart?
A. It serves as the secondary pacemaker in case of AV node failure.
B. It acts as the primary pacemaker by reaching threshold most rapidly.
C. It delays the electrical impulse to allow for ventricular filling.
D. It conducts impulses directly to the Purkinje fibers.
Correct Answer: B
Explanation: The SA node is located in the right atrium and possesses the fastest intrinsic
rate of spontaneous depolarization. By reaching threshold before other latent pacemakers,
it sets the rhythm for the entire heart under normal physiological conditions. This
dominance ensures a coordinated contraction sequence starting from the atria.
, 4. Which hormone is secreted by the posterior pituitary gland and is primarily responsible for
water reabsorption in the kidneys?
A. Aldosterone
B. Atrial Natriuretic Peptide (ANP)
C. Oxytocin
D. Antidiuretic Hormone (ADH/Vasopressin)
Correct Answer: D
Explanation: ADH is synthesized in the hypothalamus and stored in the posterior pituitary
until physiological triggers like high plasma osmolarity occur. It acts on the collecting ducts
of the nephron to insert aquaporins, thereby increasing water permeability. This
mechanism allows the body to conserve water and produce concentrated urine.
5. In the nephron, where does the majority of glucose reabsorption occur under normal
physiological conditions?
A. Loop of Henle
B. Proximal Convoluted Tubule
C. Distal Convoluted Tubule
D. Collecting Duct
Correct Answer: B
